record of decision - united states environmental ... · record of decision ... 12.6.3 soil...

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 6

RECORD OF DECISION

GRANTS CHLORINATED SOLVENTS PLUME SITE

Grants, New Mexico

CERCLIS ID # NM007271768

June 30, 2006

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GRANTS CHLORINATED SOLVENTS PLUME SITE, GRANTS, NM, RECORD OF DECISION

CONTENTS III

Contents

Part Page 1 THE DECLARATION.................................................................................................. 1-1 1.0 Site Name and Location.................................................................................. 1-1 2.0 Statement of Basis and Purpose..................................................................... 1-1 3.0 Assessment of the Site..................................................................................... 1-2 4.0 Description of the Selected Remedy ............................................................. 1-2 4.1 Institutional Controls .......................................................................... 1-4 4.2 Contingency Remedy.......................................................................... 1-5 5.0 Statutory Determinations ............................................................................... 1-5 6.0 ROD Data Certification Checklist ................................................................. 1-6 7.0 Authorizing Signature .................................................................................... 1-7 Concurrence Page, Record of Decision......................................................... 1-9 2 THE DECISION SUMMARY..................................................................................... 2-1 8.0 Site Name, Location, and Description .......................................................... 2-1 9.0 Site History of Enforcement Activities ......................................................... 2-2 9.1 History of Site Activities..................................................................... 2-2 9.2 History of Federal and State Investigations..................................... 2-4 9.2.1 Site Investigation Report ...................................................... 2-4 9.2.2 Rio San Jose Hyporheic Zone Sampling............................. 2-4 9.2.3 Allsup’s 200 Secondary Investigation Report.................... 2-5 9.2.4 EPA’s Remedial Investigation ............................................. 2-7 9.2.5 National Remedy Review Board Review........................... 2-7 9.3 History of CERCLA Enforcement Activities ................................... 2-8 10.0 Community Participation............................................................................... 2-8 10.1 Community Meetings ......................................................................... 2-8 10.2 Public Meeting for the Proposed Plan .............................................. 2-9 10.3 Technical Assistance Grant .............................................................. 2-10 10.4 Fact Sheets........................................................................................... 2-10 10.5 Local Site Repository......................................................................... 2-10 11.0 Scope and Role of Response Action............................................................ 2-10 12.0 Site Characteristics......................................................................................... 2-11 12.1 Overview of the Site .......................................................................... 2-11 12.2 Site Geology........................................................................................ 2-12 12.3 Site Hydrogeology............................................................................. 2-13 12.4 Sampling Strategy.............................................................................. 2-13 12.5 Conceptual Site Model...................................................................... 2-14

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CONTENTS IV

Contents (continued)

Part Page 12.6 Nature and Extent of Soil Contamination...................................... 2-15 12.6.1 Soil Contamination at Holiday Cleaners.......................... 2-15 12.6.2 Soil Contamination at Abandoned Dry Cleaners............ 2-16 12.6.3 Soil Contamination at R&L Laundry ................................ 2-16 12.6.4 Soil Contamination at Former Holiday Cleaners............ 2-17 12.6.5 Soil Contamination at Former MST&T Company Maintenance Yard................................................................ 2-17 12.6.6 Soil Contamination at Work Shed..................................... 2-17 12.7 Nature and Extent of Ground Water Contamination................... 2-17 12.8 Nature and Extent of Soil Vapor Contamination.......................... 2-20 12.9 Nature and Extent of Indoor Air Contamination.......................... 2-20 12.10 Potential Routes of Contaminant Migration.................................. 2-21 12.10.1 Infiltration............................................................................. 2-21 12.10.2 DNAPL Migration ............................................................... 2-21 12.10.3 Soil Vapor and Vapor Intrusion ........................................ 2-22 12.10.4 Aqueous-Phase Transport .................................................. 2-23 12.10.5 Potential Routes of Human Exposure............................... 2-23 12.11 Ground Water Flow and Transport Modeling .............................. 2-25 13.0 Current and Potential Future Land and Resource Uses .......................... 2-26 13.1 Current and Potential Future Land Uses ....................................... 2-26 13.2 Current and Potential Future Ground Water Uses....................... 2-26 14.0 Summary of Site Risks .................................................................................. 2-27 14.1 Summary of Human Health Risk Assessment .............................. 2-27 14.1.1 Identification of Chemicals of Concern ............................ 2-28 14.1.2 Exposure Assessment.......................................................... 2-31 14.1.3 Toxicity Assessment ............................................................ 2-32 14.1.4 Risk Characterization.......................................................... 2-33 14.1.5 Uncertainties......................................................................... 2-35 14.2 Ecological Risk Assessment.............................................................. 2-38 14.3 Basis for Remedial Action ................................................................ 2-38 15.0 Remedial Action Objectives ......................................................................... 2-39 15.1 Remedial Action Objectives for Ground Water ............................ 2-39 15.2 Remedial Action Objectives for Soil................................................ 2-40 15.3 Remedial Action Objectives for Vapor Intrusion.......................... 2-40 15.4 Basis and Rationale for Remedial Action Objectives.................... 2-40 15.5 Risks Addressed by the Remedial Action Objectives................... 2-41

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CONTENTS V


Part Page 16.0 Description of Alternatives .......................................................................... 2-42 16.1 Common Elements of Each Remedial Component....................... 2-43 16.1.1 Preliminary Design Field Investigation............................ 2-44 16.1.2 Ground Water Monitoring Program................................. 2-45 16.1.3 Five-Year Reviews ............................................................... 2-45 16.1.4 Institutional Controls .......................................................... 2-45 16.2 Distinguishing Features of Each Alternative................................. 2-46 16.2.1 Indoor Air Alternatives....................................................... 2-46 16.2.2 Source Area Alternatives.................................................... 2-48 16.2.3 Shallow Plume Core and Hot Spot Alternatives............. 2-54 16.2.4 Shallow Plume Periphery Alternatives ............................ 2-59 16.2.5 Deeper Ground Water Alternatives.................................. 2-65 16.3 Other Common Elements and Distinguishing Features Of Each Alternative ........................................................................... 2-70

16.3.1 Key Applicable or Relevant and Appropriate Requirements ....................................................................... 2-70

16.3.2 Long-Term Reliability of the Remedy .............................. 2-71 16.3.3 Quantities of Untreated Wastes......................................... 2-71 16.3.4 Uses of Presumptive Remedies.......................................... 2-72 16.4 Expected Outcomes of Each Alternative........................................ 2-73 17.0 Comparative Analysis of Alternatives ....................................................... 2-73 17.1 Overall Protection of Human Health and the Environment ....... 2-74 17.1.1 Indoor Air (Vapor Intrusion Mitigation).......................... 2-75 17.1.2 Source Area Treatment ....................................................... 2-75 17.1.3 Shallow Ground Water Plume Core and Hot Spot Treatment.............................................................................. 2-76 17.1.4 Shallow Ground Water Periphery..................................... 2-77 17.1.5 Deeper Ground Water......................................................... 2-79 17.2 Compliance with ARARs ................................................................. 2-80 17.3 Long-Term Effectiveness and Permanence.................................... 2-80 17.3.1 Magnitude of Residual Risk............................................... 2-81 17.3.2 Adequacy and Reliability of Controls............................... 2-86 17.4 Reduction of Toxicity, Mobility, and Volume ............................... 2-90 17.4.1 Treatment Process Used and Materials Treated.............. 2-90 17.4.2 Amount of Hazardous Materials Destroyed or Treated.............................................................................. 2-92 17.4.3 Degree of Expected Reductions in Toxicity, Mobility, and Volume ......................................................... 2-93 17.4.4 Type of Residuals Remaining After Treatment............... 2-95

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CONTENTS VI


Part Page 17.5 Short-Term Effectiveness.................................................................. 2-97 17.5.1 Protection of Community During Remedial Actions ..... 2-97 17.5.2 Protection of Workers During Remedial Actions ......... 2-101 17.5.3 Environmental Impacts..................................................... 2-102 17.5.4 Time Until Remedial Action Objectives Are Achieved...................................................................... 2-103 17.6 Implementability ............................................................................. 2-104 17.7 Cost .............................................................................................. 2-104 17.8 State Acceptance .............................................................................. 2-106 17.9 Community Acceptance ................................................................. 2-106 17.10 Summary of Comparative Analysis of Alternatives................... 2-106 18.0 Principal Threat Wastes.............................................................................. 2-107 19.0 Selected Remedy.......................................................................................... 2-108 19.1 Summary of the Rationale for the Selected Remedy .................. 2-108 19.1.1 Indoor Air: Vapor Mitigation System............................ 2-108 19.1.2 Source Area: Thermal Treatment ................................... 2-108 19.1.3 Shallow Plume Core and Hot Spot: ISCO With Follow-On Bio-Barrier (Flexible) ..................................... 2-109

19.1.4 Shallow Plume Periphery, Deeper Plume: ERD Bio-Barrier.................................................................. 2-110

19.2 Description of the Selected Remedy ............................................. 2-110 19.2.1 Indoor Air ........................................................................... 2-111 19.2.2 Source Areas....................................................................... 2-111 19.2.3 Shallow Plume Core and Hot Spot.................................. 2-114 19.2.4 Shallow Ground Water Plume Periphery ...................... 2-116 19.2.5 Deeper Ground Water Plume .......................................... 2-118 19.3 Contingency Remedy...................................................................... 2-119 19.4 Cost Estimate for the Selected Remedy........................................ 2-120 19.5 Expected Outcomes of the Selected Remedy............................... 2-121 19.5.1 Available Land Uses.......................................................... 2-121 19.5.2 Available Ground Water Uses ......................................... 2-121 19.5.3 Final Cleanup Levels......................................................... 2-121 20.0 Statutory Determinations ........................................................................... 2-122 20.1 Protection of Human Health and the Environment ................... 2-122 20.2 Compliance with Applicable or Relevant and Appropriate Requirements ............................................................ 2-122 20.3 Cost Effectiveness ........................................................................... 2-124 20.4 Utilization of Permanent Solutions to the Maximum Extent Practicable ............................................................................ 2-124

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CONTENTS VII


Part Page 20.5 Preference for Treatment as a Principal Element........................ 2-125 20.6 Five-Year Review Requirements ................................................... 2-125 21.0 Documentation of Significant Changes from Preferred Alternative of Proposed Plan..................................................................... 2-126 22.0 State Role .............................................................................................. 2-126 3 RESPONSIVENESS SUMMARY.............................................................................. 3-1 23.0 Responsiveness Summary.............................................................................. 3-1 24.0 References .................................................................................................. 3-6

Appendices A Administrative Record Index B Cost Estimate for Selected Remedy C NMED Concurrence With the Selected Remedy D Responsiveness Summary E NRRB Summary and Responses

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CONTENTS VIII

Figures Figure 1: Area Map Figure 2: Site Map Figure 3: Ground Water Elevation Contour Map Figure 4: Site Conceptual Model – Flow Chart Form Figure 5: Site Conceptual Model – Pictorial Form Figure 6: Soil Sampling Locations Figure 7: Ground Water Sampling Locations Figure 8: Indoor Air and Soil Vapor Sampling Locations Figure 9: Horizontal Extent of Chlorinated Solvents Contamination Figure 10: Vertical Extent of Chlorinated Solvents Contamination Figure 11: Structures with Vapor Intrusion Mitigation systems Figure 12: Extent of Source Area Treatment Figure 13: Conceptual Layout of ISCO w/Follow-On ERD (Shallow Plume Core) Figure 14: Conceptual Layout of ERD Bio-Barrier (Shallow Plume Core) Figure 15: Conceptual Layout of ERD Bio-Barrier (Shallow Plume Periphery) Figure 16: Conceptual Layout of ERD Bio-Barrier (Deeper Plume)

Tables Table 1: Criteria used for evaluation of indoor air Table 2: Summary of COCs and Medium-Specific Exposure Point Concentration

(Ground Water) Table 3: Summary of COCs and Medium-Specific Exposure Point Concentration

(Indoor Air) Table 4: Selection of Exposure Pathway Table 5: Values Used For Daily Intake Calculations (Ground Water) Table 6: Values Used For Daily Intake Calculations (Indoor Air) Table 7: Non-Cancer Toxicity Data Summary Table 8: Cancer Toxicity Data Summary Table 9: Risk Characterization Summary, Non-Carcinogens Table 10: Risk Characterization Summary, Carcinogens Table 11: Summary ARARs Table 12: Description of ARARs for Selected Remedy Table 13: Evaluation Criteria for Superfund Remedial Alternatives Table 14: Comparison of Remedial Alternatives, Vapor Intrusion Mitigation Table 15: Comparison of Remedial Alternatives, Source Area Treatment Table 16: Comparison of Remedial Alternatives, Shallow Ground Water Plume Core

and Hot Spot Table 17: Comparison of Remedial Alternatives, Shallow Ground Water Periphery Table 18: Comparison of Remedial Alternatives, Deeper Ground Water Table 19: Cost Summary for Remedial Alternatives Table 20: Final Cleanup Levels for Chemicals of Concern

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CONTENTS IX

Abbreviations and Acronyms

1,1-DCA 1,1-dichloroethane 1,1-DCE 1,1-dichloroethene ARAR Applicable or Relevant and Appropriate Requirements ATSDR Agency for Toxic Substances and Disease Registry BHHRA Baseline Human Health Risk Assessment bgs below ground surface BTEX benzene, toluene, ethylbenzene, and xylenes °C Celsius CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

(Superfund) CFR Code of Federal Regulations cis-1,2-DCE cis-1,2-dichloroethene COC contaminant/chemical of concern COPC chemical of potential concern CSM conceptual site model DNAPL dense non-aqueous phase liquid DOT U.S. Department of Transportation ELCR Excess Lifetime Cancer Risk EPA U.S. Environmental Protection Agency EPC exposure point concentration ERD enhanced reductive dechlorination; Enhanced Reduction Bio-barrier ERH electrical resistive heating ESD Explanation of Significant Differences

°F degrees Fahrenheit FI Facility Investigation FS Feasibility Study ft feet GAC granular activated carbon GCSP Grants Chlorinated Solvents Plume gpm gallons per minute HHMSSL Human Health Medium-Specific Screening Level (EPA Region 6) HI hazard index HQ hazard quotient

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CONTENTS X

IRIS Integrated Risk Information System (EPA) ISCO in-situ chemical oxidation (ISCO MCL maximum contaminant level MG million gallons

µg/L micrograms per liter

µg/kg micrograms per kilogram

µg/m3 micrograms per cubic meters mg/kg milligrams per kilogram mg/kg-day milligrams per kilogram per day MNA monitored natural attenuation msl mean sea level MST&T Mountain States Telephone and Telegraph Company MTBE methyl tert-butyl ether NCEA National Center for Environmental Assessment NCP National Contingency Plan NMAC New Mexico Administrative Code NMED New Mexico Environment Department NMED-PSTB New Mexico Environment Department-Petroleum Storage Tank Bureau NMED-SOS New Mexico Environment Department-Superfund Oversight Section NPL National Priorities List NRRB National Remedy Review Board O&M operations and maintenance OSE New Mexico Office of the State Engineer PA Preliminary Assessment PCE tetrachloroethene ppb parts per billion PRB permeable reactive barrier PRG Preliminary Remediation Goal PRP Potential Responsible Party PSH phase-separated hydrocarbon RAO Remedial Action Objective RCRA Resource Conservation and Recovery Act RD Remedial Design RfC reference concentration RfD reference dose RI Remedial Investigation RI/FS Remedial Investigation/Feasibility Study RME Reasonable Maximum Exposure ROD Record of Decision ROI radius of influence SARA Superfund Amendments and Reauthorization Act

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CONTENTS XI

SF slope factor (cancer) SI Sampling Inspection or Site Investigation SOD soil oxidant demand SSL soil screening level SVE soil vapor extraction TAG Technical Assistance Grant TCE trichloroethene TMV toxicity, mobility, and volume trans-1,2-DCE trans-1,2-dichloroethene UCL upper confidence level USGS U.S. Geological Survey UST underground storage tank VC vinyl chloride VOC volatile organic compound WQCC Water Quality Control Commission (New Mexico) yd3 cubic yard ZVI zero-valent iron

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Part 1. The Declaration

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PART 1 – THE DECLARATION 1-1

Part 1: The Declaration

1.0 Site Name and Location

The Grants Chlorinated Solvents Plume (GCSP) Site is located in Grants, New Mexico

(Cibola County). The National Superfund Database Identification Number is NM007271768.

2.0 Statement of Basis and Purpose

This decision document presents the “Selected Remedy” for the Grants Chlorinated Solvents

Plume Site (hereinafter “the Site or GCSP Site”). The Selected Remedy was chosen in

accordance with the Comprehensive Environmental Response, Compensation and Liability

Act of 1980 (CERCLA), 42 United States Code §9601 et seq., as amended by the Superfund

Amendments and Reauthorization Act of 1986 (SARA), and, to the extent practicable, the

National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 Code of

Federal Regulations (CFR) Part 300, as amended.

This decision is based on the Administrative Record for the Site, which has been developed

in accordance with Section 113(k) of CERCLA, 42 United States Code §9613(k). This

Administrative Record file is available for review at the University of New Mexico, Grants

Campus, Grants, New Mexico, the New Mexico Environment Department (NMED) offices

in Santa Fe, New Mexico, and at the U.S. Environmental Protection Agency (EPA Region 6)

Records Center in Dallas, Texas. The Administrative Record Index (Appendix A) identifies

each of the items comprising the Administrative Record upon which the selection of the

Remedial Action is based. The State of New Mexico (NMED) concurs with the Selected

Remedy.

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3.0 Assessment of the Site

The response action selected in this Record of Decision (ROD) is necessary to protect the

public health or welfare or the environment from actual or threatened releases of hazardous

substances into the environment.

4.0 Description of the Selected Remedy

The EPA will address the site contamination as one operable unit. The site-specific media

have been divided in to five categories to address the chlorinated solvents contamination in

indoor air, soil, and ground water.

The five categories are:

• Indoor Air – Ambient air within residential structures.

• Source Areas – two source areas exist at the GCSP site and are targeted for cleanup. The

larger Holiday Cleaners source area includes roughly the entire property, an area

approximately 150 ft by 100 ft in size. The depth interval requiring treatment extends

from the land surface to approximately 80 ft below ground surface (bgs). The

abandoned dry cleaner facility source area is approximately 30 ft by 80 ft. The depth

interval requiring treatment extends from the land surface to approximately 35 ft bgs.

• Shallow Plume Core and Hot Spot – The shallow ground water plume core is defined as

the portion of the plume with PCE and/or TCE concentrations exceeding 5,000 µg/L

(micrograms per litre), which is a value 1,000 times the ground water final cleanup goal

for PCE and TCE. Similarly, the shallow ground water hot spot is defined as the portion

of the plume on Jefferson Avenue between First Street and Geis Street, which is offset

from the primary plume core axis, where PCE and/ or TCE concentrations also exceed

5,000 µg/L.

• Shallow Ground Water Plume Periphery – The shallow ground water plume periphery

is defined as the portion of the shallow PCE ground water plume (as identified during

the Remedial Investigation [RI]) beyond the plume core where PCE concentrations still

exceed the Maximum Contaminant Level (MCL) within the upper 20 ft of the subsurface

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but are less than 5,000 µg/L. This includes an area extending approximately 1,500 ft

downgradient of the Holiday Cleaners source area, over a width of approximately 500 to

600 ft.

• Deeper Ground Water Plume – Deeper ground water is defined as all ground water

below 20 ft bgs with contamination above the MCL, based on sampling conducted

during the RI.

The components of the Selected Remedy are described in detail in Section 19 of this ROD.

Briefly, the major components of the Selected Remedy are:

1. Indoor Air: Vapor Mitigation

The EPA will install vapor intrusion mitigation systems at 14 residences that are located

directly above the ground water plume where concentrations of trichloroethene (TCE) or

tetrachloroethene (PCE) in ground water exceed 1,000 µg/L and other locations where

indoor air concentrations exceed a one in 100,000 (1x10-5) risk level.

Indoor air monitoring will be conducted prior to and following construction and at least

once every 5 years until ARARs are met to ensure remedy protectiveness.

2. Source Area: Thermal Treatment

Thermal treatment will be implemented at the source areas through heater

probes/electrode vapor extraction wells with the central onsite treatment facility located

at the Holiday Cleaners source area property.

Site-specific bench- and/or pilot–scale testing will be performed prior to Remedial

Design (RD).

Performance monitoring will be conducted during the implementation of this remedy.

3. Shallow Plume Core and Hot Spot: In-Situ Chemical Oxidation (ISCO) with Follow-On

Enhanced Reductive Dechlorination (ERD)

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The EPA will be flexible in applying this technology based on data gathered during the

Predesign Field Investigation. Based on the data collected, the EPA may choose to

implement ISCO with Follow-On ERD or only the ERD component.

Site-specific bench- and/or pilot–scale testing will be performed prior to RD.

ISCO applications (potassium or sodium permanganate) are followed by ERD (vegetable

oil) applications in permanent wells installed within the ground water plume.

Performance monitoring will be conducted throughout the active treatment period.

4. Shallow Ground Water Plume Periphery: ERD Bio-Barrier

ERD involves injecting carbon amendments (vegetable oil) into the aquifer periodically

to support the growth of in-situ bacteria capable of treating the chlorinated solvents.


The amendments will be delivered through approximately 100 permanent injection

wells once every 15 months over a 20-year period.

A total of approximately 2,400 feet (ft) of bio-barrier wall will be installed with multiple

transects spaced approximately 200 ft apart.


5. Deeper Ground Water Plume: ERD Bio-Barrier

ERD involves injecting carbon amendments (vegetable oil) into the aquifer periodically

to support the growth of in-situ bacteria capable of treating the chlorinated solvents.


ERD amendments will be delivered through approximately 50 permanent injection wells

once every 15 months over a 20-year period.

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A total of approximately 1,000 ft of bio-barrier wall will be installed to a depth of

approximately 60 ft bgs and approximately 250 ft of bio-barrier will be installed to a

depth of approximately 80 ft bgs.


The complete vertical extent of contamination is not fully defined at this time. Further

characterization will be conducted during the Preliminary Field Investigation and the

remedy will be implemented such that the entire vertical extent is addressed. The remedy

will be re-evaluated during the design phase if new information regarding the vertical and

horizontal extent of the plume is determined.

The Selected Remedy will address the principal threat wastes, Dense Nonaqueous Phase

Liquids (DNAPL) and chlorinated solvents in ground water and soil such that the Site is

made safe for residential use. The EPA will implement the Selected Remedy in a phased

manner in the order listed above.

4.1 Institutional Controls

To protect human health from exposure to the existing ground water contamination while

cleanup is ongoing, the EPA and NMED will request the New Mexico Office of the State

Engineer (OSE) to issue an order restricting future well drilling within a portion of the

aquifer contaminated by the plume until remediation goals (RGs) for the ground water are

met. The order will only apply to new requests for water well permits and cannot be

enforced against existing water well permit holders. The OSE does not have a vested

enforcement authority but has the ability to enforce with a court order. Based on interviews

the existing wells are not being used for any purpose. The EPA will work with NMED to

issue a health advisory not to consume ground water from the existing wells within the

plume area.

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4.2 Contingency Remedy

EPA will evaluate the site conditions to determine if monitored natural attenuation (MNA)

is a viable remedial alternative after the first Five-Year Review and after source control has

been established in the Source Areas and the Shallow Ground Water Plume. If ground

water data demonstrates evidence that MNA is occurring such that RAOs will be met in a

timely manner, then EPA may consider proposing MNA as the remedial strategy for the

Shallow Ground Water Periphery and the Deeper Ground Water Plume. If this alternative

is determined to be the most efficient and effective remedy, then EPA with NMED’s

concurrence will issue an Explanation of Significant Differences (ESD) to document the

change in the remedy. MNA is not a component of the Selected Remedy.

MNA is a proven ground water remedy at many sites; however, at this time there is

insufficient data to select MNA as a component of the Selected Remedy at the GCSP Site.

The EPA will collect the necessary data for MNA evaluation during the pre-design

investigation phase. The contingency will be invoked not because of a potential failure of

the Selected Remedy but rather as an alternative that would not only achieve final cleanup

goals but also provide significant cost savings to the agency.

5.0 Statutory Determinations

The Selected Remedy attains the mandates of CERCLA §121, and the regulatory

requirements of the NCP. This remedy is protective of human health and the environment,

complies with Federal and State requirements that are applicable or relevant and

appropriate to the Remedial Action, is cost-effective, and utilizes permanent solutions to the

maximum extent practicable.

The Selected Remedy also satisfies the statutory preference for treatment as a principal

element of the remedy (i.e., reduce the toxicity, mobility, or volume of hazardous substances

through treatment). The concentrations of chlorinated solvents in the ground water at the

Site indicate presence of DNAPL, which is considered a principal threat waste. The thermal

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treatment at the source areas and active treatment in the downgradient areas are expected to

remove any DNAPL present and eliminate the threat to the deeper drinking water aquifer.

Ground water restrictions area necessary because the Selected Remedy will initially

result in hazardous substances, which are above levels that allow for unlimited use

and unrestricted exposure. A statutory review will be conducted within five years

after initiation of the remedial action to ensure that the remedy continues to provide

adequate protection of human health and the environment. This review will be

conducted not less often than every five years after the date of the initiation of the

remedial action.

6.0 ROD Data Certification Checklist

The following information is included in the Decision Summary (Part 2) of this ROD, while

additional information can be found in the Administrative Record file for this site:

a) Chemicals of concern (COCs) and their respective concentrations (see Section 14.1.1

Identification of Chemicals of Concern);

b) Baseline risk represented by the COCs (see Section 14.1.4 Risk Characterization);

c) Remediation goals (i.e., cleanup goals) established for the COCs and the basis for the

goals (see Section 19.5.3 Final Cleanup Levels);

d) How source materials constituting principal threats are addressed (see Section 5.0

Statutory Determinations and Section 18.0 Principal Threat Wastes);

e) Current and reasonably anticipated future land use assumptions and current and

potential future beneficial uses of ground water used in the Baseline Human Health Risk

Assessment and this ROD (see Section 13.1 Current and Potential Future Land Uses,

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Section 13.2 Current and Potential Future Ground Water Uses, Section 19.5.1 Available

Land Uses, and Section 19.5.2 Available Ground Water Uses);

f) Potential land and ground water use that will be available at the site as a result of the

Selected Remedy (see Section 13.1 Current and Potential Future Land Uses, Section 13.2

Current and Potential Future Ground Water Uses, Section 19.5.1 Available Land Uses,

and Section 19.5.2 Available Ground Water Uses);

g) Estimated capital, lifetime operation and maintenance (O&M), and total present worth

costs; discount rate; and the number of years over which the remedy cost estimates are

projected (Section 19.4 Cost Estimate for the Selected Remedy; and Appendix B Cost

Estimate for Selected Remedy); and

h) Key factor(s) that led to selecting the remedy (see Section 14.3 Basis for Remedial

Action).

7.0 Authorizing Signature

This ROD documents the Selected Remedy for contaminated soil, ground water, and indoor

air at the GCSP Superfund Site. The EPA selected this remedy with the concurrence of the

NMED (Appendix C - NMED Concurrence with the Selected Remedy). The Director of the

Superfund Division (EPA, Region 6) has been delegated the authority to approve and sign

this ROD.

By:

Samuel Coleman, P.E., DirectorSuperfund Division (6SF)

PART 1 -THE DECLARATION

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GRANTS CHLORINATED SOLVENTS PLUME SITE, GRANTS. NM. RECORD OF DECISION

CONCURRENCE PAGERECORD OF DECISION FOR

THE GRANTS CHLORINATED SOLVENTS PLUME SUPERFUND SITE

Sai Appaji,Remedial Project Manager

Date

Don Williams,Team Leader

Wren Stenger,Chief, LA/OK/NM Bra

Date

I-Jung Chiang,Site Attorney

Date

Mark Peycke, v DateChief, Regional Counsel Superfund

1 Coleman) P.E.frector, Superfund Division

Date

PART 1 - THE DECLARATION 1-9

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THIS PAGE INTENTIONALLY LEFT BLANK.

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Part 2. The Decision Summary

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PART 2 – THE DECISION SUMMARY 2-1

Part 2: The Decision Summary

This Decision Summary provides a description of the site-specific factors and analyses that

led to the selection of the indoor air, soil, and ground water remedies for the site. It includes

background information about the site, the nature and extent of contamination found at the

site, the assessment of human health and environmental risks posed by the contaminants at

the site, and the identification and evaluation of remedial action alternatives for the site.

8.0 Site Name, Location, and Description

The GCSP Site is located in the City of Grants, Cibola County, New Mexico (Figure 1). The

site is bounded by Second Street to the west; Adams Avenue and Jefferson Avenue to the

North; Anderman Street, Washington Avenue, and Mesa View Elementary School property

to the east; and Stephens Avenue and the Rio San Jose to the south. The GCSP Site is

located in a mixed commercial and residential area.

The approximate area of ground water contamination at the GCSP Site is 20 acres. A site

map is provided in Figure 2. The geographic coordinates of the GCSP Site are

approximately 35°9’20”N latitude and 107°51’15”W longitude and within Township 11

North, Range 10 West, Section 25 of the U.S. Geological Survey (USGS) Grants Quadrangle

7.5 minute map. The approximate elevation of the Site is 6,420 ft above mean sea level (msl).

The National Superfund Database Identification Number for the Site is NM007271768. The

GCSP Site is a fund-lead site, with the EPA being the lead agency for the remedial activities,

and NMED the support agency. The Potential Responsible Party (PRP) for the site did not

participate in the Remedial Investigation/Feasibility Study (RI/FS).

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Dry cleaning operations have been historically performed at multiple facilities within the

GCSP Site, although only a single dry cleaning facility, Holiday Cleaners at 715 First Street,

is currently active. Dry cleaning has historically been performed at the R&L Laundry

(reportedly prior to approximately 1987), at an abandoned facility at 605 First Street just

north of Washington Avenue, and at a former Holiday Cleaners location at 313 First Street

north of Stephens Avenue. The active Holiday Cleaners has operated at its current location

since approximately 1969, and under the current ownership since approximately 1975.

9.0 Site History of Enforcement Activities

This section of the ROD provides the history of the site and a brief discussion of the EPA's

and the State's remedial and enforcement activities. The "Proposed Rule" proposing the site

to the National Priorities List (NPL) was published in the Federal Register on March 8, 2004.

The "Final Rule" adding the site to the NPL was published in the Federal Register on July 22,

2004.

9.1 History of Site Activities

Chlorinated solvents were first identified in ground water at the GCSP Site in 1993, during a

NMED – Petroleum Storage Tank Bureau (NMED-PSTB) investigation of leaking

underground storage tank (UST) sites in the vicinity.

Several possible sources for the release of chlorinated solvents to the ground water were

identified during the subsequent NMED Preliminary Assessment (PA), the NMED Site

Investigation (SI), and the Remedial Investigation (RI). The PA considered all of the UST

sites in the vicinity of the ground water plume as potential sources for chlorinated solvents.

However, there was no record of the use or storage of chlorinated solvents at any of these

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sites. Several other sites were identified that are presently using or may have used

chlorinated solvents in the past. These include the following locations:

• Holiday Cleaners (715 First Street)

• Former Holiday Cleaners (313 First Street) (currently Audio/Video Hill)

• R&L Laundry (604 First Street)

• Abandoned Dry Cleaning Facility (605 First Street)

• Former Wash ‘n Clean World (located in Baties Shopping Center on north side of

Stephens Avenue between First Street and Anderman Street)

• Former Mountain States Telephone and Telegraph Company (MST&T) (621 Geis Street)

maintenance yard, which is now a private residence and automotive hobby shop

• A work shed located behind a private residence at 700 First Street

Based on interviews conducted by the NMED-Superfund Oversight Section (NMED-SOS),

the current and past owners of Holiday Cleaners on 715 First Street have used PCE for a

number of years (NMED, 2001). During interviews, the current owner of Holiday Cleaners

reported that historically PCE leaked from cleaning equipment onto the building floor, as

well as from a storage container maintained in the rear portion of the building. When the

container was full, PCE occasionally overflowed onto the ground surface in response to

thermal expansion of the PCE fluid. This equipment has been removed from service and

upgraded and the PCE storage tank is no longer in use at the Holiday Cleaners.

The RI conducted by EPA identified the Abandoned Dry Cleaners property on First Street as

a secondary source of ground water contamination. The remaining suspected locations

identified above were not determined to be sources for ground water contamination based

on available information.

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9.2 History of Federal and State Investigations

9.2.1 Site Investigation Report

Following the discovery of the chlorinated solvent contamination at the GCSP Site,

NMED-SOS conducted a series of investigations from September 1998 through August 2000

to identify the sources and characterize the distribution of chlorinated solvents in soil and

ground water.

The SI Report (NMED, 2001) is the primary source of background information assembled

for the GCSP Site. The SI gathered information regarding the site description and history;

identification of potential sources; previous NMED-PSTB investigations; collection of initial

soil, soil vapor, and ground water samples; air, soil, and ground water pathway

identification; and ground water receptor identification.

In addition to the NMED SI Report, the following investigations were completed after the

SI Report had been prepared but prior to the initiation of RI field activities:

• Rio San Jose Hyporheic Zone Sampling (EPA, 2002)

• Allsup’s 200 Secondary Investigation Report (Tetra Tech EM, Inc., 2003)

9.2.2 Rio San Jose Hyporheic Zone Sampling

Concurrent with the planning phase of the RI, EPA and NMED collected water samples

from the Rio San Jose. On December 11, 2002, EPA and NMED performed a joint sampling

effort of the shallow ground water/surface water interface (hyporheic zone) of the

Rio San Jose in the vicinity of the GCSP Site. The hyporheic zone was sampled at

seven locations along the Rio San Jose from Second Street on the west to 600 ft east of

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Anderman Street on the east. An eighth location was sampled just west of the intersection

of Second Street and Monroe Avenue, within a drainage ditch along Second Street, west of

the Holiday Cleaners. A ninth location was sampled adjacent to a lint trap at a suspected

Former Dry Cleaning Facility approximately 400 ft east of the intersection of First Street and

Stephens Avenue.

The results of the laboratory analyses indicated that PCE was not detected in these samples.

However, 1,1-Dichloroethane (1,1-DCA) and cis-1,2-dichloroethene (cis-1,2-DCE) were

detected in four of the samples and TCE was detected in one of the samples. All detected

concentrations were less than their respective federal maximum contaminant levels (MCLs).

The chlorinated volatile organic compounds (VOCs) observed in the hyporheic zone first

appear at the intersection of the Rio San Jose with First Street. It does not appear that these

chlorinated VOC compounds in the hyporheic zone are related to the primary release

locations identified during the SI or RI, based on contaminant distribution discussed in

Section 5.2. Although the concentrations of chlorinated solvents were below EPA MCLs for

each of the analytes, the presence of these compounds indicates that chlorinated solvents are

entering the Rio San Jose from another undefined source, potentially near First Street.

9.2.3 Allsup’s 200 Secondary Investigation Report

The NMED-PSTB initially investigated five leaking UST sites near the GCSP Site, which

were discovered as the result of UST removal and/or upgrade activities. These sites are the

Allsup’s 200, Atex #71, Tommy’s 66, Spencer Automotive, and the Grants School

Maintenance Yard.

NMED-PSTB conducted a Secondary Investigation at the Allsup’s 200 site to further

investigate the confirmed release of petroleum hydrocarbons from this site. Investigations

performed at this leaking UST site were independent of the RI activities at the GCSP Site.

The NMED-PSTB provided EPA with the results of this Secondary Investigation. The field

investigation was completed from May 14 through July 6, 2003.

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The Secondary Investigation indicated the following items regarding site hydrogeologic

conditions and petroleum hydrocarbon compounds in ground water:

• Ground water was contaminated with dissolved-phase benzene, toluene, ethylbenzene,

and xylenes (BTEX).

• Phase-separated hydrocarbon (PSH) is present onsite at the Allsup’s 200 site and is

confined to the site boundary.

• The dissolved-phase gasoline plume migrates southeast towards Geis Street.

• Methyl tert-butyl ether (MTBE) exists downgradient of Allsup’s well MW-11 and the

horizontal extent of MTBE has not been defined in the downgradient direction.

• Ground water flow was to the southeast with a gradient of 0.003.

• Anaerobic conditions exist within the plume.

The results of the Secondary Investigation additionally indicated the following regarding

chlorinated solvents at the Allsup’s 200 site:

• Chlorinated solvents were detected in 11 of the 12 site wells.

• PCE was detected at concentrations ranging from less than 1 microgram per liter (µg/L)

to 6,200 µg/L.

• TCE was detected at concentrations ranging from less than 1 µg/L to 5,500 µg/L.

• Cis-1,2-DCE was detected at concentrations ranging from less than 1 µg/L to

3,200 µg/L.

• Trans-1,2-dichloroethene (trans-1,2-DCE) was detected at concentrations ranging from

less than 1 µg/L to 380 µg/L.

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• 1,1-dichloroethene (1,1-DCE) was detected at concentrations ranging from less than

1 µg/L to 6.2 µg/L.

9.2.4 EPA’s Remedial Investigation

Based on the results of the NMED-SOS sampling conducted from 1998 through 2000, the

EPA initiated an RI/FS for the GCSP Site to further characterize the nature and extent of

contamination and to evaluate remedial alternatives for the site. The RI sampling program

was designed based on the data previously obtained at the site and was intended to

augment the historic data.

The EPA conducted the RI in phases beginning in October 2003 and ended in April 2005.

The RI investigation included the collection and analysis of onsite soil, soil gas, ground

water, and vapor intrusion samples from indoor and outdoor locations. Soil, soil vapor, and

ground water samples were collected using the direct-push drilling technique. Indoor and

outdoor air samples were collected in summa canisters. The RI Report (EPA, 2005a),

documents in detail the nature and extent of contamination present at the site.

9.2.5 National Remedy Review Board Review

The EPA’s National Remedy Review Board (NRRB) reviewed the proposed remedy for the

site on March 29, 2006, and provided some recommendations. The NRRB has been set up

by the EPA to help control response costs and promote consistency with the NCP and

Superfund policy guidance. The NRRB comprises of cross-regional and management-level

members who evaluate cleanup actions that exceed cost-based review criteria. A copy of the

NRRB’s comments and EPA Region 6’s response are included in Appendix E.

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9.3 History of CERCLA Enforcement Activities

The EPA has conducted PRP searches and has issued 104(e) Information Requests to past

owners, operators, and current owners of Holiday Cleaners. The principal PRP for this site

is the current owner of Holiday Cleaners.

Information Requests were sent to four PRPs on March 8, 2004 and all four responded. On

August 24, 2004, the EPA followed up with another Information Request regarding their

financial status. All PRPs have complied with the request for information. At this time the

EPA is reviewing the financial viability of the PRPs and has not made a decision on

enforcement.

10.0 Community Participation

This section of the ROD describes the EPA's community involvement activities. The EPA

has actively sought a dialogue and collaboration with the affected community and has

strived to advocate and strengthen early and meaningful community participation during

the EPA's remedial activities at the site. These community participation activities during the

remedy selection process meet the public participation requirements in CERCLA §121 and

the NCP 40 CFR §300.430(f)(3).

10.1 Community Meetings

The EPA and NMED have conducted numerous community meetings during the course of

the RI/FS for the site and provided public notices of these meetings to encourage the

community's participation. Following is a brief summary of the community meetings held

by the EPA.

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On October 7, 2003, the EPA conducted the first public meeting in Grants, New Mexico to

inform the residents about the Superfund Site and the upcoming RI/FS. Residents also

were informed about indoor air sampling activities at some homes located over the plume.

Fact sheets with site information also were mailed to residents prior to the meeting.

On December 15, 2004, a second public meeting was held at Grants to inform the public

about the progress of the RI. Fact sheets with updated information were mailed and

provided during the meeting.

10.2 Public Meeting for the Proposed Plan

A public meeting was held on April 20, 2006, at the Cibola Convention Center, Grants,

New Mexico, to present the Proposed Plan (EPA, 2006a) to community members.

Representatives from the EPA answered questions about the EPA's preferred alternative for

the site. Oral and written comments were accepted at the meeting. A court reporter

transcribed the discussions held during the meeting. This transcript is included in the

Administrative Record file for the site, which is maintained at the Information Repository

located at the University of New Mexico, Grants Campus, NMED’s office located in

Santa Fe, and the EPA's office located in Dallas, Texas.

The RI (EPA, 2005a), FS Report (EPA, 2006b), Baseline Human Health Risk Assessment

(EPA, 2005b), and Proposed Plan (EPA, 2006a) for the site were made available to the public

on April 11, 2006. These documents are currently located in the Administrative Record file

for the site. The notice of the availability of these documents was published in the Cibola

Beacon on April 11, 2006. A public comment period was held from April 12, 2006 to May 11,

2006.

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10.3 Technical Assistance Grant

Information about the availability of Technical Assistance Grant (TAG) was provided

during the public meetings in October 2003 and December 2004. However, no groups came

forward to seek the grants.

10.4 Fact Sheets

Numerous fact sheets, both in English and Spanish, have been prepared during the

planning and implementation of the RI/FS. These fact sheets were placed at the GCSP Site's

repository and distributed to those community members on the mailing list.

10.5 Local Site Repository

The purpose of the local site repository is to provide the public a location near the

community to review and copy background and current information about the site.

The repository is located near the GCSP Site at:

University of New Mexico Grants Campus Library 1500 Third Street Grants, NM 87020

11.0 Scope and Role of Response Action

The entire site is addressed as one operable unit. The two main objectives for response

action at this site are to remove vapor intrusion risk and treat ground water so that COCs

are below MCLs and the site is made safe for residential use. The planned Remedial Action

is a final action for the site and is expected to successfully achieve the Remedial Action

Objectives (RAOs). Through the use of a mix of different treatment technologies, this

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response will permanently reduce the toxicity, mobility, and volume of those source

materials that constitute the principal threat wastes at the Site and restore ground water to

meet ARARs. The site-specific media impacted are the following: Indoor Air, Soil, and

Ground Water. The EPA has selected a combination of technologies to address the

contamination in the various media.

12.0 Site Characteristics

This section of the ROD provides an overview of the site's geology and hydrogeology; the

sampling strategy chosen for the site; the conceptual site model (CSM); and the nature and

extent of contamination at the site. Detailed information about the site's characteristics can

be found in the RI Report (EPA, 2005a).

12.1 Overview of the Site

The City of Grants is located in north-central Cibola County, New Mexico. Cibola County

borders Arizona and is slightly north of the north-south centerline of the state of

New Mexico. The City of Grants can be found on the “Grants” USGS 7.5-Minute

Topographic Quadrangle, primarily in Section 25, Township 11 North, Range 10 West and

Section 30, Township 11 North, Range 9 West. The City of Grants is at an elevation of

approximately 6,420 ft above msl.

The topography surrounding Grants, New Mexico is composed of mesas extending

hundreds to approximately 1,000 ft above broad valleys and dissected by steep canyons.

The highest point in the region is Mount Taylor, approximately 15 miles to the northeast, at

an elevation of 11,301 ft. Black Mesa rises just northwest of the City of Grants to an

elevation of approximately 7,200 ft. West Grants Ridge, Grants Ridge, and East Grants

Ridge rise north and northeast of Grants to elevations between 7,200 ft and 7,500 ft. Horace

Mesa, at an elevation of approximately 7,800 ft, rises east of the City of Grants.

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The Rio San Jose and its tributaries comprise the main drainage system in the area. The

Rio San Jose flows through the City of Grants, and is sourced from Bluewater Creek to the

west. Bluewater Creek is dammed by Bluewater Dam, forming Bluewater Lake,

approximately 20 miles west of the City of Grants. The Rio San Jose discharges to the

Rio Puerco approximately 50 miles to the east of Grants.

The climate in the Grants area is semiarid and characterized by low precipitation, cool and

dry winters, warm summers, and low relative humidity. During the period of record from

1953 to 2004, the mean January and July temperatures were 30.2 and 71.6 degrees

Fahrenheit (°F), respectively (NMED, 2001). The mean annual total precipitation was

10.38 inches for the period of record from 1953 to 2004 (NMED, 2001). The greatest amount

of precipitation occurs during the summer and early fall with approximately 58 percent of

the annual average precipitation occurring during the months of July, August, September,

and October. The mean annual snowfall was 13.59 inches for the period of record from 1953

to 2004 (NMED, 2001). Snowfall occurs between the months of October and April, and is

greatest during December.

12.2 Site Geology

Shallow lithology beneath the GCSP Site was characterized during Phase 1 of the RI by

direct-push sampling. A direct-push drilling rig was used to advance a total of 85 borings

throughout the site, and each boring was lithologically characterized in the field. These

borings were advanced to a maximum depth of approximately 16 ft bgs. At each of these

borings, the shallow subsurface was predominately clay and silt, with thin, laterally-

continuous sand and silty sand layers. A 6-inch to 1-ft thick sand and silty sand layer was

identified continuously from the Holiday Cleaners to at least the intersection of Washington

Avenue and Anderman Street at a depth gradually increasing from approximately 8 ft bgs

to approximately 16 ft bgs.

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Additional lithologic characterization was performed during the Phase 2 direct-push

sampling event. Lithologic information was collected to a maximum depth of

approximately 40 ft bgs at three locations during this investigation. Lithologic data also

were collected during the drilling of six monitoring wells by NMED (GMW-1 through

GMW-6). The drilling log for GMW-1 indicates fine- to medium-grained sand with some

gravel at a depth between 43 and 50 ft bgs, the greatest depth lithologically characterized at

the site.

12.3 Site Hydrogeology

Ground water is present within the shallow clay and silt alluvium at a depth of

approximately 5 to 6 ft bgs at the GCSP Site. The ground water table is somewhat deeper

(6 to 8 ft bgs) within the southeastern portion of the site. Ground water elevations have

been monitored on several occasions at the site. Figure 3 shows the ground water elevation

contour map from February 2004.

Ground water elevations varied by approximately 1 ft over the 5-year period 1999-2004, but

ground water flow directions remained consistent. In the northeast portion of the site, near

the Holiday Cleaners, ground water flows toward the southeast, turning slightly more

southward near Geis Street. In the western portion of the site, near the Atex #71 gasoline

station, ground water flows approximately due east, but quickly turns toward the southeast

to the east of the intersection of First Street and Washington Avenue. The ground water

gradient varies between approximately 0.004 and 0.006 (southeastward) near the

Tommy’s 66 gasoline station to between approximately 0.002 and 0.003 (southeastward)

near the Holiday Cleaners.

12.4 Sampling Strategy

The sampling strategy for the site addressed these key issues to determine the nature and

extent of contamination at the site:

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• Determine the presence of hazardous substances in soil, ground water and indoor air.

• Identify additional source(s) of hazardous substances to soil and ground water, if

present.

• Fully define the horizontal and vertical extent of hazardous substances in soil and

water-bearing strata underlying suspected source areas and the margins of the plume.

• Fully characterize the Site stratigraphy and hydrogeology, and evaluate temporal

variations in ground water flow and contaminant concentrations.

• Evaluate indoor air quality in buildings located over or in close proximity to the ground

water contaminant plume.

12.5 Conceptual Site Model

The CSM is presented in flow chart form in Figure 4 and in pictorial form in Figure 5. These

figures describe the primary contaminant sources, the primary release mechanisms,

secondary sources, secondary release mechanisms, and migration pathways. The primary

sources at the GCSP Site are the Holiday Cleaners at the corner of First Street and Monroe

Avenue and the Abandoned Dry Cleaning Facility on First Street north of Washington

Avenue. Contaminant release mechanisms, secondary sources, and migration pathways are

essentially the same for both sources. A potential source that cannot be ruled out based on

the data collected during the RI is a work shed near the intersection of First Street and

Jefferson Avenue. Additional characterization of the work shed location will be performed

during a preliminary design field investigation.

The primary release mechanisms at the active Holiday Cleaners facility were routine spills,

releases into a system of interior trenches, disposal of water decanted from a solvent/water

separator and discharged to the sanitary sewer, and overflowing of a former PCE storage

tank due to thermal expansion. The primary release mechanisms at the Abandoned Dry

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Cleaning Facility are less certain, since interviews were not conducted with the facility

owner. Similar release mechanisms as at the Holiday Cleaners are likely. Releases of PCE

by these mechanisms caused PCE to accumulate in surface soils, migrate into the subsurface

as DNAPL, and potentially flow through the sanitary sewer line. Soil, residual DNAPL, and

the sanitary sewer line are thus secondary sources of PCE. Secondary release mechanisms

include surface runoff, volatilization of PCE from soil and ground water, leaching of PCE

from soil and/or DNAPL during infiltration, dissolution of DNAPL in ground water, and

leakage of the sanitary sewer line. Once released into the environment at the GCSP Site,

PCE (and its degradation products) migrate within the shallow subsurface soils, soil vapor,

and ground water.

Release mechanisms at the Former Holiday Cleaners were likely similar to those at the

active Holiday Cleaners. PCE or other chlorinated VOCs, or products containing significant

quantities of these compounds, may have been stored at the work shed near the intersection

of First Street and Jefferson Avenue. Soil samples collected near the work shed indicate that

chlorinated VOCs may have been released to soil, potentially from periodic and/or routine

spills.

12.6 Nature and Extent of Soil Contamination

This section of the ROD describes the nature and extent of soil contamination found at

various suspected source locations. PCE and TCE are the primary COCs identified in

subsurface soil at the site. Figure 6 shows the sampling locations used during the RI.

12.6.1 Soil Contamination at Holiday Cleaners

Soil samples were collected from depths of 2 ft, 5 ft, and 10 ft bgs at locations surrounding

the Holiday Cleaners. PCE was detected to the maximum depth of exploration (10 ft bgs) at

several locations surrounding the Holiday Cleaners, and at a maximum concentration of

36 milligrams per kilogram (mg/kg) (nearly 70 times the EPA Region 6 Human Health

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Medium-Specific Screening Level [HHMSSL] of 0.55 mg/kg for residential soil) near the

southeast corner of the building. PCE also was detected at concentrations up to 21 mg/kg

in soil samples collected near the Holiday Cleaners southeastern property boundary. At the

Holiday Cleaners, TCE and other PCE degradation products were detected in soils

primarily near the southeastern property boundary, although TCE was detected just above

the EPA Region 6 HHMSSL (0.043 mg/kg) near the southeastern corner of the building.

12.6.2 Soil Contamination at Abandoned Dry Cleaners

PCE was detected in soil to the maximum depth of exploration (10 ft bgs) at locations

adjacent to and downgradient of the Abandoned Dry Cleaning Facility located on First

Street just north of Washington Avenue. PCE was detected at over 16 times the EPA

Region 6 HHMSSL near the east wall of the building (DP-13 at 2 ft bgs) and at over

three times the HHMSSL near the south wall (DP-12 at 5 ft bgs) of the building. PCE also

was detected at the far southeastern extent of the Abandoned Dry Cleaning Facility

property. TCE and other PCE degradation products were not identified in soil surrounding

the facility.

12.6.3 Soil Contamination at R&L Laundry

PCE was detected in two soil sampling locations in the alley behind the R&L Laundry,

which does not currently conduct dry cleaning, although it has in the past. PCE was

detected in soil below the EPA Region 6 SSL at a concentration of 0.082 mg/kg at the

northeastern building corner. PCE was detected at twice the EPA Region 6 SSL near the

building back door. PCE also was detected below the EPA Region 6 SSL at a location in

front of the building. TCE and other PCE degradation products were not detected in soil

surrounding the R&L Laundry.

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12.6.4 Soil Contamination at Former Holiday Cleaners

PCE was detected in a single soil sample collected from 2 ft bgs in the alley behind the

Former Holiday Cleaners location on First Street north of Stephens Avenue. PCE was

detected in soil below the EPA Region 6 SSL at a concentration of 0.095 mg/kg. Drilling

refusal was encountered at 2 ft bgs at all sampling locations surrounding the former facility

from an underlying basalt flow.

12.6.5 Soil Contamination at Former MST&T Company Maintenance Yard

PCE was detected at soil sampling locations near the edge of the former MST&T Company

maintenance property. PCE was detected above the EPA Region 6 SSL to the maximum

depth of exploration near the northeastern property boundary at the intersection of Geis

Street and Jefferson Avenue. PCE was detected below the Region 6 SSL at depths of 5 ft and

10 ft bgs at the eastern property boundary. TCE and other PCE degradation products were

detected primarily in samples collected near the northeastern property boundary. No VOCs

were detected in soil samples collected from the southeastern property boundary.

12.6.6 Soil Contamination at Work Shed

PCE and TCE were detected in soil samples collected on the north and south sides of a work

shed across Jefferson Avenue from the Allsup’s 200 gasoline station. These samples were

collected by NMED during the SI and identified PCE below the EPA Region 6 SSL, and TCE

above the Region 6 SSL, in samples from 1.5 ft bgs. Samples from 4 ft bgs also had

detectable PCE and TCE, but at concentrations below the EPA Region 6 SSLs.

12.7 Nature and Extent of Ground Water Contamination

This section of the ROD describes the nature and extent of ground water contamination at

the site. Ground water samples were collected using a direct-push drilling rig and existing

monitor wells present over portions of the plume (see Figure 7). Figures 9 and 10 show the

horizontal and the vertical extent of the chlorinated solvents contamination in ground water

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at the site. Horizontally, the plume extends from the two source areas to the south-

southeast approximately 1,500 ft. Vertically, the plume extends to a depth of at least 80 ft

bgs at the Holiday Cleaners source area.

The Holiday Cleaners was identified as the primary source of PCE in ground water during

the RI investigation. PCE emanating from the Holiday Cleaners follows a ground water

flow path to the southeast, gradually trending to the south-southeast beyond Geis Street.

PCE migrating along this flow path is transported within a thin silty-sand layer to a

maximum lateral extent of approximately 1,500 ft downgradient of the Holiday Cleaners,

with non-detect concentrations downgradient of this extent. The vertical extent of PCE

contamination at the site has not been completely established but will be determined during

a Pre-Design Field investigation.

PCE was detected in ground water in the parking lot of the Holiday Cleaners to a depth of

at least 55 ft bgs. PCE was detected across First Street from the Holiday Cleaners to a depth

of at least 80 ft bgs (the maximum depth explored at that location). In this boring, PCE was

detected at a maximum concentration of 3,400 µg/L (680 times the federal MCL [5 µg/L] for

ground water) at a depth of approximately 58 ft bgs.

PCE was detected at a concentration of 40,000 µg/L in well GMW-6 across First Street from

the Holiday Cleaners. PCE was detected at a maximum concentration of 51,000 µg/L (over

10,000 times the federal MCL) at sampling location DP-48, in the alley approximately 300 ft

downgradient of the Holiday Cleaners between First Street and Geis Street.

PCE was detected at high concentrations in ground water near the northeast corner of the

intersection of First Street and Jefferson Avenue. Based on ground water flow directions,

the source of this contamination would be suspected to be located at the northwest corner of

First Street and Jefferson Avenue, but both soil and ground water samples collected from

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this location have not detected chlorinated VOCs. The Holiday Cleaners is located

approximately 200 ft north on First Street, a location that is cross-gradient to the ground

water flow direction. As no other source is apparent, it is postulated that PCE and its

degradation products may be migrating preferentially within the coarse fill materials

surrounding a number of utilities (sewer, water, and gas) installed along First Street. Given

the very shallow depth to ground water, it is suspected that the utility trenches intersect the

ground water. These trenches are potentially providing a contaminant migration conduit

that transports contaminated ground water along the length of the trenches.

The work shed located across Jefferson Avenue from the Allsup’s 200 gasoline station may

be a source of PCE contamination in ground water, but high PCE detections within an

upgradient basement sump in the adjoining residential structure at the northeast corner of

First Street and Jefferson Avenue (2,300 µg/L) (NMED, 2001) suggests that the source of

ground water contamination is upgradient of the work shed, such as the utility trenches

along First Street.

Subsurface petroleum hydrocarbon contamination emanating from the Allsup’s 200

gasoline station at the intersection of First Street and Jefferson Avenue appears to be

enhancing the degradation of PCE at this location, resulting in the highest concentrations of

TCE, cis-1,2-DCE, and vinyl chloride (VC) detected at the GCSP Site.

The Abandoned Dry Cleaning Facility was identified as a second primary source of PCE

and its degradation products in ground water. A separate ground water PCE plume

emanates from this facility, extending laterally approximately 350 ft southeast of the

abandoned facility to just past the R&L Laundry across First Street. PCE was detected at a

maximum concentration of 1,600 µg/L (over 300 times the federal MCL) in a shallow

ground water sample collected from the southeast property boundary of the facility. PCE

was detected to a maximum depth of approximately 30 ft bgs near this same location during

the Phase 2 direct-push sampling event, and was non-detect at greater depths.

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12.8 Nature and Extent of Soil Vapor Contamination

Soil vapor samples were collected from locations surrounding several structures at which

vapor intrusion sampling also was conducted. Figure 8 presents the soil vapor and vapor

intrusion sampling locations and results. PCE and TCE concentrations were highest in

samples collected adjacent to structures 2 and 3, located across First Street from the Holiday

Cleaners. These structures also had the highest PCE and TCE vapor intrusion

concentrations. PCE was detected at a concentration of nearly 95,000 micrograms per cubic

meter (µg/m3) (and TCE was detected at a concentration over 857,000 µg/m3 adjacent to

structure 2 (closer to Holiday Cleaners). In general, significant concentrations of PCE and

its degradation products in soil vapor were only detected at locations within the known

lateral extent of PCE ground water contamination.

12.9 Nature and Extent of Indoor Air Contamination

Table 1 shows the criteria EPA used to evaluate indoor air data. Tier 3 action levels require

an evaluation of the need for mitigation measures to be implemented at the structure. Tier 2

action levels may require additional vapor intrusion monitoring and Tier 1 action levels do

not require any further action. Vapor intrusion (indoor air) samples collected at three

structures exceeded EPA Tier 3 PCE and TCE action levels within the GCSP Site (Figure 8).

Two of these structures are located across First Street from the Holiday Cleaners

(structures 2 and 3) and the third is located approximately 625 ft downgradient of the

Holiday Cleaners (structure 7). PCE and TCE concentrations in vapor intrusion samples

collected from structures 2 and 3 are significantly higher than at any other structure, and

approximately three times higher than detected at structure 7. These two structures are

currently unoccupied. In general, vapor intrusion samples collected from structures outside

the known lateral extent of shallow ground water contamination exhibit concentrations

below Tier 1 action levels (no further action is warranted). Structures overlying shallow

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ground water contamination typically exhibit concentrations above either Tier 2 (evaluate

whether additional sampling is warranted) or Tier 3 action levels.

12.10 Potential Routes of Contaminant Migration

Migration of contaminants at the GCSP Site occurs by means of several mechanisms,

including infiltration of water containing dissolved contaminants to shallow ground water,

DNAPL migration within the subsurface, volatilization of contaminants and migration as

subsurface soil vapor, and migration of dissolved contaminants within the ground water

aquifer.

12.10.1 Infiltration

Infiltration rates through the primarily silt and clay shallow subsurface are expected to be

relatively low. However, the very shallow depth to ground water (generally 5 to 7 ft bgs),

combined with the potential for an interconnected network of thin sand layers, may allow

infiltration of water containing dissolved contaminants to reach ground water within a

relatively short time period. Infiltration and distribution also would be facilitated within

utility trenches backfilled with coarse fill material. If PCE and its degradation products are

migrating through the sanitary sewer (due to potential disposal of water containing these

constituents at source areas), leakage of the sanitary sewer also would contribute to

enhanced infiltration and distribution of dissolved contaminants to ground water.

12.10.2 DNAPL Migration

The behavior of DNAPL in the subsurface is strongly affected by the nature and

heterogeneity of the subsurface media. When DNAPL is released to the unsaturated zone, it

can migrate downward, and capillary forces will immobilize some of the liquid in the pore

spaces as residual product. In lower permeability media (such as clays present in the

shallow subsurface of the GCSP Site), DNAPL may enter through micro-fracture networks

where dissolution and subsequent diffusive losses into the bulk matrix can occur. Pools of

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DNAPL also may form on top of lower-permeability media, be trapped within coarser

layers bounded by low permeability media (such as those observed at the GCSP Site), or

collect near the top of the capillary zone. This DNAPL can then begin to vaporize into the

gaseous phase and migrate by diffusion away from the source. Pressure or density

gradients can result in advective flow of the soil vapor, which can sometimes play a role in

the overall transport process. As they migrate, soil vapors will partition into the aqueous

phase (or dissolved phase) and the solid phase, tending to retard the rate of vapor

migration. Gaseous partitioning into the soil and water phases also will make contaminants

more readily available for aqueous transport.

Generally, the potential presence of DNAPL in or near the saturated zone is indicated if

concentrations in ground water exceed approximately 1 to 5 percent of chemical solubility

limits for the specified dissolved contaminant. The maximum detection of PCE in ground

water near the Holiday Cleaners is approximately 30 to 35 percent of the water solubility of

PCE, indicating that the presence of residual DNAPL is highly likely. These solubility levels

extend 700 ft downgradient of the Holiday Cleaners and 60 ft vertically in the Source Area.

12.10.3 Soil Vapor and Vapor Intrusion

VOCs present in the subsurface as a DNAPL, as dissolved aqueous-phase contamination,

and/or as residual soil contamination can volatilize into the vapor phase. Soil vapor may

migrate under the influence of pressure or density gradients, or by diffusion away from the

source. Advection of soil vapor from the unsaturated zone source areas is not considered

the primary source of vapor intrusion into the structures at the GCSP. Rather, local

volatilization from dissolved contaminants in shallow ground water, or DNAPL near the

source areas, are considered the primary source of soil vapor at any particular location at

the GCSP Site.

High concentrations of PCE and its degradation products present in soil vapor near

structures overlying the aqueous-phase contaminant plume may enter those structures by a

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number of means. Soil vapor may intrude through cracks in basements, into crawlspaces

beneath structures, or through cracks in structure foundations. Contaminants may then

collect within indoor air of the structure. At structure 3 at the GCSP Site, at the intersection

of First Street and Jefferson Avenue, an open sump in the basement allows for VOC

contaminants in the ground water in the sump to volatilize directly into indoor air.

12.10.4 Aqueous-Phase Transport

PCE migrates within the shallow ground water aquifer as dissolved PCE moving with

ground water flow. Shallow ground water at the GCSP Site moves preferentially through

thin, laterally extensive silty sand layers, with varying interconnectivity. A 6-inch to 1-ft

thick, laterally extensive sand layer was identified in numerous borings at the site, and is

shown in the cross sections presented in the RI Report. The lateral extent of sand and silty

sand layers within the deeper aquifer are currently unknown, but assumed to be similarly

extensive. Such sand layers are currently suspected to represent a primary migration

pathway for contaminants within the deeper aquifer.

The alluvial deposits of the shallow aquifer are known to contain thin laterally extensive

sand and silty sand layers and at least one thicker sand layer near GMW-1. These sand

layers act as the primary mechanism for lateral transport of contaminants within the

shallow aquifer. The interconnectivity of various sand layers within the alluvial deposits is

uncertain but would be a pathway for migration of contaminants from shallower to deeper

portions of the aquifer.

12.10.5 Potential Routes of Human Exposure

The exposure pathways identified for the GCSP Site are ground water exposure, soil and

exposure to vapor intrusion. As described in greater detail within the RI Report, ground

water exposure cannot be considered an incomplete pathway since property owners are not

legally prohibited from using the local ground water. Human exposure could occur

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through direct contact with shallow ground water through existing wells or excavation.

Chlorinated solvent contamination is not currently present in the Grants municipal water

supply wells, although the hydrogeologic interaction between the shallow alluvial aquifer

and the deeper regional ground water aquifer that serves as the municipal water supply has

not been investigated. Volatilization of the primary indicator constituents from the shallow

ground water surface provides an exposure pathway through vapor intrusion (indoor air).

A detailed discussion of potential exposure pathways is presented in EPA’s BHHRA,

included in the RI Report.

Potential exposure pathways from VOCs in soil are: (1) direct contact with soil (soil

ingestion, dermal contact, and inhalation of volatile emissions to outdoor air); and (2) vapor

intrusion from soil to indoor air. Vapor intrusion from soil has been addressed in part

through soil gas sampling and indoor air sampling. Further evaluation of potential direct

contact exposure pathways was conducted by comparison of total VOC results in soil with

NMED SSLs based on residential land use assumptions. The major chemicals of potential

concern (COPCs) in this evaluation were PCE and TCE.

The highest PCE concentrations in soil were found around Holiday Cleaners where PCE

concentrations were higher than the HHMSSL in selected samples. The total VOC

concentrations in soil, combined with the soil gas and indoor air data, suggest that VOCs in

soil potentially pose an unacceptable indoor air risk through vapor intrusion. In addition,

the highest PCE concentrations in soil (36 mg/kg and 21 mg/kg) are as much as 42 percent

of the soil saturation limit (calculated to be 85 mg/kg for a sandy soil), suggesting the

potential presence of DNAPL in some locations in soil. Therefore, while direct contact risks

potentially associated with VOCs in soil might not exceed risk reduction objectives (i.e.,

Excess Lifetime Cancer Risk [ELCR] of 1 x 10-5), soil remediation is warranted in the source

areas to address potential vapor intrusion risks and to address the presence of DNAPL in

soil as a continuing source of ground water contamination.

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12.11 Ground Water Flow and Transport Modeling

A simple preliminary ground water flow and transport model was constructed for the GCSP

Site using MODFLOW-SURFACT software, and available data collected during the RI. The

purposes of constructing the model were to gain a better understanding of the physical

characteristics of the aquifer and to provide an approximate timeframe for remediation of

the existing ground water contamination using various technologies (particularly pump and

treat), expected to be evaluated as part of the Feasibility Study. Many simplifying

assumptions were necessary within the ground water model due to the limited dataset

available following the RI. However, sufficient data were available to develop a

preliminary model to allow an evaluation of approximate pump-and-treat cleanup times.

The existing ground water model is anticipated to be substantially improved following

additional field investigation and data collection during a Preliminary Design Field

Investigation conducted during the RD. The expanded ground water model will be used

during the RD to evaluate selected treatment technologies and provide information

regarding expected time of remediation, dosing requirements, and other design components

for the selected remedial alternative(s).

Contaminant transport modeling was limited to a “forward-in-time” analysis due to a lack

of historical chemical time series data at the GCSP Site. The inability to model the historical

generation of the current contaminant distribution meant that a useful component of model

calibration could not be performed. However, the model was calibrated in part by adjusting

parameters until the model accurately represented the current downgradient and lateral

extent of ground water contamination using the current understanding of the time of

original release, and assuming continuous source areas.

Anticipated improvements to the preliminary ground water model include aquifer

pumping test data (rather than currently available slug test data) from several depth

intervals to provide more accurate representation of hydraulic aquifer properties, additional

lithology information to provide more accurate model layering, and additional depth

profiling of contaminants for more accurate representation of contaminant distribution. The

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installation of new permanent ground water monitoring wells also will provide improved

data on ground water flow directions and flow gradients within downgradient areas of the

contaminant plume.

13.0 Current and Potential Future Land and Resource Uses

13.1 Current and Potential Future Land Uses

Land use at the site currently includes mixed residential homes and commercial businesses.

Small businesses are mainly located along First Street and properties to the east are mostly

residential. A daycare facility is located at the corner of Monroe Avenue and Peek Street

and is just outside of the plume area. Other notable nonresidential structures within the

plume boundary are the Knights of Columbus building on Geis and Jefferson Avenue and a

bowling alley at the corner of Jefferson Avenue and Peek Street. To the east of the plume

boundary is an elementary school. Based on the history of the area the future land use is

unlikely to change from the current uses.

13.2 Current and Potential Future Ground Water Uses

The shallow ground water at the GCSP Site is currently not used by residents in the area.

However, owners are not legally prohibited from using the local ground water. The

drinking water source for the City of Grants is from two upgradient wells approximately

2 miles west (upgradient) of the Site. The City of Grants is planning to install an additional

supply well within 0.75 miles west of the Site. The interaction between the shallow aquifer

and the deeper aquifer is not well known at this time and will be the subject of investigation

prior to the design of the remedial alternatives for the GCSP Site. The future ground water

use at the Site is as a potential drinking water source for the City of Grants.

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14.0 Summary of Site Risks

This section of the ROD provides a summary of the Site's human health and environmental

risks. A BHHRA (EPA, 2005b) for the site was completed in July 2005, which estimated the

probability and magnitude of potential adverse human health and environmental effects

from exposure to contaminants associated with the Site assuming no remedial action was

taken. The BHHRA provides the basis for taking action and identifies the contaminants and

exposure pathways that need to be addressed by the remedial action.

14.1 Summary of Human Health Risk Assessment

The BHHRA followed a four-step process:

a. Hazard identification (identification of COCs)

b. Exposure assessment

c. Toxicity assessment

d. Risk characterization

The EPA used an exposure point concentration (EPC) for each COC and the reasonable

maximum exposure (RME) scenario to estimate risk. The EPC was the lesser of the

maximum detected concentration and the 95 percent upper confidence level (UCL) of the

arithmetic mean concentration of the COCs in soil or ground water. A 95 percent UCL is a

statistically derived value based on sample data within an exposure area. The RME scenario

is the maximum exposure that is reasonably expected to occur at the Site and is based on

"upper bound" and "central tendency" estimates. The use of multiple conservative exposure

factors makes the RME scenario protective of potential exposures.

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14.1.1 Identification of Chemicals of Concern

COCs are chemicals that pose a carcinogenic risk to human health greater than 1 in 1,000,000

(1 X 10-6), have a noncarcinogenic hazard index (HI) greater than (>) 1, or are found in site

ground water at concentrations that exceed MCLs. While various BTEX (benzene, toluene,

ethylbenzene, and xylene) compounds have been identified as COCs at the GCSP Site, they

are not targeted for cleanup under the CERCLA Remedial Action as they will be separately

addressed by the NMED-PSTB.

The following presents a summary of the evaluation and the constituents that are

considered to be COCs at the site:

14.1.1.1 Ground Water

The impacted shallow aquifer is not considered a source of drinking water for the city, but

the hydraulic interaction with the deep aquifer is of concern. The site is located within an

area served by a monitored public water supply system. City of Grants Ordinance No. 394

requires the “…mandatory connection of homes or other facilities within the City to the

public sewer and water system, and the City has the power to require such mandatory

connection…”.

An existing private well or a new private well could be used for drinking water in the

future. Also, the potential does exist for contamination to migrate from the shallow to the

deep aquifer and affect city water. The ground water pathway for the shallow aquifer is

therefore, considered complete for future use.

COPCs in ground water were identified by comparing the maximum detected chemical

concentrations in the wells to the following criteria:

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1. Federal MCLs and if no MCLS were available.

2. EPA Region 6 tap water maximum screening levels (MSLs) calculated with a target risk

of 1 x 10-6 for carcinogens and using a hazard index quotient (HQ) of 0.1 for

noncarcinogens.

Chemicals in ground water that were higher than EPA Region 6 tap water MSLs were

included as COPCs in the risk assessment. After the risk-based screen was completed, the

following chemicals were considered COPCs at the site: benzene; bromoform; cis-1,2-DCE;

ethylbenzene; MTBE; PCE; toluene; trans-1,2-DCE; TCE; VC; and total xylenes. Chemicals

in ground water that were detected at concentrations higher than MCLs were treated as

COCs. All the identified COPCs have MCLs with the exception of MTBE. Therefore, MTBE

was further evaluated in the risk assessment and found to pose a carcinogenic risk of 2x10-6

for future adult resident and 1 x 10-6 for future child resident. The risk from MTBE exposure

is within EPA risk range and hence it was excluded from the list of COCs for the site. Based

on this evaluation ground water COCs for the site are benzene bromoform, cis-1,2-DCE,

trans 1,2-DCE, PCE, TCE, vinyl chloride, and total xylenes.

14.1.1.2 Indoor Air COCs

Potential exposure pathways from indoor air could occur through vapor intrusion. The

process of vapor intrusion involves the migration of VOCs from ground water or subsurface

soil into overlying structures. In these structures, chemicals may accumulate to

concentrations that pose a risk of health effects from long-term exposure. Indoor air

sampling results were used to identify COPCs in indoor air, with an emphasis on

chlorinated solvents and BTEX.

Initially, the maximum concentrations detected in indoor air at any of the sampled locations

were compared with screening levels presented in EPA’s Draft Vapor Intrusion Guidance

(EPA 2002). These screening levels correspond to a 1 x 10-6 cancer risk or a noncancer HQ of

1 based on residential land use assumptions. If the maximum concentration of a chemical

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was lower than the screening level, it was excluded as a COPC. For chemicals that were

retained, a further screen was performed, evaluating COPCs on a structure-by-structure

basis. In this further screen, if the maximum concentration in an individual residence was

below the screening level, that chemical was not included as a COPC for that residence.

Uncertainties in the COPC selection process for indoor air include the presence of

background concentrations not associated with vapor intrusion. Direct measurement of

concentrations in indoor air also may detect VOCs from other indoor and outdoor sources,

such as household products (adhesives, paint, cleaners). In certain cases, COPCs identified

for a particular residence may actually be background levels from these other sources.

Including COPCs that may be background based potentially overstates risks associated with

the vapor intrusion pathway. Based on the evaluation the residential indoor air COCs for

the site are benzene, PCE, and TCE.

14.1.1.3 Soil COCs

The process of evaluating soil consisted of comparing detected concentrations of chlorinated

solvents and BTEX against NMED screening levels (SLs) for residential direct contact (RES)

and for the pathway from soil to ground water (SGW). These SLs are taken from NMED’s

Technical Background Document for Development of Soil Screening Levels, Revision 2.0 (February

2004) and are equivalent to either a carcinogenic risk of 1E-05 or a hazard quotient of 1, or to

an available MCL endpoint, in the case of the SGW pathway. In addition, for the SGW

pathway, the selected SLs correspond to a dilution-attenuation factor of 1, due to the

shallow water table.

The 2-ft depth interval was considered in the direct contact screen, and all three depth

intervals were considered in the SGW screen. In both cases, the highest detected

concentration for each chemical in the appropriate soil intervals throughout the site was

compared to its appropriate SL. If the chemical passed the screen, it was not considered

further in the process. Non-detects were included in the screen to highlight those chemicals

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with detection limits above their respective SLs. Based on this evaluation, there are no

COPCs for direct contact with the top 2 ft of soil. COPCs for the SGW pathway are PCE,

TCE, cis-1,2-DCE, and xylene. Soil COCs for direct residential contact at the site are PCE

and TCE.

Tables 2 and 3 (Summary of Chemicals of Concern and Medium-Specific Exposure Point

Concentrations for Ground Water and Soil; and Indoor Air) present the COCs and EPCs for

each of the COCs detected in ground water and/or indoor air.

14.1.2 Exposure Assessment

The objectives of the exposure assessment are to evaluate potential current and future

human exposures to COCs in all media of concern. The current and potential future human

receptors were determined by the site's configuration, land and water use, and activity

patterns. Receptors (adult/child) were identified for both current and potential future site

conditions. The receptors identified for quantitative analysis for the BHHRA are presented

in Table 4 (Selection of Exposure Pathways-Shallow Ground Water and Indoor Air), along

with a rationale for selecting the exposure pathways.

The CSM (Figures 4 and 5) shows the potential exposure pathways and human receptors at

the site. The CSM was developed based on local land and water use associated with the site.

Exposure pathways and routes identified for the site, and driving the remedial activities

specified in this ROD, are presented in Table 4 (Selection of Exposure Pathways) and are

based on the following:

a. Ground Water Exposure Pathway − Exposure to COCs in the shallow aquifer was

evaluated through ingestion, inhalation and dermal exposure routes for the future onsite

resident adult, child, and indoor worker.

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b. Indoor Air Exposure Pathway − Exposure to COCs in indoor air (via vapor intrusion)

through inhalation for the current/future adult and child residents and child attending

day care.

Mathematical models were used to calculate the intakes (i.e., the doses) of the COCs for each

receptor, using applicable exposure routes. The models used to calculate intakes are

presented in Tables 5 and 6. Each table defines the variables used in estimating doses and

includes the assumptions, known as exposure parameters, which are used in the model.

These parameters include variables, such as daily ingestion rate of water, exposure

duration, and body weight. In general, the exposure parameters that were used are

standard values recommended by national and EPA Region 6 guidance. Regardless of the

exposure route, the intake is presented as an estimated daily dose in units of milligrams of

chemical per kilogram of body weight per day (mg/kg-day).

14.1.3 Toxicity Assessment

Toxicity assessment is accomplished in two steps: hazard identification and dose-response

assessment. Hazard identification is the process of determining whether exposure to a

chemical is associated with a particular adverse health effect and involves characterizing the

nature and strength of the evidence of causation. The dose-response assessment is the

process of predicting a relationship between the dose received and the incidence of adverse

health effects in the exposed population. From this quantitative dose-response relationship,

toxicity values are derived that can be used to estimate the potential for adverse effects as a

function of potential human exposure to the chemical.

14.1.3.1 Carcinogenic and Noncarcinogenic Effects

Two general groups, carcinogens and noncarcinogens, categorize chemicals depending on

the types of effects on human health. Exposure to any substance in high enough doses can

result in toxic effects. Therefore, many carcinogens also produce known noncancer health

effects. Noncancer toxicity values (reference dose [RfD] and reference concentration [RfC])

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were used to evaluate the COCs present at the site in environmental media to determine the

noncancer toxic effects. Cancer slope factor (SF) was used to evaluate carcinogenic effects.

Tables 7 and 8 show the noncancer and cancer toxicity data for the COCs through oral,

dermal, and inhalation routes. The toxicity data were evaluated based on information from

Agency for Toxic Substances and Disease Registry (ATSDR), EPA’s Integrated Risk

Information System (IRIS) database, and National Center for Environmental Assessment

(NCEA) issue papers.

14.1.4 Risk Characterization

The risk characterization section of the ROD summarizes and combines outputs of the

exposure and toxicity assessments to characterize baseline risk at the site. Baseline risks are

those risks and hazards that the site poses if no action were taken.

14.1.4.1 Carcinogenic Risk

For carcinogens, risks are generally expressed as the incremental probability of an

individual developing cancer over a lifetime as a result of exposure to the carcinogen.

Excess lifetime cancer risk (ELCR) is calculated from the following equation:

ELCR = CDI x SF

where:

ELCR = a unitless probability (e.g., 2 x 10-5) of an individual developing

cancer

CDI = chronic daily intake averaged over 70 years, expressed as

mg/kg-day

SF = slope factor, expressed as (mg/kg-day)–1

These risks are probabilities that are expressed in scientific notation (e.g., 1 x 10-6). An ELCR

of 1 x 10-6 indicates that an individual experiencing the Reasonable Maximum Exposure

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(RME) estimate has a 1 in 1,000,000 chance of developing cancer as a result of site-related

exposure. This is referred to as an ELCR because it would be in addition to the risks of

cancer individuals face from other nonsite-related causes such as smoking or exposure to

too much sun. The chance of an individual developing cancer from all other causes has

been estimated to be as high as 1 in 3. The EPA's generally acceptable risk range for site-

related exposures is 1.0 x 10-4 to 1.0 x 10-6, or a 1 in 10,000 to 1 in 1,000,000 chance,

respectively, of an individual developing cancer.

Tables 9 and 10 present summaries of cancer risk and noncancer hazards to receptors due to

contact with COCs in shallow ground water, as well as inhalation of indoor air due to vapor

intrusion. The RME scenario is used as the basis for decision at the Site.

14.1.4.2 Noncarcinogenic Risk

For noncarcinogens (systemic toxicants), potential effects are evaluated by comparing an

exposure level over a specified time period (e.g., exposure duration) with a RfD derived for

a similar exposure period. An RfD represents a level that an individual may be exposed to

that is not expected to cause any harmful effect. The ratio of exposure to toxicity is called a

hazard quotient (HQ). An HQ of less than 1 indicates that a receptor's dose of a single

contaminant is less than the RfD, and that toxic noncarcinogenic effects from that chemical

are unlikely. The HI is generated by adding the HQs for all COCs that affect the same target

organ (e.g., liver) or that act through the same mechanism of action within a medium or

across all media to which a given individual may reasonably be exposed. An HI of less than

1 indicates that, based on the sum of all HQs from different contaminants and exposure

routes, toxic noncarcinogenic effects from all contaminants are unlikely. An HI greater than

1 indicates that site-related exposures may present a risk to human health. The HQ is

calculated as follows:

Non-cancer HQ = CDI/RfD

where:

HQ = hazard quotient (unitless)

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CDI = chronic daily intake (mg/kg-day)

RfD = reference dose (mg/kg-day)

14.1.5 Uncertainties

Some level of uncertainty is introduced into the risk characterization process every time an

assumption is made. In regulatory risk assessment, the methodology dictates that

assumptions err on the side of overestimating potential exposure and risk. The effect of

using numerous assumptions that each overestimate potential exposure provides a

conservative estimate of potential risk.

The large number of assumptions made in the risk characterization could potentially

introduce a great deal of uncertainty. Any one individual's potential exposure and

subsequent potential risk are influenced by their individual exposure and toxicity

parameters and will vary on a case-by-case basis. Understanding the uncertainties in the

assessment should result in decisions that are more informed.

At least three sources of uncertainties exist in the BHHRA:

• Uncertainty around environmental data

• Uncertainty around exposure assumptions

• Uncertainty related to toxicity assumptions

14.1.5.1 Uncertainty In Environmental Data

A sampling plan is used to determine and evaluate the full nature and extent of

contamination to support the analysis. The sampling plan in turn relies on known site data

to determine sampling locations. In addition, seasonal variation of concentrations may

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occur because of fluctuations in the water levels, and sampling and analytical procedures

are likely to introduce variability. At the GCSP Site, ground water locations were sampled

for chlorinated solvents from numerous wells and direct-push borings. Therefore,

concentration of organic chemicals are likely to be representative of fluctuations expected in

ground water and unlikely to contribute to any systemic bias of the results.

Indoor air samples were collected at least twice from most homes to account for seasonal

variability, but in a few cases, only one sample was collected. A single detected value is not

likely representative of indoor air concentration. Additionally, measured values in indoor

air were attributed solely to vapor intrusion and not to any other indoor source. This may

overestimate the risk from vapor intrusion in the homes. Finally, benzene, which was

detected in ambient outdoor air, also can produce elevated contaminant concentrations in

indoor air not related to vapor intrusion. Possible outdoor air sources of benzene include

motor vehicle emissions and emissions from a nearby gasoline service station.

14.1.5.2 Uncertainty in Exposure Assumptions

A number of uncertainties are associated with assumptions made in the exposure

assessment. Areas of uncertainty include the calculation of intakes and the selection of

exposure parameters. Uncertainties regarding exposure assumptions result from the

variability of the different parameters, such as ingestion rates and exposure durations both

within and across populations. Best estimates from data sources compiled by regulatory

agencies were used in assessing potential exposures. How well these assumptions fit the

community is unknown. The 95th percentile values from the exposure ranges were

incorporated into the exposure assumptions to make the assessment more reflective of

community demographics. Assumptions of resource use patterns may have included

unlikely scenarios, or conversely, missed likely uses. In any case, because of the use of the

95th percentile values and conservative assumptions for potential exposures reflected in the

RME, the BHHRA should provide a reasonable estimate of risk.

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14.1.5.3 Uncertainty in Toxicity Assumptions

Assumptions of toxicity at expected exposure doses were based on unit exposure values

determined by regulatory agencies. Because of uncertainties in the studies used in

determining toxicity, single to multiple order-of-magnitude adjustments were made in the

process of determining safe exposure levels. Therefore, it is anticipated that the values will

tend to overestimate expected toxicity at a given level of exposure.

Multiple chlorinated solvents may act on similar target organs and systems to produce

similar toxic responses. Additivity of responses is assumed, but it is unknown if straight

additivity is a valid assumption. Synergistic, or more than additive, responses might occur

with exposure to multiple contaminants acting on similar tissues. This potential is

somewhat balanced by the assumption that co-exposures to the highest levels of all

contaminants would occur. In reality, the composition of the plume changes with distance

from the source as PCE degrades into its breakdown products, which increase in relative

concentration. It is, therefore, difficult to predict the net effect of these predicted

interactions on risk values.

In addition, BTEX present within portions of the site might have synergistic or additive

effects if co-exposures occurred. BTEX is co-located with the chlorinated solvents in

portions of the plume, so there is a possibility that co-exposures could occur. Laboratory

data are generally difficult to find on chemical-chemical interactions because of the limitless

combinations of exposure concentrations and difficulties in interpretation for even the best-

designed studies.

Finally, although there may be sensitive subsets of the population at the site, the toxicity

reference values incorporate uncertainty factors that should be protective of these sensitive

subpopulations. Combined with the RME exposure assumptions, the net result of the

evaluation should be protective of those members of the population.

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14.2 Ecological Risk Assessment

An ecological risk assessment was not performed for the GCSP Site, primarily due to the

volatility of the contaminants. VOCs do not normally persist in surface media that would

be considered for ecological risk – namely, surface soil and surface water. Concurrent with

the planning phase of the RI, EPA and NMED collected water samples from eight locations

along the Rio San Jose to investigate the shallow ground-water/surface-water interface

(hyporheic zone) in the vicinity of the GCSP Site. PCE was not detected in these samples;

however, 1,1-Dichloroethane (1,1-DCA) and cis-1,2-DCE were detected in four of the

samples, and TCE was detected in one of the samples. All detected concentrations were less

than their respective MCLs. All detected concentrations also were less than ecological

screening values for fresh water available from various state agencies. It does not appear

that these chlorinated VOC compounds in the hyporheic zone are related to the primary

release locations identified during the SI or RI. The presence of these compounds indicates

that chlorinated solvents are entering the Rio San Jose from another undefined source,

potentially near First Street, and the concentrations are well below levels that would

indicate a concern for ecological receptors.

14.3 Basis for Remedial Action

The response action selected in this ROD is necessary to protect the public health or welfare

or the environment from actual releases of hazardous substances into the environment. The

response action is warranted because:

1. The ground water COCs are present in concentrations above their MCLs; therefore, they

present an unacceptable risk to human health and the environment.

2. The shallow aquifer that is contaminated will continue to pose vapor intrusion risk to

residents.

3. The indoor air COCs present either a carcinogenic risk greater than 1 x 10-5 or a

noncarcinogenic HQ greater than 1.

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15.0 Remedial Action Objectives

The Remedial Action Objectives (RAOs) provide general descriptions of what the

Superfund cleanup is designed to accomplish. The RAOs are established on the basis of the

nature and extent of the contamination, the resources that are currently and potentially

threatened, and the potential for human and environmental exposure. The remedial goals

are media-specific, quantitative goals that define the extent of cleanup required to achieve

the RAOs. These goals serve as the design basis for the Selected Remedy identified in this

ROD.

15.1 Remedial Action Objectives for Ground Water

RAOs, remediation goals, and remediation strategies developed for the GCSP Site assume

that the GCSP Site consists of residential and commercial properties, and will continue to

consist of residential and commercial properties for the foreseeable future. The GCSP Site

remedy will address affected residential exposure pathway. The RAOs for ground water at

the GCSP Site are:

• Protect human health from exposure to chemical constituents in concentrations above

MCLs or Applicable or Relevant and Appropriate Requirements (ARARs).

• Restore the ground water at the GCSP Site such that it contains concentrations of the

COCs less than the applicable MCLs or ARARs in a timely manner.

• Prevent DNAPL, if present, from causing concentrations of COCs in ground water to

exceed MCLs or ARARs.

• Reduce the concentration of COCs in ground water to mitigate vapor intrusion.

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15.2 Remedial Action Objectives for Soil

The RAOs for the soil at the GCSP Site are:

• Prevent the ground water from being impacted above MCLs through transport of COCs

from the unsaturated zone.

• Protect human health from exposure to chemical constituents in soil.

• Reduce the concentration of COCs in soil and soil vapor to mitigate the vapor intrusion

pathway.

15.3 Remedial Action Objectives for Vapor Intrusion

The RAO for vapor intrusion at the GCSP Site is:

• Prevent vapor intrusion into structures that results in human exposure to vapor-phase

COCs in excess of a 10-5 ELCR.

15.4 Basis and Rationale for Remedial Action Objectives

The basis for the RAOs for the ground water and soil is to clean up the site to residential

standards, the current and anticipated future land use for the site. The chlorinated solvents

in ground water are present above ARARs and have migrated beneath residential

properties. There are no prohibitions that prevent the use of the shallow ground water

contaminated by the chlorinated solvent plume. Although currently no one is exposed to

contaminated ground water in the shallow aquifer, the risk is unacceptable as the future use

of ground water in the area is potentially drinking water. It is EPA’s policy to take action at

ground water contaminated sites when contaminants exceed MCLs. Remedial Actions at

the GCSP Site are expected to reduce the chlorinated solvent concentrations to less than

MCLs and the New Mexico Water Quality Control Commission (WQCC) standards. The

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Remedial Action in the source area will address DNAPL, the principal threat waste and

eliminate the source for contamination and restore soil and ground water. The Remedial

Action in the remaining portion of the site will address any DNAPL present and restore

ground water to drinking water standards and remove vapor intrusion risk to residents in

the area.

Within the source areas at the GCSP Site, concentrations of COCs in ground water are

believed to be caused in part by residual PCE in soil. The soil RAOs are intended to address

the residual COCs in soil as part of the Selected Remedy. COCs in soil will be treated or

removed to prevent soil contamination from being a continuing source of unacceptable

dissolved- and vapor-phase COCs.

COCs have been identified in soil within source areas at the GCSP Site. Exposure to local

residents near the source areas and to construction workers working within the source areas

are of concern. The Remedial Action is intended to reduce the concentrations of COCs such

that potential exposure to the COCs at concentrations that exceed target risk levels will be

prevented. Once the COCs are no longer present in the soil at the source areas, the pathway

to the vapor phase will no longer be complete, thus preventing impact to indoor air in

adjacent residential structures.

Vapor-phase COCs from ground water and soil vapor intrusion are present in residential

structures within the GCSP Site at concentrations that exceed the target indoor air risk

levels. The Remedial Action addressing vapor intrusion in homes is intended to provide a

remedy to remove the completed pathway for the COCs to indoor air.

15.5 Risks Addressed by the Remedial Action Objectives

Implementing active remedies in the source area, shallow plume core and hot spot, shallow

plume periphery and deeper plume will address the risks associated with chlorinated

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solvents in ground water at the site. PCE concentrations vary from a high of 51,000 µg/L in

the plume core to 1,000 µg/L in the plume periphery. Implementation of the Selected

Remedy is expected to reduce the concentrations of chlorinated solvents in ground water to

safe drinking water standards. The cancer risk of 2 x 10-3 associated with inhalation of

vapors in three residences will be addressed by installing vapor mitigation system in homes.

The vapor mitigation systems are anticipated to reduce the cancer risk to below the

acceptable level of 1 x 10-5. The EPA’s decision to install an additional eleven homes with

vapor mitigation system will ensure any future risks for these residences do not exceed the

1 x 10-5 risk level.

16.0 Description of Alternatives

The following are the alternatives that EPA reviewed for each site-impacted area:

Indoor Air Alternatives

• Alternative 1 − No Action

• Alternative 2 − Vapor Mitigation (Selected Alternative)

Source Area Treatment Alternatives


• Alternative 2 − Thermal Treatment (Selected Alternative)

• Alternative 3 – ISCO w/Follow-On ERD

• Alternative 4 – ERD (Gridded)

Shallow Plume Core and Hot Spot

• Alternative 1 – No Action

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• Alternative 2 – Zero-Valent Iron (ZVI) Permeable Reactive Barrier (PRB)-Multiple

Transects

• Alternative 3 – ISCO w/Follow-On ERD (Selected Alternative)

• Alternative 4 − ERD (Bio-Barrier)

• Alternative 5 – Pump and Treat

Shallow Plume Core Periphery

• Alternative 1 – No Action

• Alternative 2 – Monitored Natural Attenuation (MNA)

• Alternative 3 – ZVI PRB-Multiple Transects

• Alternative 4 – ERD (Bio-Barrier) (Selected Alternative)

• Alternative 5 – Pump and Treat

Deeper Ground Water


• Alternative 2 − Monitored Natural Attenuation (MNA)

• Alternative 3 − ZVI PRB-with Deep ERD

• Alternative 4 − ERD (Bio-Barrier) (Selected Alternative)

• Alternative 5 − Pump and Treat

16.1 Common Elements of Each Remedial Component

This section of the ROD describes those components that are common to each of the

remedial alternatives except the No Action Alternative. Common remedial components to

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all or most of the remedial alternatives include the need for a Preliminary Design Field

Investigation to collect site-specific data for the RD, a ground water monitoring program,

and Five-Year Reviews.

16.1.1 Preliminary Design Field Investigation

Additional field work is required at the GCSP Site prior to the RD to collect essential site

data for final design of the selected treatment alternatives. Monitoring wells were not

installed as part of the RI and the current extent of the PCE ground water plume is based on

direct-push sampling results. Sufficient soil sampling to fully delineate the horizontal and

vertical extent of DNAPL and soil contamination in source areas was not performed during

the RI and the current extent of soil contamination above Preliminary Remedial Goals (RGs)

is unknown.

The Preliminary Design Field Investigation will provide a network of monitoring wells to

enable the complete horizontal and vertical delineation of PCE in ground water, particularly

at depths below 20 ft bgs. The wells will allow for continued monitoring of VOC

concentrations throughout the plume. The Preliminary Design Field Investigation will

perform additional soil and ground water sampling within the two source areas identified

during the RI, the Holiday Cleaners and the Abandoned Cleaners, and will assess the source

areas for the presence of DNAPL.

Additional lithologic characterization will be performed to better define the CSM, and

aquifer testing will be conducted within several of the new ground water monitoring wells.

Other aquifer properties specific to the treatment technologies included within the Selected

Alternative will also be evaluated, including soil oxidant demand, sulfate concentrations in

ground water, and sustainable injection rates. The additional data collected during the

Preliminary Design Field Investigation will be vital to developing the final design(s) for the

selected remedial alternatives.

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16.1.2 Ground Water Monitoring Program

Ground water sampling will be required as part of the Remedial Action for treatment of

various aspects of the GCSP Site. To confirm that treatment goals are being met, a period of

40 years of ground water sampling and monitoring is anticipated to track the progress of the

treatment alternatives. The ground water sampling program will be fully developed during

the RD, and will include an exit strategy for discontinuing the program if the RAOs are met

before the end of the sampling period.

It is assumed that approximately 36 monitoring wells will be installed during the

Preliminary Design Field Investigation and the six existing NMED monitoring wells will

serve as the monitoring well network and will adequately monitor the overall progress of

the Remedial Action, track the reduction of concentrations within the sitewide plume, and

allow monitoring of the potential migration of contaminants. Ground water monitoring at a

minimum will be conducted semi-annually for the first 5 years after remedy construction is

complete and annually thereafter unless otherwise determined in consideration of site

conditions.

16.1.3 Five-Year Reviews

Five-Year Reviews will be required at the GCSP Site since varying amounts of

contamination will remain onsite that would prohibit unlimited and unrestricted use.

Five-Year Reviews will be conducted until restoration goals are met, anticipated to take

about 40 years.

16.1.4 Institutional Controls

To protect human health from the existing ground water contamination while cleanup is

ongoing, the EPA and NMED will request the New Mexico Office of State Engineer (OSE) to

issue an order restricting future well drilling within a portion of the aquifer contaminated

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by the plume until remediation goals for the ground water are met. The order will only

apply to new requests for water well permits and cannot be enforced against existing water

well permit holders. The OSE does not have a vested enforcement authority but has the

ability to enforce with a court order. The EPA will work with NMED to issue a health

advisory not to consume ground water from the existing wells within the plume area.

16.2 Distinguishing Features of Each Alternative

16.2.1 Indoor Air Alternatives

Concentrations of PCE and/or TCE currently exceed the RGs for indoor air at

three residential structures at the GCSP Site. The alternatives selected for evaluation for

treatment of indoor air at the GCSP Site are no action or the installation of radon-type vapor

mitigation systems.

16.2.1.1 Alternative 1: No Action

Estimated Time for Design/Construction: Not applicable

Estimated Time to Reach Remediation Goals: Not applicable

Estimated Capital Cost: $ 0

Estimated Life Time O&M Costs: $ 0

Discount Factor: 7%

Estimated Total Present Worth Cost: $ 0

Numbers of Years Cost Is Projected: Not Applicable

The No Action Alternative is included as a baseline for evaluation of the other remedial

alternatives, as required by the NCP. Under Alternative 1, no remedy will be implemented

and indoor air at these structures would continue to exceed the RGs such that the RAOs for

indoor air would not be met.

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16.2.1.2 Alternative 2: Vapor Mitigation

Estimated Time for Design/Construction: Less than 1 year

Estimated Time to Reach Remediation Goals: Less than 1 year

Estimated Capital Cost: $ 425,000

Estimated Life Time O&M Costs: $ 6,500

Discount Factor: 7%

Estimated Total Present Worth Cost: $ 331,500

Number of Years Cost Is Projected: 20 years

Under Alternative 2, the EPA will install vapor intrusion mitigation systems at residential

structures where concentrations of PCE and/or TCE currently exceed the RGs for indoor air.

In addition, EPA will install vapor mitigation systems in additional residences that are

located directly above the ground water plume where concentrations of TCE or PCE exceed

1,000 µg/L. The EPA is taking this additional step to eliminate future risks to residents that

live directly above the most affected portion of the plume. The systems would be installed

in those residential structures shown in Figure 11. Following is a listing and description of

the remedy components for Alternative 2:

Vapor Intrusion

1. Treatment Components. Vapor mitigation systems do not treat indoor air but rather

prevent vapor intrusion. There is no treatment component for this alternative.

2. Containment Components. Vapor intrusion mitigation systems would be

functionally similar to radon mitigation systems and consist of placing a plastic liner

between the ground surface and the residential living space for residences with

crawlspaces, and ventilating between the liner and the ground surface to remove

vapors before they can enter the living space. Currently, only three residences

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exceed RGs for indoor air. However, EPA is proposing to install vapor intrusion

mitigation systems at 14 residences that are located directly above the ground water

plume where concentrations of TCE or PCE in ground water exceed 1,000 µg/L and

indoor air concentrations exceed a 1 x 10-5 risk level.

3. Operations and Maintenance Components. Once installed, the relatively low

electrical costs to run the system will be the responsibility of the homeowner.

NMED will pay for any replacement parts and installation within the mitigation

system during the life of the system.

4. Monitoring Components. Vapor mitigation systems have proven to be very reliable

and robust across the country. However, EPA will conduct monitoring prior to

construction and after construction to verify effectiveness of the system. EPA may

choose to monitor at least once every 5 years during the Five-Year Review cycle to

establish protectiveness of the remedy.

16.2.2 Source Area Alternatives

The EPA evaluated the following five alternatives for treating the source area soil and

ground water at the GCSP Site. Approximately a total of 47,556 cubic yards (yd3) of aquifer

matrix in the primary and secondary source areas is targeted for treatment in the Source

Area.






Discount Factor: 7%


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Number of Years Cost Is Projected: Not Applicable



and source areas will not meet RAOs for the site.

16.2.2.2 Alternative 2: Thermal Treatment

Estimated Time for Design/Construction: Less than 1 year

Estimated Time to Reach Remediation Goals: 2 years

Estimated Capital Cost: $ 8,018,000

Estimated Life Time O&M Costs: Not Applicable

Discount Factor: 7%

Estimated Total Present Worth Cost: $ 8,018,000

Number of Years Cost Is Projected: 1 year

Soil Contamination

1. Treatment Components. Approximately a total of 47,556 yd3 of aquifer matrix in the

primary and secondary source areas is targeted for treatment using an in-situ

thermal remediation system. The treatment is targeted to address principal threat

wastes in the soil and ground water in the source areas. Treated soils are left in

place and not excavated in this alternative. Thermal treatment utilizes soil vapor

extraction as a principal component of the technology, which will provide treatment

of unsaturated soils at the source areas. Given the high concentrations in the source

area, thermal treatment would need to achieve 99.9 percent or more removal rate to

meet the final clean up goals. After completion of thermal treatment, a final

polishing step requiring additional treatment via an alternative technology may be

required to treat any remaining low-level wastes.

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2. Operation and Maintenance Components. Active treatment using the thermal

technology is anticipated to require less than 1 year of system operation once

constructed. There are no long-term operations and maintenance costs for this

technology.

3. Monitoring Components. Performance monitoring would be conducted throughout

the active thermal treatment period and during the cool-down period following

treatment, and includes monitoring of ground water concentrations and subsurface

temperatures.

Ground Water Contamination


primary and secondary source areas is targeted for treatment using an in-situ

thermal remediation system. The treatment is targeted to address principal threat

wastes in the soil and ground water in the source areas. Thermal treatment raises

the temperature of the subsurface to approximately 100 degrees Celsius, inducing

volatilization and boiling of chlorinated solvents and steam flushing of the aquifer.

Steam and volatilized vapors are collected within an integral soil vapor extraction

system. Given the high ground water concentrations in the Holiday Cleaners source

area, thermal treatment would need to achieve a 99.9 percent or more removal rate

to meet the RGs. If RGs are not met following completion of thermal treatment, a

final polishing step requiring additional treatment via an alternative technology may

be required to treat any remaining low-level wastes.

2. Operation and Maintenance Components. Active treatment using the thermal

technology is anticipated to require less than 1 year of system operation once

constructed. There are no long-term operations and maintenance costs for this

technology.

3. Monitoring Components. Performance monitoring would be conducted throughout

the active thermal treatment period and during the cool-down period following

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treatment, and includes monitoring of ground water concentrations and subsurface

temperatures.

16.2.2.3 Alternative 3: ISCO with Follow-On ERD

Estimated Time for Design/Construction: 1 year

Estimated Time to Reach Remediation Goals: 7years


Estimated Life Time O&M Costs: $ 3,179,000

Discount Factor: 7%



Soil Contamination


primary and secondary source areas is targeted for treatment using ISCO with

follow-on ERD. In this alternative a total of approximately 638 yd3 of soil would be

excavated from the primary and secondary source areas. Excavated soil would be

disposed of as either hazardous or nonhazardous waste depending on soil sampling

data.

2. Operation and Maintenance Components. There are no operations and

maintenance components associated with the initial soil excavation.

3. Monitoring Components. Monitoring of ground water generated from the initial

soil excavation would be conducted prior to discharge.

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1. Treatment Components. Following excavation of soils, ISCO with follow-on ERD

would be applied to treat ground water and saturated soils. In-situ chemical

oxidation is effective for rapid mass reduction within source areas and high-

concentration portions of ground water plumes. ERD is a slower process, but has

the advantage of being a potentially more technically- and cost-effective method of

reliably reaching MCLs when COC concentrations are moderate (i.e., DNAPL is

absent). The strengths of ISCO and ERD can be combined for treatment of source

areas. In addition to ISCO with follow-on ERD, up to 100,000 gallons of PCE-

contaminated ground water may be removed from the initial soil excavations during

this period. Extracted ground water would be treated onsite and disposed either in

the Rio San Jose channel, the sanitary sewer or reinjected back in to the aquifer.

2. Operations and Maintenance Components. Five carbon source amendment

injections would occur once every 15 months following the soil excavation and ISCO

treatment. ERD injections would occur in the same permanent injection wells used

for ISCO.

3. Monitoring Components. Performance monitoring would consist of direct-push

sampling to confirm the distribution of oxidants and carbon amendments within the

subsurface, and ground water sampling during, and upon completion of, the active

treatment period.

16.2.2.4 Alternative 4: ERD (Gridded)





Discount Factor: 7%


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Soil Contamination

1. Treatment Components. Alternative 4 is similar to Alternative 3. A total of

approximately 470 yd3 of soil would be excavated from the primary and secondary

source areas. Excavated soil would be disposed of as either hazardous or

nonhazardous depending on soil sampling data.

2. Operation and Maintenance Components. There are no operations and

maintenance components associated with the initial soil excavation.

3. Monitoring Components. Monitoring of ground water generated from the initial

soil excavation would be conducted prior to discharge.


1. Treatment Components. Following excavation, ERD would be applied to treat the

ground water and saturated soils. ERD is a slower process, but has the advantage of

being a potentially more technically- and cost-effective method of reliably reaching

MCLs when COC concentrations are moderate (i.e., DNAPL is absent). In addition,

up to 100,000 gallons of PCE-contaminated ground water may be removed from the

initial soil excavation. Extracted ground water would be treated onsite and disposed

either in the Rio San Jose channel, the sanitary sewer, or reinjected back in to the

aquifer.

2. Operations and Maintenance Components. Twelve carbon source amendment

injections would occur once every 15 months following the soil excavation.


sampling to confirm the distribution of carbon amendments within the subsurface,

and ground water sampling during, and upon completion of, the active treatment

period.

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16.2.3 Shallow Plume Core and Hot Spot Alternatives

Alternative 1: No Action

Alternative 2: ZVI PRB-Multiple Transects

Alternative 3: ISCO w/Follow-On ERD

Alternative 4: ERD (Bio-Barrier)

Alternative 5: Ground Water Extraction and Ex-Situ Treatment






Discount Factor: 7%




alternatives, as required by the NCP. Under Alternative 1, no remedy would be

implemented and the shallow ground water plume core and hot spot would not meet RAOs

for the site.

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16.2.3.2 Alternative 2: ZVI PRB





Discount Factor: 7%




1. Treatment Components. A total of approximately 140 million gallons (MG) is

estimated to be impacted with chlorinated solvents contamination. A portion of the

impacted aquifer would be treated with this approach. PRB walls incorporating ZVI

provide passive treatment of contaminants as ground water flows through the wall

under natural ground water flow gradients. A total of approximately 600 ft of

ZVI-PRB walls would be installed as multiple transects across the shallow plume

core and at the downgradient extent of the shallow ground water hot spot. Under

this scenario, the ZVI-PRB wall transects would be spaced approximately 150 to

200 ft apart along the length of the shallow plume core. The ZVI-PRB walls would

be installed using slurry trenching techniques, where a biodegradable slurry is

maintained within the trench during excavation to stabilize the trench. The material

excavated during installation of PRB walls would require offsite disposal.

2. Operation and Maintenance Components. The service life of the PRB wall is

expected to be 20 years. At the end of the 20-year life cycle, a new PRB wall would

be installed to replace the existing wall.

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3. Monitoring Components. Performance monitoring would be conducted during the

active treatment period to evaluate the effectiveness of the system.

16.2.3.3 Alternative 3: ISCO with Follow-On ERD Bio-Barrier





Discount Factor: 7%



1. Treatment Components. In-situ chemical oxidation is effective for rapid mass

reduction within source areas and high concentration portions of ground water

plumes. ERD is a slower process, but has the advantage of being a more technically

and potentially cost-effective method of reliably reaching MCLs when COC

concentrations are moderate (i.e., DNAPL is absent). The strengths of ISCO and

ERD can be combined for treatment of the shallow ground water plume core and hot

spot. ISCO is initially applied to rapidly lower dissolved-phase COC concentrations

to moderate levels. The ISCO phase is then followed by injecting carbon source

amendments (ERD) as a polishing step for final reduction of COCs.

2. Operation and Maintenance Components. After the initial application of ISCO, a

total of five ERD applications would occur once every 15 months to treat the COCs.


sampling to confirm the distribution of oxidants and carbon amendments within the

subsurface, and ground water sampling, during, and upon completion of, the active

treatment period.

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16.2.3.4 Alternative 4: ERD Bio-Barrier





Discount Factor: 7%



1. Treatment Components. Treatment of the shallow ground water plume core and

hot spot would be performed using ERD in the form of injected carbon source

amendment barriers, called bio-barriers. Bio-barriers are installed as transects across

the ground water plume axis by closely spaced injection of carbon source

amendments. Within these carbon-rich zones, or barriers, biologically mediated

reductive dechlorination of the COCs is enhanced and the process forms a

continuous ERD treatment zone to intercept the plume. Installation of multiple

bio-barriers in series achieves RAOs as ground water passes through each treatment

area. Injection points along each transect will be spaced approximately 25 ft apart

with an assumed injection radius of influence (ROI) of approximately 15 ft.

Permanent injection wells would be installed, as they would be cost effective due to

the need for multiple injections of carbon source amendments over an extended time

period to meet RAOs. Each injection well will be screened from 8 ft bgs to 20 ft bgs

for treatment of shallow plume core and hot spot. Bio-barriers would be installed as

multiple transects across the shallow plume core and hot spot, with an assumed total

bio-barrier length of approximately 600 ft. Under this scenario, the bio-barriers

would be spaced approximately 150 to 200 ft apart along the length of the shallow

plume core, with short bio-barriers installed across the shallow hot spot.

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2. Operation and Maintenance Components. A total of 16 ERD applications would

occur once every 15 months to treat the COCs.

3. Monitoring Components. Performance monitoring would be conducted by

installing and sampling up to 10 ground water monitoring wells on either side of

various bio-barriers to determine the effectiveness of the treatment technology, and

to track overall progress during the active treatment period. Semi-annual sampling

will be conducted during the course of active treatment.

16.2.3.5 Alternative 5: Ground Water Extraction and Ex-Situ Treatment





Discount Factor: 7%



1. Treatment Components. Under this alternative, a network of extraction wells

would be located within the shallow plume core and hot spot. Due to the shallow

depths targeted for treatment, dual-phase extraction is anticipated. Dual-phase

extraction involves the installation of extraction wells screened both below and

slightly above the ground water table and application of vacuum to the wells to

extract both soil vapor and ground water. With dual-phase extraction, relatively

high extraction rates are used to actively dewater the upper portions of the shallow

aquifer. This dewatering provides for rapid removal of highly contaminated ground

water and exposes additional vadose zone for soil vapor extraction (SVE).

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Extracted soil vapor and ground water would be conveyed to a central treatment

plant where ex-situ treatment would include two treatment trains, one for extracted

soil vapor and one for extracted ground water. Soil vapor would be directed

through a granular activated carbon (GAC) filter prior to discharge to the

atmosphere. Ground water would be pre-filtered and pre-treated to appropriate pH

requirements prior to passage through an air-stripper unit. Air-stripper offgas

would then be directed through a GAC filter prior to discharge to the atmosphere.

Treated ground water would be reinjected into the shallow aquifer, at a location

either west or upgradient of the shallow ground water plume. A total of

approximately six dual-phase extraction wells would be installed within the shallow

ground water plume core and hot spot, the central treatment plant would be located

adjacent to the Holiday Cleaners building, and a total of approximately

10 reinjection wells would be required. Due to the low permeability of the shallow

aquifer, an extended infiltration gallery may be considered in place of reinjection.

2. Operation and Maintenance Components. Ongoing O&M will be required

throughout the active remediation period of 40 years.

3. Monitoring Components. Performance monitoring would be conducted utilizing

existing monitoring wells, and sampled as part of the long-term ground water

sampling program.

16.2.4 Shallow Plume Periphery Alternatives


Alternative 2: Monitored Natural Attenuation

Alternative 3: ZVI PRB-Multiple Transects


Alternative 5: Ground Water Extraction and Ex-Situ Treatment

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Discount Factor: 7%






16.2.4.2 Alternative 2: Monitored Natural Attenuation (MNA)





Discount Factor: 7%



1. Treatment Components. MNA is not an active treatment remedy and there are no

treatment components in this alternative. Under the right conditions, natural

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attenuation processes have the potential to address ground water contamination and

achieve RAOs over a relatively long period of time. Approximately four additional

ground water monitoring wells would be constructed using this alternative.

2. Operation and Maintenance Components. Operation and maintenance

components consist exclusively of routine ground water monitoring over the course

of the treatment period.

3. Monitoring Components. The MNA alternative would primarily utilize the

network of ground water monitoring wells installed during the Preliminary Design

Field Investigation as the means to routinely monitor the nature and extent of

contamination at the GCSP Site and track the progress of the alternative toward

meeting the RAOs at the site. Semi-annual sampling of the 36 wells installed during

the Preliminary Design Field Investigation plus the four new shallow monitoring

wells would occur for 5 years. After 5 years, sampling of all wells would reduce to

an annual basis for 35 additional years (40 total years), concurrent with the sitewide

ground water monitoring program. Sampling may be terminated earlier if RAOs are

met sooner. Sampling of all existing wells is assumed necessary to confirm that the

contaminant plume is stable during application of MNA and for comparisons of

aquifer processes at various depths.

16.2.4.3 Alternative 3: ZVI PRB





Discount Factor: 7%



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1. Treatment Components. A total of approximately 140 MG is estimated to be

impacted with chlorinated solvents contamination. A portion of the impacted

aquifer would be treated with this approach. PRB walls incorporating ZVI provide

passive treatment of contaminants as ground water flows through the wall under

natural ground water flow gradients. A total of approximately 1,700 ft of ZVI-PRB

walls would be installed as multiple transects across the shallow plume and at the

downgradient extent of the shallow plume periphery. Under this scenario, the

ZVI-PRB wall transects would be spaced approximately 200 ft to 400 ft apart along

the length of the shallow plume. The ZVI-PRB walls would be installed using slurry

trenching techniques, where biodegradable slurry is maintained within the trench

during excavation to stabilize the trench. The material excavated during installation

of PRB walls would require offsite disposal.



be installed to replace the existing wall.







Estimated Life Time O&M Costs: $2,352,000

Discount Factor: 7%

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1. Treatment Components. Treatment of the shallow ground water plume periphery

would be performed using ERD in the form of injected carbon source amendment

barriers, called bio-barriers. Bio-barriers are installed as transects across the ground

water plume axis by closely spaced injection of carbon source amendments. Within

these carbon-rich zones, or barriers, biologically mediated reductive dechlorination

of the COCs is enhanced and the process forms a continuous ERD treatment zone to

intercept the plume. Installation of multiple bio-barriers in series achieves RAOs as

ground water passes through each treatment area. Injection points along each

transect will be spaced approximately 25 ft apart with an assumed injection radius of

influence of approximately 15 ft. Permanent injection wells would be installed as

they would be cost effective due to the need for multiple injections of carbon source

amendments over an extended time period to meet RAOs. Each injection well will

be screened from 8 ft bgs to 20 ft bgs for treatment of the shallow ground water

plume periphery. Bio-barriers would be installed as multiple transects across the

shallow ground water plume periphery, with an assumed total bio-barrier length of

approximately 2,400 ft. Under this scenario, the bio-barriers would be spaced

approximately 200 ft apart along the length of the shallow plume periphery.

4. Operation and Maintenance Components. A total of sixteen ERD applications

would occur once every 15 months to treat the COCs.






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Discount Factor: 7%




would be located within the shallow plume periphery. Due to the shallow depths

targeted for treatment, dual-phase extraction is anticipated. Dual-phase extraction

involves the installation of extraction wells screened both below and slightly above

the ground water table and application of vacuum to the wells to extract both soil

vapor and ground water. With dual-phase extraction, relatively high extraction rates

are used to actively dewater the upper portions of the shallow aquifer. This

dewatering provides for rapid removal of highly contaminated ground water and

exposes additional vadose zone for SVE.

Extracted soil vapor and ground water would be conveyed to a central treatment

plant where ex-situ treatment would include two treatment trains, one for extracted

soil vapor and one for extracted ground water. Soil vapor would be directed

through a GAC filter prior to discharge to the atmosphere. Ground water would be

pre-filtered and pre-treated to appropriate pH requirements prior to passage

through an air-stripper unit. Air-stripper offgas would then be directed through a

GAC filter prior to discharge to the atmosphere. Treated ground water would be

reinjected into the shallow aquifer, at a location either west or upgradient of the

shallow ground water plume. A total of approximately eight dual-phase extraction

wells would be installed within the shallow ground water plume periphery, the

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central treatment plant would be located adjacent to the Holiday Cleaners building,

and a total of approximately 15 reinjection wells would be required. Due to the low

permeability of the shallow aquifer, an extended infiltration gallery may be

considered in place of reinjection.




existing monitoring wells, sampled as part of the long-term ground water sampling

program.

16.2.5 Deeper Ground Water Alternatives


Alternative 2: Monitored Natural Attenuation

Alternative 3: ZVI PRB-with Deep ERD


Alternative 5: Ground Water Extraction and Ex-Situ






Discount Factor: 7%



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16.2.5.2 Alternative 2: Monitored Natural Attenuation





Discount Factor: 7%



1. Treatment Components. MNA is not an active treatment remedy and there are no

treatment components in this alternative. Under the right conditions, natural

attenuation processes have the potential to address ground water contamination and

achieve RAOs over a relatively long period of time. Approximately six additional

ground water monitoring wells would be constructed using this alternative.

2. Operation and Maintenance Components. Operation and maintenance

components consist exclusively of routine ground water monitoring over the course

of the treatment period.

3. Monitoring Components. The MNA alternative would primarily utilize the

network of ground water monitoring wells installed during the Preliminary Design

Field Investigation as the means to routinely monitor the nature and extent of

contamination at the GCSP Site and track the progress of the alternative toward

meeting the RAOs at the site. Semi-annual sampling of the 36 wells installed during

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the Preliminary Design Field Investigation plus the six new shallow monitoring

wells would occur for 5 years. After 5 years, sampling of all wells would reduce to

an annual basis for 35 additional years (40 total years), concurrent with the sitewide

ground water monitoring program. Sampling may be terminated earlier if RAOs are

met sooner. Sampling of all existing wells is assumed necessary to confirm that the

contaminant plume is stable during application of MNA and for comparisons of

aquifer processes at various depths.

16.2.5.3 Alternative 3: ZVI PRB with Deep ERD Bio-Barrier



Estimated Capital Cost: $24,640,000


Discount Factor: 7%



1. Treatment Components. A total of approximately 140 MG is estimated to be

impacted with chlorinated solvents contamination. A portion of the impacted

aquifer would be treated with this approach. PRB walls incorporating ZVI provide

passive treatment of contaminants as ground water flows through the wall under

natural ground water flow gradients. A total of approximately 1,000 ft of ZVI-PRB

walls up to 60 ft deep would be installed as multiple transects across the deeper

ground water plume. The ZVI-PRB walls would be installed using slurry trenching

techniques, where biodegradable slurry is maintained within the trench during

excavation to stabilize the trench. The material excavated during installation of PRB

walls would require offsite disposal. Treatment below 60-ft depth would be

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accomplished by ERD bio-barriers since the installation of sufficiently-thick ZVI-PRB

walls at depths greater than 60 ft bgs is not considered practical.



be installed to replace the existing wall. For the deep ERD application, a total of

16 carbon source amendment injections are assumed over a 20-year period (one

injection every 15 months) to meet the RAOs for ground water at this depth.








Discount Factor: 7%



1. Treatment Components. Treatment of the deeper ground water would be

performed using ERD in the form of injected carbon source amendment barriers,

called bio-barriers. Bio-barriers are installed as transects across the ground water

plume axis by closely spaced injection of carbon source amendments. Within these

carbon-rich zones, or barriers, biologically mediated reductive dechlorination of the

COCs is enhanced and the process forms a continuous ERD treatment zone to

intercept the plume. Installation of multiple bio-barriers in series achieves RAOs as

ground water passes through each treatment area. Injection points along each

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transect will be spaced approximately 25 ft apart with an assumed injection ROI of

approximately 15 ft. Permanent injection wells would be installed as they would be

cost effective due to the need for multiple injections of carbon source amendments

over an extended time period to meet RAOs. Each injection well will be screened

from 60 ft bgs to at least 80 ft bgs. Bio-barriers would be installed as multiple

transects across the deeper ground water plume, with an assumed total bio-barrier

length of approximately 1,250 ft.

2. Operation and Maintenance Components. A total of 16 ERD applications would

occur once every 15 months to treat the COCs.











Discount Factor: 7%




would be located within the deeper ground water plume. Extracted ground water

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would be conveyed to a central treatment plant where ex-situ treatment would

include air-stripping and offgas control. Ground water would be pre-filtered and

pre-treated to appropriate pH requirements prior to passage through an air-stripper

unit. Air-stripper offgas would then be directed through a GAC filter prior to

discharge to the atmosphere. Treated ground water would be reinjected into the

deeper aquifer, at a location either west or upgradient of the shallow ground water

plume. A total of approximately six extraction wells would be installed within the

deeper ground water, the central treatment plant would be located adjacent to the

Holiday Cleaners building, and a total of approximately 10 reinjection wells would

be required.




existing monitoring wells, sampled as part of the long-term ground water sampling

program.

16.3 Other Common Elements and Distinguishing Features

of Each Alternative

Common elements and distinguishing features unique to each alternative include key

ARARs, long-term reliability of the remedy, quantities of untreated wastes, and uses of

presumptive remedies. Table 11 (Summary ARARs) and Table 12 (Description of ARARs

for Selected Remedy) summarize the ARARs pertaining to the main elements of each of the

remedial alternatives and the Selected Remedy. Several of the remedial alternatives have

elements in common, including excavation and waste disposal requirements.

16.3.1 Key Applicable or Relevant and Appropriate Requirements

With the exception of the No Action Alternative, it is assumed that an appropriate design

for all retained technologies, or technology combinations, can be developed for each media

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of concern to meet applicable ARARs. The primary difference in technology combinations

for the different contaminated media with regard to complying with ARARs is the length of

time required before ARARs would be achieved. Table 11 (Summary of ARARs)

summarizes the ARARs for alternatives and shows how they will be complied with.

16.3.2 Long-Term Reliability of the Remedy

The magnitude of risk will remain indefinitely if no action is taken at the site. All of the

alternative technologies considered for remedial action will provide long-term reliability

once all DNAPL is removed, provided that ICs remain effective until that time. However if

residual DNAPL cannot be completely removed from the ground water at the site, the

remedy may no longer provide long-term reliability. If the remedy cannot be implemented

as planned then EPA will develop an alternate plan. At this time the EPA cannot determine

the cost for replacement of the remedy, as there is insufficient data for analysis of such site

circumstances.

16.3.3 Quantities of Untreated Wastes

16.3.1.1 Indoor Air (Vapor Intrusion Mitigation)

The No Action Alternative does not provide treatment. The vapor mitigation systems do

not provide active treatment, but physically block contaminants from entering a structure.

16.3.1.2 Source Area, Shallow Plume Core and Hot Spot, Shallow Plume Periphery,

and Deeper Ground Water Treatment

Approximately 44.5 MG of ground water and 6,500 yd3 of soil will be treated at the site.

Pilot-scale and bench-scale testing is required to determine the exact quantity of COCs,

which will be treated by the various technologies, including thermal treatment, ISCO, ERD,

ZVI PRBs, MNA, and pump and treat. It is anticipated that each of the proposed

technologies can remove sufficient COCs to meet the site RAOs.

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16.3.4 Uses of Presumptive Remedies

The following presumptive remedies prescribed by EPA guidance (EPA, 1993) were

evaluated in the FS.

16.3.4.1 VOCs in Soil

• Soil Vapor Extraction (SVE)

• Ex-Situ Thermal Desorption

• Ex-Situ Thermal Incineration

The only presumptive technology provided in current EPA guidance for VOCs in soils that

was retained is soil vapor extraction, with enhancements such as pneumatic fracturing,

sealing the ground surface, and the use of horizontal vapor wells. The other presumptive

technologies were each rejected based on site-specific conditions, which severely limit the

effectiveness of the technologies at the GCSP Site. A dual-phase SVE technology was

selected as part of the thermal treatment system for the Source Areas.

16.3.4.2 VOCs in Ground Water

• Ground Water Extraction and Ex-Situ Treatment

Current EPA guidance for treatment of VOCs dissolved in ground water includes only

ground water extraction and ex-situ treatment. Ground water extraction and ex-situ

treatment is a proven technology for treatment of VOCs in ground water, and can be

implemented at the GCSP Site. Ground water extraction and ex-situ treatment was not

selected for the site based on current site conditions.

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16.4 Expected Outcomes of Each Alternative

Implementation of any of the alternatives considered for this site, other than the No Action

Alternative, is expected to reduce the human health risk over time at the GCSP Site.

However, the time required to achieve the RAOs for each site-impacted media varies

anywhere from 1 years for to 40 years depending on the alternative used. The vapor

mitigation systems will be able to achieve RAOs for indoor air as soon as installation is

complete. In the Source Areas implementation of the thermal treatment is expected to be

achieve RAOs relatively sooner than ISCO and ERD. In the shallow ground water and hot

spot area, implementation of the ISCO with follow-on ERD is expected to achieve the RAOs

sooner than with ZVI-PRB, ERD and pump and treat. In the shallow ground water plume

periphery, implementation of the ERD bio-barrier is expected to achieve the RAOs sooner

than with MNA, ZVI and pump and treat. For deeper ground water implementation of the

ERD bio-barrier is expected to achieve the RAOs sooner than with the MNA, ZVI-PRB

followed with ERD, pump and treat.

The outcome of the remedy is not expected to change the land and ground water use at the

site as it will likely continue to be residential and light commercial. Implementation of the

Selected Remedy will reduce risk to human health and restore the ground water to

beneficial use.

17.0 Comparative Analysis of Alternatives

The EPA uses nine NCP criteria to evaluate remedial alternatives for the cleanup of a

release. These nine criteria are categorized into three groups: threshold, balancing, and

modifying. The threshold criteria must be met for an alternative to be eligible for selection.

The threshold criteria are overall protection of human health and the environment and

compliance with ARARs. The balancing criteria are used to weigh major tradeoffs among

alternatives. The five balancing criteria are long-term effectiveness and permanence;

reduction of toxicity, mobility or volume through treatment; short-term effectiveness;

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implementability; and cost. The modifying criteria are State acceptance and community

acceptance. Table 13 (Evaluation Criteria for Superfund Remedial Alternatives) briefly

describes the evaluation criteria.

Based on the initial screening of technologies and evaluation of alternatives, a number of

remedial alternatives were evaluated for each site-impacted area. Tables 14 through 18

(Comparison of Remedial Alternatives) summarize how these alternatives comply with the

nine evaluation criteria specified in the NCP §300.430(f)(5)(i). The No Action Alternative for

each media is not considered further in the comparative analysis of alternatives as it cannot

meet the threshold criteria or address risks at the site. Following is a comparative analysis

of the remedial alternatives other than the No Action Alternative.

17.1 Overall Protection of Human Health and the Environment

Overall protection of human health and the environment addresses whether each

alternative provides adequate protection of human health and the environment and

describes how risks posed through each exposure pathway are eliminated, reduced, or

controlled through treatment, engineering controls, and/or institutional controls.

All of the alternatives, except the No Action Alternative, are protective of human health and

the environment by eliminating, reducing, or controlling risks posed by the site through

treatment of soil and ground water contaminants, engineering controls, and/or institutional

controls. Basic comparative analyses for the technologies, or technology combinations, for

the different media of concern are presented below.

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17.1.1 Indoor Air (Vapor Intrusion Mitigation)

Only two technical approaches were identified pertaining to indoor air. These technical

approaches included either No Action or Installation of Radon-Type Vapor Mitigation

Systems.

Under the Installation of Radon-Type Vapor Mitigation Systems, the contaminated vapors

are physically isolated from the overlying structure by installing an impermeable vapor

barrier and a ventilation system to remove the vapors from beneath the barrier. Human

health and the environment are protected since the vapor barrier and venting system

remove the pathway for volatile organics present in the subsurface to enter the structure.

17.1.2 Source Area Treatment

Four approaches including the No Action Alternative were identified for source area

treatment at the GCSP Site. The three technical approaches to remediating the source area

(thermal treatment, ISCO with Follow-on ERD, and ERD Applied in a Grid) would be

expected to remove COCs from the source area under the implementation of an

appropriately designed program. If residual DNAPL or sorbed soil source material remains

after the active treatment periods, these approaches may not achieve RAOs.

Thermal treatment may be less subject to non-uniform treatment distribution in the source

area as it is less sensitive to fine-grained or heterogeneous subsurface conditions and would

be accomplished in a single treatment event. However, as a one-time event, thermal

treatment would need to achieve very high removal efficiency (99.9 percent or more) in that

single event to approach RAOs. Since 99.9 percent or more reduction in contaminant

volume would constitute very high removal efficiency for any type of remedial technology,

it is possible that additional final polishing by another remedial technology may need to be

instituted to achieve RAOs.

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Since both ISCO and ERD rely on amendments being able to come in contact with COCs in

the subsurface, the fine-grained heterogeneous soils in the treatment area may impact the

effectiveness and implementability of these technologies. Multiple injection events for both

ISCO and ERD carbon-source amendments would be required for these technologies. With

regard to ERD or bio-barriers, if reductive dechlorination of the COCs is retarded by site-

specific conditions then equally, or more toxic, intermediary by-products of biodegradation

may persist.

While the thermal treatment and ISCO option technologies do have the capability of directly

treating residual DNAPL to some degree, the effectiveness of all technology options in

meeting or approaching RAOs will be limited if residual DNAPL or sorbed soil

contamination persists after active remediation.

All of the three technical approaches considered are protective of human health and the

environment. The length of time required to achieve protectiveness varies for each

approach with thermal treatment being the quickest compared to ISCO and ERD. Thermal

treatment also is cost-competitive and will have the least impact on the community.

17.1.3 Shallow Ground Water Plume Core and Hot Spot Treatment

Five approaches including the No Action Alternative were identified for treatment of the

shallow ground water plume core and hot spot at the GCSP Site to depths of 20 ft bgs. The

four technical approaches to remediating the shallow ground water plume core and hot spot

(ZVI-PRB, ISCO with Follow-on ERD, ERD Bio-barriers, and Pump and Treat) would be

expected to remediate COCs within the shallow plume core under the implementation of an

appropriately designed program. If any residual DNAPL or sorbed soil source material

remains after the active treatment periods, these approaches may not achieve RAOs. ISCO

is the only identified technology that would have the capability of directly treating residual

DNAPL.

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Since both ISCO and ERD rely on amendments being able to come in contact with COCs, the

fine-grained heterogeneous soils in the treatment area may impact the effectiveness and

implementability of these technologies. The low permeability soils at the GCSP Site also

may pose difficulties in achieving full ground water capture under the Pump and Treat

option. Also, multiple injection events for both ISCO and ERD carbon-source amendments

would be specified for these technologies. And with regard to ERD or bio-barriers, if

reductive dechlorination of the COCs is retarded by site-specific conditions then equally, or

more toxic, intermediary by-products of biodegradation may persist.

PRB application would have the most substantial short-term installation impacts and would

require replacement once every 20 years. The natural ground water velocity would limit the

treatment time for the shallow ground water plume core and hot spot by PRBs.

The Pump and Treat option is expected to take the longest time period and would require

ongoing O&M throughout that period.

Among the four technical approaches considered for the Shallow Plume Core and Hot Spot,

ISCO with follow-on ERD would achieve protection of human health and environment

relatively quicker than ERD and PRB. ISCO with follow-on ERD is the only technology that

can reliably treat any principal threat waste if found in the Shallow Plume Core and Hot

Spot.

17.1.4 Shallow Ground Water Periphery


shallow ground water periphery at the GPSC Site to depths of 20 ft bgs.

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The four technical approaches to remediating the shallow ground water periphery (MNA,

ZVI-PRB, ERD Bio-barriers, and Pump and Treat) would be expected to remediate COCs

within the shallow plume periphery under the implementation of an appropriately

designed program. If any residual DNAPL or sorbed soil source material remains after the

active treatment periods, these approaches may not achieve RAOs. None of the identified

technologies have the capability of directly treating residual DNAPL during

implementation of the Remedial Action.

Since ERD relies on amendments being able to come in contact with COCs, the fine-grained

heterogeneous soils in the treatment area may impact the effectiveness and

implementability of this technology. The low permeability site soils also may pose

difficulties in achieving full ground water capture under the Pump and Treat option.

Multiple injection events of ERD carbon-source amendments would be specified for this

technology and if reductive dechlorination of the COCs by the bio-barriers is limited by site-


may persist.

PRB application would have the most substantial short-term installation impacts. The

natural ground water velocity would limit the treatment time for the shallow ground water

periphery by PRBs. The Pump and Treat option and MNA are expected to take the longest

time periods to achieve RAOs. While the Pump and Treat option would require ongoing

O&M throughout that period, actions to support MNA would be limited to ongoing ground

water monitoring.

Among the four technical approaches considered for the Shallow Plume Periphery, ERD

Bio-barriers is the least expensive and would achieve protection of human health and

environment relatively quicker than MNA, ZVI-PRB and Pump and Treat.

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17.1.5 Deeper Ground Water


deeper ground water at the GCSP Site below 20 ft bgs. The ground water would remain a

continuing source to the downgradient plume and could potentially migrate even deeper in

the aquifer, potentially impacting the drinking water aquifer.

The four technical approaches to remediating the deeper ground water (MNA, Bio-barriers,

ZVI-PRB in Conjunction with ERD Bio-barriers, and Pump and Treat) would be expected to

remediate COCs within the deeper plume under the implementation of an appropriately

designed program. If any residual DNAPL or sorbed soil source material remains after the

active treatment periods, these approaches may not achieve RAOs. None of the identified

technologies have the capability of directly treating residual DNAPL during

implementation of the Remedial Action.

Since ERD relies on amendments being able to come in contact with COCs, the fine-grained

heterogeneous soils in the treatment area may impact the effectiveness and

implementability of this technology. The low permeability site soils also may pose

difficulties in achieving full ground water capture under the Pump and Treat option.

Multiple injection events of ERD carbon-source amendments would be specified for this

technology and if reductive dechlorination of the COCs by the bio-barriers is limited by site-


may persist.

PRB application would have the most substantial short-term installation impacts. The

natural ground water velocity would limit the treatment time for the deeper ground water

periphery by PRBs. The Pump and Treat option and MNA are expected to take the longest

time periods to achieve RAOs. While the Pump and Treat option would require ongoing

O&M throughout that period, actions to support MNA would be limited to ongoing ground

water monitoring.

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Among the four technical approaches considered for the Deeper Ground Water, ERD

Bio-barriers is the least expensive and would achieve protection of human health and

environment relatively quicker than MNA, ZVI-PRB in conjunction with ERD and Pump

and Treat.

17.2 Compliance with ARARs

Section 121(d) of CERCLA and NCP §300.430(f)(1)(ii)(B) require that remedial actions at

CERCLA sites at least attain legally applicable or relevant and appropriate Federal and State

requirements, standards, criteria, and limitations, which are collectively referred to as

“ARARs,” unless such ARARs are waived under CERCLA §121(d)(4). Compliance with

ARARs addresses whether a remedy will meet all of the ARARs or provides a basis for

invoking a waiver.

With the exception of the No Action Alternative, an appropriate design for all retained

technologies, or technology combinations, can be developed for each media of concern to

meet applicable RAOs. The primary difference in technology combinations for the different

contaminated media with regard to complying with ARARs is the length of time required

before RAOs would be achieved.

A key assumption in evaluating technology combinations’ ability to comply with ARARs is

that an appropriately designed program can be developed to meet ARARs with each

technology type. This assumption is based solely on the existing site data.

17.3 Long-Term Effectiveness and Permanence

Long-term effectiveness and permanence refers to expected residual risk and the ability of a

remedy to maintain reliable protection of human health and the environment over time,

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once cleanup levels have been met. This criterion includes the consideration of residual risk

that will remain onsite following remediation and the adequacy and reliability of controls.

17.3.1 Magnitude of Residual Risk

With the exception of the No Action Alternative, all of the alternatives are expected to meet

RAOs given an appropriate design. This assumption is based on only evaluation of the

technologies relative to available site data. Achieving RAOs would provide a substantial

reduction in long-term residual risk for all impacted media using any of the technology

approaches and will be protective of human health in the long-term.


Installation of radon-type vapor mitigation systems will prevent vapor intrusion of COCs

above acceptable risk levels, as long as the barrier and ventilation system are kept in good

working order. Human health and the environment are protected since the vapor barrier

and venting system remove the pathway for volatile organics present in the subsurface to

enter the structure.

17.3.1.2 Source Area Treatment

Each of the active treatment alternatives is anticipated to ultimately lower the risk from

vapor intrusion and ground water exposure. An appropriately designed, thermal source-

area treatment is expected to approach RGs and RAOs and reduce residual risk in the

source areas. Final polishing following thermal treatment may be necessary to meet RGs

and RAOs, and may include targeted ERD or ISCO treatments.

ISCO with follow-on ERD treatment can be appropriately designed to meet long-term RGs

and RAOs and will reduce residual risk. If DNAPL or sorbed-soil contamination persists

following completion of ISCO and ERD treatments, a dissolved-phase plume is likely to

persist or rebound within the aquifer and the treatment will no longer limit residual risk.

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ERD treatment can be appropriately designed to meet long-term RGs and RAOs and will

reduce residual risk. As with ISCO, if DNAPL or sorbed-soil contamination persists



Among the alternatives considered for the Source Area, thermal treatment is relatively

better in not leaving any residual risk in the long-term and be protective of human health

and the environment.

17.3.1.3 Shallow Ground Water Plume Core and Hot Spot Treatment

PRBs designed for the site-specific dissolved-phase ground water plume will achieve long-

term RGs and RAOs. If DNAPL or sorbed soil contamination persists in the areas between

the PRBs and continues to propagate a dissolved-phase plume beyond the designed service

life of the PRBs, then this technology will no longer achieve RAOs or limit residual risk.

Given the passive nature of this technology, high concentrations of COCs will persist in

shallow ground water and continue to support a vapor intrusion risk for many years.

ISCO with follow-on ERD treatment can be appropriately designed to meet long-term RGs

and RAOs and will reduce residual risk. If DNAPL or sorbed-soil contamination persists



Until shallow ground water COC concentrations meet RGs, they may continue to support a

significant vapor intrusion risk.


reduce residual risk. Once the cleanup goals are achieved this alternative will be protective

in the long-term. As with ISCO, if DNAPL or sorbed soil contamination persists following

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completion of ERD treatments, a dissolved-phase plume is likely to persist or rebound

within the aquifer and the treatment will no longer limit residual risk. Until shallow ground

water COC concentrations meet RGs, they may continue to support a significant vapor

intrusion risk.

Pump and treat methods can be designed to treat the shallow ground water plume and hot

spot and meet long-term RGs and RAOs, and eventually limit residual risk. If DNAPL or

sorbed soil contamination is present, pump and treat technology in low permeability

sediments typical of the GCSP Site may take longer than 40 years to achieve RAOs.

Additionally, portions of the aquifer that have been partially remediated may be subject to

recontamination or rebound from remaining sorbed or DNAPL contaminant sources. Until

shallow ground water COC concentrations meet RGs, they may continue to support a

significant vapor intrusion risk.

All of the technologies considered for the Shallow Plume Core and Hot Spot would

probably be effective in the long-term and leave no residual risk at the site. However, if

principal threat waste is encountered in the Shallow Plume Core and Hot Spot Area, using

ISCO with follow-on ERD has the best chance of ensuring long-term effectiveness and

permanence.

17.3.1.4 Shallow Ground Water Periphery

MNA of the shallow ground water periphery may achieve long-term RGs and RAOs and

eventually limit residual risk. However, given the passive nature of the alternative, high

concentrations of COCs will persist in the shallow ground water periphery for an extended

period of time, presenting continuing residual risk. If DNAPL or sorbed soil contamination

persists in the area, a dissolved-phase plume will persist in the aquifer and MNA may not

achieve RAOs or limit residual risk. The ongoing monitoring of the remedial alternative

will limit some residual risk by allowing regular evaluation of the effectiveness of the

alternative.

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PRBs designed for the site-specific, dissolved-phase ground water plume will achieve long-

term RGs and RAOs. If DNAPL or sorbed-soil contamination persists in the areas between

the PRBs and continues to propagate a dissolved-phase plume beyond the designed service

life of the PRBs, then this technology will no longer achieve RAOs or limit residual risk.


reduce residual risk. If DNAPL or sorbed-soil contamination persists following completion

of ERD treatments, a dissolved-phase plume is likely to persist or rebound within the

aquifer and the treatment will no longer limit residual risk.

Pump and treat methods can be designed to treat the shallow ground water plume

periphery and meet long-term RGs and RAOs, and eventually limit residual risk. If DNAPL

or sorbed soil contamination is present, pump and treat technology in low permeability

sediments typical of the GCSP Site may take longer than 40 years to achieve RAOs.

Additionally, portions of the aquifer that have been partially remediated may be subject to

recontamination or rebound from remaining sorbed-soil or DNAPL contaminant sources.

All of the technologies considered for the Shallow Plume Periphery would probably be

effective in the long-term and leave no residual risk at the site. PRB and Pump and Treat are

more expensive and will relatively take longer to achieve cleanup goals compared to ERD.

MNA is not proven at the site and may take a long time to achieve cleanup goals.

17.3.1.5 Deeper Ground Water

MNA of the deeper ground water below 20 ft bgs may achieve long-term RGs and RAOs

and eventually limit residual risk. However, given the passive nature of the alternative,

high concentrations of COCs will persist in the deeper ground water periphery for an

extended period of time, presenting continuing residual risk. If DNAPL or sorbed soil

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contamination persists in the area, a dissolved-phase plume will persist in the aquifer and

MNA may not achieve RAOs or limit residual risk. The ongoing monitoring of the remedial

alternative will limit some residual risk by allowing regular evaluation of the effectiveness

of the alternative.

PRBs, along with supplemental bio-barriers, designed for the site-specific dissolved-phase

ground water plume will achieve long-term RGs and RAOs. If DNAPL or sorbed soil

contamination persists in the areas between the PRBs and continues to propagate a

dissolved-phase plume beyond the designed service life of the PRBs, then this technology

will no longer achieve RAOs or limit residual risk.


reduce residual risk. If DNAPL or sorbed soil contamination persists following completion

of ERD treatments, a dissolved-phase plume is likely to persist or rebound within the

aquifer and will no longer limit residual risk.

Pump and treat methods can be designed to treat the deeper ground water plume and meet

long-term RGs and RAOs, and eventually limit residual risk. If DNAPL or sorbed soil

contamination is present, pump and treat technology in low permeability sediments typical

of the GCSP Site may take longer than 40 years to achieve RAOs. Additionally, portions of

the aquifer that have been partially remediated may be subject to recontamination or

rebound from remaining sorbed or DNAPL contaminant sources.

All of the technologies considered for the Deeper Ground Water would probably be

effective in the long-term and leave no residual risk at the site. PRB and Pump and Treat are

more expensive remedies and will relatively take longer to achieve cleanup goals compared

to ERD. MNA is not proven at the site and may take a long time to achieve cleanup goals.

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17.3.2 Adequacy and Reliability of Controls

With the exception of the No Action alternatives, each of the proposed remedial

technologies can provide adequate and reliable treatment of COCs. Long-term adequacy

and reliability of any controls for the downgradient portions of the site also will ultimately

depend on the corresponding remediation of the source area media.


For the indoor air media, the Radon-type Vapor Mitigation System is expected to provide

more adequate and reliable controls in meeting RAOs than the No Action Alternative.

However, long-term adequacy and reliability of this control will ultimately depend on

elimination of the vapor intrusion pathway by remediation of the shallow ground water

sources.


Thermal treatment involves volatilization of COCs from the subsurface and collection of

vapors using soil vapor extraction. Thermal heating is a highly reliable method of causing

volatilization and soil vapor extraction is a reliable method of vapor collection when

appropriately designed and implemented. Thermal resistive treatment of the source area

would be accomplished in a single application event at the site and would not require

repeat treatments. However, meeting RAOs at the source area with a single application will

require an extremely high removal efficiency and thermal treatment alone may not fully

meet RAOs following the single application. Additional polishing treatment may be

required and can include natural active biological treatment during the cool-down period,

or active application of ISCO or ERD. A loss of process control (incomplete vapor recovery

using SVE) could lead to escape of COC vapors to the atmosphere or into structures

overlying the treatment zone or the recondensing of COC vapors outside the treatment area.

Both ISCO and ERD would, by design, require multiple treatments over an extended time

period to meet RAOs due to the limited residence times of the injected materials in the

aquifer (although ERD amendments far outlast oxidant amendments). Individual treatment

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events over time would be discrete efforts and substantial O&M of these technologies would

not be required between events. Both ISCO and ERD have been proven reliable methods of

treating the COCs, but both require injection of amendments into the subsurface that can be

difficult to control. ISCO is more sensitive to injection uniformity and initial contact with

contaminants than is ERD since ERD amendments have a much longer residence time and

can migrate with ground water to interact with contaminants. Ineffective distribution of

ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase

contaminants.


For the shallow ground water plume core and hot spot media, appropriately designed and

implemented measures should adequately and reliably meet RAOs. If sorbed-phase

contaminants remain following any of treatments, it would substantially impact the

adequacy of the control. The ZVI-PRBs have been designed for a service life of 20 years, and

will require replacement at this time since RAOs are not expected to be met for 40 years.

Once installed, the ZVI-PRB walls would not require subsequent O&M other than the single

replacement of the wall at 20 years.

The adequacy and effectiveness of PRBs will decrease over time as the reactive material in

the PRBs degrades, but they have been designed to provide effective treatment through

20 years. The effectiveness of the ZVI-PRB walls also is dependent upon a thorough

understanding of the hydraulic flow conditions within the aquifer and, if not properly

designed or installed, bypass of ground water around, below, or above the barrier can

occur.

Both ISCO and ERD would, by design, require multiple treatments over an extended time

period to meet RAOs due to the limited residence times of the injected materials in the

aquifer. Individual treatment events over time would be discrete efforts and substantial

O&M of these technologies would not be required between events. Both ISCO and ERD

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have been proven reliable methods of treating the COCs, but both require injection of

amendments into the subsurface, which can be difficult to control. ISCO is more sensitive to

injection uniformity and initial contact with contaminants than is ERD since ERD

amendment have a much longer residence time and can migrate with ground water to

interact with contaminants. Ineffective distribution of ISCO or ERD amendments can lead

to untreated residual sorbed-phase contaminants.

The infrastructure associated with the pump and treat option for the shallow ground water

core and hot spot would be subject to regular O&M needs and components may exceed

their service life and require replacement over the course of the extended implementation of

this technology. Damage, fouling, or loss of specific capacity of the pump and treat system

extraction and/or injection wells may require replacement of these components as well.

Significant failures of equipment during treatment may require the cessation of treatment

while repairs are conducted.

Although all technologies considered are reliable and adequate, the ISCO with follow-on

ERD and ERD Bio-barriers remedy are less expensive; reliable and adequate; and would

take the shortest time to achieve cleanup goals compared to PRB, and Pump and Treat.

17.3.2.4 Shallow Ground Water Periphery and Deeper Ground Water

Long-term adequacy and reliability of any controls for the either the shallow or deep

ground water periphery will ultimately be dependent on corresponding remediation of

upgradient or overlying contamination in the source area, the shallow ground water plume

core and hot spot, or the shallow ground water periphery. With MNA, no specific controls

or infrastructure are installed. Given appropriate site conditions, MNA can be a reliable

method (reductive dechlorinated of site COCs) of reaching RAOs over long time periods.

The ZVI-PRBs have been designed for a service life of 20 years, and will require replacement

at this time since RAOs are not expected to be met for 40 years. Once installed, the ZVI-PRB

walls would not require subsequent O&M other than the single replacement of the wall at

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20 years. The adequacy and effectiveness of PRBs will decrease over time as the reactive

material in the PRBs degrades, but they have been designed to provide effective treatment

through 20 years. The effectiveness of the ZVI-PRB walls also is dependent upon a

thorough understanding of the hydraulic flow conditions within the aquifer and, if not

properly designed or installed, bypass of ground water around, below, or above the barrier

can occur.

ERD would, by design, require multiple treatments over an extended time period to meet

RAOs due to the limited residence times of the injected materials in the aquifer. Individual

treatment events over time would be discrete efforts and substantial O&M of these

technologies would not be required between events. ERD has been proven to be a reliable

method of treating the COCs, but requires injection of amendments into the subsurface,

which can be difficult to control. Ineffective distribution of ERD amendments can lead to

untreated residual sorbed-phase contaminants.

The infrastructure associated with the pump and treat option for the shallow ground water

core and hot spot would be subject to regular O&M needs and components may exceed

their service life and require replacement over the course of the extended implementation of

this technology. Damage, fouling, or loss of specific capacity of the pump and treat system

extraction and/or injection wells may require replacement of these components as well.

Significant failures of equipment during treatment may require the cessation of treatment

while repairs are conducted.

Although all technologies considered are reliable and adequate, the ERD Bio-barrier remedy

is the least expensive technology; reliable and adequate; and would take the shortest time to

achieve cleanup goals compared to MNA, PRB and Pump and Treat.

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17.4 Reduction of Toxicity, Mobility, and Volume

Reduction of toxicity, mobility, or volume through treatment refers to the anticipated

performance of the treatment technologies that may be included as part of a remedy.

With the exception of the No Action Alternative, it is assumed that an appropriate design

for all retained technologies, or technology combinations, would be able to be developed to

permanently reduce toxicity, mobility, and volume of COCs. One exception is in the case of

the Vapor Mitigation option for the indoor air media. In that case, COCs are simply blocked

from entering structures to eliminate a completed exposure pathway and the toxicity,

mobility, and volume (TMV) of COCs is not affected. Therefore, this technology relies on

other methods of treatment within source areas and the shallow ground water plume core

to reduce COCs in the subsurface to concentrations that no longer support vapor intrusion

above human health risk-based action levels.

17.4.1 Treatment Process Used and Materials Treated

17.4.1.1 Indoor Air (Vapor Mitigation System)

Radon-type vapor mitigation systems do not technically treat any of the COCs but rather

prevents them from entering the structure via vapor intrusion. The vapor mitigation system

incorporates a plastic barrier between the ground surface and the overlying structure, with

the operation of a vapor extraction blower beneath the barrier, which allows vapors to

bypass the interior of the structure and be exhausted above the roof.


Thermal technologies provide treatment via the volatilization and steam flushing of VOCs

(including the COCs) induced by heating of the subsurface, with soil vapor extraction used

to recover the vapors and steam. The steam and vapors are collected, condensed, and

treated prior to discharge of clean effluent water. ISCO treatment occurs via destructive

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oxidation of organic contaminants (including the COCs) and mineralization to carbon

dioxide, water, and chloride. ISCO is generally capable of treating all organic compounds if

adequate contact with oxidant can be achieved. ISCO treatment would be followed by

enhanced biologically-mediated reductive dechlorination (ERD) in which carbon-source

amendments are injected to enhance natural biological treatment. ERD also can be used as a

stand-alone treatment.

All of the technologies considered are effective in permanently reducing toxicity, mobility

and volume of COCs. However, thermal treatment would be quicker, cost-competitive and

have the least impact on the community.

17.4.1.3 Shallow Ground Water Plume and Hot Spot Treatment

ZVI-PRBs provide treatment via reductive dechlorination as ground water passes through

the PRB under natural ground water flow gradients. ZVI-PRBs are effective for treatment of

chlorinated ethenes and ethanes (including the COCs), select chlorinated pesticides, and

some metals. ISCO treatment occurs via destructive oxidation of organic contaminants

(including the COCs) and mineralization to carbon dioxide, water, and chloride.

ISCO is generally capable of treating all organic compounds if adequate contact with

oxidant can be achieved. ISCO treatment would be followed by enhanced biologically-

mediated reductive dechlorination (ERD) in which carbon-source amendments are injected

to enhance natural biological treatment. ERD also can be used as a stand-alone treatment.

Ground water extraction and treatment provides treatment by extracting ground water,

stripping (volatilizing) VOCs (including the COCs), and treating the vapor stream using

granular activated carbon prior to discharge to the atmosphere. The treated water effluent

is then re-injected into the subsurface.

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and volume of COCs. However, even though ISCO with follow-on ERD is more expensive

than ERD Bio-barrier cleanup goals would be reached quicker.


MNA provides treatment via naturally-occurring bacteria, which provide biologically-

mediated reductive dechlorination given appropriate site conditions. MNA can be effective

for many organic compounds, including the COCs. ZVI-PRBs provide treatment via

reductive dechlorination as ground water passes through the PRB under natural ground

water flow gradients. ZVI-PRBs are effective for treatment of chlorinated ethenes and

ethanes (including the COCs), select chlorinated pesticides, and some metals.

ERD provides treatment via enhanced biologically-mediated reductive dechlorination in

which carbon-source amendments are injected to enhance natural biological treatment.

ERD is effective for a variety of organic compounds, including chlorinated ethenes and

ethanes (COCs). Ground water extraction and treatment provides treatment by extracting

ground water, stripping (volatilizing) VOCs (including the COCs), and treating the vapor

stream using granular activated carbon prior to discharge to the atmosphere. The treated

water effluent is then re-injected into the subsurface.


and volume of COCs. However, ERD is less expensive than the other alternatives.

17.4.2 Amount of Hazardous Materials Destroyed or Treated


The vapor mitigation systems do not provide active treatment, but physically block

contaminants from entering a structure.

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17.4.2.2 Source Area, Shallow Plume Core and Hot Spot, Shallow Plume Periphery,

and Deeper Ground Water Treatment

Approximately 44.5 MG of ground water and 6,500 yd3 of soil will be treated at the site. It is

anticipated that each of the proposed technologies can remove the quantity of COCs to meet

the site RAOs.

17.4.3 Degree of Expected Reductions in Toxicity, Mobility, and Volume


The vapor mitigation systems do not provide active treatment of COCs, but physically block

contaminants from entering a structure.


The thermal treatment is anticipated to provide substantial reductions in toxicity, mobility,

and contaminant volume (TMV) and is likely to provide the greatest percent reduction in

source-area concentrations following a single treatment. ISCO is anticipated to provide

substantial reductions in TMV if the oxidants can be adequately distributed to provide

contact with COCs. Follow-on ERD also is anticipated to provide substantial reductions in

TMV if the carbon-source amendments can adequately sustain biologically-mediated

subsurface reactions. Depending on site-specific conditions to be further characterized

during the Remedial Design, ISCO and ERD can lead to the generation of equally or more

toxic intermediary products during treatment. These intermediary products are generally

only temporarily present during treatment and can include cis-1,2-DCE or VC with ERD, or

acetone and leached metals (such as hexavalent chromium) with ISCO. As with follow-on

ERD, stand-alone ERD is anticipated to provide substantial reductions in TMV.


ZVI-PRBs have been designed to provide complete treatment of ground water to the RAOs

upon a single pass through the wall and therefore provide substantial reduction of TMV,

although technically the ZVI-PRB results in an increase in anthropogenic materials in the

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subsurface due to the placement of iron. The presence of sorbed-phase COCs between PRB

walls will provide for continued dissolution and recontamination of ground water between

the walls, and will require an extended treatment time.

ISCO is anticipated to provide substantial reductions in TMV if the oxidants can be

adequately distributed to provide contact with COCs. Follow-on ERD also is anticipated to

provide substantial reductions in TMV if the carbon-source amendments can adequately

sustain biologically-mediated subsurface reactions. Depending on site-specific conditions to

be further characterized during the Remedial Design, ISCO and ERD can lead to the

generation of equally or more toxic intermediary products during treatment. These

intermediary products are generally only temporarily present during treatment and can

include cis-1,2-DCE or VC with ERD, or acetone and leached metals (such as hexavalent

chromium) with ISCO. As with follow-on ERD, stand-alone ERD is anticipated to provide

substantial reductions in TMV.

The pump and treat technology is anticipated to quickly reduce toxicity by removing

ground water with high-concentrations of COCs, and will limit mobility by providing

hydraulic plume containment. The volume of the plume is expected to gradually be

reduced as treatment proceeds. As with ZVI-PRBs, sorbed-phase contaminants are expected

to provide a long-term source of COCs in ground water, requiring an extended treatment

time.


MNA may provide sustained moderate reductions in TMV over long time periods if

appropriate site conditions are confirmed at the Site. ZVI-PRBs have been designed to

provide complete treatment of ground water to the RAOs upon a single pass through the

wall and therefore provide substantial reduction of TMV, although technically the ZVI-PRB

results in an increase in anthropogenic materials in the subsurface due to the placement of

iron. The presence of sorbed-phase COCs between PRB walls will provide for continued

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dissolution and recontamination of ground water between the walls, and will require an

extended treatment time.

ERD is anticipated to provide substantial reductions in TMV if the carbon-source

amendments can adequately sustain biologically-mediated subsurface reactions.

Depending on site-specific conditions to be further characterized during the Remedial

Design, ERD can lead to the generation of equally or more toxic intermediary products

during treatment. These intermediary products are generally only temporarily present

during treatment and can include cis-1,2-DCE or VC.

The Pump and Treat technology is anticipated to quickly reduce toxicity by removing

ground water with high-concentrations of COCs, and will limit mobility by providing

hydraulic plume containment. The volume of the plume is expected to gradually be

reduced as treatment proceeds. As with ZVI-PRBs, sorbed-phase contaminants are expected

to provide a long-term source of COCs in ground water, requiring an extended treatment

time.

17.4.4 Type of Residuals Remaining After Treatment


With the vapor mitigation systems, the vapor intrusion pathway is removed by installing a

physical barrier and residual COCs inside the structure will quickly dissipate. If no other

active treatment is conducted at the site, the original COCs will remain in the subsurface as

residuals since the barriers do not provide treatment. Given active treatment of the site,

virtually no residuals are ultimately anticipated in the subsurface.


Completely successful thermal treatment leaves virtually no residual volatile COCs behind,

as they are all volatilized. Residuals following direct oxidation by ISCO will include carbon

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dioxide, water, and chloride. Depending on the oxidant used, other residuals may include

metal oxides (such as manganese oxide) or dissolved metals (such as dissolved manganese).

After follow-on ERD (or stand-alone ERD), residuals will proceed through the series of

degradation products TCE, DCE, VC, ethene, and ultimately to carbon dioxide, water, and

chloride. If an oversupply of carbon-source amendment is applied, then residual

amendment could remain in the subsurface for a period of time following treatment, but

will ultimately be consumed.


As ground water passes through each ZVI-PRB wall, reductive dechlorination will progress

from PCE through TCE, DCE, VC, and ethene, then ultimately to carbon dioxide, water, and

chloride as water passes out of the barrier. Following treatment, the ZVI material will

remain in the subsurface. Residuals following direct oxidation by ISCO will include carbon

dioxide, water, and chloride. Depending on the oxidant used, other residuals may include

metal oxides (such as manganese oxide) or dissolved metals (such as dissolved manganese).

After follow-on ERD (or stand-alone ERD), residuals will proceed through the series of

degradation products TCE, DCE, and VC, ethene, and ultimately to carbon dioxide, water,

and chloride. If an oversupply of carbon-source amendment is applied, then residual

amendment could remain in the subsurface for a period of time following treatment, but

will ultimately be consumed. Residuals following pump and treat include GAC, which will

require offsite disposal or recycling and remediated ground water that will require

reinjection.


With MNA, residuals following reductive dechlorination of PCE will proceed through TCE,

DCE, VC, ethene, and ultimately to carbon dioxide, water, and chloride. As ground water

passes through each ZVI-PRB wall, reductive dechlorination will progress from PCE

through TCE, DCE, VC, and ethene, then ultimately to carbon dioxide, water, and chloride

as water passes out of the barrier. Following treatment, the ZVI material will remain in the

subsurface. As ERD is applied, residuals will proceed through the series of degradation

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products TCE, DCE, VC, ethene, and ultimately to carbon dioxide, water, and chloride. If

an oversupply of carbon-source amendment is applied, then residual amendment could

remain in the subsurface for a period of time following treatment, but will ultimately be

consumed. Residuals following pump and treat include granular activated carbon, which

will require offsite disposal or recycling and remediated ground water that will require

reinjection.

17.5 Short-Term Effectiveness

Short-term effectiveness addresses the period of time needed to implement the remedy and

any adverse impacts that may be posed to workers, the community and the environment

during construction and operation of the remedy until cleanup levels are achieved.

The technology combinations for all impacted media have variable impacts with respect to

requiring protection of workers during remedial construction, protection of community

during Remedial Action, and environmental impacts of Remedial Action. The No Action

Alternatives have no impact because there is no remedial construction. For essentially all

active remedial technologies for any impacted media, intrusive work and installation of

required infrastructure, ranging from monitoring wells to PRBs, will present some exposure

to site workers. Risks to site workers can be managed through appropriate health and

safety practices.

17.5.1 Protection of Community During Remedial Actions

All active treatments may require appropriate traffic or access control and notification to

prevent community members from entering a hazardous condition or to prevent

community members from posing a risk to workers conducting remedial activities.

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17.5.1.1 Indoor Air

The vapor mitigation systems involve short-term inconvenience impacts to the specific

property owners where vapor mitigation systems will be installed. The installation of the

systems will require access to the crawlspace or basement beneath the structure for

placement of the plastic barrier, the installation of ventilation piping through the floor and

to the roof within a wall or other inconspicuous location, and installation of a roof vent.

RAOs in indoor air will be achieved by eliminating the vapor intrusion pathway into the

homes.

17.5.1.2 Source Area

The implementation of thermal treatment will require several actions for the protection of

the surrounding community. Air monitoring will be required during drilling, excavation,

and other intrusive infrastructure installation activities. Recovery of vapors with an SVE

system would be necessary to prevent discharge of vapors to the atmosphere or into

overlying structures. Large electricity-handling devices and aboveground treatment

equipment also will be present onsite (electricity distribution system would be

underground) during treatment and will require adequate fencing, setbacks, and warning

notifications. The implementation of ISCO also will require several actions for the

protection of the surrounding community. Air monitoring will be required during drilling

and other intrusive activities. Appropriate safety measures must be implemented when

handling oxidants to prevent contact by community members. Injection of oxidants also

must be controlled to prevent surfacing of oxidants. The implementation of ERD will

require air monitoring during drilling or other invasive activities. RAOs will be achieved in

the Source Area by treating principal threat waste.

17.5.1.3 Shallow Ground Water Plume Core and Hot Spot

The installation of ZVI-PRBs will require several actions for the protection of the

community. Air monitoring will be required during excavation and other invasive

installation activities. Depending on the installation method selected, large open trenches

that may or may not be filled with supportive liquid slurries will be excavated within

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residential areas. Substantial notification, fencing, and other access control will be required

to prevent community members from entering the trenches (especially children). The

excavation of soil during installation is likely to generate hazardous waste, which will

require offsite disposal and must be transported through the community.

Due to the shallow nature of ground water, highly contaminated ground water also may be

generated and will require onsite storage and treatment or offsite disposal. In addition, the

installation activities are likely to produce significant disruptions to local traffic and could

impact the ability of property owners to access their driveways or to utilize their property.

To be effective, PRBs must be installed in precise orientations, and it is unlikely that such an

installation could be performed in a residential area without requiring trenching across

private property.

The implementation of ISCO also will require several actions for the protection of the

surrounding community. Air monitoring will be required during drilling and other

intrusive activities. Appropriate safety measures must be implemented when handling

oxidants to prevent contact by community members. Injection of oxidants also must be

controlled to prevent surfacing of oxidants. The implementation of ERD will require air

monitoring during drilling or other invasive activities.

The implementation of pump and treat will require air monitoring during drilling or other

invasive activities. Air monitoring or modeling also will be necessary to demonstrate

protection of the community from unacceptable air emissions from the treatment plant.

Community-protection measures also will be necessary during trenching activities for the

installation of conveyance piping.

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During implementation of MNA, there would be limited impacts to the community;

however, air monitoring would be necessary during drilling and well installation activities.

The installation of ZVI-PRBs will require several actions for the protection of the

community. Air monitoring will be required during excavation and other invasive

installation activities. Depending on the installation method selected, large open trenches

that may or may not be filled with supportive liquid slurries will be excavated within

residential areas. Substantial notification, fencing, and other access control will be required

to prevent community members from entering the trenches (especially children). The

excavation of soil during installation is likely to generate hazardous waste, which will

require offsite disposal and must be transported through the community. Due to the

shallow nature of ground water, highly contaminated ground water also may be generated

and will require onsite storage and treatment or offsite disposal. In addition, the installation

activities are likely to produce significant disruptions to local traffic and could impact the

ability of property owners to access their driveways.

The implementation of ERD will require air monitoring during drilling or other invasive

activities. The implementation of pump and treat will require air monitoring during drilling

or other invasive activities. Air monitoring or modeling also will be necessary to

demonstrate protection of the community from unacceptable air emissions from the

treatment plant.

Community-protection measures also will be necessary during trenching activities for the

installation of conveyance piping.

The MNA Alternative presents the least potential for exposure or risk to site workers, the

community, or the environment as no, or minimal, intrusive work would be conducted.

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17.5.2 Protection of Workers During Remedial Actions

All active treatments may require appropriate traffic or access control to provide protection

to workers conducting remedial activities. Risks posed to workers can be effectively

managed through appropriate health and safety practices and use of appropriate personal

protective equipment (PPE).


During installation of vapor mitigation systems, air monitoring will be conducted and

workers will wear appropriate PPE including respirators, if conditions warrant.


Air monitoring will be required during installation of thermal treatment infrastructure and

appropriate measures must be taken to protect those working with electrical-handling

equipment, both during installation and during active treatment. Air monitoring will be

required during drilling and other invasive activities associated with ISCO and ERD.

Appropriate safety precautions must be taken to prevent exposure to workers from oxidants

when applying ISCO.


Air monitoring will be required during installation of ZVI-PRBs. Excavation and intrusive

onsite work may pose a threat to workers during installation of ZVI-PRBs. The potential

presence and offsite transport of hazardous waste or highly-contaminated ground water

poses additional threats to workers. Risks can be managed through appropriate waste-

handling practices. Air monitoring will be required during drilling and other invasive

activities associated with ISCO and ERD, and appropriate safety precautions must be taken

to prevent worker exposure to oxidants when applying ISCO. Protection of workers during

installation of a pump and treat system will primarily involve air monitoring during drilling

and invasive activities, trenching safety for conveyance piping, and general construction

safety.

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Air monitoring will be required during drilling and well-installation activities associated

with MNA. Air monitoring also will be required during installation of ZVI-PRBs.

Excavation and intrusive onsite work may pose a threat to workers during installation of

ZVI-PRBs. The potential presence and offsite transport of hazardous waste or highly-

contaminated ground water poses additional threats to workers. Risks can be managed

through appropriate waste-handling practices. Air monitoring will be required during

drilling and other invasive activities associated with ERD. Protection of workers during

installation of a pump and treat system will primarily involve air monitoring during drilling

and invasive activities, trenching safety for conveyance piping, and general construction

safety.

17.5.3 Environmental Impacts


The vapor mitigation systems will exhaust extracted soil vapors into the atmosphere. The

extracted vapors are treated onsite prior to discharge into the atmosphere.


Thermal treatment will require the control of offgas emissions during the active treatment

period. No adverse environmental conditions are anticipated for the ISCO or ERD

treatments other than the potential generation of intermediary products during treatment

(such as, acetone or leached metals for ISCO or VC for ERD).


The installation of ZVI-PRBs can pose a threat to the environment since hazardous waste is

likely to be generated and transported offsite for disposal. Environmental risk can be

managed using appropriate hazardous waste handling practices. There may be limited

environmental risk due to the residual iron in the subsurface following treatment, but little

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study has been conducted regarding any such risk. No adverse environmental conditions

are anticipated for the ISCO or ERD treatments other than the potential generation of

intermediary products during treatment (such as, acetone or leached metals for ISCO or VC

for ERD). For the pump and treat system, no environmental impacts are anticipated if

appropriate air emissions treatment is incorporated and ground water reinjection is

successful.


Treatment using MNA is passive in nature and high concentrations of COCs may persist in

ground water for an extended period of time, and may present unacceptable risk to the

environment. The installation of ZVI-PRBs can pose a threat to the environment since

hazardous waste is likely to be generated and transported offsite for disposal.

Environmental risk can be managed using appropriate hazardous waste handling practices.

There may be limited environmental risk due to the residual iron in the subsurface

following treatment, but little study has been conducted regarding any such risk. No

adverse environmental conditions are anticipated for the ERD treatment other than the

potential generation of intermediary products during treatment (such as, VC). For the

pump and treat system no environmental impacts are anticipated if appropriate air

emissions treatment is incorporated and ground water reinjection is successful.

17.5.4 Time Until Remedial Action Objectives Are Achieved

The time over which RAOs would be met varies by technology combination and media.

Generally speaking, based on the available information, the following extended Remedial

Action time periods are assumed for the following technologies to meet RAOs: PRB wall

remediation applications will require over 40 years; ISCO with follow-on ERD would

roughly require 8 years; ERD or bio-barrier applications will require roughly 20 years;

Pump and Treat options will require 40 years of operation or more; and MNA options are

assumed to require at least 40 years of active monitoring. The indoor air vapor mitigation

option would essentially immediately achieve RAOs although long-term compliance with

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RAOs would likely require additional source area and shallow ground water treatment

options to be implemented.

Key assumptions in evaluating the potential time it will take for technology combinations to

meet RAOs are the currently understood site conceptual models for each medium.

17.6 Implementability

Implementability addresses the technical and administrative feasibility of a remedy from

design through construction and operation. Factors such as availability of services and

materials, administrative feasibility, and coordination with other governmental entities are

also considered.

Technical or administrative implementability issues are not expected to be substantially

different for the different technology combinations for the different media. Generally

speaking, the technologies as described in this ROD are considered constructible and

appropriate vendors and equipment are available for hire. However, certain options such as

thermal treatment and PRB installation are somewhat specialized technologies so there are

fewer vendors from which to choose. Administrative exemptions or approvals will

probably be required prior to injection of oxidants, carbon amendments, or reinjection of

treated ground water into the subsurface. Additionally, administrative notifications may be

necessary for the discharge of treated offgas streams.

17.7 Cost

Cost includes estimated capital and O&M costs as well as present worth costs. Present

worth cost is the total cost of an alternative over time in terms of today’s dollar value. Cost

estimates are expected to be accurate within a range of +50 to -30 percent. Estimated costs

associated with each of the remedial alternatives are summarized in Table 18 (Cost

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Summary for Remedial Alternatives). The estimated costs associated with the Selected

Remedy are detailed in Appendix B (Cost Estimate Details for Selected Remedy). The total

cost for the Preferred Remedy for the Site is approximately $29.5 million.

Source Area

The cost is competitive among all alternatives with the exception of the No Action

Alternative and is within 1 percent difference. The cost for thermal treatment, the

Preferred Alternative, is approximately $8.02 million.

Shallow Ground Water Plume Core and Hot Spot

The cost for the Pump and Treat remedy is the most expensive and the ERD Bio-

barriers is the least expensive. ZVI-PRB and ISCO with ERD are of intermediate

cost. ISCO with Follow-On ERD, the Preferred Alternative is approximately

$6.73 million.

Shallow Ground Water Plume Periphery

ZVI-PRB and Pump and Treat are the most expensive remedies. MNA is the least

expensive and ERD Bio-barriers, the Preferred Alternative, is approximately

$3.27 million.

Deeper Ground Water Plume

ZVI-PRB in combination with ERD Bio-barriers and Pump and Treat are the most

expensive remedies. MNA is the least expensive and ERD Bio-barriers alone, the

Preferred Alternative, is approximately $7.22 million.

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17.8 State Acceptance

The NMED agrees with EPA’s recommendations of the Selected Remedy.

17.9 Community Acceptance

The EPA conducted a public meeting on April 20, 2006, to present the Proposed Plan (EPA

2006) to the public and presented the following preferred alternative for the various

impacted media at the site:

1. Indoor Air – Vapor Mitigation

2. Source Area – Thermal Treatment

3. Shallow Plume Core and Hot Spot – ISCO with Follow-on ERD (Flexible)

4. Shallow Ground Water Plume Periphery – ERD Bio-barrier

5. Deeper Ground Water – ERD Bio-barrier

The community did not present any opposition to any of the alternatives presented

including the Selected Remedy either during the meeting or during the 30-day comment

period. Based on the comments received the community accepts all of the alternatives

including the Selected Remedy presented in this ROD.

17.10 Summary of Comparative Analysis of Alternatives

A summary of the comparative analysis is shown in Tables 14 through 18.

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18.0 Principal Threat Wastes

The NCP establishes an expectation that EPA will use treatment to address the principal

threats posed by a Site wherever practicable (NCP §300.430(a)(1)(iii)(A)). Identifying

principal threat wastes combines concepts of both hazard and risk. In general, principal

threat wastes are those source materials considered to be highly toxic or highly mobile,

which generally cannot be contained in a reliable manner or would present a significant risk

to human health or the environment should exposure occur. Conversely, nonprincipal

threat wastes are those source materials that generally can be reliably contained and that

would present only a low risk in the event of exposure. The manner in which principal

threats are addressed generally will determine whether the statutory preference for

treatment as a principal element is satisfied.

The source areas and portions of the downgradient ground water at the site are

contaminated with chlorinated solvents possibly containing DNAPL. DNAPL’s are

considered to be "principal threat wastes" because COCs concentrations are present that

pose a significant risk under a residential exposure scenario. Through the use of treatment

as a principal element, the response action will satisfy the preference for treatment and

reduce the mobility of the hazardous source material that constitutes the principal threat

wastes at the site. The EPA has determined that the potential future use of ground water at

the site is drinking water. The principal threat wastes, if left in the source areas and

downgradient ground water, would pose a significant risk to residents living in the area.

In the Source Area, thermal Treatment and ISCO with follow-on ERD will treat the principal

threat waste to achieve RGs. ERD alone may not be sufficient to treat principal threat waste

in the Source Area. The shallow plume core and hot spot is not anticipated to contain

principal threat waste. However, should principal threat waste be present within the

Shallow Plume Core and Hot Spot, ISCO with follow-on ERD is expected to provide

effective treatment. Other considered technologies may not be sufficient to treat principal

threat waste, if present within the shallow plume core and hot spot.

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19.0 Selected Remedy

The EPA will implement the Selected Remedy in phases to optimize the treatment in the

various site-impacted media. The Selected Remedy for the various impacted media and the

order in which they will be implemented is as follows:

• Indoor Air – Installation of Vapor Mitigation Systems

• Source Area – Thermal Treatment

• Shallow Ground Water Plume Core and Hot Spot – ISCO with Follow-On ERD

• Shallow Ground Water Plume Periphery – ERD Bio-Barrier

• Deeper Ground Water – ERD Bio-Barrier

19.1 Summary of the Rationale for the Selected Remedy

19.1.1 Indoor Air: Vapor Mitigation System

The EPA chose to install vapor mitigation systems as they were the only active remedy that

would protect human health. Vapor mitigation systems are proven and used extensively

across the country to mitigate radon. Chlorinated solvents would be mitigated similar to

radon gas through use of this alternative.

19.1.2 Source Area: Thermal Treatment

The EPA chose the thermal treatment alternative over the other alternatives because this

alternative best meets the cleanup objectives by treating contaminated soils and ground

water with concentrations exceeding RGs at the site. This alternative reduces mobility and

toxicity at the Site by removing the source materials. This alternative is expected to be

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completed in approximately 1 year following construction. Implementation of this

alternative will have less impact on the community than the other alternatives. The cost for

implementation of this remedy is slightly less than other active alternatives.

19.1.3 Shallow Plume Core and Hot Spot – ISCO with Follow-On ERD (Flexible)

The EPA chose ISCO with Follow-on ERD for the shallow plume core because ISCO is more

effective in rapidly removing source materials in the core area. The ISCO technology

combined with follow-on ERD, though more expensive than some of the other alternatives,

will be more effective in removing the COCs in the shortest amount of time. EPA and the

NMED believe this alternative would be protective of human health and the environment,

would comply with ARARs, would be cost-effective, and would utilize permanent solutions

to the maximum extent practicable.

The EPA will be flexible in applying this component of the Selected Remedy in the Shallow

Plume Core and Hot Spot Area. Based on additional information gathered during the Pre-

Design Field Investigation and after implementation of the Thermal Treatment at the Source

Area, EPA will determine the suitability of using the ISCO component and the degree of

ERD bio-barrier treatment required. If the Predesign Field Investigation indicates the

presence of DNAPL in the Shallow Plume Core and Hot Spot Area, EPA will fully

implement the ISCO with Follow-On ERD. If on the other hand ground water investigation

does not indicate DNAPL and ERD is demonstrated to be an effective alternative, then EPA

may choose to implement only the ERD bio-barrier component.

The EPA believes the flexible approach is more prudent for the Shallow Plume Core and

Hot Spot Area because of existing data gaps. While this approach will ensure that the

remedy is protective of human health and the environment, it could save unnecessary costs.

If the ISCO component is not required and only ERD bio-barrier is implemented, the cost for

the Selected Remedy will be reduced by approximately $5 million dollars.

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19.1.4 Shallow Plume Periphery, Deeper Plume: ERD Bio-barrier

The EPA chose this alternative over others for the above two impacted areas because this

alternative best meets the cleanup objectives by treating ground water contaminants

exceeding RGs from the site. Using ERD bio-barriers for both of these impacted ground

water areas would optimize the infrastructure necessary for the remedy and in turn save

costs. Although it is slower than chemical oxidation, ERD provides longer residence time

for the amendments to act. ERD is less dependent on uniform distribution during injection

than ISCO, and the longer residence time allows penetration into low-permeability

sediments. It is less intrusive on private properties since public access can be used for

injecting the amendments. It is the least expensive alternative. Based on information

available at this time, the EPA and the NMED believe the Preferred Alternative would be

protective of human health and the environment, would comply with ARARs, would be

cost-effective, and would utilize permanent solutions to the maximum extent practicable.

Because it would treat the source materials constituting principal threats, the remedy also

would meet the statutory preference for the selection of a remedy that involves treatment as

a principal element for these areas.

19.2 Description of the Selected Remedy

Following is a description of each component of the Selected Remedy. Although the EPA

does not expect significant changes to this remedy, it may change "somewhat" as a result of

the RD and construction processes. Any changes to the remedy described in this ROD

would be documented using a technical memorandum in the Administrative Record, an

Explanation of Significant Differences, or a ROD Amendment, as appropriate and consistent

with the applicable regulations.

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19.2.1 Indoor Air

Vapor intrusion mitigation systems will be installed in those residential structures shown in

Figure 11. The vapor intrusion mitigation systems would be designed and installed

consistent with the EPA Office of Air and Radiation guidance Building Radon Out, A Step-by-

Step Guide on How to Build Radon-Resistant Homes (EPA, 2001).

Specific design elements would depend on the type of foundation at the home. Currently,

only three residences have been evaluated for installation of the vapor mitigation systems.

Of these, two of the residences are built over crawlspaces and one residence has a basement.

The remaining 11 structures in the area are assumed to be similar in construction to the

three evaluated, although one of the structures may be of slab-on-grade construction. Vapor

intrusion mitigation systems would be functionally similar to radon mitigation systems and

consist of placing a plastic liner between the ground surface and the residential living space

for residences with crawlspaces, and ventilating between the liner and the ground surface to

remove vapors before they can enter the living space. Structures with basements and slab-

on-grade construction will require additional components in the design of the vapor

mitigation systems. Specific design elements will be developed during the RD. The

structure located behind the Holiday Cleaners requires further evaluation because of close

proximity to the Holiday Cleaners building. The structure will be monitored further to

ensure that the indoor air is not influenced by the operations of the dry cleaner. Once the

background sources are evaluated further, the EPA will determine if installation of a vapor

mitigation system is warranted for this structure.

19.2.2 Source Areas

Figure 12 shows the extent of source areas at the Holiday Cleaners and the Abandoned Dry

Cleaners buildings. Thermal treatment technology can involve either conductive or

electrical resistance heating of the subsurface. Conductive heating utilizes high

temperatures at subsurface heater probes, installed within steel-cased, steel-screened vapor

extraction wells, to induce heating of the adjacent aquifer matrix by heat conduction. Water

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adjacent to the heater probe/ extraction well is fully vaporized, and steam is extracted using

the vapor extraction well. Electrical resistive heating (ERH) utilizes the subsurface

resistance to electrical current applied between subsurface electrodes/extraction wells to

heat the subsurface less vigorously, vaporizing only a portion of the water within the

subsurface. Steam generated by volatilizing water flushes volatile contaminants to the

vadose zone for extraction by the vapor extraction wells. The two methods are

competitively priced and either can be an effective thermal source area treatment at the

GCSP Site.

The selection of the specific thermal treatment version (conductive versus electrical

resistive) would be made during the RD, based on more detailed Site characterization data

collected during the Preliminary Design Field Investigation.

Regardless of the specific version, thermal treatment would be applied to raise the

subsurface temperature within the treatment volume of the source area to approximately

100 degrees Celsius (°C). The period of time required to reach this temperature is

dependent upon the number and spacing of heater probes/electrodes installed at the site,

but typically requires between 2 to 4 months. During this period of increasing subsurface

temperatures, volatilization of volatile contaminants is encouraged and vapors are collected

within the vapor extraction wells. Once the subsurface temperature reaches the boiling

point of the solvent (typically in the range of 88 to 92°C for PCE depending on its depth

below ground water), the PCE begins to boil, and PCE vapors rise to the vadose zone where

they are collected by the SVE system. When the subsurface temperature has been brought

to 100°C, water begins to vaporize and steam begins flushing volatile contaminants from the

subsurface for collection in the vapor extraction wells. The heating is continued until

concentrations approach the treatment goals. The SVE system provides process control

during thermal treatment, and prevents the migration of vapor or steam outside the

treatment area.

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Final polishing to treatment goals can sometimes be achieved through additional

volatilization over subsequent months as the subsurface slowly cools. Bioactivity is also

likely to increase during the cool-down period and can act as a polishing treatment.

However, due to the one-time nature of this technology, if DNAPL or sorbed-phase soil

contamination remains in the subsurface after the thermal treatment is complete, additional

final polishing by another remedial technology may need to be instituted to achieve RAOs.

For the GCSP Site, it is likely that thermal treatment would need to continue for an extended

period of time once the target subsurface temperature has been reached to even approach

the treatment goals. Additionally, given the very elevated COC levels in the source area,

thermal treatment would need to achieve a very high percentage removal rate (e.g.

99.9 percent or more) to meet the strict RAOs and RGs for the site. It is possible that final

polishing via another treatment technology within the source area or in downgradient

locations, or MNA over time might be necessary.

For either thermal treatment method, a network of heater probes or subsurface electrodes

would be installed within steel-cased, steel-screened vapor extraction wells. The heater

probe/electrode vapor extraction wells would be spaced approximately 15 to 25 ft apart,

with approximately 60 heater probe/electrode vapor extraction wells located across the

larger Holiday Cleaners source area and approximately 10 to 20 heater probe/electrode

wells located across the Abandoned Dry Cleaner source area. Each heater probe/electrode

vapor extraction well would be plumbed to a vapor extraction system to collect steam and

volatilized contaminants and process them at an onsite treatment facility. In addition to the

vapor extraction plumbing, electrical power cables also would be extended to each well to

provide the electricity for the thermal treatment. Temperature monitoring probes also

would be installed to track the increase in subsurface temperatures during treatment. If a

site were undeveloped, the piping and electrical cables would generally be left

aboveground; however, this is not viable in the developed GCSP source areas. Therefore, all

plumbing and electrical components would need to be installed in the subsurface. As a

potential enhancement to the SVE system, horizontal vapor extraction wells could be

installed at the same time as other subgrade plumbing and electrical infrastructure, using a

coarse backfill to enhance vapor recovery.

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19.2.3 Shallow Plume Core and Hot Spot

ISCO is initially applied to rapidly lower dissolved-phase COC concentrations to moderate

levels. The ISCO phase is then followed by injecting carbon-source amendments as a

polishing step for final reduction of COCs.

For treatment of the shallow ground water plume core and hot spot, ISCO would be applied

using a network of closely spaced permanent injection points, screened within the targeted

treatment zone. In this case, the injection points are anticipated to be placed using on-center

spacing of approximately 24 ft. Approximately 221 injection points will be required for

treatment of the area encompassing the shallow plume core and hot spot using ISCO. The

ISCO treatments would be applied from a depth of approximately 8 ft bgs (the top of the

silty sand layer that has been identified as a preferential pathway) to a depth of

approximately 20 ft bgs using the permanent injection points. A conceptual layout of the

ISCO treatment area under this alternative is presented in Figure 13.

The injected oxidant is assumed to be potassium and/or sodium permanganate. Other

oxidants are similarly priced and a final product selection will be made during the RD,

based on more detailed Site characterization data collected during the Preliminary Design

Field Investigation.

ISCO would be applied at the GCSP Site with the intent to replace one full pore volume

with oxidant during an initial injection event, followed by a similar injection at only one-half

the injection wells on a second event. The second injection event would be conducted

within approximately 6 months following the conclusion of the initial event, and would

specifically target plume core or hot spot locations with remaining contamination.

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Site-specific soil oxidant demand (SOD) significantly impacts the dosing frequency required

to reach RAOs in a cost-effective manner. Oxidant dosing assumptions utilized in the FS

(EPA, 2006b) are based on a conservative assumed SOD of 5 mg/kg. SOD values in the

range of 1 mg/kg may reduce the cost of ISCO by 15 to 20 percent, while SOD values in the

range of 10 mg/kg could make ISCO both technically infeasible and cost prohibitive. SOD

will be characterized during the Preliminary Design Field Investigation and those data will

be used to establish appropriate oxidant dosing during the RD.

ISCO injections are anticipated to be performed using high-pressure injection pumps and a

mobile injection trailer. It is assumed that oxidant can be injected into the subsurface at a

rate of 6 gallons per minute (gpm) based on assumptions utilized in the FS (EPA, 2006b). If

this injection rate, at a minimum, cannot be supported at the site, the costs associated with

this alternative may increase significantly due to the large volume of oxidant that must be

injected. Significant additional labor and perhaps infrastructure would be required to

deliver the needed volume of oxidant into the subsurface. If only very low injection rates

can be achieved, it may not be technically feasible to implement this alternative. The

supportable injection rate will be characterized during the Preliminary Design Field

Investigation and those data will be utilized during the RD.

As a polishing treatment for the shallow plume core and hot spot areas, ERD will be applied

within the same permanent injection wells. Each injection well is assumed to be screened

from approximately 8 ft bgs (the top of the silty sand layer that has been identified as a

preferential pathway) to approximately 20 ft bgs for treatment of the shallow plume core

and hot spot.

The carbon-source injections will be performed following conclusion of the ISCO injection

events. For cost estimation purposes, the carbon-source amendment was assumed to be

emulsified vegetable oil (EPA, 2006b). Other carbon-source amendments are similarly

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priced and a final product selection will be made during the RD, based on more thorough

Site characteristics data collected during the Preliminary Design Field Investigation.

The ERD polishing injections will be applied within the shallow plume core and hot spot

areas with the intent to replace one-half of a full pore volume, within the ROI of each

injection well, with the carbon-source amendment during each injection event. Carbon-

source amendment dosing is based on an assumed dissolved-sulfate concentration of

2,000 mg/L, based on available data from the RI. Dissolved-sulfate concentrations and

other geochemical conditions will be further characterized during the Preliminary Design

Field Investigation for use in the RD. A total of five carbon-source injections, performed

once every 15 months, are assumed to complete the ground water polishing and meet the

RAOs.

If the Preliminary Design does not indicate the presence of DNAPL, the EPA in concurrence

with NMED may choose to implement only the ERD bio-barrier component of the remedy.

A conceptual layout of the ERD bio-barrier is shown in Figure 14.

19.2.4 Shallow Ground Water Plume Periphery

Bio-barriers are installed as transects across the ground water plume axis by closely-spaced

injection of carbon-source amendments. Within these carbon-rich zones, or barriers,

biologically mediated reductive dechlorination of the COCs is enhanced and the process

forms a continuous ERD treatment zone to intercept the plume. Installation of multiple bio-

barriers in series achieves RAOs as ground water passes through the treatment areas. At the

GCSP Site, the bio-barriers will be placed utilizing linear transects of permanent injection

points. Injection points along each transect are anticipated to be spaced approximately 25 ft,

on center, with an assumed injection ROI of approximately 15 ft. The use of permanent

wells versus remobilization of a direct-push drilling rig over multiple events will provide

significant cost savings.

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Each injection well is assumed to be screened from approximately 8 ft bgs (the top of the

silty sand) to approximately 20 ft bgs for treatment of the shallow plume periphery.

Bio-barriers will be installed as multiple transects across the shallow plume periphery, with

an assumed total bio-barrier length of approximately 2,400 ft. Under this scenario, the bio-

barriers will be spaced approximately 200 ft apart along the length of the shallow ground

water plume. If combined with the bio-barrier treatment portion of the shallow ground

water plume core and hot spot, bio-barriers would be located so as to provide multiple

transects across the full width of the plume. A conceptual layout of the bio-barrier plume

periphery treatment is presented in Figure 15, and illustrates how the plume periphery bio-

barriers could be used in conjunction with plume core bio-barriers.

The injected ERD carbon-source amendment is assumed to be emulsified vegetable oil.

Emulsified vegetable oil has advantages of being one of the longer lasting available carbon

sources as well as being one of the less viscous amendments, which aids distribution within

low-permeability materials. Other carbon-source amendments are similarly priced and a

final product selection will be made during the RD, based on more detailed site

characterization data collected during the Preliminary Design Field Investigation.

The bio-barriers will be applied within the shallow ground water plume periphery with the

intent to replace approximately one-half the full pore volume, within the ROI of each

injection well, with the carbon-source amendment during each injection event. Site-specific

geochemical conditions, particularly sulfate concentrations, will impact the carbon-source

amendment dosing selected in the RD. Sulfate generally dominates the carbon demand,

interrupting the reductive dechlorination of the COC, and thereby having a significant

impact on carbon-source amendment dosing needs to reach RAOs in a reasonable

timeframe. Dissolved-sulfate concentrations and other geochemical conditions will be

further characterized during the Preliminary Design Field Investigation for use in the RD.

Carbon-source amendment dosing is based on an assumed dissolved-sulfate concentration

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of 2,000 mg/L, based on available data from the RI. A total of 16 carbon-source amendment

injections are assumed over a 20-year period (one injection every 15 months) to meet the

RAOs within the shallow ground water plume periphery.

19.2.5 Deeper Ground Water Plume

The complete vertical extent of contamination is not fully defined at this time. Further

characterization will be conducted during the Preliminary Field Investigation and the

remedy will be implemented such that the entire vertical extent is addressed. The remedy

will be re-evaluated during the design phase if new information regarding the vertical and

horizontal extent of the plume is determined.

Bio-barriers are installed as transects across the ground water plume axis along which

closely-spaced injection of carbon-source amendments will occur to form a continuous ERD

treatment zone across the plume. The bio-barriers will be placed using permanent injection

wells, due to the extended time period and numerous injections required to meet RAOs

with ERD. The use of permanent wells versus remobilization of a direct-push drilling rig

over multiple events will provide significant cost savings.

Bio-barriers will be installed as multiple transects across the deeper ground water plume,

with an assumed bio-barrier length of approximately 1,000 ft for treatment of contamination

at a depth up to 60 ft bgs, and an additional bio-barrier length of approximately 250 ft for

treatment of contamination at a depth up to 80 ft bgs. Two 80-ft deep bio-barriers, each

approximately 125-ft long, are anticipated to be installed to address the deepest known

contamination at the Site, with one transect anticipated to be located on First Street and

another anticipated to be located in the alleyway between First Street and Geis Street.

Injection wells along these deeper transects will be screened between approximately 60 ft

and 80 ft bgs. Multiple approximately 60-ft-deep bio-barriers will be installed with short

lengths anticipated to be located along First Street, in the alleyway between First Street and

Geis Street, near the midpoint of the plume on Geis Street, near the downgradient extent of

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the deeper plume, and limited injections at accessible points at the far downgradient extent

of the deeper plume. A conceptual layout of this arrangement is presented in Figure 16.

The injected ERD carbon-source amendment is assumed to be emulsified vegetable oil.

Other carbon-source amendments are similarly priced and a final product selection will be

made during the RD, based on more detailed Site characterization data collected during the

Preliminary Design Field Investigation. The bio-barriers will be applied within the deeper

ground water plume with the intent to replace approximately one-half the full pore volume,

within the ROI of each injection well, with the carbon-source amendment during each

injection event. Carbon-source amendment dosing is based on an assumed dissolved-

sulfate concentration of 2,000 mg/L, based on available data from the RI. Dissolved-sulfate

concentrations will be further characterized during the Preliminary Design Field

Investigation, since sulfate generally dominates the carbon demand and has a significant

impact on carbon-source amendment dosing. A total of 16 carbon-source amendment

injections are assumed over a 20-year period (one injection every 15 months) to meet the

RAOs within the deeper ground water plume.

19.3 Contingency Remedy

EPA will evaluate the site conditions to determine if monitored natural attenuation

(MNA) is a viable remedial alternative after the first Five-Year Review and after

source control has been established in the Source Areas and the Shallow Ground

Water Plume. If ground water data demonstrates evidence that MNA is occurring

such that RAOs will be met in a timely manner, then EPA may consider proposing

MNA as the remedial strategy for the Shallow Ground Water Periphery and the

Deeper Ground Water Plume. If this alternative is determined to be the most

efficient and effective remedy, then EPA with NMED’s concurrence will issue an

Explanation of Significant Differences (ESD) to document the change in the remedy.

MNA is not a component of the Selected Remedy.

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insufficient data to select MNA as a component of the Selected Remedy at the GCSP

Site. The EPA will collect the necessary data for MNA evaluation during the pre-

design investigation phase. The contingency will be invoked not because of a

potential failure of the Selected Remedy but rather as an alternative that would not

only achieve final cleanup goals but also provide significant cost savings to the

agency.


insufficient data to select MNA as a component of the Selected Remedy at the GCSP Site.

The EPA will collect the necessary data for MNA evaluation during the predesign

investigation phase. The contingency will be invoked not because of a potential failure of

the Selected Remedy but rather as an alternative that would not only achieve final cleanup

goals but also provide significant cost savings to the agency.

If the Selected Remedy does not appear to be making progress toward achieving the

remedial objectives, the EPA may propose a new remedy in the form of a ROD amendment

or other appropriate regulatory mechanism. “Triggers” that will signal unacceptable

performance of the Selected Remedy include, but are not limited to, the following:

a. Contaminant concentrations in the groundwater at specified locations exhibit an

increasing trend not originally predicted during remedy selection,

b. Near-source wells exhibit large concentration increases indicative of a new or renewed

release,

c. Contaminants are identified in MWs located outside of the original plume boundary,

d. Contaminant concentrations are not decreasing at a sufficiently rapid rate to meet the

remediation objectives, and

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e. Changes in land and/or groundwater use

19.4 Cost Estimate for the Selected Remedy

Appendix B includes details of the estimated costs to implement and construct the Selected

Remedy. The estimated total cost to implement and construct the Selected Remedy

presented in this ROD is $29,500,000. The information in this cost estimate for the Selected

Remedy is based on the best available information regarding the anticipated scope of the

Remedial Alternative.

Changes in the cost elements are likely to occur as a result of new information and data

collected during the engineering design of the Remedial Alternative. Major changes may be

documented in the form of a technical memorandum in the Administrative Record file, an

ESD, or a ROD amendment. This is an order-of-magnitude engineering cost estimate that is

expected to be within +50 to -30 percent of the actual project cost.

19.5 Expected Outcomes of the Selected Remedy

Following are the expected outcomes of the Selected Remedy in terms of resulting land and

ground water uses, the cleanup levels and the risk reduction achieved as a result of the

response action, and the anticipated community impacts.

19.5.1 Available Land Uses

The homes that have indoor vapor mitigation systems will no longer present long-term risk

to residents. The cancer risk from inhalation in the three homes that exceeded the Tier 3

level will be reduced to below the EPA risk of 1 x 10-5. An additional eleven homes will

receive vapor mitigation system to prevent future risk from vapor intrusion.

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19.5.2 Available Ground Water Uses

The remedy will be protective of ground water because all of the source areas will be

removed and active treatment of the plume will reduce the ground water concentrations of

chlorinated solvents below the federal MCL. Remediation at the site will prevent any

potential for vertical migration of contaminants into the deeper aquifer that is the source of

drinking water for the City of Grants. The planned implementation of the Institutional

Controls will help prevent use of ground water before cleanup goals are met.

19.5.3 Final Cleanup Levels

Table 20 shows the final cleanup level for the COCs. The results of the BHHRA indicate that

existing conditions at the site pose an ELCR of greater than 1 x 10-5 for indoor air. In

addition ground water COCs exceed MCLs and state ARARs. Soil COCs exceed NMED

safe levels for residential use. The Selected Remedy will address indoor air through the

installation of vapor mitigation systems and will address ground water and soil through

active treatment. The final cleanup levels are protective of human health and are expected

to restore the ground water and soil. The site is expected to be available for continued

unrestricted residential and commercial land use as a result of the remedy.

20.0 Statutory Determinations

Under CERCLA §121 and the NCP §300.430(f)(5)(ii), the EPA must select remedies that are

protective of human health and the environment, comply with ARARs (unless a statutory

waiver is justified), are cost effective, and utilize permanent solutions and alternative

treatment technologies or resource recovery technologies to the maximum extent

practicable. In addition, CERCLA includes a preference for remedies that employ treatment

that permanently and significantly reduces the volume, toxicity, or mobility of hazardous

wastes as a principal element and a bias against offsite disposal of untreated wastes. The

following sections discuss how the Selected Remedy meets these statutory requirements.

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20.1 Protection of Human Health and the Environment

The Selected Remedy for the indoor air, soil, and ground water at this site will be protective

of human health and the environment. Installation of vapor mitigation systems will address

vapor intrusion and reduce cancer risk to below safe levels.

Removal of the principal threat wastes in the soil and ground water in the source areas and

active treatment of ground water in the shallow plume core and hot spot, shallow plume

periphery, and deeper plume is expected to restore the ground water to below drinking

water standards.

20.2 Compliance with Applicable or Relevant and Appropriate Requirements

The NCP §300.430(f)(5)(ii)(B) and (C) require that a ROD describe the Federal and State

ARARs that the Selected Remedy will attain or provide justification for any waivers.

ARARs include substantive provisions of any promulgated Federal or more stringent State

environmental standards, requirements, criteria, or limitations that are determined to be

legally ARARs for a CERCLA site or action. Applicable requirements are those cleanup

standards, standards of control, and other substantive environmental protection

requirements, criteria, or limitations promulgated under Federal or State law that

specifically address a hazardous substance, pollutant, contaminant, remedial action,

location, or other circumstance found at a CERCLA site. Relevant and appropriate

requirements are requirements that, while not legally "applicable" to circumstances at a

particular CERCLA site, address problems or situations sufficiently similar to those

encountered at the site that their use is relevant and appropriate. The ARARs are presented

below and in more detail in Table 12.

Chemical, location, and action-specific ARARs include the following:

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• Safe Drinking Water Act MCLs (40 CFR Part 141), which specify acceptable

concentration levels in ground water that serves as a potential drinking water aquifer

• Clean Air Act applicable to emissions from stationary sources

• Clean Water Act for any discharges from the site

• Hazardous Waste Regulations (40 CFR 261) for waste disposal

• U.S. Department of Transportation (DOT) Regulations for transportation of hazardous

waste (49 CFR 171 and 180)

• New Mexico Hazardous Waste Regulations (20.4 New Mexico Administrative Code

[NMAC])

• New Mexico Air Regulations (20.2 NMAC)

• New Mexico Water Quality Control Commission Regulations (20.6.2 NMAC)

20.3 Cost Effectiveness

The Selected Remedy is cost effective because the remedy's costs are proportional to its

overall effectiveness (see 40 CFR §300.430(f)(l)(ii)(D)). This determination was made by

evaluating the overall effectiveness of those alternatives that satisfied the threshold criteria

(i.e., that are protective of human health and the environment and comply with all Federal

and any more stringent State ARARs, or as appropriate, waive ARARs). Overall

effectiveness was evaluated by assessing three of the five balancing criteria in combination

(long-term effectiveness and permanence; reduction in toxicity, mobility, and volume

through treatment; and short-term effectiveness). The overall effectiveness of each

alternative was then compared to each alternative's costs to determine cost effectiveness.

The relationship of the overall effectiveness of this remedial alternative was determined to

be proportional to its costs and hence represents a reasonable value for the money to be

spent.

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The estimated present worth cost of one component (ISCO with Follow-On ERD for Shallow

Plume Core and Hot Spot) is pushing the total cost of the Selected Remedy slightly higher

compared to other alternative combinations providing active treatment. However, the

Selected Remedy offers a much higher degree of protectiveness and overall effectiveness

than any of the other alternatives because it offers mitigation, treatment, and removal of all

wastes versus no action.

20.4 Utilization of Permanent Solutions to the Maximum Extent Practicable

EPA has determined that the Selected Remedy represents the maximum extent to which

permanent solutions and treatment technologies can be utilized in a practicable manner at

the site. Of those alternatives that are protective of human health and the environment and

comply with ARARs, the EPA has determined that the Selected Remedy provides the best

balance of tradeoffs in terms of the five balancing criteria, while also considering the

statutory preference for treatment as a principal element, bias against offsite treatment and

disposal, and considering State and community acceptance.

The Selected Remedy treats the source area soil and ground water potentially containing

DNAPL constituting principal threats at the Site. The Selected Remedy satisfies the criteria

for long-term effectiveness by removing all chlorinated solvents contamination from the soil

and ground water. The Selected Remedy does not present short-term risks different from

the other treatment alternatives. There are no special implementability issues that set the

Selected Remedy apart from any of the other alternatives evaluated.

20.5 Preference for Treatment as a Principal Element

The EPA has determined that the treatment of the source area wastes satisfies the statutory

preference for the selection of a remedy that involves treatment as a principal element. By

treating the contaminated soils and ground water by active remediation technologies, the

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Selected Remedy addresses principal threats posed at the site utilizing treatment as a

significant portion of the remedy.

20.6 Five-Year Review Requirements

CERCLA §121(c) and the NCP §300.430(f)(5)(iii)(C) provide the statutory and legal bases for

conducting Five-Year Reviews. Because this remedy is expected to take at least 20 years to

achieve the RAOs within portions of the GCSP Site, it will result in hazardous substances

remaining onsite in the ground water and possibly in the soils (below 1.5 ft bgs) above levels

that allow for unlimited use and unrestricted exposure. A statutory review will be

conducted within 5 years after initiation of the RA to ensure that the remedy is, or will be,

protective of human health and the environment.

21.0 Documentation of Significant Changes

From Preferred Alternative of Proposed Plan

The EPA has not made any significant changes to the remedy, as originally identified in the

Proposed Plan. The Proposed Plan was released for public comment on April 12, 2006. The

public comment period for the Proposed Plan was held from April 12, 2006 to May 11, 2006.

The EPA held a public meeting on April 20, 2006 to present the preferred alternative in the

Proposed Plan. The EPA reviewed and responded to written and verbal comments

submitted during the public comment period in the Responsiveness Summary (Part 3 of this

ROD).

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22.0 State Role

The NMED, on behalf of the State of New Mexico, has reviewed the various alternatives and

has indicated its support for the Selected Remedy. NMED’s position on the other

alternatives are indicated in Tables 14-18.

The State has also reviewed the RI/FS (EPA, 2005a), BHHRA (EPA, 2005b), to determine if

the Selected Remedy is in compliance with applicable or relevant and appropriate State

environmental laws and regulations. The State of New Mexico concurs with the Selected

Remedy for the Site (Appendix C − NMED Concurrence with the Selected Remedy).

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Part 3. Responsiveness Summary

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PART 3 – RESPONSIVENESS SUMMARY 3-1

Part 3: Responsiveness Summary

23.0 Responsiveness Summary

The Responsiveness Summary (Appendix D) summarizes information about the views of

the public and the support agency regarding both the remedial alternatives and general

concerns about the site submitted during the public comment period. This summary also

documents, in the record, how public comments were integrated into the decision making

process.

The Administrative Record file for the site, located at the University of New Mexico

Campus, Grants and the EPA's Region 6 office, contains all of the information and

documents supporting this ROD. The comment period for the Proposed Plan for the Site

opened on April 12, 2006 and ended on May 11, 2006. This Administrative Record file

includes a transcript of the public meeting held by the EPA on April 20, 2006 to describe the

preferred alternative.

23.1 Stakeholder Issues and Lead Agency Responses

23.1.1 NMED Comments

Comment 1

In reference to the Land and Ground Water Use Assumptions - NMED emphasizes that the

New Mexico Water Quality Control Commission (NMWQCC) Regulations, NMAC

20.6.2.4101.A(1) requires that all ground water of the State of New Mexico with a TDS of

<10,000 mg/l be remediated or protected for use as domestic and agricultural water supply.

Although the contaminated ground water (from 5 to 80 ft bgs) at the site is not currently

used as a drinking water supply, there are no enforceable institutional controls that would

prohibit the use of this aquifer, now or in the future, as a drinking water supply. The fact

that three shallow private wells exist within the site boundaries is evidence that the aquifer

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can be used for beneficial use. As proposed, ground water must be remediated to the more

stringent requirements of the Federal Safe Drinking Water standards (MCLs) and/or

NMWQCC standards.

EPA Response:

Comment noted. EPA’s final clean up levels for the COCs at this Site is federal MCL and

NMWQCC standards.

Comment 2

Preliminary Remediation Goals and use of 1x10-4 excess lifetime cancer risk (ELCR) as the

targeted cleanup level - The National Contingency Plan established a targeted risk level 1 x

10-6 as a “point of departure” for determining remediation goals. There has been no

justification presented by EPA to modify this targeted risk level and justify the use of a less

stringent risk-based clean up level. At a minimum, an ELCR of 1 x 10-5 and an HI of 1

which is consistent with the NMWQCC Regulations and NMED’s Technical Background

Document for Development of Soil Screening Levels, Revision 3.0, August 2005, should be used

for establishing targeted cleanup levels for indoor air and soil. NMED requests that the

PRGs for COCs in soil and from vapor impacts be established using at least a 1 x 10-5 ELCR

and an HI of 1 and a residential land use scenario.

EPA Response:

1E-06 is the point of departure, and EPA has the flexibility to modify cleanup levels for

carcinogens within the range of 1E-06 to 1E-04, especially when considering site-specific

conditions. This is indicated in the NCP (40 CFR 300.430(e)(2)(i)(A)(2 ):

“For known or suspected carcinogens, acceptable exposure levels are generally concentration levels

that represent an excess upper bound lifetime cancer risk to an individual of between 10-4 and 10-6

using information on the relationship between dose and response.”

The EPA agrees with NMED’s concerns regarding uncertainties at the Site and will take

Remedial Action at the lower risk level (1x10-5).

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Comment 3

In reference to risk and the preliminary remediation goals. NMED does not support the use

risk based clean up levels that are less stringent than residential clean up levels for this site.

The site is located in a mixed commercial and residential use area and there are no

enforceable institutional controls that can be implemented to restrict future land use.

Therefore, the more restrictive clean up levels, i.e. residential, should be used.

EPA Response:

EPA will use NMED’s Guidance document (Technical Background Document for

Development of Soil Screening Levels, Revision 3.0, August 2005) on Soil Screening Levels

to establish clean up levels based on residential use.

Comment 4

In reference to the flexible approach in selection of the final remedy for the Shallow Plume

Core and Hot Spot Area - NMED is concerned with how the final selection between ISCO

and ERD will be determined due to the difficulties associated with detecting the DNAPL in

the field. NMED is concerned that a significant amount of time and expense could be

expended without conclusively determining whether or not DNAPL is absent from this

area. In addition, the pre-design investigations proposed in the Feasibility Study did not

include investigation activities associated with determining the nature and extent of

DNAPL but instead concentrated on definition of the dissolved phase plume and soil

contamination in the two source areas. As stated in the RI report and in literature on the

subject, it is generally assumed that DNAPL is present if ground water exceeds 1 to 5

percent of the chemicals solubility limit in water and the dissolved PCE concentrations

observed within the Plume Core Area are as high as 35%. At this concentration it should be

assumed that DNAPL is present in close proximity to the sample locations and ISCO is

better suited for this condition. Finally, because ISCO with follow-on ERD alternative

addresses the entire plume through the installation of a grid pattern of wells the ISCO

alternative is more amenable to treating the Core Plume/Hotspot area verses the passive

nature of diffusion associated with the ERD alternative. If residual DNAPL is present

between the ERD bio-barriers, the likelihood of effective and timely clean-up using the ERD

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bio-barrier alternative is greatly reduced. Therefore, NMED may not support the use of

ERD as the stand alone remedial technology for the Shallow Plume Core and Hot Spot area.

EPA Response:

EPA’s policy is to treat principal threats posed by the Site through use of treatment

technologies. By utilizing treatment as a significant portion of the Selected Remedy, the

statutory preference for remedies that employ treatment as a principal element is satisfied.

The EPA agrees and will select ISCO with Follow-On ERD (Flexible) treatment approach for

the Shallow Plume Core and Hot Spot for the following reason:

Thermal treatment at the Source Area is expected to achieve complete removal of principal

threat waste. After Source Area treatment is complete and if it can be demonstrated that the

principal threat waste no longer exists in the Shallow Plume Core and Hot Spot area then

the EPA will re-evaluate the two treatment technologies (ISCO/with Follow-On ERD or

ERD alone) to determine which one of these better meets the Statutory Preference for

Treatment. Based on this determination the EPA will implement either of the two

technologies to address the Shallow Plume Core and Hot Spot Area.

23.1.2 Community Comments

The following comments were received from members of the public that were in attendance

at the Proposed Plan public meeting held on April 20, 2006.

Comment 1

How was the contamination originally verified at the GCSP Site?

EPA Response:

The NMED-PSTB discovered chlorinated solvents in ground water at the GCSP Site during

a UST investigation at the Allsup’s 200 gas station in 1993. Following the discovery, NMED

conducted two years of ground water monitoring at the Allsup’s monitoring wells to verify

contamination.

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Comment 2

Are the depths of the City Drinking Water wells known?

EPA Response:

Yes. City well Grants B-40 is screened at a depth from 246 feet (ft) below ground surface

(bgs) to 346 ft bgs and the total depth of the well is 367 ft bgs. The second City well, Grants

B-38, is screened between 149 ft bgs and 300 ft bgs and the total depth of this well is 300 ft

bgs. Both of these wells are upgradient and are located approximately 1.5 miles northwest

of the GCSP Site.

Comment 3

Are the City wells located in the same aquifer that is impacted at the GCSP Site?

EPA Response:

No. The contamination at the GCSP Site is in a shallow aquifer and the vertical extent is not

fully known at this time. The City drinking water wells pump water from much greater

depths, and are upgradient of the GCSP Site. The maximum depth at which contamination

was detected during the RI is 85 ft bgs. The EPA will fully characterize the maximum depth

of contamination during the Pre-Design Field Investigation.

Comment 4

Is the project funded for the Remedial Design?

EPA Response:

Yes. Funding for Remedial Design has been planned for fiscal Year 2006.

Comment 5

Are there many other sites in the country similar to Grants?

EPA Response:

Yes. There are a number of other Superfund sites in the country that are similar to Grants.

In New Mexico alone there are five sites, including the GCSP Site, where EPA is cleaning up

ground water contaminated with chlorinated solvents. These five sites include Fruit

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Avenue Plume, Albuquerque; North Railroad Avenue Plume, Espanola; McGaffey and

Main, Roswell; Griggs and Walnut, Las Cruces; and the GCSP Site, Grants.

Comment 6

Is the bio-barrier wall a physical wall installed underground?

EPA Response:

Bio-barrier walls are not actual physical walls but function as a wall when nutrients are

injected across sections of the plume. Injection points are closely spaced along a line across

the plume, such that the aquifer between each injection point is filled with the injected

oxidant or carbon source amendment. When the oxidant or carbon source amendments are

injected into the ground they permeate into the aquifer and begin treating the ground water.

Zero-valent iron permeable reactive barriers are actual physical walls constructed of iron

filings installed within trenches dug across the plume. The walls required for the GCSP Site

would be as thick as 36 inches and up to 60 ft deep. A zero-valent iron permeable reactive

barrier was considered as one of the alternatives for the Site but was not chosen as the

Selected Remedy.

Comment 7

Will the public be notified when a final decision is made regarding the Preferred Remedy?

EPA Response:

Yes. The EPA will notify the community of the final selection of the remedy after it reviews

and responds to all the comments received during the comment period. Newspaper

notification will be made in the local newspaper when the Record of Decision is signed.

24.0 References

EPA, 2006a. Proposed Plan (referenced on pg 2-9) EPA, 2006b. FS (referenced on pg 2-10) EPA, 2005a. Remedial Investigation Report, Grants Chlorinated Solvents Plume Site, Grants, Cibola County, New Mexico. U.S. Environmental Protection Agency. July.

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EPA, 2005b. Baseline Human Health Risk Assessment, Grants Chlorinated Solvents Plume, Superfund Site, Grants, New Mexico. July. EPA, 2002. Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils. U.S. Environmental Protection Agency. EPA, 2001. Building Radon Out, A Step-by-Step Guide on How to Build Radon-Resistant Homes. EPA, 1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites. OSWER Directive Number 9200.4-17P. April. EPA, 1993. Presumptive Remedies: Site Characterization and Technology Selection for CERCLA Site With Volatile Organic Compounds in Soils. NMED, Ground Water Quality Bureau, Superfund Oversight Section, 2001. Site Inspection Report, Grants Chlorinated Solvents Plume Site, CERCLIS ID: NM0007271768, Cibola County, New Mexico. April. Tetra Tech EM, Inc., 2003. Secondary Investigation Report, Allsup’s 200.

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Tables and Figures

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Table 1Criteria Used for Evaluation of Indoor Air

Tier Action

References for the non-Cal-EPA Action

Levels Notes

PCE TCETCE

Cal-EPAcis-1,2-

DCEVinyl

ChlorideCPL Evaluate the need for temporary relocation of

occupants from a structure during implementation of mitigation measures.

1,360 11,000 11,000 790 1,290 ATSDR, 2003 Action level is based on Agency for Toxic Substances and Disease Registry (ATSDR) minimal risk level (MRL) for 14 day exposure. They are set below levels that, based on current information, might cause adverse health effects in the peoplemost sensitive to such substance-induced effects.

Tier 1 No further action is warranted to evaluate potential concentrations in indoor air.

<3.2or outdoor

background

<0.17or outdoor

background

<12.2 <35or outdoor

background

<1.1or outdoor

background

EPA, 2002a; EPA, 2002b Action level is based on target cancer risk level of 10-5 or a noncancer HQ of 1. Values presented here are based on EPA Region 6 media-specific screening levels in air.

Tier 2 Evaluate the need for additional sampling (outdoor soil gas sampling) in these locations. Offer to perform indoor air monitoring annual at residences where these concentrations were detected.

3.2 - 32or outdoor

background

0.17 - 1.7or outdoor

background

12.2 - 122 35 -105or outdoor

background

1.1 - 11or outdoor

background

EPA, 2002a; EPA, 2002b Action levels correspond to a target cancer risk range between 10-5 and 10-4. For noncarcinogens, action levels correspond to a noncancer hazard quotient between 1 and 3. A HQ of 1 corresponds to a concentration in air that is intended to protect the public including sensitive populations over a lifetime of exposure, and is based on the most sensitive noncancer health effect associated with that chemical. Some EPA Regions use a hazard quotient of 3 for evaluating selection of remedial alternatives.

Tier 3 Evaluate the need for mitigation measures (including additional investigation) at the structure. Mitigation measures that may be considered could include soil vapor extraction (outdoors), sealing cracks and crevices indoors, installation of subsurface depressurization systems or other measures as appropriate.

Review site conditions, evaluate the need to conduct sampling at additional structures located nearby.

>32 >1.7 >122 >105 >11 EPA, 2002a; EPA, 2002b Action levels correspond to a target cancer risk of 10-4. For noncarcinogens, action levels correspond to a noncancer hazard quotient between 1 and 3. A HQ of 1 corresponds to a concentration in air that is intended to protect the public including sensitive populations over a lifetime of exposure, and is based on the most sensitive noncancer health effect associated with that chemical. Some EPA Regions use a hazard quotient of 3 for evaluating selection of remedial alternatives.

Key

CPL - Contingency Planning LevelATSDR, 2003. Minimal Risk Levels for Hazardous Substances, January 2003 http://www.atsdr.cdc.gov/mrls.htmlEPA. 2002a. EPA Region 6 media-specific screening levels, October 2002.EPA. 2002b. Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils. November 2002Benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl-tert-butyl ether (MTBE) were evaluated by comparison with ambient background concentrations in air.

Action Levels (µg/m3)

Updated TCE action level has been calculated based on toxicity values developed by the California Environmental Protection Agency. Reportedly, the U.S. Office of Research and Development has encouraged Regions to use alternate toxicity values for TCE than the those values presented in USEPA's Draft Risk Characterization for TCE, prepared August 2001. USEPA Regions 4 and 8 have stated that they will be using an alternative toxicity value for addressing TCE risks. This alternative value, provided by Cal-EPA has been recommended for use by USEPA Region 4, and is provided here for evaluation of indoor air analytical data.

Page 1 of 1 December 2005

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Table 2Summary of Chemicals of Concern and

Medium-Specific Exposure Point Concentrations (Ground Water)

Scenario Timeframe: FutureMedium: Ground WaterExposure Medium: Ground Water

UnitsMin Max

Tap Water Benzene 0.32 LJv 930 Jv µg/L 5/18 930 µg/L MAX

Bromoform 0.59 LJ 89 = µg/L 8/18 89 µg/L MAX

cis-1,2-Dichloroethene 1.9 LJ 1500 = µg/L 17/18 1500 µg/L MAX

Tetrachloroethene 2.7 = 31000 = µg/L 15/18 31000 µg/L MAX

trans-1,2-Dichloroethene 0.12 LJ 140 = µg/L 16/18 140 µg/L MAX

Trichloroethene 13 = 4800 = µg/L 16/18 4800 µg/L MAX

Vinyl Chloride 0.081 LJ 14 LJ µg/L 11/18 14 µg/L MAX

Xylenes (total) 1.1 LJv 1500 Jv µg/L 3/18 1500 µg/L MAXKey

µg/L: microgram per literMAX: Maximum ConcentrationLJv: Reported concentration is below the contract-required quantitation limit (CRQL) and should be considered estimated and biased lowJv: Reported concentration should be considered estimated and biased lowLJ: Reported concentration was below the CRQL and should be considered estimated=: Analytical result is valid with no QC qualifier

This table presents the chemicals of concern (COCs) and exposure point concentration for each of the COCs detected in ground water (i.e., the concentration that will be used to estimate the exposure and risk from each COC in ground water). The table includes the range of concentrations detected for each COC, as well as the frequency of detection (i.e., the number of times the chemical was detected in the samples collected at the site), the exposure point concentration (EPC), and how the EPC was derived. The table indicates that chlorinated solvents (PCE, TCE, cis-1,2-DCE, trans-1,2-DCE, and vinyl chloride) were the most frequently detected COCs in ground water at the site. The maximum concentration detected was used as the default exposure point concentration for all ground water COCs.

1. No cleanup levels have been established for benzene or xylenes at the Grants Chlorinated Solvents Plume Site since these compounds are being addressed by the New Mexico Environment Department - Petroleum Storage Tank Bureau

Exposure Point Concentration Units

Statistical Measure

Concentration DetectedExposure Point Chemical of Concern1 Frequency of Detection

Exposure Point Concentration

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Table 3Summary of Chemicals of Concern and

Medium-Specific Exposure Point Concentrations (Indoor Air)

Scenario Timeframe: Current/FutureMedium: Ground WaterExposure Medium: Air (Vapor Intrusion)

UnitsMin Max

Residence A Tetrachloroethene 0.13 = 0.46 = µg/m3 2/2 0.460 µg/m3 MAX

Trichloroethene 0.042 = 0.069 = µg/m3 2/2 0.069 µg/m3 MAX

Benzene 0.92 J 0.97 J µg/m3 2/2 0.970 µg/m3 MAXResidence B Tetrachloroethene 0.33 = 0.33 = µg/m3 1/1 0.330 µg/m3 MAX


Benzene 1.9 J 1.9 J µg/m3 1/1 1.900 µg/m3 MAX

Residence C Tetrachloroethene 0.057 = 0.48 = µg/m3 2/2 0.480 µg/m3 MAX



Residence D Tetrachloroethene 0.099 = 1.1 = µg/m3 2/2 1.100 µg/m3 MAX



Residence E Tetrachloroethene 0.25 = 0.25 = µg/m3 1/1 0.250 µg/m3 MAX



Residence F Tetrachloroethene 1.4 = 1.4 = µg/m3 1/1 1.400 µg/m3 MAX


Benzene 6.3 = 6.3 = µg/m3 1/1 6.300 µg/m3 MAX

Residence G Tetrachloroethene 4.3 = 4.3 = µg/m3 1/1 4.300 µg/m3 MAX


Benzene 4.1 = 4.1 = µg/m3 1/1 4.100 µg/m3 MAX

Residence H Tetrachloroethene 1.5 = 1.5 = µg/m3 1/1 1.500 µg/m3 MAX



Residence I Tetrachloroethene 7.2 = 8.1 = µg/m3 2/2 8.100 µg/m3 MAX



Residence J Tetrachloroethene 0.49 = 0.88 = µg/m3 2/2 0.880 µg/m3 MAX


Benzene 4.3 = 5 = µg/m3 2/2 5.000 µg/m3 MAX

Residence K Tetrachloroethene 21.9 = 21.9 = µg/m3 1/1 21.900 µg/m3 MAX

Trichloroethene 0.066 J 0.066 J µg/m3 1/1 0.066 µg/m3 MAX


Residence L Tetrachloroethene 131 = 161 = µg/m3 2/2 161.000 µg/m3 MAX



Residence M Tetrachloroethene 16.7 = 16.7 = µg/m3 1/1 16.700 µg/m3 MAX



Day Care Tetrachloroethene 0.094 = 0.13 = µg/m3 2/2 0.130 µg/m3 MAX

(6/15/04) Trichloroethene 0.029 = 0.055 = µg/m3 2/2 0.055 µg/m3 MAX

Benzene 0.85 J 1.2 J µg/m3 2/2 1.200 µg/m3 MAXKey

µg/m3: microgram per cubic meterMAX: Maximum Concentration=: Analytical result is valid with no QC qualifierJ: Estimated concentration below the reporting limit but above the detection limit

This table presents the chemicals of concern (COCs) and exposure point concentration for each of the COCs detected in indoor air (i.e., the concentration that will be used to estimate the exposure and risk from each COC in indoor air). The table includes the range of concentrations detected for each COC, as well as the frequency of detection (i.e., the number of times the chemical was detected in the samples collected at the site), the exposure point concentration (EPC), and how the EPC was derived. The table indicates that PCE, TCE, andbenzene were detected in all indoor air samples at the site. The maximum concentration detected was used as the default exposure point concentration for all indoor air COCs.

Exposure Point Concentration Units

Statistical Measure

Concentration DetectedExposure Point Chemical of Concern Frequency of Detection

Exposure Point Concentration

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Table 4Selection of Exposure Pathways

Scenario Medium Exposure Exposure Receptor Receptor Exposure Type of Rationale for Selection or ExclusionTimeframe Medium Point Population Age Route Analysis of Exposure Pathway

Current Ground Water Tap Water Resident Adult Ingestion None

Inhalation None

Dermal None

Child Ingestion None

Inhalation None

Dermal None

Indoor Worker Adult Ingestion None

Inhalation None

Dermal None

Future Ground Water Tap Water Resident Adult Ingestion Quantitative

Inhalation Quantitative

Dermal Quantitative

Child Ingestion Quantitative

Inhalation Quantitative

Dermal Quantitative

Indoor Worker Adult Ingestion Qualitative

Inhalation None

Dermal None

Current/Future Indoor Air Resident Adult Inhalation Quantitative

Child Inhalation Quantitative

Indoor Worker Adult Inhalation Quantitative

Shallow aquifer is present at 5 feet bgs, so indoor air measurements were collected. Shallow aquifer is present at 5 feet bgs, so indoor air measurements were collected.

All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.

Ground Water - Shallow Aquifer

All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.All area businesses are currently on city water, and any affected city well would be out of service until remediated. As the resident is the receptor with the greater degree of exposure, the resident The indoor worker is not expected to engage in activities utilizing ground water that would result in large concentrations of volatiles in indoor air (showering, etc.).The indoor worker is not expected to engage in activity that would result in substantial dermal contact (showering, etc.).

Air (via vapor intrusion)

Shallow aquifer is present at 5 feet bgs, so indoor air measurements were collected.

All area businesses are currently on city water, and any affected city well would be out of service until remediated. All area businesses are currently on city water, and any affected city well would be out of service until remediated.

All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.

All area homes are currently on city water, and any affected city well would be out of service until remediated.



All area homes are currently on city water, and any affected city well would be out of service until remediated. Analysis will address only those COPCs without MCLs.

All area homes are currently on city water, and any affected city well would be out of service until remediated. All area homes are currently on city water, and any affected city well would be out of service until remediated. All area homes are currently on city water, and any affected city well would be out of service until remediated. All area homes are currently on city water, and any affected city well would be out of service until remediated. All area homes are currently on city water, and any affected city well would be out of service until remediated.All area businesses are currently on city water, and any affected city well would be out of service until remediated.

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Table 5Values Used for Daily Intake Calculations (Ground Water)

Scenario Timeframe: FutureMedium: Ground WaterExposure Medium: Ground Water

Exposure Route Receptor

PopulationReceptor

Age Exposure Point Parameter Code Parameter Definition Value Units Rationale/Reference Intake Equation/Model NameIngestion Resident Adult Tap Water IRw Ingestion Rate of Water 2 L/day US EPA, 1997

MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 350 days/year US EPA, 1991ED Exposure Duration 30 years US EPA, 1988 Intake = IRw x MF x EF x EDBW Body Weight 70 kg US EPA, 1988 BW x ATc (or ATnc)ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 10950 days US EPA, 1988

Child Tap Water Irw Ingestion Rate of Water 1.1 L/day US EPA, 2002MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 350 days/year US EPA, 1991ED Exposure Duration 6 years US EPA, 1991BW Body Weight 15 kg US EPA, 1991ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 2190 days US EPA, 1988

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Table 6Values Used for Daily Intake Calculations (Indoor Air)

Scenario Timeframe: Current/FutureMedium: Ground WaterExposure Medium: Indoor Air (via Vapor Intrusion)

Exposure Route Receptor

PopulationReceptor

Age Exposure Point Parameter Code Parameter Definition Value Units Rationale/Reference Intake Equation/Model NameInhalation Resident Adult Indoor Air InhR Inhalation Rate 20 m3/day US EPA, 1991

InhRadj Age-adjusted Inhalation Rate 11 m3-yr/kg-d US EPA, 2004MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 350 days/year US EPA, 1991ED Exposure Duration 30 years US EPA, 1988BW Body Weight 70 kg US EPA, 1988ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 10950 days US EPA, 1988

Child Indoor Air InhR Inhalation Rate 10 m3/day US EPA, 2002MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 350 days/year US EPA, 1991 Intake =ED Exposure Duration 6 years US EPA, 1991 InhR x MF x EF x EDBW Body Weight 15 kg US EPA, 1991 BW x ATc (or ATnc)ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 2190 days US EPA, 1988

Day Care Worker Adult Indoor Air InhR Inhalation Rate 13 m3/day US EPA, 1997MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 250 days/year US EPA, 1991ED Exposure Duration 25 years US EPA, 1991BW Body Weight 70 kg US EPA, 1988ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 9125 days US EPA, 1988

Dare Care Child Child Indoor Air InhR Inhalation Rate (0.68 X 8) 5.5 m3/day US EPA, 2004MF Modifiying Factor 0.001 mg/µg US EPA, 1988EF Exposure Frequency 250 days/year US EPA, 1991ED Exposure Duration 6 years US EPA, 1991BW Body Weight 15 kg US EPA, 1991ATc Averaging Time - carcinogen 25550 days US EPA, 1988ATnc Averaging Time - non-carcinogen 2190 days US EPA, 1988

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Table 7Non Cancer Toxicity Data Summary

Pathway Inhalation

Chemical of Concern

Tetrachloroethene (PCE)

Tnchloroethene (TCE)

Benzene

Chronic/Subchromc

chronic

chronic

chronic

InhalationRfC

4 OOE 01

4 OOE 02

3 OOE-02

InhalationRfC Units

mg/m3

mg/m3

mg/m3

InhalationRfD

1 10E 01

1 10E 02

8 60E 03

Inhalation RfDUnits

mg/kg-day

mg/kg-day

mg/kg-day

Primary TargetOrgan

CNS liver

CNS liver

immune system

CombinedUncertainty/Modifying

Factors

1000

1000

300

Sources of RfDTarget Organ

R6 MSSLs/NCEA

R6 MSSLs/NCEA

IRIS

Dates of RfD TargetOrgan (MM/DD/YYYY)

12/21/2004

12/21/2004

12/21/2004Key

mg/m3 milligram per cubic meterR6 MSSLs/NCEA The Region 6 Medium Specific Screening Levels (R6 MSSLs) utilize some toxicity data from the National Center for Environmental Assessment (NCEA)IRIS Integrated Risk Information System U S EPACNS Central nervous system

This table provides non carcinogenic nsk information which is relevant to the contaminants of concern in indoor air PCE TCE and benzene have toxicity data indicating their potential for adversenon carcinogenic health effects in humans

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Table 8Cancer Toxicity Data Summary

Pathway: Inhalation

Chemical of Concern Unit Risk Units

Inhalation Cancer

Slope Factor Units

Weight of Evidence/Cancer

Guideline Description Source Date (MM/DD/YYYY)

Tetrachloroethene 5.90E-03 (mg/m3)-1 2.00E-02 (mg/kg-day)-1 N/A Cal-EPA 12/21/2004

Trichloroethene (low) 2.00E-03 (mg/m3)-1 7.00E-03 (mg/kg-day)-1 N/A Cal-EPA 12/21/2004

Trichloroethene (high) 1.10E-04 (mg/m3)-1 4.00E-01 (mg/kg-day)-1 N/A NCEA 12/21/2004

Benzene (low) 2.20E-03 (mg/m3)-1 7.70E-03 (mg/kg-day)-1 A IRIS 12/21/2004

Benzene (high) 7.80E-03 (mg/m3)-1 2.70E-02 (mg/kg-day)-1 A IRIS 12/21/2004Key

mg/m3: milligram per cubic meter A - Human carcinogenmg/kg: milligram per kilogramCal-EPA: California Environmental Protection AgencyNCEA: National Center for Environmental AssessmentIRIS: Integrated Risk Information System, U.S. EPAN/A: not applicable - this chemical is not currently classified as to weight-of-evidence

This table provides carcinogenic risk information which is relevant to the contaminants of concern in indoor air. Benzene is considered carcinogenic via the inhalation route.

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Table 9Risk Characterization Summary

Non-Carcinogens

FutureResidentAdult

Ingestion Inhalation Dermal

Exposure Routes Total

Indoor Air Indoor Air Residence 15 Benzene Immune system N/A 3.0E-02 N/A 3.0E-02Tetrachloroethene CNS, liver N/A 7.5E-04 N/A 7.5E-04Trichloroethene CNS, liver N/A 1.4E-03 N/A 1.4E-03

Residence 11 Benzene Immune system N/A 6.0E-02 N/A 6.0E-02Tetrachloroethene CNS, liver N/A 8.2E-04 N/A 8.2E-04Trichloroethene CNS, liver N/A 3.0E-03 N/A 3.0E-03










Residence 3 Benzene Immune system N/A 6.7E-02 N/A 6.7E-02Tetrachloroethene CNS, liver N/A 3.7E-01 N/A 3.7E-01Trichloroethene CNS, liver N/A 2.3E+00 N/A 2.3E+00


FutureResidentChild



Indoor Air Indoor Air Residence 15 Benzene Immune system N/A 7.1E-02 N/A 7.1E-02Tetrachloroethene CNS, liver N/A 1.7E-03 N/A 1.7E-03Trichloroethene CNS, liver N/A 3.3E-03 N/A 3.3E-03




7.6E-02

1.5E-01

1.1E-01

2.0E-01

6.7E-01

Non-Carcinogenic Total Hazard

Index


Index

8.2E-02

1.6E-01

9.5E-02

2.7E+00

2.8E-02

2.0E-01

5.6E-02

1.1E-01

3.2E-02

6.4E-02

4.9E-02

8.6E-02

Non-Carcinogenic Hazard QuotientExposure Medium

Exposure Point

Primary Target Organ

Scenario Timeframe:Receptor Population:Receptor Age:

Scenario Timeframe:

Medium Exposure Medium

Non-Carcinogenic Hazard QuotientPrimary Target Organ

Receptor Population:Receptor Age:

Chemical of Concern

Chemical of Concern

Exposure Point

Medium

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Non-Carcinogens










CurrentDay Care WorkerAdult



Indoor Air Indoor Air Day Care Benzene Immune system N/A 1.7E-02 N/A 1.7E-02(Structure 5) Tetrachloroethene CNS, liver N/A -- N/A --

Trichloroethene CNS, liver N/A 6.8E-02 N/A 6.8E-02CurrentDay Care ChildChild



Indoor Air Indoor Air Day Care Benzene Immune system N/A 5.5E-02 N/A 5.5E-02(Structure 5) Tetrachloroethene CNS, liver N/A -- N/A --

Trichloroethene CNS, liver N/A 5.7E-01 N/A 5.7E-01Key

µg/L: micrograms per literN/A: Route of exposure is not applicable to this medium.CNS: Central nervous system

Risk Characterization Summary - Non-Carcinogens

6.3E-01

1.6E+00

8.5E-02


Index


Index

2.0E-01

3.7E-01

2.2E-01

6.3E+00

1.3E-01

4.9E-01

4.7E-01

2.5E-01

Non-Carcinogenic Hazard Quotient

Exposure Medium

Exposure Point

Chemical of Concern

Exposure Medium

Exposure Point

Chemical of Concern


Table 9 provides hazard quotients (HQs) for each route of exposure and the hazard index (sum of hazard quotients) for all routes of exposure. The Risk Assessment Guidance (RAGS) for Superfund states that, generally, a hazard index (HI) greater than 1 indicates the potential for adverse noncancer effects. The estimated residential indoor air H Is of 2.7 (adult) and 6.3 (child) indicate that the potential for adverse noncancer effects could occur within Structure 3 from exposure to contaminated residential indoor air containing benzene, tetrachloroethene, and trichloroethene. The estimated HI within Residence 2 (1.6 for a child) also indicates the potential for adverse noncancer effects for children. The estimated indoor air HIs for the day care (both workers and children) are less than 1, and do not indicate a potential for adverse noncancer effects. The HQs shown are from the Baseline Human Health Risk Assessment which did not include samples collected from Residences 8, and 10 described in the RI/FS reports.



Non-Carcinogenic Hazard Quotient

Medium


--: Tetrachloroethene was detected below the risk-based screening level in day care indoor air, and an HQ was not calculated inthe Baseline Human Health Risk Assessment.

Medium

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Carcinogens

FutureResidentAdult

Ingestion Inhalation DermalExposure

Routes TotalIndoor Air Indoor Air Residence 15 Benzene (low) * N/A 8.5E-07 N/A Low*

Benzene (high) * N/A 3.0E-06 N/A 1.6E-06Tetrachloroethene N/A 7.0E-07 N/ATrichloroethene (low) * N/A 4.6E-08 N/A High*Trichloroethene (high) * N/A 2.6E-06 N/A 6.3E-06

Residence 11 Benzene (low) * N/A 1.7E-06 N/A Low*Benzene (high) * N/A 5.9E-06 N/A 2.6E-06Tetrachloroethene N/A 7.8E-07 N/ATrichloroethene (low) * N/A 9.8E-08 N/A High*Trichloroethene (high) * N/A 5.6E-06 N/A 1.2E-05












Exposure Point

Carcinogenic Risk *Chemical of Concern



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Carcinogens

FutureResidentChild


Routes TotalIndoor Air Indoor Air Residence 15 Benzene (low) * N/A 4.0E-07 N/A Low*

Benzene (high) * N/A 1.4E-06 N/A 7.4E-07Tetrachloroethene N/A 3.2E-07 N/ATrichloroethene (low) * N/A 2.2E-08 N/A High*Trichloroethene (high) * N/A 1.2E-06 N/A 3.0E-06














Exposure Medium

Exposure Point

Chemical of Concern

Scenario Timeframe:

Carcinogenic Risk *Medium

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Carcinogens

CurrentDay Care WorkerAdult


Routes TotalIndoor Air Indoor Air Day Care Benzene (low) * N/A 4.2E-07 N/A Low*

(Structure 5) Benzene (high) * N/A 1.5E-06 N/A 4.4E-07Tetrachloroethene N/A -- N/ATrichloroethene (low) * N/A 1.8E-08 N/A High*Trichloroethene (high) * N/A 1.0E-06 N/A 2.5E-06

CurrentDay Care ChildChild


Routes TotalIndoor Air Indoor Air Day Care Benzene (low) * N/A 2.0E-07 N/A Low*

(Structure 5) Benzene (high) * N/A 7.0E-07 N/A 2.1E-07Tetrachloroethene N/A -- N/ATrichloroethene (low) * N/A 8.4E-09 N/A High*Trichloroethene (high) * N/A 4.8E-07 N/A 1.2E-06

Key

µg/L: micrograms per literN/A: Route of exposure is not applicable to this medium.

Risk Characterization Summary - Non-Carcinogens

--: Tetrachloroethene was detected below the risk-based screening level in day care indoor air, and a cancer risk was not calculated in the Baseline Human Health Risk Assessment.

*: For some chemicals, cancer risks were calculated using two slope factors. In the case of benzene and TCE, slope factor ranges were used, representing a high-end and low-end risk.


Medium


Carcinogenic Risk *

Table 10 provides risk estimates for the indoor air route of exposure. These risk estimates are based on a reasonable maximum exposure and were developed by taking into account various conservative assumptions about the frequency and duration of exposure to indoor air, as well as the toxicity of the COCs. The total risk from direct exposure to contaminated indoor air at each residence is provided as a low total and a high total, based on two different slope factors used for benzene and TCE. Estimated risk at individual residences is frequently equal to or greater than the 10 -5 range. A 10-5 risk level indicates that if no clean up action is taken, an individual would have an increased probability of 1 in 100,000 of developing cancer as a result of site-related exposure to the COCs.

Carcinogenic Risk *

Exposure Medium

Exposure Point

Chemical of Concern

Scenario Timeframe:


Exposure Point

Chemical of Concern

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1 2No Action Install Vapor Mitigation System

Activity-Specific ARARsAir40 CFR 61 Subpart V–National Emission Standards for Hazardous Air Pollutants: Equipment Leaks

- - Vapor venting system only, no vapor treatment.

40 CFR 264.AA–Air Emission Standards for Process Vents - - Vapor venting system only, no vapor treatment.

20.2 NMAC - - Potentially applicable if vapor mitigation activities involve sufficient quantities of solvents to be subject to regulation.

Water

Federal Water Pollution Control Act as amended by the Clean Water Act of 1977, Section 208(b)

- - No water discharges associated with this alternative.

Federal Water Pollution Control Act as amended by the Clean Water Act of 1977, Section 402


40 CFR Part 122 Subpart B - - No water discharges associated with this alternative.

40 CFR 122.41(l)–Monitoring Requirements - - No water discharges associated with this alternative.

40 CFR 136–Guidelines Establishing Test Procedures for the Analysis of [Water] Pollutants (40 CFR 136.1-136.4)


Solid and Hazardous Waste

40 CFR 261–Identification and Listing of Hazardous Waste - - Vapor venting system only, no vapor treatment.

40 CFR 262-Hazardous Waste Generator Requirements - - Vapor venting system only, no vapor treatment.

40 CFR 264, 265 - - Vapor venting system only, no vapor treatment.

Location-Specific ARARs40 CFR Part 6-Floodplain or Wetland Environments - - NA at GCSP Site; site is not within floodplain or wetlands.

Endangered Species Act - - NA at GCSP Site; no endangered species present.

National Historical Preservation Act, 16 USC 661 et seq., 36 CFR Part 65 - - NA at GCSP Site; no historic structures identified.

Archaeological and Historic Preservation Act - - NA at GCSP Site; no archaeological or historic relics identified.

Chemical-Specific ARARs

20.6.2 NMAC – New Mexico Water Quality Control Regulations - - - -

40 CFR 268-Land Disposal Restrictions - - - -

40 CFR 50–National Primary and Secondary Ambient Air Quality Standards - - - -

20.6.4 NMAC–Water Quality Standards for Interstate and Intrastate Surface Waters - - - -

40 CFR 141, Subpart B –National Primary Drinking Water Regulations - - - -

NotesCFR - Code of Federal RegulationsNMAC - New Mexico Administrative CodeMCLs - Maximum Contaminant Levels

GCSP - Grants Chlorinated Solvents Plume

NPDES - National Pollutant Discharge Elimination System

ARARIndoor Air Alternatives

Table 11Summary of ARARs

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40 CFR 264.AA–Air Emission Standards for Process Vents

20.2 NMAC

Water



40 CFR Part 122 Subpart B

40 CFR 122.41(l)–Monitoring Requirements



40 CFR 261–Identification and Listing of Hazardous Waste

40 CFR 262-Hazardous Waste Generator Requirements

40 CFR 264, 265

Location-Specific ARARs40 CFR Part 6-Floodplain or Wetland Environments

Endangered Species Act

National Historical Preservation Act, 16 USC 661 et seq., 36 CFR Part 65

Archaeological and Historic Preservation Act


20.6.2 NMAC – New Mexico Water Quality Control Regulations

40 CFR 268-Land Disposal Restrictions

40 CFR 50–National Primary and Secondary Ambient Air Quality Standards

20.6.4 NMAC–Water Quality Standards for Interstate and Intrastate Surface Waters

40 CFR 141, Subpart B –National Primary Drinking Water Regulations




ARAR 1 2 3 4No Action Thermal Treatment ISCO w/ Follow-on ERD ERD (Gridded)

- - Potentially applicable if remedial alternative includes regulated compounds or equipment.

NA at GCSP Site; no air emissions/treatment


- - Potentially applicable if RCRA hazardous waste is treatedin designated equipment.



- - Potentially applicable if remedial activities involve sources subject to regulation.



- -

Substantive requirements adopted by the state pursuant to Section 208 of the Clean Water Act would be applicable to direct discharge of treatment system effluenor other discharges to surface water.

NA, no discharges associated with this alternative.


- -

Although remedial alternatives are unlikely to include a source category subject to NPDES effluent limitations, some limitations may be relevant and appropriate to discharges to surface water if the remedial alternative includes a technology substantially similar to that employed by a regulated source category.



- -

Although NPDES permit coverage is not required for on-site discharges of storm water, substantive requirements, including implementing best management practices to prevent discharge of pollutants to storm water, are applicable to construction activities disturbing one acre ormore.



- - Administrative requirement applicable only for discharges to offsite surface water (potentially the Rio San Jose).



- -

Applicable to analyses performed under NPDES permit; relevant and appropriate to analyses of onsite direct discharge of treatment system effluent or other process waters.



- -Applicable for determining which wastes are hazardous and potentially subject to the hazardous waste management requirements in Parts 262-268.

Applicable for determining which wastes are hazardous and potentially subject to the hazardous waste management requirements in Parts 262-268.


- -Substantive management standards are applicable to hazardous waste generated during remedial activities, including investigation.

Substantive management standards are applicable to hazardous waste generated during remedial activities, including investigation.


- -

Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed todetermine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.


- - NA at GCSP Site; site is not within floodplain or wetlands.NA at GCSP Site; site is not within floodplain or wetlands.

NA at GCSP Site; site is not within floodplain or wetlands.

- - NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species present.

NA at GCSP Site; no endangered species present.

- - NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures identified.

NA at GCSP Site; no historic structures identified.

- - NA at GCSP Site; no archaeological or historic relics identified.

NA at GCSP Site; no archaeological or historic relics identified.


- -These regulations must be complied with for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

These regulations must be complied with for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

The substantive provisions of these regulations must be met as part of a reinjection program. These regulations must be complied with for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

- -Applicable to off-site land disposal of listed or characteristic hazardous wastes, and to on-site remedies that include placement of these wastes.



- - Discharges of process air will meet the air qualtiy standards.

No discharges associated with this alternative.


- - Water quality criteria may be relevant and appropriate to ground water or other discharges to surface water.



- -MCLs are applicable. MCLs are relevant and appropriatesince there is no mechanism to prevent the ground water from being used for drinking.

MCLs are applicable. MCLs are relevantand appropriate since there is no mechanism to prevent the ground water from being used for drinking.


Source Area Treatment Alternatives


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20.2 NMAC

Water









40 CFR 264, 265














ARAR 1 2 3 4 5No Action ZVI PRB - Multiple Transects ISCO w/ Follow-on ERD ERD (Bio-Barrier) Pump and Treat

- - NA at GCSP Site; no air emissions/treatment NA at GCSP Site; no air emissions/treatment NA at GCSP Site; no air emissions/treatment Would apply to air stripper offgas.



- - NA, no discharges associated with this alternative. NA, no discharges associated with this alternative.


Substantive requirements adopted by the state pursuant to Section 208 of the Clean Water Act would be applicable to direct discharge of treatment system effluent or other discharges to surface water.



Although remedial alternatives are unlikely to include a source category subject to NPDES effluent limitations, some limitations may be relevant and appropriate to discharges to surface water if the remedial alternativeincludes a technology substantially similar to that employed by a regulated source category.



Although NPDES permit coverage is not required for on-site discharges of storm water, substantive requirements, including implementing best management practices to prevent discharge of pollutants to storm water, are applicable to construction activities disturbing one acre or more.



Administrative requirement applicable only for discharges to offsite surface water (potentially the Rio San Jose).




- - This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation.

Applicable for determining which wastes are hazardous and potentially subject to the hazardous waste management requirements inParts 262-268.


This alternative may generate hazardous waste during system installation and operation of the ground water extraction and treatment system.

- - This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation.




- -

This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation. Investigation-derived waste generated during investigationand construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.



This alternative may generate hazardous waste during system installation and operation of the ground water extraction and treatment system. Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

- - NA at GCSP Site; site is not within floodplain or wetlands. NA at GCSP Site; site is not within floodplain orwetlands.

NA at GCSP Site; site is not within floodplain orwetlands. NA at GCSP Site; site is not within floodplain or wetlands.

- - NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species present.

NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species present.

- - NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures identified.

NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures identified.



NA at GCSP Site; no archaeological or historic relics identified. NA at GCSP Site; no archaeological or historic relics identified.




The substantive provisions of these regulations must be met as part of areinjection program. These regulations must be complied with for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

- -Applicable to off-site land disposal of listed or characteristic hazardous wastes, and to on-site remedies that include placement of these wastes.




- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this alternative. Discharges of process air will meet the air qualtiy standards.

- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this alternative. Water quality criteria may be relevant and appropriate to ground water or other discharges to surface water.

- -MCLs are applicable. MCLs are relevant and appropriate since there is no mechanism to prevent the ground water from being used for drinking.

MCLs are applicable. MCLs are relevant and appropriate since there is no mechanism to prevent the ground water from being used for drinking.



Shallow Plume Core and Hot Spot


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20.2 NMAC

Water









40 CFR 264, 265














ARAR 1 2 3 4 5No Action MNA ZVI PRB - Multiple Transects ERD (Bio-Barrier) Pump and Treat




- - NA, no discharges associated with this alternative. NA, no direct discharges associated with this alternative. NA, no discharges associated with this

alternative.



alternative.


- - NA, no discharges associated with this alternative.





alternative.Administrative requirement applicable only for discharges to offsite surface water (potentially the Rio San Jose).


alternative.


- -


This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation.



- -





- -


This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation. Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed todetermine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

Investigation-derived waste generated duringinvestigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

This alternative may generate hazardous waste during system installation and operation of the ground water extraction and treatment system. Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

- - NA at GCSP Site; site is not within floodplain orwetlands. NA at GCSP Site; site is not within floodplain or wetlands. NA at GCSP Site; site is not within floodplain

or wetlands. NA at GCSP Site; site is not within floodplain or wetlands.

- - NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species

present. NA at GCSP Site; no endangered species present.

- - NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures

identified. NA at GCSP Site; no historic structures identified.



NA at GCSP Site; no archaeological or historic relics identified. NA at GCSP Site; no archaeological or historic relics identified.



These regulations must be complied with for compounds where the State of NM allowablelimits are more stringent than EPA MCLs.

The substantive provisions of these regulations must be met as part of a reinjection program. These regulations must be compliedwith for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

- - NA for this alternative, no generation of hazardous waste will occur.


Investigation-derived waste generated duringinvestigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.


- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this alternative. Discharges of process air will meet the air qualtiy standards.

- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this alternative.

Water quality criteria may be relevant and appropriate to ground water or other discharges to surface water.

- -



MCLs are applicable. MCLs are relevant andappropriate since there is no mechanism to prevent the ground water from being used for drinking.


Shallow Plume Core Periphery


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20.2 NMAC

Water









40 CFR 264, 265














ARAR 1 2 3 4 5No Action MNA ZVI PRB - with Deep ERD ERD (Bio-Barrier) Pump and Treat

- - NA at GCSP Site; no air emissions/treatment NA at GCSP Site; no air emissions/treatment NA at GCSP Site; no air

emissions/treatment Would apply to air stripper offgas.






alternative.



alternative.

Although remedial alternatives are unlikely to include a sourcecategory subject to NPDES effluent limitations, some limitations may be relevant and appropriate to discharges to surface water if the remedial alternative includes a technology substantially similar to that employed by a regulated source category.

- - NA, no discharges associated with this alternative.

Although NPDES permit coverage is not required for on-site discharges of storm water, substantive requirementsincluding implementing best management practices to prevent discharge of pollutants to storm water, are applicable to construction activities disturbing one acre or more.




alternative.Administrative requirement applicable only for discharges to offsite surface water (potentially the Rio San Jose).


alternative.

Applicable to analyses performed under NPDES permit; relevant and appropriate to analyses of onsite direct dischargeof treatment system effluent or other process waters.

- -




This alternative may generate hazardous waste during systeminstallation and operation of the ground water extraction and treatment system.

- -




This alternative may generate hazardous waste during systeminstallation and operation of the ground water extraction and treatment system.

- -


This alternative may generate hazardous waste during excavation and dewatering for the ZVI wall installation. Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.


This alternative may generate hazardous waste during systeminstallation and operation of the ground water extraction and treatment system. Investigation-derived waste generated during investigation and construction activities will be sampledand analyzed to determine whether it is a hazardous waste and appropriate waste storage and disposal practices will be followed.

- - NA at GCSP Site; site is not within floodplain or wetlands.

NA at GCSP Site; site is not within floodplain or wetlands.

NA at GCSP Site; site is not within floodplain or wetlands. NA at GCSP Site; site is not within floodplain or wetlands.

- - NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered species present. NA at GCSP Site; no endangered

species present. NA at GCSP Site; no endangered species present.

- - NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures identified. NA at GCSP Site; no historic structures

identified. NA at GCSP Site; no historic structures identified.





- -


These regulations must be complied with for compoundswhere the State of NM allowable limits are more stringent than EPA MCLs.


The substantive provisions of these regulations must be met as part of a reinjection program. These regulations must be complied with for compounds where the State of NM allowable limits are more stringent than EPA MCLs.

- - NA for this alternative, no generation of hazardous waste will occur.




- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this

alternative. Discharges of process air will meet the air qualtiy standards.

- - No discharges associated with this alternative. No discharges associated with this alternative. No discharges associated with this

alternative.Water quality criteria may be relevant and appropriate to ground water or other discharges to surface water.

- -





Deeper Ground Water


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Table 12Description of ARARs for Selected Remedy

Authority Medium Regulation / Requirement Status Synopsis of Requirement Action to be Taken to Attain Requirement

Federal Regulatory Requirement

Air 40 CFR 50–National Primary and Secondary Ambient Air Quality Standards

Applicable Establishes Ambient Air Quality Standards. Compliance is achieved through compliance with state and local rules established pursuant to a State Implementation Plan (SIP).

The selected remedy, including thermal source-area treatment and residential indoor air vapor mitigation systems, will comply with these regulations. The vapor mitigation systems are not anticipated to emit vapor at concentrations exceeding any regulated levels.


Air 40 CFR 61 Subpart V–National Emission Standards for Hazardous Air Pollutants: Equipment Leaks

Potentially applicable if remedial alternative includes regulated compounds or equipment.

Establishes requirements for controlling fugitive emissions of volatile hazardous air pollutants from designated equipment.

The selected remedy, including thermal source-area treatment and residential indoor air vapor mitigation systems, will be designed to control fugitive emissions.


Air 40 CFR 264.AA–Air Emission Standards for Process Vents

Potentially applicable if RCRA hazardous waste is treated in designated equipment.

Requires total organic emissions from air strippers or steam strippers to be reduced below 1.4 kg/hr and 2.8 Mg/yr or that total organic emissions be reduced by 95 percent by weight.

Off-gas controls for treatment systems (such as thermal treatment at source areas) will be designed to meet the emissions reduction requirements.

State Regulatory Requirement

Air 20.2 New Mexico Administrative Code (NMAC)

Potentially applicable if remedial activities involve sources subject to regulation.

Establishes ambient air quality standards, performance standards for specific sources of air pollutants, and specifies monitoring methods.

The selected remedy, including thermal source-area treatment and residential indoor air vapor mitigation systems, will be designed to comply with these regulations.


Surface Discharges of

Treated Ground Water


Relevant and appropriate The proposed action must be consistent with regional water quality management plans as developed under Section 208 of Clean Water Act. Substantive requirements adopted by the state pursuant to Section 208 of the Clean Water Act would be applicable to direct discharge of treatment system effluent or other discharges to surface water.

Treated ground water effluent from treatment systems will comply with these regulations, if discharged to surface water.





Water quality criteria may be relevant and appropriate to groundwater or other discharges to surface water.

Establishes water quality criteria for specific pollutants for the protection of human health and for the protection of aquatic life. These federal water quality criteria are non-enforceable guidelines used by the state to set water quality standards for surface water

Treated ground water effluent from treatment systems will comply with enforceable regulations, if discharged to surface water.






Establishes effluent limitations for the discharge of specific pollutants. Section 402 establishes the National Pollutant Discharge Elimination System (NPDES). which enforces effluent limitations on point source discharges through site-specific and general permits.

Treated ground water effluent from treatment systems will comply with these regulations, if discharged to surface water.




40 CFR Part 122 Subpart B Although NPDES permit coverage is not required for on-site discharges of storm water, substantive requirements, including implementing best management practices to prevent discharge of pollutants to storm water, are applicable to construction activities disturbing one acre or more.

Requires obtaining an NPDES permit for discharge of storm water from specified industrial and construction activities, developing a storm water pollution prevention plan, implementing best management practices to prevent discharge of pollutants to storm water, and monitoring storm water discharges.

The substantive requirements for discharge would be completed, if applicable.

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Applicable to direct discharge of treatment system effluent or other process waters.

States are granted enforcement jurisdiction over direct discharges and may adopt reasonable standards to protect or enhance the uses and qualities of surface water bodies in the state.

The direct surface water discharge standards imposed by the State would be met, if applicable.


Ground Water 40 CFR 141–National Primary Drinking Water Regulations

MCLs are applicable if the water will be supplied directly to a drinking water distribution system with a specified number of consumers or connections. MCLs are relevant and appropriate if the water could be used for drinking. MCLGs set above

l l l d

Establishes maximum contaminant levels (MCLs) and maximum contaminant level goals (MCLGs) for specific chemicals to protect drinking water quality.

The preliminary remediation goals (PRGs) for treatment of ground water have been established as the Federal MCLs.

The substantive provisions of these regulations must be met as part of a reinjection program.

Establishes the New Mexico Water Quality Control Commission Regulations regarding the re-injection of water into the subsurface.

The substantive provisions of the NMWQCC regulations would be complied with for any re-injection of water.

These regulations must be complied with should the NM standards be more stringent than EPA MCLs.

Establishes the New Mexico Water Quality Control Commission Regulations regarding discharges to ground water.

The NMWQCC regulations will apply for chemicals where the NMWQCC regulated concentration is lower than the Federal MCL.










Administrative requirement applicable only for discharges to offsite surface water (potentially the Rio San Jose).


Substantive requirements for appropriate testing procedures would be followed within the compliance monitoring program.

A compliance monitoring program would be conducted, if applicable.

These sections require adherence to specified test methods and sample preservation procedures including container materials and sample holding times for analyses performed to comply with NPDES permit requirements.

Requires monitoring of discharges to ensure compliance. Monitoring programs shall include data on the mass, volume, and frequency of all discharge events.


Ground Water

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Hazardous Waste



Identifies those wastes subject to regulation as hazardous wastes

Investigation-derived waste generated during investigation and construction activities will be sampled and analyzed to determine whether it is a hazardous waste, and appropriate waste storage and disposal practices will be followed.


Hazardous Waste


Substantive management standards are applicable to hazardous waste generated during remedial activities.

Specifies standards for management of hazardous waste by hazardous waste generators, including management in tanks and containers.



Hazardous Waste

40 CFR 264, 265 Substantive management standards are applicable to remedial activities involving on-site treatment, storage or disposal of hazardous waste.

Specifies standards for hazardous waste treatment, storage and disposal facilities, including requirements for construction, design, monitoring, operation, and closure.



Hazardous Waste


Applicable to off-site land disposal of listed or characteristic hazardous wastes, and to on-site remedies that include placement of these wastes.

The land disposal restrictions prohibit land-based disposal of listed and characteristic hazardous wastes that do not meet specified treatment standards.


Building Structures or

Archaeological Artifacts


If scientific, historical, or archaeological artifacts are discovered at the site, work in the area of the site affected by such discovery will be halted pending the completion of any data recovery and preservation activities required pursuant to the act and its implementing regulations.

National Historical Preservation Act 16 USC 661 et seq. 36 CFR Part 65

Establishes procedures to provide for preservation of scientific, historical, and archaeological data that might be destroyed through alteration of terrain as a result of a federal construction project or a federally licensed activity or program.

Will be relevant and appropriate at the GCSP site during the remedial activities if scientific, historic, or archaeological artifacts are identified during implementation of the remedy.

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Table 13Evaluation Criteria for Superfund Remedial Alternatives

Threshold Criteria

Primary Balancing Criteria

Modifying Criteria 1

General NCP CriteriaOverall Protection of Human Health and the Environment

Specific NCP CriteriaHow Alternative Provides Human Health and Environmental Protection

Compliance with ARARsCompliance with Chemical-Specific ARARsCompliance with Action-Specific ARARsCompliance with Location Specific ARARs

Ability to Construct and Operate the TechnologyReliability of the Technology

Magnitude of Residual RiskAdequacy and Reliability of ControlsTreatment Process Used and Materials TreatedAmount of Hazardous Materials Destroyed or TreatedDegree of Expected Reductions in Toxicity, Mobility, and VolumeDegree to Which Treatment is IrreversibleType of Residuals Remaining After TreatmentProtection of Community During Remedial ActionsProtection of Workers During Remedial ActionsEnvironmental ImpactsTime Until Remedial Action Objectives are Achieved

Capital Costs

Present Worth Cost

Ease of Undertaking Additional Remedial Actions, if NecessaryAbility to Monitor Effectiveness of Remedy

1: These criteria are fully assessed following comment on the RI/FS Report and the Proposed Plan, and are fully addressed in the ROD.

Features of the Alternative About Which the State has ReservationsElements of the Alternative the State Strongly OpposesFeatures of the Alternative the Community SupportsFeatures of the Alternative About Which the Community has Reservations

State Acceptance

Community Acceptance

Features of the Alternative the State Supports

Specific NCP CriteriaLong Term Effectiveness and Permanence

Reduction of Toxicity, Mobility, and Volume Through Treatment

Elements of the Alternative the Community Strongly Opposes

Ability to Obtain Approvals from Other AgenciesAvailability of Offsite Treatment, Storage, and Disposal Services and CapacityAvailability of Necessary Equipment and SpecialistsAvailability of Prospective Technologies

Specific NCP Criteria

Operating and Maintenance Costs

Implementability

Cost

General NCP Criteria

General NCP Criteria

Short Term Effectiveness

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Table 14Comparison of Remedial Alternatives

Vapor-Intrusion Mitigation

Evaluation CriteriaRemedial

Alternative1. Overall Protection of Human Health and the

Environment2. Compliance with ARARs

How Alternative Provides Human Health and Environmental Protection

a. Compliance with Chemical-Specific ARARs

b. Compliance with Action-Specific ARARs

c. Compliance with Location Specific ARARs

Alternative 1 - No Action

Human health and the environment are not protected because COCs in indoor air exceeding PRGs remain in place. Exposure to residents occurs under this alternative.

Does not comply with chemical-specific ARARs for indoor air.

No action, so no action-specific ARARs apply.

Not applicable - no location-specific ARARs have been identified for the GCSP site.

Alternative 2 - Install Radon-Type Vapor Mitigation System

The contaminated vapors are physically isolated from the overlying structure by installing an impermeable vapor barrier and a ventilation system to remove the vapors from beneath the barrier. Human health and the environment are protected since the vapor barrier and venting system remove the pathway for volatile organics present in the subsurface to enter the structure. Once installed, contaminated soil vapors entering the structure will be reduced to an acceptable level. The measure is permanent with infrequent checks of the physical condition of the barrier and continuing operation of the ventilation system.

The reduction of COC-containing vapors from entering the interiors of the residences will result in indoor air meeting chemical-specific ARARs.

This alternative meets the action-specific ARARs for the reduction of COCs in indoor air to acceptable risk levels.


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Alternative 3. Long Term Effectiveness and Permanence 4. Reduction of Toxicity, Mobility, and Volume Through Treatment

a. Magnitude of Residual Risk

b. Adequacy and Reliability of Controls

a. Treatment Process Used and Materials Treated

b. Amount of Hazardous Materials Destroyed or Treated


Vapor intrusion of COCs above acceptable risk levels is allowed to continue.

No controls implemented. Not applicable. Not applicable.


As long as the barrier and ventilation system are kept in good working order (i.e. no tears or abrasions in the barrier and operation of the ventilation fan), the system will not allow vapor intrusion of COCs above acceptable risk levels.

The installation of barrier and ventilation materials is adequate to prevent vapor intrusion. The control is reliable as it is commonly used to prevent radon intrusion into residential structures. Long-term adequacy and reliability of this control ultimately depends on elimination of the vapor intrusion pathway by remediation of shallow ground water. Failure of any of the vapor mitigation system components or significant downtime due to maintenance can result in loss of vapor intrusion control.

Treatment is via the installation of a synthetic liner and ventilation system. Chlorinated VOCs are prevented from entering the residential structure via vapor intrusion.

COCs are not treated or destroyed. They are physically blocked from entering the residential structures.

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Alternative 4. Reduction of Toxicity, Mobility, and Volume Through Treatment

c. Degree of Expected Reductions in Toxicity, Mobility, and Volume




Not applicable. Not applicable. Original COCs would remain as residuals since no treatment occurs.


The volume of COCs will be reduced to meet RAOs. COCs are not treated or destroyed, they are prevented from entering the residential structure using a synthetic vapor barrier and ventilation system.

Treatment is reversible should the vapor barrier and ventilation system be removed. However, other remedies forthe GCSP site are expected to mitigate the source of vapor intrusion, which is contaminated soil and ground water.

Vapor intrusion pathway is removed by installing a physical barrier. Residual COCs inside the residence would quickly dissipate. If no other active treatment is conducted at the site, the original COCs will remain in the subsurface as residuals since the vapor barriers do not provide treatment. Given active treatment of the site, no residuals are ultimately anticipated in the subsurface.

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Alternative 5. Short Term Effectiveness

a. Protection of Community During Remedial Actions

b. Protection of Workers During Remedial Actions

c. Environmental Impacts d. Time Until Remedial Action Objectives are

Achieved


The No Action Alternative does not involve construction and does not impact the community. However, the original community risks due to presence of COCs will remain.

Not applicable. Not applicable. RAOs would not be achieved.


The installation of this alternative will not disturb COCs or increase their concentration in indoor air. The vapor mitigation systemsinvolve short-term inconvenience to the specific property owners where systems are installed. Installation will require access to the crawl space or basement beneath the structure for placement of thevapor barrier, and installation of vapor piping within walls tothe roof.

Workers will wear appropriate PPE (i.e. respirators) if site conditions warrant. However, the vapor intrusion risk is for long term exposure to COCs, not exposure above permissible exposure limits.

Subsurface soil vapors will be exhausted into the atmosphere above the roof of structures where systems are installed.

RAOs will be achieved upon completion of the installation of the vapor barrier and ventilation system.

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Alternative 6. Implementability

a. Ability to Construct and Operate the Technology

b. Reliability of the Technology

c. Ease of Undertaking Additional Remedial Actions, if

Necessary

d. Ability to Monitor Effectiveness of Remedy


Not applicable. Not applicable. Since this alternative involves no action it would provide no obstructions to other future action.

No actions and no continued monitoring would be undertaken.


This alternative is easily implemented using readily available materials and labor.

Vapor barriers and ventilation systems are reliable methods of preventing vapor intrusion. The technology has been commonly used to mitigate radon intrusion into residential structures.

Easy to take on other actions such as more aggressive ventilation measures.

Indoor air sampling and analysis is easily performed on a routine basis to monitor COC concentrations in indoor air.

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Alternative 6. Implementability

e. Ability to Obtain Approvals from Other Agencies

f. Availability of Offsite Treatment, Storage, and Disposal Services and

Capacity

g. Availability of Necessary Equipment and Specialists

h. Availability of Prospective Technologies


Since no actions would be taken there would be no approvals or coordination with other agencies for implementation of this alternative. However, it may be difficult to gain approval from other stakeholder agencies for no action to meet RAOs.

Not applicable. Not applicable. Not applicable.


Access to private residential property will be required. However, approval is likely because the alternative results in an immediate cessation in vapor intrusion into the residential structures.

Not required for performance of this alternative.

Would be able to hire the equipment and specialists to accomplish this alternative. However, it is a rather specialized technology, so there are fewer companies to choose from.

Vapor barriers and ventilation systems are readily available methods of preventing vapor intrusion. The technology hasbeen commonly used to mitigate radon intrusion into residential structures.

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Alternative 7. Cost

a. Capital Costs

b. Operating and

Maintenance Costs

c. Present Worth Cost

Lower Range Cost (-30%)

Upper Range Cost (+50%)


$0.00 $0.00 $0.00 No Not Acceptable


$381,661.00 $0.00 $381,661.00 $267,162.70 $572,491.50 Yes Acceptable

8. State Acceptance

9. Community Acceptance

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Source Area Treatment

Evaluation CriteriaRemedial Alternative 1. Overall Protection of Human Health and the Environment


Alternative 1 - No Action Existing ground water COCs in the shallow ground water plume core and hot spot exist at concentrations three orders of magnitude greater than the MCLs. Ground water in the source area are a continuing source to the downgradient plume and ground water contamination is a source of vapor intrusion into residential structures. This approach cannot meet the RAOs in a timely fashion.

Human health and the environment are not protected because ground water exceeding PRGs remains in place. Exposure to residents and construction / utility workers could occur under this alternative.

The vapor intrusion pathway remains and indoor air exceeding PRGs remains in place. Exposure to residents and workers could occur under this alternative.

Alternative 2 - Thermal Resistive Heating

Removal of COCs within source area soils and groundwater will reduce the source of the ongoing ground water contamination. With reduction in ground water contamination, the source of the vapor intrusion COCs will also be reduced.

Once the COCs are remediated at the source, downgradient ground water concentrations are expected to decrease and vapor intrusion risk to decrease.

Alternative 3 - ISCO with Follow-On ERD

An appropriately designed ISCO and ERD injection program will result in the removal of COCs within the source area to achieve PRGs. Source area contaminated ground water will be treated to PRGs if adequate oxidant contact and/or complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved for all COCs, in all areas of the source area, equally or possibly more toxic intermediary products could persist. If DNAPL or sorbed soil contamination persists following completion of ISCO and ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated in the source area downgradient ground water concentrations and resulting risk are expected to decrease over time.

As concentrations of COCs in the source area ground water are reduced the risk of vapor intrusion will decrease.

Alternative 4 - ERD (Gridded)

An appropriately designed ERD injection program will result in the removal of COCs within the source area to achieve PRGs. Source area contaminated ground water will be treated to PRGs if complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved for all COCs, in all areas of the source area, equally or or possibly more toxic intermediary products could persist. If DNAPL or sorbed soil contamination persists following completion of ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated in the source area downgradient ground water concentrations and resulting risk are expected to decrease over time.

As concentrations of COCs in the source area ground water are reduced the risk of vapor intrusion will decrease.

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Evaluation CriteriaRemedial Alternative 2. Compliance with ARARs

a. Compliance with Chemical-Specific ARARs b. Compliance with Action-Specific ARARs


Alternative 1 - No Action Does not comply with chemical-specific ARARs for ground water or indoor air.

The proposed alternative will have no action so action-specific ARARs will not apply.



Source area ground water may approach chemical-specific ARARs upon completion of the alternative although it is unlikely that this technology will fully achieve RAOs. Polishing via an additional technology either in the source area or in the downgradient plume core may be necessary. The depth of treatment is to 80 ft bgs at Holiday Cleaners source area and 35 ft bgs at the abandoned dry cleaners source area.

The proposed alternative will meet action-specific ARARs during the implementation of the alternative.



The source area ground water is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to 80 ft bgs at the Holiday Cleaners source area and 35 ft bgs at the abandoned dry cleaners source area.

Remediation of dissolved contamination in shallow water will contribute to complying with indoor air PRGs over time.




The source area ground water is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to 80 ft bgs at the Holiday Cleaners source area and 35 ft bgs at the abandoned dry cleaners source area.




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Evaluation CriteriaRemedial Alternative 3. Long Term Effectiveness and Permanence


Alternative 1 - No Action Source of both ground water and vapor intrusion impacts is not removed under this alternative. Significant residual risk remains.


An appropriately-designed thermal source area treatment is expected to approach PRGs and RAOs and reduce residual risk at the source areas. Final polishing following thermal treatment may be necessary to meet PRGs and RAOs, and may include targeted ERD or ISCO treatments. Residual risk may remain at depths greater than 80 ft bgs at the Holiday Cleaners and 35 ft bgs at the abandoned dry cleaners, since these zones are not actively treated.

When RAOs are achieved at the source area the residual risk in the downgradient aquifer will also be slowly achieved.

This alternative is anticipated to ultimately lower the risk from vapor intrusion and ground water exposure.

A 5-year review will be required to assess performance of this alternative and evaluate whether RAOs are being met.


Source area treatment via ISCO with follow-on ERD can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ISCO and ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 80-ft bgs at Holiday Cleaners and greater than 35-ft bgs at the Abandoned Cleaners since these zones are not actively treated by this alternative.

Until source area ground water COC concentrations meet PRGs they may continue to support a significant vapor intrusion risk.




Source area treatment via ERD can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 80-ft bgs at Holiday Cleaners and greater than 35-ft bgs at the Abandoned Cleaners since these zones are not actively treated by this alternative.

Until source area ground water COC concentrations meet PRGs they may continue to support a significant vapor intrusion risk.



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Alternative 1 - No Action No controls implemented.


Thermal resistive heating removes the COCs from the aquifer and vadose zone soils. Control is permanent as the COCs are removed to PRGs at the source.

If appropriately designed the thermal resistance heating remediation would occur over the course of one implementation event. Subsequent thermal treatments over time would not be required. However, meeting RAOs at the source area with a single application will require an extremely high removal efficiency and thermal treatment alone may not fully meet all ARARs and RAOs. Implementation of some additional polishing technology in the source area or in the downgradient plume core may be necessary.

If any residual DNAPL is present, the treated source area may become recontaminated and this alternative may not meet RAOs..

A loss of process control (incomplete vapor recovery using SVE) could lead to escape of COC vapors to the atmosphere or the recondensing of COC vapors outside the treatment area.


ISCO and ERD consume the COCs to RAOs. Control is permanent as the COCs are removed to PRGs at the source.

Both injected oxidants and carbon-source amendments have limited residence times in the aquifer. Materials are consumed and will require multiple injection events. Both ISCO and ERD have been proven reliable methods of treating the COCs, but both require injection of amendments into the subsurface which can be difficult to control. ISCO is more sensitive to injection uniformity and initial contact with contaminants than is ERD since ERD amendments have a longer residence time and can migrate with ground water to interact with contaminants. Ineffective distribution of ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase contaminants.

If untreated dissolved phase contamination persists, or DNAPL source material remains, after the conclusion of the ISCO and/or carbon-source amendment injections, additional injection of materials may be required.

If any residual DNAPL is present, this alternative may not meet RAOs.


ERD consumes the COCs to RAOs. Control is permanent as the COCs are removed to PRGs at the source.

Injected carbon-source amendments have limited residence times in the aquifer. Materials are consumed and will require multiple injection events. ERD has been proven a reliable method of treating the COCs, but requires injection of amendments into the subsurface which can be difficult to control. Ineffective distribution of ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase contaminants.

If untreated dissolved phase contamination persists, or DNAPL source material remains, after the carbon-source amendment injections, additional injection of materials may be required.

If any residual DNAPL is present, this alternative may not meet RAOs.

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Evaluation CriteriaRemedial Alternative 4. Reduction of Toxicity, Mobility, and Volume Through Treatment

a. Treatment Process Used and Materials

Treated

b. Amount of Hazardous Materials Destroyed or

Treated

c. Degree of Expected Reductions in Toxicity, Mobility,

and Volume

d. Degree to Which Treatment is Irreversible

e. Type of Residuals Remaining After

Treatment

Alternative 1 - No Action Not applicable. Not applicable. Not applicable. Not applicable. Original COCs would remain as residuals since no treatment occurs.


Treatment via volatilization of COCs induced by heating of the subsurface and recovery of the COCs using soil vapor extraction. The offgas is collected and treated prior to discharge. Treats volatile organic compounds including the site-specific COCs.

Pilot-scale testing would provide information on quantity of PCE (and other chlorinated VOCs) treated by the thermal resistive heating alternative. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

A substantial degree of reductions in toxicity, mobility, and contaminant volume are anticipated since the alternative will be designed to reduce COC concentrations.

This alternative is irreversible but the treatment zone could be recontaminated if DNAPL remains present in the treatment zone after the completion of the remedial action.

Completely successful thermal treatment leaves no residual volatile COCs behind, as they are all volatilized.


ISCO treatment occurs via destructive oxidation of organic contaminants and mineralization to carbon dioxide, water, and chloride ISCO is capable of treating all organic compounds if adequate contact can be achieved. Remaining COC concentrations will be treated via biologically-mediated reductive dechlorination which is enhanced through carbon-source amendments into the aquifer matrix.

Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by ISCO and follow-on ERD. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

If adequate oxidant contact and sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist.

If able to fully proceed, the components of this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, and chloride via direct oxidation or reductive dechlorination over time. However the treatment zone could be recontaminated if DNAPL remains present in the treatment zone after the completion of the remedial action.

Residuals following oxidation by ISCO will include carbon dioxide, water, and chloride, and possibly acetone, dissolved metals, or Mn-oxides. Residuals following reductive dechlorination of PCE via ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride.


Treatment of chlorinated halocarbons via reductive dechlorination as carbon-source amendments are injected into the aquifer matrix.

Pilot-scale testing would also provide information on quantity of PCE (and other chlorinated VOCs) treated by ERD, following each ERD injection. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist.

If able to fully proceed, the components of this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, and chloride via reductive dechlorination over time. However the treatment zone could be recontaminated if DNAPL remains present in the treatment zone after the completion of the remedial action.

Residuals following reductive dechlorination of PCE following ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride.

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Evaluation CriteriaRemedial Alternative 5. Short Term Effectiveness

a. Protection of Community During Remedial Actions

Alternative 1 - No Action Not applicable.


Recovery of vapors would need to be performed during thermal heating.

Air monitoring would need to performed during intrusive activities such as drilling and excavation for installation of supporting infrastructure.

Large electricity-handling devices would be present during alternative implementation and would require appropriate fencing and setback from public.


Air monitoring would need to performed during intrusive activities such as drilling or installation of supporting infrastructure.

Appropriate safety measures would need to be implemented when handling oxidants to protect community members from contact with oxidants prior to injection.



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c. Environmental Impacts d. Time Until Remedial Action Objectives are Achieved

Alternative 1 - No Action Not applicable. Not applicable. RAOs would not be achieved.


Would require measures to protect workers from COCs during installation of thermal treatment equipment and during operation of electrical devices.

Will need to control offgas emissions when technology is implemented.

Thermal treatment requires a period between nine months and one year to heat the subsurface to the point where COCs are mobilized (volatilized) and operate until the RAOs are met. A several-month long cool down period then follows and polishing treatments can be conducted. Total time to meet RAOs is assumed to be 18 months to 2 years.


Intrusive onsite work may pose a threat to site workers. Risk can be managed through appropriate health and safety practices.

No environmental impacts are anticipated.

Given available ground water flow velocities, this alternative is anticipated to require 1 year of ISCO injections followed by 6 years of ERD treatments to achieve RAOs based on a gridded application.




The ERD alternative is anticipated to require 15 years to achieve RAOs at the source areas, based on a gridded application.

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Evaluation CriteriaRemedial Alternative 6. Implementability


b. Reliability of the Technology c. Ease of Undertaking Additional Remedial Actions, if Necessary

Alternative 1 - No Action Not applicable. Not applicable. Since this alternative involves no action it would provide no obstructions to other future action.


Thermal treatment requires specialized equipment installed in traditionally drilled and constructed wells.

The technology requires access to the entire ground surface overlying the treatment zone.

A relatively limited number of vendors specializing in thermal treatment technology are available.

Since the technology is installed in wells that are relatively easily installed, that portion of the alternative is reliably executed. The operation of the thermal probes requires substantial quantities of electricity. The availability of the electricity may not be reliable as it is subject to periodic outages, which will require restart of the system.

Other additional remedial actions would be relatively easy to implement at the site. Other remedial actions may be limited only by application near the thermal treatment probes which could damage or reduce the effectiveness of the probes.


ISCO and carbon-source amendment treatments require specialized equipment which is readily available. ISCO and carbon-source amendments (i.e. permanganate, emulsified vegetable oil) are readily available.

ISCO and ERD are reliable technologies as they are relatively easy to implement. The technologies are less reliable as to how rapidly they can inject amendments into the subsurface and how well those amendments are distributed during and after injection. Also, the presence of significant quantities of DNAPL may impact the reliability of the alternatives to treat the COCs.

Other remedial actions could be implemented at the site. However, additional actions would need to be compatible with injected oxidants and/or maintaining a reductive environment in the aquifer to promote biodegradation.


ERD treatments require specialized equipment which is readily available through numerous vendors. ERD amendments (i.e. emulsified vegetable oil) are readily available.

Same as Alternative 3 for source area treatment. ERD as a stand-alone source area treatment can be successful provided that suitable quantities of the ERD amendment remains in the subsurface over time.

Other remedial actions could be implemented at the site. However, additional actions would need to be compatible with maintaining a reductive environment in the aquifer to promote biodegradation.

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d. Ability to Monitor Effectiveness of

Remedy

e. Ability to Obtain Approvals from Other

Agencies

f. Availability of Offsite Treatment,

Storage, and Disposal Services

and Capacity

g. Availability of Necessary Equipment

and Specialists


Alternative 1 - No Action No actions and no continued monitoring would be undertaken.

Since no actions would be taken there would be no approvals or coordination with other agencies for implementation of this alternative. However, it may be difficult to gain approval from other stakeholder agencies for no action to meet RAOs.



Ground water monitoring wells can be readily installed to track the performance of this alternative. Soil borings can be completed using direct-push technology to monitor the performance in source area soils.

This alternative will require access to public and private property, air quality permitting, and may also require the relocation of buried utilities. Each of these requirements will require approval or authorization from owners/agencies.

Offsite treatment, storage, and disposal services not required for this alternative.

Specialty vendors are available to hire with the appropriate equipment and specialists to accomplish this alternative. However, it is a rather specialized technology, so there are fewer companies to choose from.

Performance of Thermal Resistive Heating is an available technology, and currently expanding in availability and implementation at various sites. This technology requires pilot-scale testing to determine the ideal spacing for the heater and vapor recovery probes to effectively reach the entire treatment zone in order to reach PRGs.


Ground water monitoring wells can be readily installed to track the performance of this alternative.

This alternative will require access to public and private property and approval to inject ISCO and/or ERD amendments into the subsurface. This will require approval or authorization from owners/agencies.



ISCO and ERD are readily available technologies. ISCO requires pilot-scale testing to confirm oxidant dosing, injection spacing, and other final remedy requirements. Enhanced biodegradation is a readily available technology, but also requires pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.



This alternative will require access to public and private property and approval to inject ERD amendments into the subsurface. This will require approval or authorization from owners/agencies.



ERD is a readily available technology but requires pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.

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Evaluation Criteria7. Cost

Capital Costs Operating and Maintenance

Costs

Present Worth Cost




$0 $0 $0.00 $0.00 $0.00 No Not Acceptable


$8,018,000.00 $0.00 $8,018,210.00 $5,612,747.00 $12,027,315.00 Yes Acceptable


$6,256,961.00 $3,178,948.00 $9,435,910.00 $6,605,137.00 $14,153,865.00 No Acceptable


$2,391,198.00 $6,074,342.00 $8,465,540.00 $5,925,878.00 $12,698,310.00 No Acceptable

8. State Acceptance


Remedial Alternative

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Evaluation CriteriaRemedial Alternative 1. Overall Protection of Human Health and the Environment



Existing ground water COCs in the shallow ground water plume core and hot spot exist at concentrations three orders of magnitude greater than the MCLs. Ground water in the shallow plume core and hot spot area continuing source to the downgradient plume and ground water contamination is a source of vapor intrusion into residential structures. Natural attenuation mechanisms cannot meet the RAOs in a timely fashion.



Alternative 2 - Zero-Valent Iron PRB

Appropriately designed PRB walls should be able to remediate dissolved phase ground water contamination to meet PRGs in the shallow plume core and hot spot area at the conclusion of the remedial action. However, since ground water remediation rates are limited by the naturalground water velocity potential for human exposure to ground water exceeding PRGs will continue for several years before achieving the RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs, this alternative will no longer effectively achieve RAOs or limit residual risk. Additionally, the extended residence of ground water exceeding PRGs in the shallow plume core provides potential for additional vertical migration of contamination.

Once the COCs are remediated at the plume core and hot spot, downgradient ground water concentrations and resulting risk are expected to decrease over time.

The slow treatment rate of the highly contaminated shallow ground water in the shallow ground water plume core and hot spot as it moves between PRB wall transects will continue to support vapor intrusion for an extended period of time.


An appropriately designed ISCO and ERD injection program will result in the removal of COCs within the shallow plume core and other shallow hot spots to achieve PRGs. Shallow contaminated ground water will be treated to PRGs if adequate oxidant contact and/or complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist. If DNAPL or sorbed soil contamination persists following completion of ISCO and ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated in the shallow plume core and hot spot downgradient ground water concentrations and resulting risk are expected to decrease over time.

As concentrations of COCs in the shallow ground water plume core and hot spot are reduced the risk of vapor intrusion will decrease.

Alternative 4 - ERD (Bio Barriers)

Appropriately designed ERD bio barriers will result in the removal of COCs within the shallow plume core and other shallow hot spots to achieve PRGs. Shallow contaminated ground water will be treated to PRGs if adequate and complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist. If DNAPL or sorbed soil contamination persists following completion ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated at the shallow plume core and hot spot, downgradient ground water concentrations and resulting risk are expected to decrease over time.


Alternative 5 - Pump & Treat

An appropriately designed pump and treat system will result in the removal of COCs within the shallow plume core and other shallow hot spots . The shallow plume core and hotspot ground water may achieve PRGs although remediation would likely take a very extended period. If DNAPL or sorbed soil contamination is present a dissolved phase plume will persist or rebound in the aquifer and this alternative may not achieve RAOs or limit residual risk within an acceptable time period.

Once the COCs are remediated at the shallow ground water plume core and hotspot downgradient ground water concentrations and resulting risk are expected to decrease over time.


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Evaluation CriteriaRemedial Alternative 2. Compliance with ARARs

a. Compliance with Chemical-Specific ARARs b. Compliance with Action-Specific ARARs



Does not comply with chemical-specific ARARs for ground water or indoor air.

The proposed alternative will have not action so action-specific ARARs will not apply.



Ground water exiting appropriately designed PRB walls will meet chemical-specific ARARs. However, the slow ground water flow velocity will result in extended periods of time for all ground water between individual PRB transects to reach and exit a PRB. Therefore, the primary shallow plume core ground water will not rapidly meet chemical-specific ARARs. The depth of treatment is to 20 ft bgs.


The alternative will meet action-specific ARARs during the implementation of the alternative.



The shallow ground water plume core and hot spot area is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to 20 ft bgs.














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Source of both ground water and vapor intrusion impacts is not removed under this alternative. Significant residual risk remains.


PRBs designed for site-specific dissolved phase ground water plume conditions will achieve long term PRGs and RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs, this alternative will no longer effectively achieve RAOs or limit residual risk.

Given the passive nature of the alternative high concentrations of COCs will persist in shallow ground water and continue to support a significant vapor intrusion risk for many years.

If upgradient source treatment is not implemented this alternative may not successfully achieve RAOs for the shallow ground water plume core and hot spot.



Shallow ground water plume core and hot spot treatment via ISCO with follow-on ERD can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ISCO and ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative.

Until shallow ground water plume core and hot spot COC concentrations meet PRGs they may continue to support a significant vapor intrusion risk.




Shallow ground water plume core and hot spot treatment via ERD bio barriers can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternativewill no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative.





Shallow ground water plume core and hot spot treatment via pump and treat methods can be designed to meet long term PRGs and RAOS and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination is present, pump and treat technology in low permeability GCSP site sediments may take greater than 40 years to achieve RAOs. Additionally, portions of the aquifer that have been partially remediated may be subject to recontamination or rebound from remaining sorbed or DNAPL contaminant sources. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative.




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No controls implemented.


The long-term effectiveness of PRBs will decrease over time as the reactive material in the PRBs degrades. The ZVI-PRB walls have been designed for a 20-year service life, and will require replacement at 20 years since RAOs are not expected to be met for 40 years. The effectiveness of the PRB walls is dependant upon a thorough understanding of the hydraulic flow conditions within the aquifer and, if not properly designed or installed, bypass of ground water around, below, or above the barrier can occur. During installation, the smearing of clays on the trench-wall face can limit the permeability of the barrier, as can fouling over time within the ZVI wall.

If untreated dissolved phase contamination persists, or DNAPL source material remains, beyond the service life of the PRBs, re-installation of the PRBs may be required.


Both injected oxidants and carbon-source amendments have limited residence times in the aquifer. Materials are consumed and will require multiple injection events. Both ISCO and ERD have been proven reliable methods of treating the COCs, but both require injection of amendments into the subsurface which can be difficult to control. ISCO is more sensitive to injection uniformity and initial contact with contaminants than is ERD since ERD amendments have a longer residence time and can migrate with ground water to interact with contaminants. Ineffective distribution of ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase contaminants.

If untreated dissolved phase contamination persists, or DNAPL source material remains, after the conclusion of the ISCO and/or carbon-source amendment injections, additional injection of materials may be required.


Injected carbon-source amendments have limited residence time in the aquifer. Materials are consumed and will require multiple injection events. ERD has been proven a reliable method of treating the COCs, but requires injection of amendments into the subsurface which can be difficult to control. Ineffective distribution of ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase contaminants.

If untreated dissolved phase contamination persists, or DNAPL source material remains, after the conclusion of the carbon-source amendment injections, additional injection of materials may be required.


Damage, fouling, or loss of specific capacity of pump and treat system extraction and injection wells may require replacement of these components over the extended operational period of this alternative. Based on site-specific geochemical conditions, extracted ground water may require addition of conditioning chemicals to modify pH or other factors which may degrade system components more rapidly and necessitate replacement. Significant failures of equipment during treatment may require the cessation of treatment while repairs are conducted.

If untreated dissolved phase contamination persists, or DNAPL source material remains after the conclusion of the anticipated pump and treat remedial period, continued operation of the system may be required for a very long additional time.

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ZVI-PRB walls are effective for treatment of chlorinated ethenes and ethanes (including the COCs), select chlorinated pesticides, and some metals.

Bench-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) treated by passing through the PRBs. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

Using site-specific data PRBs will be designed to meet PRGs on the discharge side of the treatment walls.


ISCO treatment occurs via destructive oxidation of organic contaminants and mineralization to carbon dioxide, water, and chloride ISCO is capable of treating all organic compounds if adequate contact can be achieved. Remaining COC concentrations will be treated via biologically-mediated reductive dechlorination which is enhanced through carbon-source amendments into the aquifer matrix.

Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by ISCO and follow-on ERD. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

If adequate oxidant contact and sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist.


Treatment of VOC COCs occurs via biologically-mediated reductive dechlorination which is enhanced through carbon-source amendments into the aquifer matrix.

Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by ERD bio barriers. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow plume core and hot spot, equally or more toxic intermediary products may persist.


COCs are stripped (volatilized) from ground water. The vapor stream is recovered and volatile components are further treated by passage through GAC. The final polished offgas stream is discharged to the atmosphere. The final remediated ground water stream is re-injected into the aquifer. The COCs at the site are generally amenable to treatment via air stripping.

Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by the pump and treat alternative. Since total volume of hazardous materials is not known, total amount of material destroyed or treated can not be estimated.

Using site-specific data a pump and treat system will be designed to reduce ground water concentrations to PRGs prior to re-injection.

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d. Degree to Which Treatment is Irreversible e. Type of Residuals Remaining After Treatment


Not applicable. Original COCs would remain as residuals since no treatment occurs.


Treatment will permanently reductively dechlorinate the COCs.

Residuals following reductive dechlorination of the PCE will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. Additionally, the emplaced ZVI will remain in the subsurface.


If able to fully proceed, the components of this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, and chloride via direct oxidation or reductive dechlorination over time.

Residuals following direct oxidation by ISCO will include carbon dioxide, water, and chloride. Residuals following reductive dechlorination of PCE following ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. A limited residual amount of the carbon-amendment substrate may persist in the aquifer materials.


If able to fully proceed, this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, and chloride via reductive dechlorination over time.

Residuals following reductive dechlorination of PCE following ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. A limited residual amount of the carbon-amendment substrate may persist in the aquifer materials.


Removal of COCs from the ground water is generally irreversible with an appropriately designed air stripper treatment system.

Residuals following pump and treat implementation include GAC that will require offsite disposal or recycling and remediated ground water that will require re-injection.

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a. Protection of Community During Remedial Actions b. Protection of Workers During Remedial Actions


Since no action would take place there would be no impacts to the community from implementation of this alternative. Original risks to the community from COCs would remain.

No remedial action would be implemented.


Air monitoring would need to performed during intrusive activities such as excavation and PRB installation. Large open trenches will be excavated in residential areas and pose a threat to the community. Significant traffic disruption would also occur.

Installation of the PRBs will likely generate hazardous waste for offsite treatment and disposal during excavation of soil for ZVI placement. Due to the shallow ground water table it is likely that some highly contaminated ground water may also be generated during some of the trenching activities which will require containment and treatment or disposal.

Excavation and intrusive onsite work as well as offsite transport of hazardous materials may pose a threat to site workers. Risk can be managed through appropriate health and safety and hazardous waste handling practices.



Appropriate safety measures would need to be implemented when handling oxidants to protect community members from contact with oxidants prior to injection.







Additionally, air monitoring or modeling will need to be performed to demonstrate protection of the community from unacceptable air emissions from the air stripper.


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Ground water and indoor air at concentrations greater than PRGs would remain. There would be no other alternative specific environmental impacts since no remedial action occurs.

RAOs would not be achieved.


Generation of highly contaminated ground water may pose a threat to site workers. Risk can be managed through appropriate health and safety monitoring and waste handling practices.

Offsite transport and disposal of hazardous materials may pose a threat to the environment. Risk can be managed through appropriate hazardous waste handling and practices.

Due to the passive nature of this alternative, the treatment rate of the shallow ground water plume will be limited by the ground water flow velocity. Ground water within the shallow plume core and hot spot is anticipated to pass through a PRB wall transect within 2 to 4 years. However, significant sorbed-phase contamination is anticipated in the regions between the PRBs and many aquifer flushings will be required to meet RAOs. This treatment method is anticipated to require 40 years to meet RAOs.




Two rounds of oxidant injection would be performed which will require a period of up to 2 years. Following ISCO, a total of 5 carbon-source amendment injections at a frequency of once every 15 months are anticipated for final ground water polishing although RAOs may still not be achieved following the final injection. RAOs are expected to be achieved within two years following the final carbon-source amendment injection. The total time for the ISCO and ERD components of the remedial action would be roughly 8 years.




A total of 16 carbon-source amendment injections at a frequency of once every 15 months are anticipated although RAOs will still not be achieved following the final injection. RAOs are expected to be achieved within two years following the final carbon-source amendment injection or at roughly 20 years.



If appropriate air emissions treatment is implemented and successful ground water reinjection can be achieved no environmental impacts are anticipated.

Due to the low hydraulic conductivity of the geologic materials at the site, the very high COC concentrations in the shallow ground water plume core and hot spot, and significant sorbed-phase contamination, the pump and treat alternative is anticipated to take over 40 years to achieve RAOs.

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d. Ability to Monitor Remedy

Effectiveness





Construction of PRB walls is similar to, but somewhat more complicated than, traditionaltrenching. Slurry trenching uses traditional equipment but requires maintenance of the slurry during construction. Single-pass trenching can also be used, but involves specialized equipment. PRB walls have been routinely installed at similar sites over the last ten years.

PRBs can be reliably designed and installed once site specific data collection and bench testing are complete. The reliability of implementing this technology can be impacted by lack of site-specific geologic, geochemical, and contaminant distribution data.

Other additional remedial actions would be relatively easy to implement at the site. Other remedial actions may be limited in application of certain technologies near the PRB walls which could damage or reduce the effectiveness of the walls.

Ground water monitoring wells can readily track the performance of this alternative as it pertains to remediation of the shallow ground water plume core and hot spot.


ISCO and carbon-source amendment treatments require specialized equipment which is readily available through numerous direct-push drilling vendors. Direct-push drilling is an easily operated technology. ISCO and carbon-source amendments (i.e. permanganate, emulsified vegetable oil) are readily available.

ISCO and ERD are reliable technologies as they are relatively easy to implement. The technologies are less reliable as to how rapidly they can inject amendments into the subsurface and how well those amendments are distributed during and after injection. Also, the presence of significant quantities of DNAPL may impact the reliability of the alternatives to treat the COCs.

Other remedial actions could be implemented at the site. However, additional actions would need to be compatible with injected oxidants and/or maintaining a reductive environment in the aquifer to promote biodegradation.



Carbon-source amendment treatments require specialized equipment which is readily available through numerous direct-push drilling vendors. Direct-push drilling is an easily operated technology. Carbon-source amendments (i.e. emulsified vegetable oil) are readily available.

ERD is a reliable technology as it is relatively easy to implement. The technology is less reliable as to how rapidly amendments can be injected into the subsurface and how well those amendments are distributed during and after injection. Also, the presence of significant quantities of DNAPL may impact the reliability of the alternatives to treat the COCs.




Pump and treat alternatives utilize routine, available well installation techniques and materials and basic air stripping systems. However, site-specific geochemical conditions can present substantial challenges in bringing a successfully operating extraction, treatment, and reinjection system online. Additionally, although ground water re-injection utilizes basic well installation techniques and technology the process is subject to high operational and maintenance requirements.

Pump and treat is reliable technology as it is relatively easy to implement and uses basic ground water extraction well and technologically sound air stripping principles. However, as an operating treatment plan system it is subject to mechanical failures.

Other remedial actions could be implemented at the site. However, additional actions would need to take into account aquifer amendments that might be recovered by the pump and treat system and foul the system or reduce the effectiveness of the air stripping process.


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d. Ability to Monitor Remedy Effectiveness



Capacity



Since no actions would be taken there would be no approvals or coordination with another agencies for implementation of this alternative. However, it may be difficult to gain approval from other stakeholder agencies for no action to meet RAOs.

Not applicable.


Due to the extended time period it will take this alternative to address the shallow ground water concentrations that support indoor air vapor intrusion, ongoing air monitoring would continue tobe required and can be readily performed.

The installation and use of PRB walls in themselves are not anticipated to provide particular difficulties in gaining stakeholder agency approval. The extended time period over which it will take PRB walls to address ground water exceeding PRGs may not be acceptable to some stakeholder agencies. The relatively large scale construction aspect of installing PRBs may require extensive coordination with local agencies and utilities.

Material excavated during the installation of the PRB walls may generate hazardous waste which may require the selection of an offsite RCRA landfill disposal location. The volume of hazardous material generated will depend on the final designed size of the PRBs and where they would be installed at the site. The nature of the hazardous material generated and the potential treatment and disposal options will require additional site specific data and design considerations.


Until shallow ground water concentrations are adequately reduced to the point that they can not support indoor air vapor intrusion, ongoing air monitoring would continue to be required and can be readily performed.

This alternative will require access to public and private property and approval to inject ISCO and/or ERD amendments into the subsurface. This will require approval or authorization from owners/agencies.








This alternative will require access to public and private property, approval to reinject treated ground water, and approvals to discharge the treated air stream. This will require approval or authorization from owners/agencies.

Offsite recycling of GAC is readily available. Treated ground water will be reinjected back into the aquifer. The availability of reinjection is not limited, however, the technical viability of reinjection can be challenging. If offsite disposal of treated ground water was required an appropriate disposal option would need to be identified.

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Capacity






Some highly contaminated ground water is likely to be generated during trenching activities due to the shallow ground water table. Contaminated water will need to be contained and potentially treated onsite or possibly discharged to the City POTW. The potential volume of ground water generated and the contaminant concentrations of that ground water and potential treatment and disposal options require additional site specific data and design considerations.


Installation of PRB walls is an available technology, having greatly expanded over the last ten years. This technology requires bench-scale testing to determine the ideal reactive media to use within the wall, the amount of reactive material required to treat site contaminants, and the thickness of material required to meet the PRGs.




ISCO and ERD are readily available technologies. ISCO requires pilot-scale testing to confirm oxidant dosing, injection spacing, and other final remedy requirements. Enhanced biodegradation is a readily available technology, but also requires pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.




ERD is a readily available technology but requires pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.



Drilling contractors for well installation and air stripper treatment vendors are available to hire with the appropriate equipment and specialists to accomplish this alternative. These technologies are not specialized, therefore there are various vendors from which to chose.

Pump and treat systems are readily available technologies but require some level of pilot-scale testing to design final remedy requirements.

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Evaluation CriteriaRemedial Alternative 7. Cost

a. Capital Costs b. Operating and Maintenance







$4,937,170.00 $837,108.00 $5,774,278.00 $4,041,994.60 $8,661,417.00 No Acceptable


$4,443,940.00 $2,286,786.00 $6,730,726.00 $4,711,508.20 $10,096,089.00 Yes Acceptable


$576,130.00 $1,300,147.00 $1,876,277.00 $1,313,393.90 $2,814,415.50 No Acceptable


$3,538,986.00 $9,970,356.00 $13,509,342.00 $9,456,539.40 $20,264,013.00 No Acceptable

8. State Acceptance


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Shallow Ground Water Periphery

Evaluation Criteria1. Overall Protection of Human Health and the Environment



Existing ground water COCs in the shallow ground water periphery exist at concentrations greater than the MCLs. Ground water in the shallow periphery is a continuing source to the downgradient plume and ground water contamination is a source of vapor intrusion into residential structures. Natural attenuation mechanisms cannot meet the RAOs in a timely fashion.



Alternative 2 - Monitored Natural Attenuation (MNA)

An appropriately designed MNA program may be able to monitor the reduction of COCs until levels meet PRGs in the shallow ground water periphery at the conclusion of theremedial action. However, the period of time to achieve RAOs may be on the order of 30 years of more and over much of the course of the remedial alternative a substantialamount of the shallow ground water periphery may not meet chemical-specific ARARs. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow ground water periphery, equally or more toxic intermediary products may persist. Additionally, the extended residence of ground water exceeding PRGs in the shallow ground water periphery provides potential for additional vertical migration of contamination.

If DNAPL or sorbed soil contamination persists in the area a dissolved phase plume will persist in the aquifer and this alternative will not effectively achieve RAOs or limit residual risk. The ongoing monitoring of the remedial alternative will limit some residual risk by allowing regular evaluation of the effectiveness of the alternative.

Once the COCs are remediated in the ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time. However, the time periods to achieve COC reduction in the shallow ground water periphery itself and then subsequent COC reduction in the remaining downgradient plume may not be acceptable.


Appropriately designed PRB walls should be able to remediate dissolved phase ground water contamination to meet PRGs in the shallow ground water periphery at the conclusion of the remedial action. However, since ground water remediation rates are limited by the natural ground water velocity potential for human exposure to ground water exceeding PRGs will continue for several years before achieving the RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs, this alternative will no longer effectively achieve RAOs or limit residual risk. Additionally, the extended residence of ground water exceeding PRGs in the shallow ground water periphery provides potential for additional vertical migration of contamination.

Once the COCs are remediated in the ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time. However, the time periods to achieve COC reduction in the shallow ground water periphery with the use of PRBs and then subsequent COC reduction in the remaining downgradient plume may not be acceptable.


Appropriately designed ERD bio barriers may result in the removal of COCs within the shallow ground water periphery to achieve PRGs. Shallow contaminated ground water will be treated to PRGs if adequate and complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved forall COCs, in all areas of the shallow ground water periphery, equally or more toxic intermediary products may persist. If DNAPL or sorbed soil contamination persists following completion ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated in the shallow ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time.


An appropriately designed pump and treat system will result in the removal of COCs within the shallow ground water periphery however remediation may take in excess of 40 years to achieve PRGs. If DNAPL or sorbed soil contamination is present a dissolved phase plume will persist or rebound in the aquifer and this alternative may not achieve RAOs or limit residual risk within an acceptable time period.

Once the COCs are remediated at the source, downgradient ground water concentrations and resulting risk are expected to decrease over time.

Once the COCs are remediated in the shallow ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time.


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Evaluation Criteria2. Compliance with ARARs









Ground water at a designated downgradient point of compliance is expected to meet chemical-specific ARARs over time, although the period of time may be on the order of 30 years of more. Additionally, over much of the course of the remedial alternative a substantial amount of the shallow ground water periphery upgradient of the point of compliance may not meet chemical-specific ARARs.








The shallow ground water periphery is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to 20 ft bgs.




The shallow ground water plume periphery is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to 20 ft bgs.




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Evaluation Criteria3. Long Term Effectiveness and Permanence





MNA of the shallow ground water periphery can be expected to meet long term PRGs and RAOs and therefore eventually reduce residual risk. However, given the passive nature of the alternative high concentrations of COCs will persist in the shallow ground water periphery for an extended period of time presenting continuing residual risk. If DNAPL or sorbed soil contamination persists in the area a dissolved phase plume will persist in the aquifer and this alternative will not effectively achieve RAOs or limitresidual risk. The ongoing monitoring of the remedial alternative will limit some residual risk by allowing regular evaluation of the effectiveness of the alternative.




PRBs designed for site-specific dissolved phase ground water plume conditions will achieve long term PRGs and RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs, this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative.




The shallow ground water periphery treatment via ERD bio barriers can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative.




Shallow ground water periphery treatment via pump and treat methods can be designed to meet long term PRGs and RAOS and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination is present, pump and treat technology in low permeability GCSP site sediments may take greater than 40 years to achieve RAOs. Additionally, portions of the aquifer that have been partially remediated may be subject to recontamination or rebound from remaining sorbed of DNAPL contaminant sources. Residual risk may remain within the aquifer greater than 20-ft bgs since this zone is not actively treated by this alternative




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No specific controls or components are installed as part of this alternative. Given appropriate site conditions, MNA can be a reliable method (reductive dechlorination of site COCs) of reaching RAOs over long time periods.


The long-term effectiveness of PRBs will decrease over time as the reactive material in the PRBs degrades. The ZVI-PRB walls have been designed for a 20-year service life, and will require replacement at 20 years since RAOs are not expected to be met for 40 years. The effectiveness of the PRB walls is dependant upon a thorough understanding of the hydraulic flow conditions within the aquifer and, if not properly designed or installed, bypass of ground water around, below, or above the barrier can occur. During installation, the smearing of clays on the trench-wall face can limit the permeability of the barrier, as can fouling over time within the ZVI wall.

If untreated dissolved phase contamination persists, or DNAPL source material remains, beyond the service life of the PRBs, re-installation of the PRBs may be required.





Damage, fouling, or loss of specific capacity of pump and treat system extraction and injection wells may require replacement of these components over the extended operational period of this alternative. Based on site-specific geochemical conditions, extracted ground water may requireaddition of conditioning chemicals to modify pH or other factors which may degrade system components more rapidly and necessitate replacement. Significant failures of equipment during treatment may require the cessation of treatment while repairs are conducted.



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Evaluation Criteria4. Reduction of Toxicity, Mobility, and Volume Through Treatment



c. Degree of Expected Reductions in Toxicity, Mobility,




Treatment of VOC COCs occurs via biologically-mediated reductive dechlorination.

Site-specific MNA parameter data will need to be collected in order to calculate the projected quantity and rate of PCE (and other chlorinated VOCs) degradation through natural attenuation.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow ground water periphery, equally or more toxic intermediary products may persist.


Treatment of VOC COCs occurs via reductive dechlorination as ground water passes through the PRBs by natural ground water flow.

Bench-scale testing will provide information on the specific volumeof PCE (and other chlorinated VOCs) treated by passing throughthe PRBs.

Using site-specific data PRBs will be designed to meet PRGs on the discharge side of the treatment walls.



Pilot-scale testing will provide information on the specific volumeof PCE (and other chlorinated VOCs) that will be expected to be treated by ERD bio barriers.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow ground water periphery, equally or more toxic intermediary products may persist.



Pilot-scale testing will provide information on the specific volumeof PCE (and other chlorinated VOCs) that will be expected to be treated by the pump and treat alternative.

Using site-specific data a pump and treat system will be designed to reduce ground water concentrations to PRGs prior to reinjection.


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If able to fully proceed, this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, andchloride via reductive dechlorination over time.



Treatment will permanently reductively dechlorinate the COCs.

Residuals following reductive dechlorination of the PCE will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. Additionally, the emplaced ZVI will remain in the subsurface.


If able to fully proceed, this alternative will ultimately permanently mineralize COCs to carbon dioxide, water, andchloride via reductive dechlorination over time.

Residuals following reductive dechlorination of PCE following ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. A limited residual amount of the carbon-amendment substratemay persist in the aquifer materials.





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Evaluation Criteria5. Short Term Effectiveness






No remedial actions would take place so there would be limited impacts to the community from implementation of this alternative. Installation of ground water monitoring wells and regular sampling would have limited impacts on the community. Air monitoring would need to performed during intrusive activities. Given the passive nature of the alternative high concentrations of COCs may persist in the shallow ground water periphery for an extended period of timeand may present an unacceptable ongoing risk to the community.



Air monitoring would need to performed during intrusive activities such as excavation and PRB installation. Large open trenches will be excavated in residential areas and pose a threat to the community. Significant traffic disruption would also occur.








Additionally, air monitoring or modeling will need to performed to demonstrate protection of the community from unacceptable air emissions from the air stripper.



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Given the passive nature of the alternative high concentrations of COCs may persist in the shallow ground water periphery for an extended period of time and may present an unacceptable risk to the environment.

Ground water at a designated downgradient pointof compliance is not expected to meet chemical-specific ARARs for a period of probably 40 years of more. If full reductive dechlorination is not achieved for all COCs, in all areas of the shallow ground water periphery, RAOs may not be met bythis alternative.



Offsite transport and disposal of hazardous materials may pose a threat to the environment. Risk can be managed through appropriate hazardous waste handling and practices.

Due to the passive nature of this alternative, the treatment rate of the shallow ground water periphery will be limited by the ground water flow velocity. Assuming a continuing dissolved COC plume is not propagated by DNAPL or sorbed soilCOCs that remain between the PRB wall transects the RAOs for the shallow ground water periphery could be met within a period of four to five pore volume flushings. Due to the greater distances over which fewer PRB walls would be placed to address the larger shallow ground water periphery area, RAOs are estimated to be met by this alternative in roughly 20 to 25 years.




A total of 16 carbon-source amendment injections at a frequency of once every 15 monthsare anticipated although RAOs will still not be achieved following the final injection. RAOs are expected to be achieved within two years following the final carbon-source amendment injection or at roughly 20 years.




Due to the low hydraulic conductivity of the geologic materials at the site, the pump and treat alternative is anticipated to take over 40 years to achieve RAOs


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Evaluation Criteria6. Implementability

a. Ability to Construct and Operate the Technology b. Reliability of the Technology c. Ease of Undertaking Additional Remedial Actions, if Necessary




No specific construction related to this alternative would be required. Standard monitoring wells are easily constructable and have no operational requirements.

Since this alternative does not include active implementation of a constructed alternative there would be few limitations on reliably implementing this technology.

Other remedial actions could be easily implemented at the site. However, additional actions wouldneed to be compatible with maintaining a reductive environment in the aquifer to promote biodegradation if this component of natural attenuation was expected to continue to operate.


Construction of PRB walls is similar to, but somewhat more complicated than, traditional trenching. Slurry trenching uses traditional equipment but requires maintenance of the slurry during construction. Single-pass trenching can also be used, but involves specialized equipment. PRB walls have been routinely installed at similar sites over the last ten years.

PRBs can be reliably designed and installed once site specific data collection and bench testing are complete. The reliability of implementing this technology can be impacted by lack of site-specific geologic, geochemical, and contaminant distribution data.

Other additional remedial actions would be relatively easy to implement at the site. Other remedial actions may be limited in application of certain technologies near the PRB walls which could damage or reduce the effectiveness of the walls.




Other remedial actions could be implemented at the site. However, additional actions wouldneed to be compatible with maintaining a reductive environment in the aquifer to promote biodegradation.



Pump and treat is reliable technology as it is relatively easy to implement and uses basic ground water extraction well and technologically sound air stripping principals. However, as an operating treatment plan system it is subject to mechanical failures.

Other remedial actions could be implemented at the site. However, additional actions wouldneed to take into account aquifer amendments that might be recovered by the pump and treat system and foul the system or reduce the effectiveness of the air stripping process.


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Not applicable.



This alternative will require access to public and private property to install monitoring wells. This will require approval or authorization from owners/agencies. The extended time period over which it will take MNA to address ground water exceeding PRGs may not be acceptable to some stakeholder agencies.

No substantial offsite treatment, storage, and disposal services are required for this alternative. Limited amounts of ground water monitoring well purge water would be generated that would require coordination for treatment or offsite disposal.


Ground water monitoring wells can readily track the performance of this alternative as it pertains to remediation of the shallow ground water periphery.

The installation and use of PRB walls in themselves are not anticipated to provide particular difficulties in gaining stakeholder agency approval. The extended time period over which it will take PRB walls to address ground waterexceeding PRGs may not be acceptable to some stakeholder agencies. The relatively large scale construction aspect of installing PRBs may require extensive coordination with local agencies and utilities.

Material excavated during the installation of the PRB walls may generate hazardous waste which may require the selection of an offsite RCRA landfill disposal location. The volume of hazardous material generated will depend on the final designed size of the PRBs and where they would be installed at the site. The nature of the hazardous material generated and the potential treatment and disposal options will require additional site specific data and design considerations.










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No substantial offsite treatment, storage, and disposal services not required for this alternative. Limited amounts of ground water monitoring well purge water would be generated that would require coordination for treatment or offsite disposal.

Drilling contractors for well installation are available for hire with the appropriate equipment and personnel to accomplish the monitoring well installation tasks for this alternative. These technologies are not specialized, therefore there are various vendors from which to chose.

MNA is an available technology which iseasily implemented.


Some highly contaminated ground wateris likely to be generated during trenching activities due to the shallow ground water table. Contaminated water will need to be contained and potentially treated onsite or possibly discharged to the City POTW. The potential volume of ground water generated and the contaminant concentrations of that ground water and potential treatment and disposal options require additional site specific data and design considerations.






ERD is a readily available technology but requires some level of pilot-scale testing to confirm carbon-source dosing,injection spacing, and other final remedy requirements.






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a. Capital Costs b. Operating and







$268,878.00 $1,632,212.00 $1,901,090.00 $1,330,763.00 $2,851,635.00 No Acceptable


$12,998,556.00 $926,966.00 $13,925,522.00 $9,747,865.40 $20,888,283.00 No Acceptable


$921,191.00 $2,352,052.00 $3,273,243.00 $2,291,270.10 $4,909,864.50 Yes Acceptable


$3,948,021.00 $9,970,356.00 $13,136,371.00 $9,195,459.70 $19,704,556.50 No Acceptable

8. State Acceptance



lgonzale

003191


Deeper Ground Water

Evaluation Criteria1. Overall Protection of Human Health and the Environment



Existing ground water COCs in the deeper ground water periphery up to 80-ft bgs exist at concentrations greater than the MCLs. Ground water contamination in this zone is a continuing source to the downgradient plume and ground water contamination is a source of vapor intrusion into residential structures. Natural attenuation mechanisms cannot meet the RAOs in a timely fashion.




An appropriately designed MNA program may be able to monitor the reduction of COCs until levels meet PRGs in the deeper ground water periphery up to 80 ft bgs at the conclusion of the remedial action. However, the period of time to achieve RAOs may be on the order of 30 years of more and over much of the course of the remedial alternative a substantial amount of round water may not meet chemical-specific ARARs. If full reductive dechlorination is not achieved for all COCs, in all areas of the deeper ground water periphery, equally or more toxic intermediary products may persist. Additionally, the extended residence of ground water exceeding PRGs provides potential for additional vertical migration of contamination to the drinking water aquifer.

If DNAPL or sorbed soil contamination persists in the area a dissolved phase plume will persist in the aquifer and this alternative will not effectively achieve RAOs or limit residual risk. The ongoing monitoring of the remedial alternative will limit some residual risk by allowing regular evaluation of the effectiveness of the alternative.

Once the COCs are remediated in the ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time. However, the time periods to achieve COC reduction in the shallow ground water periphery itself and then subsequent COC reduction in the remaining downgradient plume may not be acceptable.

Alternative 3 - Zero-Valent Iron PRB with ERD from 60 to 80-ft bgs

Appropriately designed PRB walls, supplemented with ERD to achieve greater remediation depths, should be able to remediate dissolved phase ground water contamination to meet PRGs in the deeper ground water periphery at the conclusion of the remedial action. However, since ground water remediation rates for PRBs are limited by the natural ground water velocity potential for human exposure to ground water exceeding PRGs will continue for several years before achieving the RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs or ERD zones and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs or the ERD carbon-source amendments, this alternative will no longer effectively achieve RAOs or limit residual risk. Additionally, the extended residence of ground water exceeding PRGs in the deeper ground water periphery provides potential for additional vertical migration of contamination.

Once the COCs are remediated in the deeper ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time.


Appropriately designed ERD bio barriers may result in the removal of COCs within the deeper ground water periphery at depths of up to 80 ft bgs to achieve PRGs. Contaminated ground water will be treated to PRGs if adequate and complete biologically mediated reductive dechlorination can be achieved. If full reductive dechlorination is not achieved for all COCs, in all areas of the deeper ground water periphery up to 80 ft bgs, equally or more toxic intermediary products may persist. If DNAPL or sorbed soil contamination persists following completion ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk.

Once the COCs are remediated in the deeper ground water periphery, downgradient ground water concentrations and resulting risk are expected to decrease over time.


An appropriately designed pump and treat system will result in the removal of COCs within the deeper ground water periphery, at depths of up to 80 ft bgs, however remediation may take in excess of 40 years to achieve PRGs. If DNAPL or sorbed soil contamination is present a dissolved phase plume will persist or rebound in the aquifer and this alternative may not achieve RAOs or limit residual risk within an acceptable time period.

Once the COCs are remediated in the deeper ground water periphery zone, downgradient ground water concentrations and resulting risk are expected to decrease over time.


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003192


Deeper Ground Water

Evaluation Criteria2. Compliance with ARARs









Ground water at a designated downgradient point of compliance is expected to meet chemical-specific ARARs over time, although the period of time may be on the order of 30 years of more. Additionally, throughout much of the remedial alternative period a portion of the ground water upgradient of the point of compliance and up to depths of 80-ft bgs may not meet chemical-specific ARARs.




The deeper ground water periphery is expected to meet chemical-specific ARARs upon completion of the alternative. The depth of treatment is to up to 80 ft bgs.












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003193


Deeper Ground Water






MNA of the deeper ground water up to 80 ft bgs can be expected to meet long term PRGs and RAOs and therefore eventually reduce residual risk. However, given the passive nature of the alternative concentrations of COCs that do not meet PRGs will persist up to 80 ft bgs at least for an extended period of time presenting continuing residual risk. If DNAPL or sorbed soil contamination persists in the area a dissolved phase plume will persist in the aquifer and this alternative will not effectively achieve RAOs or limit residual risk. The ongoing monitoring of the remedial alternative will limit some residual risk by allowing regular evaluation of the effectiveness of the alternative.

If upgradient source treatment and shallower zone aquifer treatment are not implemented this alternative may not successfully achieve RAOs for the shallow ground water plume core and hot spot.



PRBs, along with supplemental ERD bio barriers, designed for site-specific dissolved phase ground water plume conditions will achieve long term PRGs and RAOs. If DNAPL or sorbed soil contamination persists in the areas between the PRBs or bio barriers and continues to propagate a dissolved phase plume beyond the designed service life of the PRBs, this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer at depths greater than 80-ft bgs since this zone is not actively treated by this alternative.




The deeper ground water periphery treatment via ERD bio barriers can be designed to meet long term PRGs and RAOs and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination persists following completion of ERD amendment injections a dissolved phase plume will persist or rebound in the aquifer and this alternative will no longer effectively achieve RAOs or limit residual risk. Residual risk may remain within the aquifer at depths greater than 80-ft bgs since this zone is not actively treated by this alternative.




Deeper ground water periphery treatment, up to 80 ft bgs, via pump and treat methods can be designed to meet long term PRGs and RAOS and therefore eventually reduce residual risk. If DNAPL or sorbed soil contamination is present, pump and treat technology in low permeability GCSP site sediments may take greater than 40 years to achieve RAOs. Additionally, portions of the aquifer that have been partially remediated may be subject to recontamination or rebound from remaining sorbed of DNAPL contaminant sources. Residual risk may remain within the aquifer greater than 80-ft bgs since this zone is not actively treated by this alternative.




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003194


Deeper Ground Water






No specific controls or components are installed as part of this alternative. Given appropriate site conditions, MNA can be a reliable method (reductive dechlorination of site COCs) of reaching RAOs over long time periods.


The long-term effectiveness of PRBs will decrease over time as the reactive material in the PRBs degrades. The ZVI-PRB walls have been designed for a 20-year service life, and will require replacement at 20 years since RAOs are not expected to be met for 40 years. The effectiveness of the PRB walls is dependant upon a thorough understanding of the hydraulic flow conditions within the aquifer and, if not properly designed or installed, bypass of ground water around, below, or above the barrier can occur. Injected carbon-source amendments have limited residence time in the aquifer. Materials are consumed and will require multiple injection events. Ineffective distribution of ISCO or ERD amendments can lead to untreated DNAPL or residual sorbed-phase contaminants. During installation, the smearing of clays on the trench-wall face can limit the permeability of the barrier, as can fouling over time within the ZVI wall.

If untreated dissolved phase contamination persists, or DNAPL source material remains, after the end of the service life of the PRBs or following the final carbon-source amendment injections, reinstallation of the PRBs or additional injection of materials may be required.





Damage, fouling, or loss of specific capacity of pump and treat system extraction and injection wells may require replacement of these components over the extended operational period of this alternative. Based on site-specific geochemical conditions, extracted ground water may require addition of conditioning chemicals to modify pH or other factors which may degrade system components more rapidly and necessitate replacement. Significant failures of equipment during treatment may require the cessation of treatment while repairs are conducted.



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003195


Deeper Ground Water








Treatment of VOC COCs occurs via biologically-mediated reductive dechlorination.

Site-specific MNA parameter data will need to be collected in order to calculate the projected quantity and rate of PCE (and other chlorinated VOCs) degradation through natural attenuation.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the deeper ground water periphery, equally or more toxic intermediary products may persist.


PRB treatment of VOC COCs occurs via reductive dechlorination as ground water passes through the PRBs by natural ground water flow. Bio barrier treatment of VOC COCs occurs via biologically-mediated reductive dechlorination which is enhanced through carbon-source amendments into the aquifer matrix.

Bench-scale and pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) treated by passing through the PRBs.

Using site-specific data PRBs will be designed to meet PRGs on the discharge side of the PRB treatment walls. If sustained biologically mediated reductive dechlorination can be achieved substantial reductions will also be expected for the bio barriers. If full reductive dechlorination is not achieved within the bio barriers for all COCs, in all areas of the deeper ground water periphery, equally or more toxic intermediary products may persist.



Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by ERD bio barriers.

If sustained biologically mediated reductive dechlorination can be achieved substantial reductions are expected. If full reductive dechlorination is not achieved for all COCs, in all areas of the deeper ground water periphery, equally or more toxic intermediary products may persist.



Pilot-scale testing will provide information on the specific volume of PCE (and other chlorinated VOCs) that will be expected to be treated by the pump and treat alternative.

Using site-specific data a pump and treat system will be designed to reduce ground water concentrations to PRGs prior to re-injection.


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003196


Deeper Ground Water









PRB treatment will permanently reductively dechlorinate the COCs. If able to fully proceed, ERD will also ultimately permanently mineralize COCs to carbon dioxide, water, and chloride via reductive dechlorination over time.

Residuals following reductive dechlorination of the PCE will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. Additionally, the emplaced ZVI will remain in the subsurface and limited residual amount of the carbon-amendment substrate may also persist in the aquifer materials..



Residuals following reductive dechlorination of PCE following ERD will proceed through TCE, DCE, VC, ethene, and ultimately carbon dioxide, water, and chloride. A limited residual amount of the carbon-amendment substrate may persist in the aquifer materials.





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003197


Deeper Ground Water







No remedial actions would take place so there would be limited impacts to the community from implementation of this alternative. Installation of ground water monitoring wells and regular sampling would have limited impacts on the community. Air monitoring would need to performed during intrusive activities. Given the passive nature of the alternative high concentrations of COCs may persist in the shallow ground water periphery for an extended period of time and may present an unacceptable ongoing risk to the community.



Air monitoring would need to performed during intrusive activities such as excavation, PRB installation and drilling and installation of ERD infrastructure. Large open trenches will be excavated in residential areas and pose a threat to the community. Significant traffic disruption would also occur.








Additionally, air monitoring or modeling will need to performed to demonstrate protection of the community from unacceptable air emissions from the air stripper.



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003198


Deeper Ground Water










Given the passive nature of the alternative concentrations of COCs greater than PRGs may persist in the deeper ground water periphery for an extended period of time and may present an unacceptable risk to the environment.

Ground water at a designated downgradient point of compliance is not expected to meet chemical-specific ARARs for a period of probably 40 years of more. If full reductive dechlorination is not achieved for all COCs, in all areas of the deeper ground water periphery RAOs may not be met by this alternative.



Offsite transport and disposal of hazardous materials generated during PRB installation may pose a threat to the environment. Risk can be managed through appropriate hazardous waste handling and practices. No environmental impacts from installation of the bio barriers are anticipated.

Due to the passive nature of this alternative, the treatment rate of the shallow ground water periphery will be limited by the ground water flow velocity. Assuming a continuing dissolved COC plume is not propagated by DNAPL or sorbed soil COCs that remain between the PRB or bio barrier wall transects the RAOs for the deeper ground water periphery could be met within a period of four to six pore volume flushings. A total of 16 carbon-source amendment injections at a frequency of once every 15 months are anticipated although RAOs will still not be achieved following the final injection. Due to the greater distances over which fewer PRB/bio barrier walls would be placed to address the deeper ground water periphery area, RAOs are estimated to be met by this alternative in roughly 20 to 25 years.




A total of 16 carbon-source amendment injections at a frequency of once every 15 months are anticipated although RAOs will still not be achieved following the final injection. RAOs are expected to be achieved within two years following the final carbon-source amendment injection or at roughly 20 years.




Due to the low hydraulic conductivity of the geologic materials at the site, the pump and treat alternative is anticipated to take over 40 years to achieve RAOs


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Deeper Ground Water


a. Ability to Construct and Operate the Technology b. Reliability of the Technology


Not applicable. Not applicable.


No specific construction related to this alternative would be required. Standard monitoring wells are easily constructable and have no operational requirements.



Construction of PRB walls is similar to, but somewhat more complicated than, traditional trenching. Slurry trenching uses traditional equipment but requires maintenance of the slurry during construction. Single-pass trenching can also be used, but involves specialized equipment. Installation of PRBs to depths of 60 ft bgs will approach the limits of constructability. Based on site specific conditions and PRB design needs installation of PRBs may not be feasible.


PRBs can be reliably designed and installed once site specific data collection and bench testing are complete. The reliability of implementing this technology can be impacted by lack of site-specific geologic, geochemical, and contaminant distribution data. The PRB installation to depths that will be limits of constructability will most likely result in slow-paced field installations with a high likelihood of delays.








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003200


Deeper Ground Water





Not applicable. Since this alternative involves no action it would provide no obstructions to other future action.




Other remedial actions could be easily implemented at the site. However, additional actions would need to be compatible with maintaining a reductive environment in the aquifer to promote biodegradation if this component of natural attenuation was expected to continue to operate.




Other additional remedial actions could be implemented at the site. Other remedial actions may be limited in application of certain technologies near the PRB walls which could damage or reduce the effectiveness of the walls. Likewise, additional actions would need to be compatible with maintaining a reductive environment in the aquifer to promote biodegradation.








Other remedial actions could be implemented at the site. However, additional actions would need to take into account aquifer amendments that might be recovered by the pump and treat system and foul the system or reduce the effectiveness of the air stripping process.



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003201


Deeper Ground Water


e. Ability to Obtain Approvals from Other Agencies f. Availability of Offsite Treatment, Storage, and Disposal Services and Capacity



Not applicable.


This alternative will require access to public and private property to install monitoring wells. This will require approval or authorization from owners/agencies. The extended time period over which it will take PRB walls to address ground water exceeding PRGs may not be acceptable to some stakeholder agencies.

No substantial offsite treatment, storage, and disposal services not required for this alternative. Limited amounts of ground water monitoring well purge water would be generated that would require coordination for treatment or offsite disposal.


This alternative will require access to public and private property. The substantial undertaking to install the PRBs to the 60-ft depths may require specialized large equipment that would require coordination to remove overhead utilities, divert traffic, etc. Additionally, approval to inject ERD amendments into the subsurface would be required. This will require approval or authorization from owners/agencies.

The very large volume of material excavated during the installation of the PRB walls would require offsite disposal. Material generated would not be expected to require disposal as hazardous waste. Volumes generated for offsite disposal and an appropriate disposal location would require additional site specific data and design considerations. Offsite treatment, storage, and disposal services would not be required for the bio barrier component of this alternative.








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003202


Deeper Ground Water





Not applicable. Not applicable.


Drilling contractors for well installation to hire with the appropriate equipment and personnel to accomplish the monitoring well installation tasks for this alternative. These technologies are not specialized, therefore there are various vendors from which to chose.

Not applicable.


Specialty vendors are available to hire for both PRB and ERD applications with the appropriate equipment and specialists to accomplish this alternative. However, it is a rather specialized technology, so there are fewer companies to choose from. Installation to the PRBs to depths of 60 ft bgs would be highly specialized and a vendor capable of executing the work may not be able to be identified.


ERD is a readily available technology but requires some level of pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.



ERD is a readily available technology but requires some level of pilot-scale testing to confirm carbon-source dosing, injection spacing, and other final remedy requirements.





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003203


Deeper Ground Water


a. Capital Costs b. Operating and Maintenance







$344,006.00 $1,692,940.00 $2,036,946.00 $1,425,862.20 $3,055,419.00 No Acceptable


$24,639,667.00 $3,092,791.00 $27,732,458.00 $19,412,720.60 $41,598,687.00 No Acceptable


$1,630,186.00 $5,592,046.00 $7,222,232.00 $5,055,562.40 $10,833,348.00 Yes Acceptable


$3,828,902.00 $9,970,356.00 $13,799,258.00 $9,659,480.60 $20,698,887.00 No Acceptable


8. State Acceptance


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003204

Table 19Cost Summary for Remedial Alternatives

Remedial Action ComponentPreferred Remedy Cost

Alternative OptionNo Action Vapor Mitigation System

Indoor Air $0 381,661.00$ 381,661.00$

Alternative OptionNo Action Thermal Treatment ISCO w/ Follow-On ERD ERD (Gridded)

Source Area Treatment $0 8,018,000.00$ 9,436,000.00$ 8,446,000.00$ 8,018,000.00$

Alternative OptionNo Action ZVI PRB - Multiple

TransectsISCO w/ Follow-On ERD ERD (Bio Barriers) Pump and Treat (1)

Shallow Plume Core & Hot Spot $0 5,774,000.00$ 6,731,000.00$ 1,876,000.00$ 13,509,000.00$ 6,731,000.00$

Alternative OptionNo Action Monitored Natural

AttenuationZVI PRB - Multiple

TransectsERD (Bio Barriers) Pump and Treat (1)

Shallow Plume Periphery $0 1,901,000.00$ 13,926,000.00$ 3,273,000.00$ 13,918,000.00$ 3,273,000.00$

Alternative OptionNo Action Monitored Natural

AttenuationZVI PRB w/ Deep ERD ERD (Bio Barriers) Pump and Treat (1)

Deeper Ground Water $0 2,037,000.00$ 27,732,000.00$ 7,222,000.00$ 13,799,000.00$ 7,222,000.00$

Subtotal of Preferred Alternatives Options 25,625,661.00$

Project Management 589,730.00$ Project Planning Documents (Work Plan, Field Sampling Plan, Quality Assurance Project Plan, Health and Safety Plan) 138,668.00$ Preliminary Design Field Investigation 1,230,019.00$ Ground Water Sampling Program 1,383,910.00$ 5-Year Reviews 240,000.00$

Subtotal of Required Components 3,582,327.00$

Total Remedial Action Cost 29,207,988.00$ Notes:1) The costs shown for pump and treat are the costs to install and operate a treatment plant to address contamination only within each specific plume area (core, periphery, or deep). If a pump and treat option was selected to treat the entire site (core, periphery, and deep), a single system would be installed which would be designed to handle the combined flows. As a result a cost benefit would be derived because each media specific option would not individually incur the full capital cost associated with a pump and treat system. The cost for the combined treatment system has been estimated to be $17,132,000.

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003205

Table 20Final Cleanup Levels for Chemicals of Concern

Media: SoilSite Area: AllAvailable Use: ResidentialControls to Ensure Restricted Use (if applicable): N/A

Chemical of Concern Cleanup Level 1 Basis for Cleanup LevelRisk at Cleanup

Level 2

Tetrachloroethene 3.52 mg/kgProtection of Human

Health Cancer risk = 1 x 10-5

Trichloroethene 0.226 mg/kgProtection of Human


Cis-1,2-Dichloroethene d 24.9 mg/kgProtection of Human


Trans-1,2-Dichloroethene d 37.1 mg/kgProtection of Human


Vinyl chloride d 1.04a / 2.02b mg/kgProtection of Human


Tetrachloroethene 0.327 mg/kgProtection of Ground

Water at MCL Cancer risk = 1 x 10-6

Trichloroethene 0.327 mg/kgProtection of Ground


Cis-1,2-Dichloroethene d 2.18 mg/kgProtection of Ground

Water at MCL HQ=1

Trans-1,2-Dichloroethene d 3.27 mg/kgProtection of Ground

Water at MCL HQ=1

Vinyl chloride d 0.076 mg/kgProtection of Ground


Media: Ground WaterSite Area: AllAvailable Use: ResidentialControls to Ensure Restricted Use (if applicable): N/A

Chemical of Concern Cleanup Level Basis for Cleanup LevelRisk at Cleanup

Level 3

Tetrachloroethene 5 µg/LCompliance with Federal or

State ARARs Cancer risk = 1 x 10-6

Trichloroethene 5 µg/LCompliance with Federal or


Cis-1,2-Dichloroethene 70 µg/LCompliance with Federal or

State ARARs HQ=1

Trans-1,2-Dichloroethene 100 µg/LCompliance with Federal or

State ARARs HQ=1

Vinyl chloride 1 µg/LCompliance with Federal or


Bromoform 80 µg/LCompliance with Federal or


lgonzale

003206

Table 20Final Cleanup Levels for Chemicals of Concern

Media: Indoor Air (Vapor Intrusion)Site Area: AllAvailable Use: Residential

Controls to Ensure Restricted Use (if applicable): N/A

Chemical of Concern Cleanup Level Basis for Cleanup LevelRisk at Cleanup

Level 4

Tetrachloroethene 3.2 µg/m3Protection of Human


Trichloroethene c 12.2 µg/m3 Protection of Human


Cis-1,2-Dichloroethene d 35 µg/m3Protection of Human

Health HQ=1

Vinyl chloride d 1.1 µg/m3Protection of Human


Key

1. Cleanup levels will be to the most stringent standard when there is more than one basis of cleanup.

mg/kg: milligram per kilogramµg/L: microgram per literµg/m3: microgram per cubic meterARARs: Applicable or Relevant and Appropriate RequirementsMCL: Maximum Contaminant LevelHQ: Hazard Quotient

Cleanup Levels for Chemicals of Concern

2. Cleanup levels and residual risk information presented for soil are based on the risk associated with exposure to soil contamination through dermal contact by future on-site residents (lifetime).3. Cleanup levels and residual risk information presented for ground water are based on the risk associated with ingestion of contaminated ground water.4. Cleanup levels and residual risk information presented for indoor air are based on the risk associated with inhalation of contaminated air.a: Cleanup level for child exposure.

The purpose of this response action is to minimize migration of contaminants to ground water and to control risks posed by direct contact with soil and ground water and inhalation of indoor air. The results of the baseline risk assessment indicate that existing conditions at the site pose an excess lifetime cancer risk (ELCR) of 2x10-6 for a future resident's exposure to ground water, an ELCR of 1x10-6 for a future child resident's exposure to ground water, an ELCR range of 1x10-6 to 5x10-3 for an adult exposure to indoor air, and an ELCR range of 1x10-6 to 2x10-3 for a child exposure to indoor air. While sufficient direct soil exposure risk warranting soil cleanup was not identified in the baseline risk assessment, this remedy will address soil contamination to the extent necessary to protect ground water at the federal MCL. Treatment shall be monitored to ensure that cleanup levels are achieved. The site is expected to be available for unrestricted residential land use as a result of the remedy.

d: This compound is a potential COC for this medium.

c: The TCE action level has been calculated based on toxicity values developed by the California Environmental Protection Agency. Reportedly, the U.S. Office of Research and Development has encouraged Regions to use alternate toxicity values for TCE than the those values presented in USEPA's Draft Risk Characterization for TCE, prepared August 2001. USEPA Regions 4 and 8 have stated that they will be using an alternative toxicity value for addressing TCE risks. This alternative value, provided by Cal-EPA has been recommended for use by USEPA Region 4, and is provided here for evaluation of indoor air analytical data.

b: Cleanup level for adult exposure.

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PrimarySource

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Figure 4Site Conceptual ModelFlow-Chart FormGrants Chlorinated Solvents Plume SiteGrants, Cibola County, New Mexico

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Structure With Indoor Air ConcentrationsWithin Tier 2 Action Level

Structure With Indoor Air ConcentrationsAt Or Above Tier 3 Action Level

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Refer to RI Tables 5-3 and 5-4 for indoor air sampling results.

Refer to RI Table 5-5 for soil vapor sampling results andexplanation of data qualifiers.

�� January 2004 Soil Vapor Sampling Location

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Soil Vapor Concentration in �g/m3

PCE = Tetrachloroethene.

TCE = Trichloroethene.

C12 = Cis-1,2-Dichloroethene.

VC = Vinyl Chloride.

B = Benzene.

T = Toluene.

E = Ethylbenzene.

Xm,p = m,p-Xylene.

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MTBE = Methyl Tert-Butyl Ether.

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PCE = tetrachloroethene.

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PCE Concentration Greater Than50,000 �g/L

PCE Concentration Ranging From5,000 �g/L to < 50,000 �g/L

PCE Concentration Ranging From500 �g/L to < 5,000 �g/L

PCE Concentration Ranging From50 �g/L to < 500 �g/L


PCE Concentration Ranging FromLab Detection Limit to < 5 �g/L

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PCE maximum contaminant level (MCL) is 5 �g/L.

Direct-push sampling locations not on the map, or shown without a posted concentration, were non-detect for PCEduring the Phase 1 sampling event. Lab detection limitwas typically 1 �g/L.

L = Reported concentration is below the CRQL.

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Figure 11Structures With VaporIntrusion Mitigation SystemsGrants Chlorinated Solvents Plume Site


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Figure 12Extent of Source AreaTreatmentGrants Chlorinated Solvents Plume Site


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Legend

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Notes:











Source Area

Extent of Source Area Soil Excavation

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Figure 13Conceptual Layout ofISCO with Follow-On ERD(Shallow Plume Core)Grants Chlorinated Solvents Plume Site


�0 100 200 300 400

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Notes:











Source Treatment Area

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ISCO = In-situ chemical oxidation

ERD = Enhanced reductive dechlorination

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003220

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Figure 14Conceptual Layout of ERDBio-Barrier(Shallow Plume Core)Grants Chlorinated Solvents Plume Site


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Figure 15Conceptual Layout of ERDBio-Barrier(Shallow Plume Periphery)Grants Chlorinated Solvents Plume Site


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Bio Barrier for Shallow Plume Core

Shallow ground water plume core bio-barriers shown forreference only, and are not included in costs for peripherybio-barriers

Bio Barrier for Shallow Plume Periphery

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Figure 16Conceptual Layout of ERDBio-Barriers(Deeper Plume)Grants Chlorinated Solvents Plume Site


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003223

Appendix A. Administrative Record Index

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Prepared for

United States Environmental Protection Agency

Region 6

RECORD OF DECISION ADMINISTRATIVE RECORD

for

GRANTS CHLORINATED SOLVENTS SUPERFUND SITE

EPA ID No. NM0007271768

GS09K99BHD0010Task Order No. T0703BG1026

Sairam AppajiRemedial Project Manager

U.S. EPA Region 6

Prepared by

Science Applications International Corporation555 Republic Drive, Suite 300

Plano, TX 75074

JULY 17, 2006

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003225

1

PREAMBLE

The purpose of this document is to provide the public with an index to the AdministrativeRecord File (AR File) for the U.S. Environmental Protection Agency’s (EPA) selected remedialaction to respond to conditions at the Grants Chlorinated Solvents (the “Site”). EPA’s action isauthorized by the Comprehensive Environmental Response, Compensation, and Liability Act(CERCLA), 42 U.S.C. Section 9601 et seq.

Section 113 (j)(1) of CERCLA, 42 U.S.C. Section 9613 (j)(1), provides that judicial reviewof the adequacy of a CERCLA response action shall be limited to the Administrative Record (AR).Section 113 (k)(1) of CERCLA, 42 U.S.C. Section 9613 (k)(1), requires the EPA to establish an ARupon which it shall base the selection of its remedial actions. As the EPA decides what to do at thesite of a release of hazardous substances, it compiles documents concerning the site and it’s decisioninto an “AR File.” This means that documents may be added to the AR File from time to time.After the EPA Regional Administrator or the Administrator’s delegate signs the ActionMemorandum or the Record of Decision memorializing the selection of the action, the documentswhich form the basis for the selection of the response action are then known as the AdministrativeRecord “AR.”

Section 113(k)(1) of CERCLA requires the EPA to make the AR File available to the publicat or near the site of the response action. Accordingly, the EPA has established a repository wherethe AR File may be reviewed near the Site at:

New Mexico State UniversityGrants Campus

1500 Third StreetGrants, New Mexico

Contact: Steven ThomasTelephone:

The public also may review the AR File at the EPA Region 6 office in Dallas, Texas, bycontacting the Remedial Project Manager at the address listed below. The AR File is available forpublic review during normal business hours. The AR File is treated as a non-circulating referencedocument. Any document in the AR File may be photocopied according to the procedures used atthe repository or at the EPA Region 6 office. This index and the AR File were compiled inaccordance with the EPA’s Final Guidance on Administrative Records for Selecting CERCLAResponse Actions, Office of Solid Waste and Emergency Response (OSWER) Directive Number9833.3A1 (December 3, 1990).

Documents listed as bibliographic sources for other documents in the AR File might not belisted separately in the index. Where a document is listed in the index but not located among thedocuments which the EPA has made available in the repository, the EPA may, upon request, includethe document in the repository or make the document available for review at an alternate location.This applies to documents such as verified sampling data, chain of custody forms, guidance andpolicy documents, as well as voluminous site-specific reports. It does not apply to documents inEPA’s confidential file. (Copies of guidance documents also can be obtained by calling theRCRA/Superfund/Title 3 Hotline at (800) 424-9346.)

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2

These requests should be addressed to:

Sairam AppajiRemedial Project Manager

U.S. EPA Region 61445 Ross Avenue

Dallas, Texas 75202-2733(214) 665-3126

The EPA response selection guidance compendium index has not been updated sinceMarch 22, 1991 (see CERCLA Administrative Records: First Update of the Compendium ofDocuments Used for Selecting CERCLA Response Actions [March 22, 1991]); accordingly, it is notincluded here. Moreover, based on resource considerations, the Region 6 Superfund DivisionDirector has decided not to maintain a Region 6 compendium of response selection guidance.Instead, consistent with 40 CFR Section 300.805(a)(2) and 300.810(a)(2) and OSWER Directive No.9833.3A-1 (page 37), the AR File Index includes listings of all guidance documents which may forma basis for the selection of the response action in question.

The documents included in the AR File index are arranged predominantly in chronologicalorder. The AR File index helps locate and retrieve documents in the file. It also provides anoverview of the response action history. The index includes the following information for eachdocument:

• Doc ID- The document identifier number.• Date - The date the document was published and/or released. “01/01/2525" means no

date was recorded.• Pages - Total number of printed pages in the document, including attachments.• Title - Descriptive heading of the document.• Document Type - General identification, (e.g. correspondence, Remedial Investigation

Report, Record of Decision.)• Author - Name of originator, and the name of the organization that the author is

affiliated with. If either the originator name or the organization name is not identified,then the field is captured with the letters “N/A”.

• Addressee- Name and affiliation of the addressee. If either the originator name or theorganization name is not identified, then the field is captured with the letters “N/A”.

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ADMINISTRATIVE RECORD INDEX07/17/2006

ADMINISTRATIVE RECORDSite Name:CERCLIS:OUID:SSID:Action:

GRANTS CHLORINATED SOLVENTSNM0007271768

HERECORD OF DECISION

198864Docid:000001Bates: 000026To:09/01/1993Date:26Pages:PRESUMPTIVE REMEDIES: SITE CHARACTERIZATION AND TECHNOLOGY SELECTION FOR CERCLA SITES WITH VOLATILE ORGANIC COMPOUNDS IN SOIL

Title:

Doc Type: FACTSHEET

Name OrganizationAuthor: NONE, U.S. ENVIRONMENTAL PROTECTION AGENCY

Name OrganizationAddressee: NONE, NONE

103935Docid:000027Bates: 000114To:10/01/1998Date:88Pages:PRELIMINARY ASSESSMENT FOR THE GRANTS CHLORINATED SOLVENTS SITETitle:

Doc Type: REPORT / STUDY

Name OrganizationAuthor: GATTERMAN, DAVID NEW MEXICO ENVIRONMENT DEPARTMENT


934847Docid:000115Bates: 001234To:04/01/2001Date:1120Pages:SITE INSPECTION REPORT FOR THE GRANTS CHLORINATED SOLVENTS PLUME SITE (PART 1)

Title:


Name OrganizationAuthor: NONE, NEW MEXICO ENVIRONMENT DEPARTMENT


Page 1 of 1007/17/2006

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198886Docid:001235Bates: 001317To:04/20/2001Date:83Pages:BUILDING RADON OUT: A STEP-BY-STEP GUIDE ON HOW TO BUILD RADON-RESISTANT HOMES

Title:

Doc Type: FACTSHEET



198837Docid:001318Bates: 001495To:11/01/2002Date:178Pages:OSWER DRAFT GUIDANCE FOR EVALUATING THE VAPOR INTRUSION TO INDOOR AIR PATHWAY FROM GROUNDWATER AND SOILS

Title:

Doc Type: FORM



199036Docid:001496Bates: 001500To:10/29/2003Date:5Pages:[REDACTED] VALIDATED INDOOR AIR SAMPLING RESULTS SUMMARY FOR 10/20/2003 THROUGH 10/29/2003

Title:

Doc Type: SAMPLING / ANALYSIS

Name OrganizationAuthor: NONE, NONE


Page 2 of 1007/17/2006

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163866Docid:001501Bates: 001668To:11/21/2003Date:168Pages:[SOIL - GAS SAMPLING FOR OCTOBER 2003]Title:


Name OrganizationAuthor: THOMPSON, BEN NONE

Name OrganizationAddressee: MINCHAK, JEFF NONE

159760Docid:001669Bates: 002052To:12/01/2003Date:384Pages:SAMPLING AND ANALYSIS PLAN FOR GRANTS CHLORINATED SOLVENTS PLUME SITETitle:

Doc Type: SAMPLING / ANALYSISELECTRONIC RECORD

Name OrganizationAuthor: NONE, SCIENCE APPLICATIONS INTERNATIONAL

CORPORATION GEOMARINE, INCORPORATIONNONE, CH2M HILL

Name OrganizationAddressee: NONE, U.S. ENVIRONMENTAL PROTECTION AGENCY

174944Docid:002053Bates: 002057To:12/23/2003Date:5Pages:TECHNICAL MEMORANDUM: INDOOR AIR SAMPLING RESULTS FOR 10/20/2003 THRUGH 10/21/2003

Title:

Doc Type: REPORT / STUDYELECTRONIC RECORD

Name OrganizationAuthor: MINCHAK, JEFFREY D CH2M HILL

Name OrganizationAddressee: APPAJI, SAIRAM U.S. ENVIRONMENTAL PROTECTION AGENCY

Page 3 of 1007/17/2006

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Title:




163865Docid:002063Bates: 002069To:02/03/2004Date:7Pages:HEALTH CONSULTATION - ATSDRTitle:

Doc Type: HEALTH ASSESSMENT

Name OrganizationAuthor: NONE, U.S. DEPARTMENT OF HEALTH AND HUMAN

SERVICES


174945Docid:002070Bates: 002071To:03/02/2004Date:2Pages:[INDOOR AIR DATA REVIEW OF RESIDENTIAL SAMPLING EVENTS ON 10/20/2003 AND 01/20/2004]

Title:

Doc Type: CORRESPONDENCEELECTRONIC RECORD

Name OrganizationAuthor: RILEY, DAVID U.S. ENVIRONMENTAL PROTECTION AGENCY

Name OrganizationAddressee: APPAJI, SAIRAM U.S. ENVIRONMENTAL PROTECTION AGENCY

Page 4 of 1007/17/2006

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Title:




198559Docid:002078Bates: 002081To:03/01/2005Date:4Pages:VALIDATED INDOOR AIR SAMPLE RESULTS FOR 01/21/2005 THROUGH 01/21/2005Title:

Doc Type: ELECTRONIC RECORDSAMPLING / ANALYSIS



198581Docid:002082Bates: 002082To:04/15/2005Date:1Pages:USGS STATEMENT OF WORK FOR GRANTS CHLORINATED SOLVENTS PLUME SITETitle:

Doc Type: ELECTRONIC RECORDREPORT / STUDY



Page 5 of 1007/17/2006

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195881Docid:002083Bates: 002096To:11/01/2005Date:14Pages:TECHNICAL MEMO: DESCRIPTION OF FS ALTERNATIVES FOR GRANTS CHLORINATED SOLVENTS PLUME SITE

Title:


Name OrganizationAuthor: STERLING, DARNELL NONE

Name OrganizationAddressee: APPAJI, SAI U.S. ENVIRONMENTAL PROTECTION AGENCY

195882Docid:002097Bates: 002099To:11/08/2005Date:3Pages:CONFERENCE CALL MEETING MINUTES - GRANTS FS MEMOTitle:

Doc Type: ELECTRONIC RECORDCORRESPONDENCE



195877Docid:002100Bates: 002607To:12/01/2005Date:508Pages:FINAL REMEDIAL INVESTIGATION REPORTTitle:


Name OrganizationAuthor: NONE, CH2M HILL


Page 6 of 1007/17/2006

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197898Docid:002608Bates: 002621To:12/01/2005Date:14Pages:[RESPONSE TO COMMENTS ON THE DRAFT REMEDIAL INVESTIGATION REPORT FOR GRANTS CHLORINATED SOLVENTS]

Title:




198835Docid:002622Bates: 002634To:12/30/2005Date:13Pages:HEALTH CONSULTATION FOR GRANTS CHLORINATED SOLVENTTitle:

Doc Type: ELECTRONIC RECORDHEALTH ASSESSMENT

Name OrganizationAuthor: NONE, AGENCY FOR TOXIC SUBSTANCES AND DISEASE

REGISTRY


196272Docid:002635Bates: 002637To:01/09/2006Date:3Pages:SITE STATUS SUMMARY FOR GRANTS CHLORINATED SOLVENTSTitle:

Doc Type: ELECTRONIC RECORDFACTSHEET



Page 7 of 1007/17/2006

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197376Docid:002638Bates: 002646To:02/24/2006Date:9Pages:[COMMENTS ON THE DRAFT FS REPORT AND RECOMMENDATIONS OF ALTERNATIVES FOR GRANTS CHLORINATED SOLVENTS PLUME SITE]

Title:


Name OrganizationAuthor: JETTER, STEVE STATE OF NEW MEXICO ENVIRONMENT

DEPARTMENT

Name OrganizationAddressee: APPAJI, SAI U.S. ENVIRONMENTAL PROTECTION AGENCY

198474Docid:002647Bates: 002910To:03/01/2006Date:264Pages:FINAL FEASIBILITY STUDY REPORT FOR GRANTS CHLORINATED SOLVENTS PLUME SITETitle:



NONE, SCIENCE APPLICATIONS INTERNATIONAL CORPORATION GEOMARINE, INCORPORATION

Name OrganizationAddressee: NONE, U.S. ENVIRONMENTAL PROTECTION AGENCY

198834Docid:002911Bates: 002912To:03/16/2006Date:2Pages:COMMENTS ON THE DRAFT ATSDR HEALTH CONSULTATIONTitle:

Doc Type: CORRESPONDENCE

Name OrganizationAuthor: BAHAR, DANA NEW MEXICO ENVIRONMENT DEPARTMENT

Name OrganizationAddressee: MANN, JOHN AGENCY FOR TOXIC SUBSTANCES AND DISEASE

REGISTRY

Page 8 of 1007/17/2006

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198580Docid:002913Bates: 002943To:03/30/2006Date:31Pages:RESPONSE TO COMMENTS ON THE DRAFT FEASIBILITY STUDY REPORTTitle:




198937Docid:002944Bates: 002969To:04/01/2006Date:26Pages:EPA ANNOUNCES PROPOSED PLAN FOR GRANTS CHLORINATED SOLVENTSTitle:

Doc Type: FACTSHEET



198935Docid:002970Bates: 002970To:04/12/2006Date:1Pages:[PUBLIC NOTICE: EPA ANNOUNCES PROPOSED PLAN FOR THE GRANTS CHLORINATED SOLVENTS]

Title:

Doc Type: FACTSHEET



Page 9 of 1007/17/2006

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204145Docid:002970.001Bates: 002970.002To:05/26/2006Date:2Pages:NMED COMMENTS AND RECOMMENDATIONS ON RECORD OF DECISION FOR THE GRANTS CHLORINATED SOLVENTS SITE

Title:

Doc Type: TABLEELECTRONIC RECORD



203745Docid:002971Bates: 003259To:06/30/2006Date:289Pages:RECORD OF DECISION FOR GRANTS CHLORINATED SOLVENTSTitle:

Doc Type: RECORD OF DECISION / AMENDMENT



948605Docid:003260Bates: 003261To:01/01/2525Date:2Pages:[COMMENTS ON DRAFT SAMPLING AND ANALYSIS PLAN]Title:

Doc Type: CORRESPONDENCE

Name OrganizationAuthor: WILLIAMS, DONALD U.S. ENVIRONMENTAL PROTECTION AGENCY

Name OrganizationAddressee: HALLORAN, AMY CH2M HILL

Page 10 of 1007/17/2006

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Appendix B. Cost Estimate for Selected Remedy

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Table B-1Cost Estimate Summary for the Selected Remedy

Remedy Component Item Description Quantity Unit Unit Cost CostInstall 14 Vapor Mitigation Systems LS 425,000.00$ One-time Vapor Pump Replacement 14 EACH 500.00$ 7,000.00$

Vapor Intrusion Mitigation Capital Costs 395,000.00$ Vapor Intrusion Mitigation O&M Costs (see Table B-2) 46,560.00$

NM Gross Receipts Tax (7.5%) 33,120.00$ Vapor Intrusion Mitigation Subtotal 474,680.00$

Vendor Design and Permitting Input LS 150,000.00$ Mobilization and Procurement LS 79,000.00$ Drill and Install Borings, Wells, and Sub-Grade Infrastructure LS 1,523,000.00$ Vapor Cover Installation LS 104,000.00$ Electrical Construction LS 105,000.00$ Mechanical Construction LS 185,000.00$ Vapor and Water Treatment System LS 750,000.00$ Commissioning LS 80,000.00$ Maintenance Hardware, Etc. LS 218,000.00$ Operations Labor, Per Diem LS 417,000.00$ Power ($0.072 per kWh) LS 1,014,000.00$ Process Sampling and Analysis LS 37,000.00$ Waste and GAC LS 32,500.00$ Rental and Fees LS 30,000.00$ Demobilization LS 55,000.00$ Vendor Reporting LS 30,000.00$ Vendor Travel, Office, and Engineering Support LS 647,000.00$ Licensing Fees LS 199,000.00$ Vendor Contingency and Indirect Cost LS 774,000.00$

Total Thermal Source Area Treatment Vendor Costs 6,429,500.00$ Total Thermal Source Area Treatment O&M Costs (see Table B-2) -$

Thermal Source Area Program Management and Support (10%) 643,000.00$ Thermal Source Area Project Design (6% of Capital Costs) 386,000.00$

NM Gross Receipts Tax (7.5%) 559,000.00$ Thermal Source Area Treatment Subtotal 8,017,500.00$

Pre-Construction Activities (Including Pilot-Scale Testing) LS 419,450.00$

Injection and Monitoring Well Construction LS 474,100.00$ Trailer-Mounted Injection System LS 36,000.00$ Initial ISCO Injection - Mobilization LS 51,000.00$ Initial ISCO Injection - Potassium Permanganate 527,793 LBS 1.55$ 818,079.00$ Initial ISCO Injection - Potassium Permanganate Shipping 527,793 LBS 0.13$ 68,613.00$ Initial ISCO Injection - Sodium Thiosulfate (Oxidant Neutralizer) 550 GAL 7.25$ 3,988.00$ Initial ISCO Injection - Sodium Thiosulfate Shipping 1 LOAD 600.00$ 600.00$ Initial ISCO Injection - Water 1,795 1,000 GAL 1.64$ 2,944.00$ Initial ISCO Injection - Mixing Equipment and Material LS 50,000.00$ Initial ISCO Injection - Equipment Setup and Related Expenses LS 59,900.00$ Initial ISCO Injection - Royalties, Construction Management Fees, and Markup LS 126,600.00$ Initial ISCO Injection Labor LS 241,375.00$ Second ISCO Injection - Mobilization LS 22,500.00$ Second ISCO Injection - Potassium Permanganate 263,945 LBS 1.55$ 409,115.00$ Second ISCO Injection - Potassium Permanganate Shipping 263,945 LBS 0.13$ 34,313.00$ Second ISCO Injection - Sodium Thiosulfate (Oxidant Neutralizer) 550 GAL 7.25 3,988.00$ Second ISCO Injection - Sodium Thiosulfate Shipping 1 LOAD 600.00$ 600.00$ Second ISCO Injection - Water 898 1,000 GAL 1.64$ 1,473.00$ Second ISCO Injection - Mixing Equipment and Material LS 5,000.00$

Source Area - Thermal Treatment Capital Costs (vendor price quote with

adjustment for local drilling rates)

Vapor Intrusion Mitigation Capital Costs

Shallow Plume Core and Hot Spot - ISCO With Follow-On ERD Capital Costs

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Table B-1Cost Estimate Summary for the Selected Remedy

Remedy Component Item Description Quantity Unit Unit Cost Cost

Shallow Plume Core and Hot Spot - ISCO With Follow-On ERD Capital Costs Second ISCO Injection - Equipment Setup

and Related Expenses LS 34,000.00$ Second ISCO Injection - Royalties, Construction Management Fees, and Markup LS 61,300.00$ Second ISCO Injection Labor LS 127,700.00$ Primary Performance Monitoring LS 15,000.00$ Reporting LS 31,200.00$ Undefined Scope and Market Allowance LS 464,800.00$

Total ISCO With Follow-On ERD Shallow Plume Core Treatment Capital Costs 3,563,638.00$ Total ISCO With Follow-On ERD Shallow Plume Core Treatment O&M (ERD Treatments) Costs (see Table B-2) 1,933,857.00$

Shallow Plume Core and Hot Spot Treatment Program Management and Support (10%) 549,750.00$ Shallow Plume Core and Hot Spot Project Design (6% of Capital Costs) 213,800.00$

NM Gross Receipts Tax (7.5%) 469,600.00$ Shallow Plume Core and Hot Spot Treatment Subtotal 6,730,645.00$


Injection and Monitoring Well Construction LS 355,600.00$ Trailer-Mounted Injection System LS 36,000.00$ Undefined Scope and Market Allowance LS 96,360.00$

Total ERD Shallow Plume Periphery Treatment Capital Costs 738,730.00$ Total ERD Shallow Plume Periphery Treatment O&M (ERD Treatments) Costs (see Table B-2) 1,989,050.00$

Shallow Plume Periphery Treatment Program Management and Support (10%) 272,800.00$ Shallow Plume Periphery Project Design (6% of Capital Costs) 44,320.00$

NM Gross Receipts Tax (7.5%) 228,370.00$ Shallow Plume Periphery Treatment Subtotal 3,273,270.00$


Injection and Monitoring Well Construction LS 837,500.00$ Trailer-Mounted Injection System LS 36,000.00$ Undefined Scope and Market Allowance LS 170,520.00$

Total ERD Deep Plume Treatment Capital Costs 1,307,290.00$ Total ERD Deep Plume Treatment O&M (ERD Treatments) Costs (see Table B-2) 4,729,000.00$

Deep Plume Treatment Program Management and Support (10%) 603,630.00$ Deep Plume Project Design (6% of Capital Costs) 78,440.00$

NM Gross Receipts Tax (7.5%) 503,880.00$ Deep Plume Treatment Subtotal 7,222,240.00$

RD/RA Project Management 589,730.00$ Project Planning Documents (Work Plan, QAPP, HASP) 138,668.00$ Preliminary Design Field Investigation 1,230,019.00$ Ground Water Sampling Program 1,383,910.00$ Five-Year Reviews 180,000.00$

Required RD/RA Components Subtotal 3,522,327.00$

Total Present Worth Estimated Cost of Preferred Remedy 29,240,662.00$

Notes

LS = Lump SumGAL = GallonLBS = PoundkWh = Kilowatt-hourQAPP = Quality Assurance Project PlanHASP = Health and Safety Plan

Capital cost estimates are not discounted because the construction work will be performed in the first year. O&M costs are reported as present worth estimates given a 7% discount rate over the duration of the respective treatment period (6 years for shallow plume core; 20 years for shallow plume periphery; 20 years for deep plume). O&M costs are detailed in subsequent Tables B-2 and B-3. Cost estimates are based on estimated quantities and assumptions described in the Feasibility Study, and may be refined following the Preliminary Design Field Investigation and during the Remedial Design. Cost estimates are within +50 to -30% accuracy expectation.

Shallow Plume Periphery - ERD Bio Barriers Capital Costs

Deep Plume Treatment - ERD Bio Barriers Capital Costs

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Table B-2Estimated O&M Costs for the Selected Remedy

Remedy Component Item Description Quantity Unit Unit Cost Cost Present Worth O&M Cost 1

Five-Year Indoor Air Sampling Event LS 38,118.00$ Ten-Year Indoor Air Sampling Event LS 38,118.00$

Vapor Intrusion Mitigation O&M Costs 76,236.00$ Present Worth Cost of $38,118 expended during years 5 and 10 at 7% discount rate = 46,560.00$

Thermal Source Area Treatment O&M Costs No O&M Costs for Thermal Treatment -$ -$

Thermal Source Area Treatment O&M Subtotal -$ -$ Injection Mobilization; Site Trailer LS 12,000.00$ Emulsified Edible Oil 121 DRUM 1,050.00$ 127,050.00$ Emulsified Edible Oil - Shipping 2 LOAD 1,200.00$ 2,400.00$ Water 875 1,000 GAL 1.64$ 1,435.00$ Rentals, Equipment, and Materials LS 6,500.00$ Injection Labor LS 167,280.00$ Reporting LS 24,850.00$

Performance/Effectiveness Monitoring LS 64,200.00$ Total ISCO With Follow-On ERD Shallow Plume Core Treatment O&M Costs 405,715.00$

O&M Period 6 YearsPresent Worth Cost of $405,715 per year for 6 years at 7% discount rate = 1,933,900.00$

Shallow Plume Periphery - ERD O&M Costs Injection Mobilization; Site Trailer LS 9,000.00$

Emulsified Edible Oil 66 DRUM 1,050.00$ 69,300.00$ Emulsified Edible Oil - Shipping 2 LOAD 1,200.00$ 2,400.00$ Water 317 1,000 GAL 1.64$ 519.88$ Rentals, Equipment, and Materials LS 9,500.00$ Injection Labor LS 62,320.00$ Reporting LS 24,850.00$

Performance/Effectiveness Monitoring LS 56,800.00$ O&M Period 20 Years

Total ERD Shallow Plume Periphery Treatment O&M Costs 234,689.88$ Total Annual Shallow Plume Periphery Treatment O&M Costs (Injection Every 15 Months) 187,751.90$

Present Worth Cost of $187,752 per year for 20 years at 7% discount rate = 1,989,050.00$

Deep Plume - ERD O&M Costs Injection Mobilization; Site Trailer LS 21,000.00$ Emulsified Edible Oil 184 DRUM 1,050.00$ 193,200.00$ Emulsified Edible Oil - Shipping 6 LOAD 1,200.00$ 7,200.00$ Water 1,000 1,000 GAL 1.64$ 1,640.00$ Rentals, Equipment, and Materials LS 14,000.00$ Injection Labor LS 190,240.00$ Reporting LS 48,900.00$

Performance/Effectiveness Monitoring LS 81,800.00$ O&M Period 20 Years

Total ERD Deep Plume Treatment O&M Costs 557,980.00$ Total Annual Deep Plume Treatment O&M Costs (Injection Every 15 Months) 446,384.00$

Present Worth Cost of $446,384 per year for 20 years at 7% discount rate = 4,729,000.00$ Notes1: Present value costs use a discount rate of 7% over the O&M performance period.2: Vapor mitigation system O&M costs include indoor air sampling after 5 years and 10 years. Present value costs assume a 7% discount rate.Thermal source area treatment does not have an O&M component as costs are expected to be incurred during the first year of the RA.LS = Lump SumGAL = Gallon

Vapor Intrusion Mitigation O&M Costs 2

Shallow Plume Core and Hot Spot - ISCO With Follow-On ERD O&M (ERD Treatments) Costs

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Appendix C. NMED Concurrence With

the Selected Remedy

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06/19/06 _15:07_FAX_ 5058272965 GROUND WATER BUREAU |gj002

•?State of New Mexico

ENVIRONMENT DEPARTMENTOffice of the Secretary

Harold Runnels Building

*' im St-Francis Drive> p-°-Box 2611°Sattta Fe, New Mexico 87502-6110

'- " Telephone: (505) 827-2855BILL RICHARDSON pnr. fc(ic\ 017 joi* RON CURRY

GOVERNOR FaX- (5°5) S27~2836 SECRETARY

DERRITH WATCHMAN-MOOREDEPUTY SECRETARY

June 16,2006

Mr. Samuel J. Coleman, P.E.DirectorSuperfund DivisionUSEPA Region 61445 Ross Avenue, Suite 1200Dallas, TX 75202-2733

RE: Concurrence on Record of Decision for the Grants Chlorinated Solvents Plume SuperfundSite, Grants, New MexicoEPA CERCLIS ID #NM007271768

Dear Mr. Coleman,

The New Mexico Environment Department (NMED) has reviewed the United States EnvironmentalProtection Agency's (EPA) Draft Record of Decision (ROD) for the Grants Chlorinated SolventsPlume Superfund Site located in Grants, New Mexico.

NMED concurs with the remedial 3.ctions outlined in the draft ROD to address contaminationassociated with this Site including:

1. Indoor Air - Vapor Mitigation System2. Source Area-Thermal Treatment3. Shallow Ground Water Plume and Hot Spot - In-Situ Chemical Oxidation (ISCO) with

Follow-On Enhanced Reductive Dechlorination (ERD)4. Shallow Ground Water Plume Periphery-ERD5. Deeper Ground Water contamination - ERD

NMED appreciates EPA's acceptance of a 1 x 10~5 risk factor for soil and vapor intrusion clean uplevels which are in line with NMED risk based clean up guidance. In addition, NMED is pleased withthe aggressive treatment technology selected to address Indoor Air Vapor Intrusion, the Source Areaand the Shallow Ground Water Plume Core and Hot Spot

NMED's concurrence is based on (he facts presented in the draft ROD and on available-data collectedto date. NMED understands that any changes to the selected remedy will require NMED concurrence.

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06/19/0615:08 FAX 5058272965 GROUND WATER BUREAU@003

Mr. Samuel J. ColemanJune 16,2006Page 2

Please note that based upon the current available site data, NMED does not support the contingency inthe draft ROD for potentially using EJ thanced Reductive Dechlorination (ERD) as a stand alonetechnology in the Shallow Ground Water Plume Core and Hot Spot Area as it may adversely impactthe overall effectiveness and timeframe of the clean up. Similarly, at this time, it is NMED's positionthat the contingency in the draft ROD for the potential use of Monitored Natural Attenuation as aremedial strategy for the Shallow Ground Water Plume Periphery and Deeper Ground Watercontamination is not appropriate for ttie same reasons listed above. NMED also understands that anynew information associated with this site, including adverse health risks or data regarding the extent ofcontamination and migration of contaminants, identified during subsequent design investigations andnot presented in this draft ROD will be addressed by EPA as part of this Superfund site.

This draft ROD is a culmination of cooperative work conducted by the EPA and NMED. As in thepast, NMED project staff will continue to work closely with EPA staff on design and implementationof the remedy. NMED appreciates uhe continued supportive working relationship with EPA in thesematters. If you have any questions, please call me at (505) 827-2855, or Steve letter of my staff at(505) 827-2334.

Sim

RC:sj

cc: Sai Appaji, EPA Remedial Project ManagerDon Williams, EPA, Team LeaderDana Bahar, NMED Superfrmd Oversight Section ManagerSteve Jetter, NMED Projec: Manager

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Appendix D. Responsiveness Summary

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Stakeholder Issues and Lead Agency Responses

NMED Comments

Comment 1 In reference to the Land and Ground Water Use Assumptions - NMED emphasizes that

the New Mexico Water Quality Control Commission (NMWQCC) Regulations, NMAC

20.6.2.4101.A(1) requires that all ground water of the State of New Mexico with a TDS of

<10,000 mg/l be remediated or protected for use as domestic and agricultural water

supply. Although the contaminated ground water (from 5 to 80 ft bgs) at the site is not

currently used as a drinking water supply, there are no enforceable institutional controls

that would prohibit the use of this aquifer, now or in the future, as a drinking water

supply. The fact that three shallow private wells exist within the site boundaries is

evidence that the aquifer can be used for beneficial use. As proposed, ground water

must be remediated to the more stringent requirements of the Federal Safe Drinking

Water standards (MCLs) and/or NMWQCC standards.

EPA Response:

Comment noted. EPA’s final clean up levels for the COCs at this Site is federal MCL

and NMWQCC standards.

Comment 2 Preliminary Remediation Goals and use of 1x10-4 excess lifetime cancer risk (ELCR) as

the targeted cleanup level - The National Contingency Plan established a targeted risk

level 1 x 10-6 as a “point of departure” for determining remediation goals. There has

been no justification presented by EPA to modify this targeted risk level and justify the

use of a less stringent risk-based clean up level. At a minimum, an ELCR of 1 x 10-5 and

an HI of 1 which is consistent with the NMWQCC Regulations and NMED’s Technical

Background Document for Development of Soil Screening Levels, Revision 3.0, August 2005,

should be used for establishing targeted cleanup levels for indoor air and soil. NMED

requests that the PRGs for COCs in soil and from vapor impacts be established using at

least a 1 x 10-5 ELCR and an HI of 1 and a residential land use scenario.

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EPA Response:

1E-06 is the point of departure, and EPA has the flexibility to modify cleanup levels for

carcinogens within the range of 1E-06 to 1E-04, especially when considering site-specific

conditions. This is indicated in the NCP (40 CFR 300.430(e)(2)(i)(A)(2 ):

“For known or suspected carcinogens, acceptable exposure levels are generally concentration

levels that represent an excess upper bound lifetime cancer risk to an individual of between 10-4

and 10-6 using information on the relationship between dose and response.”

The EPA agrees with NMED’s concerns regarding uncertainties at the Site and will take

Remedial Action at the lower risk level (1x10-5).

Comment 3 In reference to risk and the preliminary remediation goals. NMED does not support the

use risk based clean up levels that are less stringent than residential clean up levels for

this site. The site is located in a mixed commercial and residential use area and there are

no enforceable institutional controls that can be implemented to restrict future land use.

Therefore, the more restrictive clean up levels, i.e. residential, should be used.

EPA Response:

EPA will use NMED’s Guidance document (Technical Background Document for

Development of Soil Screening Levels, Revision 3.0, August 2005) on Soil Screening

Levels to establish clean up levels based on residential use.

Comment 4 In reference to the flexible approach in selection of the final remedy for the Shallow

Plume Core and Hot Spot Area - NMED is concerned with how the final selection

between ISCO and ERD will be determined due to the difficulties associated with

detecting the DNAPL in the field. NMED is concerned that a significant amount of time

and expense could be expended without conclusively determining whether or not

DNAPL is absent from this area. In addition, the pre-design investigations proposed in

the Feasibility Study did not include investigation activities associated with determining

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the nature and extent of DNAPL but instead concentrated on definition of the dissolved

phase plume and soil contamination in the two source areas. As stated in the RI report

and in literature on the subject, it is generally assumed that DNAPL is present if ground

water exceeds 1 to 5 percent of the chemicals solubility limit in water and the dissolved

PCE concentrations observed within the Plume Core Area are as high as 35%. At this

concentration it should be assumed that DNAPL is present in close proximity to the

sample locations and ISCO is better suited for this condition. Finally, because ISCO with

follow-on ERD alternative addresses the entire plume through the installation of a grid

pattern of wells the ISCO alternative is more amenable to treating the Core

Plume/Hotspot area verses the passive nature of diffusion associated with the ERD

alternative. If residual DNAPL is present between the ERD bio-barriers, the likelihood

of effective and timely clean-up using the ERD bio-barrier alternative is greatly reduced.

Therefore, NMED may not support the use of ERD as the stand alone remedial

technology for the Shallow Plume Core and Hot Spot area.

EPA Response:

EPA’s policy is to treat principal threats posed by the Site through use of treatment

technologies. By utilizing treatment as a significant portion of the Selected Remedy, the

statutory preference for remedies that employ treatment as a principal element is

satisfied. The EPA agrees and will select ISCO with Follow-On ERD (Flexible) treatment

approach for the Shallow Plume Core and Hot Spot for the following reason:

Thermal treatment at the Source Area is expected to achieve complete removal of

principal threat waste. After Source Area treatment is complete and if it can be

demonstrated that the principal threat waste no longer exists in the Shallow Plume Core

and Hot Spot area then the EPA will re-evaluate the two treatment technologies

(ISCO/with Follow-On ERD or ERD alone) to determine which one of these better meets

the Statutory Preference for Treatment. Based on this determination the EPA will

implement either of the two technologies to address the Shallow Plume Core and Hot

Spot Area.

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Community Comments

The following comments were received from members of the public that were in

attendance at the Proposed Plan public meeting held on April 20, 2006.

Comment 1 How was the contamination originally verified at the GCSP Site?

EPA Response:

The NMED-PSTB discovered chlorinated solvents in ground water at the GCSP Site

during a UST investigation at the Allsup’s 200 gas station in 1993. Following the

discovery, NMED conducted two years of ground water monitoring at the Allsup’s

monitoring wells to verify contamination.

Comment 2 Are the depths of the City Drinking Water wells known?

EPA Response:

Yes. City well Grants B-40 is screened at a depth from 246 feet (ft) below ground surface

(bgs) to 346 ft bgs and the total depth of the well is 367 ft bgs. The second City well,

Grants B-38, is screened between 149 ft bgs and 300 ft bgs and the total depth of this well

is 300 ft bgs. Both of these wells are upgradient and are located approximately 1.5 miles

northwest of the GCSP Site.

Comment 3 Are the City wells located in the same aquifer that is impacted at the GCSP Site?

EPA Response:

No. The contamination at the GCSP Site is in a shallow aquifer and the vertical extent is

not fully known at this time. The City drinking water wells pump water from much

greater depths, and are upgradient of the GCSP Site. The maximum depth at which

contamination was detected during the RI is 85 ft bgs. The EPA will fully characterize

the maximum depth of contamination during the Pre-Design Field Investigation.

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Comment 4 Is the project funded for the Remedial Design?

EPA Response:

Yes. Funding for Remedial Design has been planned for fiscal Year 2006.

Comment 5 Are there many other sites in the country similar to Grants?

EPA Response:

Yes. There are a number of other Superfund sites in the country that are similar to

Grants. In New Mexico alone there are five sites, including the GCSP Site, where EPA is

cleaning up ground water contaminated with chlorinated solvents. These five sites

include Fruit Avenue Plume, Albuquerque; North Railroad Avenue Plume, Espanola;

McGaffey and Main, Roswell; Griggs and Walnut, Las Cruces; and the GCSP Site,

Grants.

Comment 6 Is the bio-barrier wall a physical wall installed underground?

EPA Response:

Bio-barrier walls are not actual physical walls but function as a wall when nutrients are

injected across sections of the plume. Injection points are closely spaced along a line

across the plume, such that the aquifer between each injection point is filled with the

injected oxidant or carbon source amendment. When the oxidant or carbon source

amendments are injected into the ground they permeate into the aquifer and begin

treating the ground water.

Zero-valent iron permeable reactive barriers are actual physical walls constructed of iron

filings installed within trenches dug across the plume. The walls required for the GCSP

Site would be as thick as 36 inches and up to 60 ft deep. A zero-valent iron permeable

reactive barrier was considered as one of the alternatives for the Site but was not chosen

as the Selected Remedy.

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Comment 7 Will the public be notified when a final decision is made regarding the Preferred

Remedy?

EPA Response:

Yes. The EPA will notify the community of the final selection of the remedy after it

reviews and responds to all the comments received during the comment period.

Newspaper notification will be made in the local newspaper when the Record of

Decision is signed.

6

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Appendix E. NRRB Comments and EPA Region 6 Responses

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UNITED STATES ENVIRONMENTAL PROTECTION AGENCYDALLAS, TX 75202

MEMORANDUM

SUBJECT: Response to the National Remedy Review Board (NRRB) Comments for theGrants Chlorinated Solvents Plume Superftmcf Site

FROM: Samuel Coleman, DirectorNational Remedy Review Board

^THROUGH: Donald WilliamsTeam Leader, Supefund Division

TO:

Purpose

David E. Cooper, ChairNational Remedy Review BoardU.SEPA

This memorandum documents the Region 6's response on the Grants ChlorinatedSolvents Plume Site (Site) comments received from the NRRB's advisory committee.

NRRB Comments and EPA Region 6 Responses

NRRB Comment 1The site information package acknowledges that data characterizing subsurface conditions,contaminant distribution, fate and transport, and risk are limited. These unknowns producesignificant uncertainties in the selection, design, and implementation of remedial options andthe estimated costs and time frames associated with these options. The Board recommendsthat the Region consider a ROD that contains a phased approach that allows flexibility inremedy design and implementation as additional characterization and performancemonitoring data become available. For example, Phase 1 could include actions to eliminateexposure to vapors intruding into homes and thermal treatment of the source area. Phase IIcould include remediation of the Shallow Ground Water Plume Core and Hot Spot Area,along with shallow ground water peripheral plume and deep ground water actions.

NRRB Comments and Region 6 Responses

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EPA Region 6 Response to Comment 1Region 6 agrees with the Board comment and believes that a phased approach and a RODproviding flexibility during Remedial Design (RD) and implementation will work better atthe Site. Using a phased approach, additional site characterization data collected during theearly phases will allow a more detailed evaluation of how best to implement subsequentphases and will streamline the work effort and provide the greatest opportunity for costsavings.

A phased approach would allow data collection efforts conducted during early phases ofwork to provide the evidence necessary to support the selection of MNA for certain portionsof the Site. The ROD for the Site will have a contingency to switch to MNA if it can bedemonstrated as an effective alternative.

NRRB Comment 2The Board notes there is uncertainty regarding the existence of dense non-aqueous phaseliquids (DNAPL) in the Shallow Plume Core and Hot Spot Area. As a result, the Boardunderstands the concern expressed by the State of New Mexico that the enhanced reductivedechlorination (ERD) remedy may not be sufficiently effective. Therefore, the Boardrecommends that the Region consider the results of Phase 1 (as recommended in comment #1above) and investigate the presence or-absence of DNAPL in the Shallow Plume Core andHot Spot Area prior to implementing a final remedy, for this area.

EPA Region 6 Response to Comment 2Region 6 agrees with the Board recommendation and has selected the more aggressiveISCO/with follow-on ERD for the Shallow Plume Core and Hot Spot Area. However, theROD will be flexible enough to revert to using only ERD if conditions warrant. EPA Region6 will evaluate ground water data after source removal and if it can be demonstrated thatDNAPL no longer exists then EPA with NMED's concurrence will implement only the ERDcomponent for the Shallow Plume Core and Spot Area.

NRRB Comment 3The Board recommends, based on the results of Phase I and the investigations for thepresence or absence of DNAPL, that the Region consider evaluating an alternative whichuses ISCO followed by a less extensive ERD component for the Shallow Plume Core andHot Spot Area. If ISCO is used to treat the Shallow Plume Core and Hot Spot Areaaggressively, ISCO could address the potential DNAPL and significantly reduce the highconcentrations of volatile organic compounds (VOCs) in ground water. The ERDcomponent could then be optimized, which should result in a reduced number of wells, thusreducing cost. This approach would likely eliminate the bulk of the VOC contaminationquickly, but may result in a longer timeframe to achieve cleanup levels. This approach maystill be protective and consistent with the NCP expectation to restore ground water tobeneficial use in a time frame that is reasonable given the particular circumstances of the site(e.g., given that the shallow aquifer is not currently being used).


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EPA Region 6 Response to Comment 3The EPA Region 6 agrees with the board recommendation and has structured the ROD to beflexible in applying treatment in the Shallow Plume Core and Hot Spot Area.

NRRB Comment 4The Board recommends that the Region further evaluate the implementation of ISCO as aremedial alternative in the Source Area. In the ISCO alternative presented to the Board forthe Source Areas, significant costs are included for soil excavation and disposal, as well astrench dewatering and water treatment. However, the soil excavation and disposal followedby trench dewatering and treatment components may not be required. ISCO can be aneffective option for remediating organic contaminants in the unsaturated zone and its use inunsaturated zones is becoming increasingly common, thereby eliminating the need toexcavate and dispose of contaminated soils. ISCO also could be used to treat organiccompounds in water that collects in trenches. Oxidant injection and mixing directly in thetrench, would be easily implementable and likely to be successful at this site for oxidizingthese contaminants, as well as for providing residual oxidant to the underlying aquiferthrough infiltration. Potential limitations to using the ISCO technology at the site givensubsurface conditions at the site (soil, geologic, and hydrologic settings), as expressed by theNew Mexico Environmental Department (NMED), also need to be considered. Furtherevaluation of these technical issues is recommended.

EPA Region 6 Response to Comment 4EPA Region 6 agrees with the Board recommendation and further evaluated the ISCOalternative for the Source Area. However, given the soil conditions at the site Region 6believes that Thermal Treatment is a better technology than ISCO for treating the SourceArea. Thermal Treatment will remove the principal waste in a relatively very short timeframe compared to ISCO that will require at least six years.

NRRB Comment 5The Board agrees with the Region's preference not to include a zero-valent iron permeablereactive barrier as part of the preferred alternative. The clay and thin sandy layers present atthe site may not lend themselves to this technology. Smearing of the clay along the face ofthe trench during excavation could significantly decrease permeability. Also, a barriercontaining 100% iron and constructed to depths of 60 feet would need further study todemonstrate implementability and effectiveness. The Board recommends that the Regioninclude a discussion of the potential limitations of installing such a deep trench and the likelydecrease in permeability due to the 100% iron composition of the barrier in the decisiondocuments to further explain its preference against this alternative.

tEPA Region 6 Response to Comment 5Comment Noted. The ZVI-PRB alternative is very expensive and would be extremelydisruptive to the community when installed in a residential area. The recommendeddiscussion will be provided in the decision document.

NRRB Comment 6As part of the Region's preferred alternative presented to the Board, vapor intrusionmitigation systems would be installed in three residential structures. Long-term indoor air


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monitoring would be undertaken at a larger number of residences situated above the groundwater plume. Given the high costs of air monitoring in relation to the mitigation systems, theBoard recommends that the Region consider expanding the installation of mitigation systemsto all residences potentially impacted by indoor air contamination. In the event that long-term monitoring is chosen, homes above and in the proximity of the ground water plume,especially the homes near the Source Area, should be monitored to take into accountpreferential subsurface pathways that may exist at this site. The Board also recommends thatthe Region consider taking action under removal authorities at those occupied residenceswith vapor intrusion risks exceeding 1 x 10"4 lifetime excess cancer risk.

EPA Region 6 Response to Comment 6Region 6 agrees with the Board's recommendation and has plans to install vapor mitigationsystems in all homes potentially impacted by indoor air contamination (14 homes).However, the Region prefers to address vapor intrusion under its Remedial authority, as therisk is more a long term issue than imminent.

NRRB Comment 7The Region's preferred remedial alternative for indoor air consists of the installation of three

vapor mitigation systems and an indoor air monitoring program for a minimum period of fiveyears. If the Region decides to implement the air monitoring program as described to theBoard, then indoor air samples will be collected from within 14 structures overlying thegroundwater plume where it exceeds a concentration of 1,000 ug/1 perchloroethylene (PCE)in ground water. The Board suggests that the area to be considered for indoor air monitoringalso be based on concentrations of trichloroethylene (TCE) in ground water. The Boardrecommends this because the Region's indoor air preliminary remediation goals (PRGs) arebased on PCE and TCE, and the risks from TCE appear to be driving the indoor air responseaction more than PCE. The Board also recommends that the Region not define the study areatoo narrowly, considering the uncertainties in the correlation between TCE concentrations inground water and vapor concentration.

EPA Region 6 Response to Comment 7The text of the FS report was modified to provide for indoor air monitoring of structuresoverlying portions of the ground water plume exceeding PCE and/or TCE concentrations ofl,OOOug/L.

NRRB Comment 8It is unclear from the package presented to the Board whether benzene, toluene,ethylbenzene, xylene, and methyl tert-butyl ether (MTBE) are contaminants of concern forthe site, because they are related to a different source and are being addressed by NMED-Petroleum Storage Tank Bureau. Similarly, the package does not provide much informationon bromoform, but it is also identified as a contaminant of concern. The Region should beclear in decision documents whether these contaminants are actually contaminants of concernfor the site. If they are, then remedial goals addressing these contaminants should bedeveloped.


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EPA Region 6 Response to Comment 8MTBE was not identified as a contaminant of concern (COC) for site ground water withinthe Baseline Human Health Risk Assessment Report (BHHRA). BTEX compounds wereidentified as COCs for the site within the BHHRA, but the FS report discusses the fact that.the BTEX compounds are being addressed separately under the NMED Petroleum StorageTank Bureau (PSTB). BTEX compounds that are co-mingled in the chlorinated solventplume will be addressed as part of the remedy. However, Region 6 is concerned that BTEXremedial goal will not be attained in areas that are not co-mingled. Therefore no specificremedial goals have been set for BTEX.

Bromoform was identified in samples submitted to the Contract Laboratory Program (CLP)labs during the Remedial Investigation, but was not detected in split samples submitted to aseparate laboratory. Bromoform is not considered a common laboratory contaminant, but isone of three trihalomethane compounds commonly associated with water disinfectionprocesses. A determination of the presence or absence of bromoform in site ground water isanticipated during the Preliminary Field Investigation.

NRRB Comment 9The Board recommends that the cost estimates provided be reviewed and, as appropriate,revised to ensure accuracy and consistent consideration of costs in the decision documents.The following are specific concerns identified by Board members that should, at a minimum,be addressed in this cost review:

a. Ground water pump and treat costs for the three zones are shown as individualcost estimates in the package. The decision documents should also containinformation on the cost for pump and treat as a stand-alone, site-wide remedy.

. . This alternative can clarify that all ground water pump and treat costs are notcumulative; for example, the cost to install the treatment plant will not be incurreda second time if pump and treat is selected for both Shallow Ground Water PlumeCore and Deeper Ground Water.

b. The thermal treatment costs are not sufficiently itemized and appear to be low,based on the experience of other Regions.

c. The costs to conduct five-year review evaluations appear to be over-estimatedbased on the experience of other Regions.

d. The O&M for vapor intrusion remediation should not be zero, as the cost ofblower replacements should be considered.

e. It was unclear to the Board how cost of treatability studies was included.f. Costs for the ISCO alternative for the Source Area appear to be over-estimated

based on the experience of other Regions. See comment 4 on components thatmay warrant reconsideration.

EPA Region 6 Response to Comment 10The EPA has reviewed the cost estimates as recommended by the Board and has thefollowing responses to the specific concerns raised by the Board:

a. Region 6 has evaluated the pump and treat costs for the three zones as a stand-alone, site-wide remedy. However, based on site characteristics, the region didnot include this stand-alone remedial alternative in the Record of Decision.


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b. The thermal treatment costs are based on two separate vendor quotes and wereincreased based on the contractor's experience with costs for drilling in NewMexico. The vendors did not provide a detailed breakdown of costs but thecontractor has provided a more detailed cost estimated to Region 6. One potentialreason for a reduced estimated cost for thermal treatment at the GCSP site is thelow permeability of the shallow aquifer leading to a low flux of recharge waterthrough the treatment zone which otherwise create a significant cooling effect.

c. The Five-Year Review costs are comparable to other sites in the region. Theregion expects that after the first Five-Year Review subsequent review costs to belower.

d. The region has included O&M Costs for vapor mitigation systems and providedthese in the Record of Decision.

e. Treatability studies (pilot-scale tests) of applicable treatment technologies wereincluded in the estimated costs for 'Pre-Construction Activities' within thesummary cost tables provided in the FS report.

f. Region 6 has requested the experts at the National Risk Management ResearchLaboratory, Ada, OK, to review costs for the ISCO alternative in the Source Area.Any revisions to the estimated costs will be updated as part of the RemedialDesign.

NRRB Comment 10 .Based on the information presented to the Board, the Board understands that the Region hasbeen planning to implement the remedy in the primary Source Area while leaving therelatively large building housing the dry cleaner in place. Because the effectiveness of theshallow ground water remedy is dependent on thorough removal of the Source Area, theRegion should fully evaluate the effectiveness of any remedy for the area under the building.

EPA Response to Comment 10While Source Area treatment would be greatly simplified (and less expensive) without anoverlying building, the thermal treatment and the other alternatives considered in the FS areeffective even with the building in place. The region evaluated the implementation of theSource Area remedy without the dry cleaner building in place. However, cleanup can beaccomplished without removing the building. This reduces EPA costs and any hardship tothe business related to removing the building.

NRRB Comment 11The Board notes that the New Mexico soil screening guidance is not an Applicable orRelevant and Appropriate Requirement (ARAR). It might be a "to be considered" guidanceunder the National Contingency Plan for the soil cleanup itself. The Board recommends thatthe Region explain the role, if any, of the soil screening guidance in selecting soil cleanuplevels for ground water protection, where maximum contaminant levels are ARARs at thissite.

EPA Response to Comment 11Region 6 agrees that New Mexico soil screening levels (SSLs) are not ARARs, but they areTo-Be-Considered (TBC) criteria. However, NMED has clearly stated that because of the


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residential setting at the site soil cleanup should be performed to protect the public fromexposure to contaminated soil.

NRRB Comment 12The preferred alternative includes monitored natural attenuation (MNA) as a contingentremedy. However, no data were presented to the board to demonstrate that MNA isoccurring or will occur in the future; consequently, the Board cannot evaluate the

• effectiveness of MNA. However, based on the presentation and discussion at the meeting,the Board recommends that the Region consider MNA as a component of the preferredalternative which will follow active remediation rather than as a contingent remedy if theactive remedy does not work. Active remediation can be used to significantly reduce themass of contamination, with the MNA component used to achieve final cleanup levels. TheBoard recommends that the Region clarify in the decision documents how MNA may betriggered and its technical basis, consistent with Use of Monitored Natural Attenuation atSuperfund, RCRA, Corrective Action, and Underground Storage Tank Sites, OSWERDirective 9200.4-1 IP, April 21, 1999.

EPA Response to Comment 12Region 6 will evaluate the site conditions to determine if monitored natural attenuation(MNA) is a viable remedial alternative during the Five-Year Review reporting period. Oncesource control has been established in the source areas and Shallow Ground Water Plumedata indicates evidence of MNA, EP.A, with NMED concurrence, may switch from the activeremedy to MNA for the Shallow Ground Water Periphery and Deeper Ground WaterPlume. The ROD for the site documents the stated language.

NRRB Comment 13The.Board notes that one of the costs associated with site cleanup appears to be payment ofState tax on engineering services. The Board encourages the Region's efforts in workingwith the State to reach agreement on issues involving a waiver of this tax. The Boardrecommends for this situation that the Region ensure that the New Mexico tax be handled ina manner that is consistent with the Agency's ongoing cost management initiative.

EPA Response to Comment 12Comment noted. Region 6 will continue to pursue relief from the tax where appropriate withthe New Mexico Department of Taxation and Revenue regulations.

Region 6 thanks the NRRB for the recommendations and appreciates the value it bringsto the Superfund Program. Please call me at (214) 665-6701 should you have any questions.

cc: M. Cook (OSRTI)E. Southerland (OSRTI)S. Bromm (OSRE)

' J. Woolford (FFRRO)Rafael Gonzalez (OSRTI)NRRB members


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