technical memo: comparison of perched zone treatment alternatives at site, w… · ·...

Oneida Total Integrated Enterprises of 7

317 E. Main Street Ventura, CA 93001

Tel: (805) 585-2110 Fax: (805) 585-2111

TECHNICAL MEMORANDUM

DATE: December 20, 2016

PREPARED FOR: Rose Marie Caraway, Remedial Project Manager/Environmental Scientist

U.S. Environmental Protection Agency, Region 9 75 Hawthorne Street, SFD 7-2 San Francisco, California 94105

PREPARED BY: Lindsey Larsen, Environmental Scientist, OTIE

John Wingate, PE, Project Manager, OTIE Sonja Donaldson, Regulatory Specialist, OTIE

RE: Comparison of Perched Zone Treatment Alternatives

Pemaco Superfund Site, Maywood, California

1.0 INTRODUCTION Oneida Total Integrated Enterprises, LLC. (OTIE) prepared this Technical Memorandum (TM) for the United States Environmental Protection Agency (U.S. EPA) under contract with the United States Army Corps of Engineers contract number W912PL-13-D-0017, Task Order 0002. The U. S. EPA is currently implementing the Long-Term Response Action at the Pemaco Superfund Site (the Site) located in Maywood, California, as shown in Figure 1.

The Perched Zone has been treated using high vacuum dual phase extraction (HVDPE) since 2007. Concentrations of major volatile organic compounds (VOCs) in Perched Zone groundwater have been reduced by an average of 99% from their maximum concentrations identified in the Record of Decision (ROD) (U.S. EPA, 2005). Several VOCs remain above their respective site-specific remediation levels (SSRLs); therefore, HVDPE treatment continues beyond the ROD-forecasted treatment period of five years and some VOCs appear to have reached asymptotic concentrations. This TM considers potential optimization alternatives that may improve protectiveness, reduce costs, improve technical operation, and facilitate site closure.

The ROD identified additional treatment alternatives including Enhanced In Situ Bioremediation (EISB), In Situ Chemical Oxidation (ISCO), and Monitored Natural Attenuation (MNA) that may provide options to augment treatment of VOCs impacting Site groundwater (U.S. EPA, 2005).

The objective of this TM is to present a technical, administrative, and relative cost comparison between, EISB, ISCO, HVDPE, optimized HVDPE, and MNA to determine whether augmentation of HVDPE treatment will accelerate the cleanup. The objective is reached through a qualitative comparison of conceptual design, overall effectiveness, implementability, advantages, disadvantages, estimated time to reach remedial action objectives (RAOs), costs, and sustainability for each treatment alternative.

SEMS-RM DOCID # 1163831

Technical Memorandum Comparison of Perched Zone Treatment Alternatives


of 7 Oneida Total Integrated Enterprises

2.0 SITE BACKGROUND AND ENVIRONMENTAL SETTING 2.1 PERCHED ZONE REMEDIAL ACTION HISTORY AND CURRENT STATUS The ROD divided the Site into three remediation zones, each with a selected remedy as summarized in Table 1.

Table 1 ROD Remedial Zones and Selected Remedies Remediation Zone Selected Remedy

Surface and near-surface soil remediation zone (0 – 3 feet below ground surface [bgs]) Soil capping

Upper vadose-zone soil and Perched Zone groundwater (3-35 feet bgs) High-vacuum dual-phase extraction

Lower vadose-zone soil and Exposition Aquifer groundwater

Electrical resistance heating to thermally treat highest contamination zone (35 – 100 feet bgs); In-situ treatment of groundwater to augment cleanup, if needed; Vacuum enhanced groundwater extraction for the areas of the plume between 10 - 1,000 parts per billion (trichloroethene [TCE]); and Monitored natural attenuation for areas of the plume below 10 parts per billion (TCE).

The ROD established the following RAOs for Site Groundwater:

• Restore groundwater quality in Perched groundwater zone and Exposition Zones to drinking water standards (Maximum Contaminant Levels [MCLs]);

• Prevent vertical migration of contaminants of concern (COCs) from the Perched groundwater and deeper Exposition Zones at rates that would cause groundwater to exceed drinking water standards;

• Prevent further offsite migration of contaminated groundwater beneath adjacent properties; and

• Prevent migration of contaminated groundwater to local production wells.

To accomplish these objectives, the U.S. EPA adopted SSRLs for each remediation zone based on contaminant MCLs, preliminary remediation goals, dilution attenuation factors, and site-specific hydrogeologic conditions.

2.1.1 Remedial Action Activities HVDPE has been used since 2007 to remediate the upper vadose zone soils and Perched Zone groundwater. The system experienced approximately one year of downtime from April 2012 to April 2013 due to expiration of the Los Angeles County Sanitation District sewer discharge permit. The Site treatment plant has operated full-time since April 1, 2013.

Current operation of the Perched Zone DPE wells occurs approximately biweekly in “pulsed” or intermittent operational mode with an uptime goal set at 40 percent to maximize vapor-phase contaminant extraction while minimizing unnecessary power consumption by the extraction blowers.

Technical Memorandum Comparison of Perched Zone Treatment Alternatives Pemaco Superfund Site, Maywood, California


Since the COC concentrations in the Perched Zone have been reduced to relatively low levels (Section 2.2), intermittent operation optimizes contaminant removal by using downtime to allow contaminant diffusion into pore spaces, rather than a continuous operation schedule that eventually promotes extraction of mostly uncontaminated air. A subset of the Perched Zone HVDPE wells is selected for operation each quarter based on analytical data and corresponding capture zones for each HVDPE well (OTIE, 2016a).

2.2 NATURE AND EXTENT OF CONTAMINATION IN THE PERCHED ZONE The ROD lists tetrachloroethene (PCE), trichloroethene (TCE) and vinyl chloride (VC) as the most prevalent COCs in the Perched Zone groundwater, with hot spot areas of these plumes exceeding concentrations of 1,000 μg/L (U.S. EPA, 2005). Perched Zone contaminant plumes are described as extending up to 250 feet to the south and up to 200 feet southwest of the Pemaco property.

Groundwater contaminant concentrations and distribution in the Perched Zone have changed since the 2005 ROD due to remedial activities and contaminant migration. Analytical results from the July 2016 Semiannual Groundwater Monitoring Event provides the most current characterization of the Perched Zone (OTIE, 2016b). Eighteen Perched Zone wells were sampled during the July 2016 semiannual sampling event and samples were analyzed for VOCs and 1,4-dioxane. The COCs with concentrations that exceeded the SSRLs in the Perched Zone were naphthalene, PCE, TCE, cis-1,2-dichloroethene (DCE), VC, 1,1-DCE, and 1,4-dioxane.

The Perched Zone is characterized by widely distributed 1,4-dioxane detections above the Notification Level1 of 1 µg/L (Figure 2). The remaining COCs with SSRL exceedances were detected in groundwater samples from wells in the central region of the former Pemaco property, extending from PC-06 in the east bordering the Los Angeles River to PB-03 in the west towards the center of the Park. Numerous dry wells in the Perched Zone, especially in the southern region of the Pemaco property and offsite to the south, reduce the ability to evaluate the extent and continuity of COC plumes in this Zone. During the July 2016 semiannual monitoring event, 22 of the 52 Perched Zone wells gauged were dry.

Floating free product has been observed in well PD-04 since approximately December 2014. The quantity of free product observed during semiannual groundwater monitoring events has fluctuated based on operation of the extraction wells. An 18-inch layer of floating free product was observed in well PD-04 during the July 2016 monitoring event. Analytical results from the sample collected at PD-04 showed detections of benzene and benzene-related compounds and naphthalene (150 μg/L). A grab sample was collected from PD-04 in February 2015 and analyzed using U.S. EPA method 8270C for semi-volatile organic compounds. The chromatograph from that analysis suggests that the free product observed in PD-04 is comparable to weathered diesel or highly weathered gasoline (OTIE, 2015).

3.0 TREATMENT ALTERNATIVES This TM considered four treatment alternatives that were identified in the ROD as effective technologies: ISCO, EISB, HVDPE, and MNA. In addition, this TM also considers an Optimized HVDPE alternative. These five treatment alternatives are reevaluated in an effort to identify optimization strategies that would expedite remediation of remaining COCs in the Perched Zone. HVDPE has reduced

1 The ROD defined an SSRL of 3 μg/L for 1,4-dioxane in the Perched Zone based on the California Division of Drinking Water Notification Level (Notification Level) established in 1998 (U.S. EPA, 2005). The State revised the Notification Level in 2010 to 1 μg/L.




concentrations of COCs in the Perched Zone to near-asymptotic levels except in the vicinity of PC-06 and PD-04 (Section 2.2).

3.1 REMEDIAL ALTERNATIVE DESCRIPTIONS

3.1.1 EISB EISB involves injecting an organic substrate (electron donor) that supports microbiological processes that degrade chlorinated solvents in the subsurface. The micro-organisms, either indigenous or inoculated, utilize the substrate to facilitate metabolizing organic contaminants in groundwater, converting them to innocuous end products. EISB treatment would include collecting and analyzing groundwater samples to monitor the bioremediation process. The contaminant concentrations and general chemistry parameters (selected anions, degradation by-products, and environmental indictors) would be documented prior to and following the injection activity.

Reductive dechlorination is one of the primary attenuation mechanisms by which chlorinated groundwater plumes can be remediated. This process involves sequential degradation of PCE to TCE to cis-1,2- DCE to VC to ethene. Reductive dechlorination is not effective for treating non-chlorinated compounds such as 1,4-dioxane and benzene.

Recent research has identified microorganisms that can biodegrade 1,4-dioxane either co-metabolically in the presence of a fuel or alcohol substrate such as tetrahydrofuran, propane, methane, 1-butanol (Li, M., J. Mathieu, Y. Yang, S. Fiorenza, Y. Deng, Z. He, J. Zhou, and P.J.J. Alvarez [Li et al.], 2013) or metabolically (Mahendra, S., Alvarez-Cohen, L. [Mahendra and Alvarez-Cohen], 2005). Biodegradation of 1,4-dioxane is a relatively new development that is being tested at the bench scale in engineered bioreactors (U.S. EPA, 2014), but full-scale implementation of EISB for 1,4-dioxane treatment at the Pemaco Site would require a site-specific pilot test.

3.1.2 ISCO ISCO involves injecting a selected oxidizing agent into the subsurface and collecting and analyzing groundwater samples to monitor the degradation process. The contaminant concentrations and general chemistry parameters pertinent to the process such as total organic carbon, peroxide, chloride, sulfate, manganese, and ferrous iron; and environmental indicators such as pH, specific conductivity, oxidation-reduction potential, and turbidity are documented prior to and following the injection events. Long-term monitoring includes additional parameters such as natural attenuation indicators (e.g., dissolved gases and selected anions). ISCO is a proven technology for reducing VOCs such as PCE, TCE, DCE isomers, and VC, but also 1,4-dioxane from the same treatment event.

3.1.3 Continued HVDPE The ROD estimated that the Perched Zone treatment system would operate for five years, followed by an additional five years of monitoring (U.S. EPA, 2005). Perched Zone HVDPE wells have been operating at the Site since 2007. COC concentrations in the Perched Zone are generally decreasing (OTIE, 2016b). However, based on the concentration trend forecast for well PC-06 (Graph 1), COCs including PCE and TCE will require at least four to eight additional years of HVDPE operation to reach their respective SSRLs. The continued HVDPE alternative assumes operation of the current Perched Zone HVDPE system without modification.



3.1.4 Optimized HVDPE Optimized HVDPE would include construction of additional extraction wells and associated infrastructure in the vicinity of PD-04 to assist with free product removal. This would expand the radius of influence for HVDPE to increase and expedite mass removal.

3.1.5 MNA MNA is a remedial alternative that relies on natural attenuation processes to achieve site-specific remediation objectives within a time frame similar to active remediation. MNA includes a variety of physical, chemical, or biological processes that passively reduce the mass, toxicity, mobility, volume, and/or concentration of contaminants in soil or groundwater. These in situ processes may include biodegradation, dispersion, dilution, sorption, volatilization, radioactive decay, and chemical and or biological stabilization, transformation, or destruction of contaminants (U.S. EPA Office of Solid Waste and Emergency Response [OSWER], 1999).

MNA is commonly used in conjunction with an active remediation system such as pump and treat or EISB in hot spot areas. MNA is also typically used in low concentration areas or as a polishing step after active remediation has reduced contamination to relatively low concentrations and active remediation is no longer cost effective.

Previous investigation at the Pemaco Site provides evidence that bioattenuation of chlorinated ethenes is naturally occurring in both the Perched and Exposition Zones (T N & Associates, Inc. [TN&A], 2003). Biodegradation of 1,4-dioxane has not been investigated at the Site. Chlorinated solvent sites with 1,4-dioxane releases, such as Pemaco, may be suitable for MNA as a long-term remedy if it can be verified that there are no potential receptors and that beneficial uses will not become impaired over the planned timeframe of the MNA (Mohr, Thomas K.G., Julie A. Stickney, and William H. DiGuiseppi [Mohr et al.], 2010).

4.0 COMPARISON OF ALTERNATIVES Comparison of EISB, ISCO, HVDPE, Optimized HVDPE, and MNA was performed in Table 2. Each treatment alternative was compared according to the following key factors: conceptual design description; effectiveness; implementability; advantages; disadvantages; estimated time to achieve RAOs; relative cost; and sustainability. The main conclusions for each treatment alternative are provided in Section 5.

5.0 CONCLUSIONS AND RECOMMENDATIONS Based on the comparisons provided in Table 2, the following conclusions for each treatment alternative are presented:

• Previous investigation at the Pemaco Site provides evidence that EISB for treatment of chlorinated ethenes is a viable remediation alternative in the Perched Zone (TN&A, 2003). EISB may reduce the time it would take to achieve Perched Zone RAOs in localized areas of elevated VOC contamination, potentially reducing the HVDPE operating period and improving sustainability by reducing energy demand and waste generation. However, semiannual monitoring data from July 2016 indicates that VOC concentrations at the target EISB injection area in the vicinity of PC-06 are below the concentration threshold generally considered economically justifiable for EISB technology. In addition, EISB efficacy has not been evaluated for 1,4-dioxane at the Site, nor would EISB be effective for treating the free product in well PD-04.




Continued operation of HVDPE would likely be required to address the sitewide presence of 1,4-dioxane and the free product in PD-04;

• ISCO is highly effective for treating all VOCs and 1,4-dioxane and is therefore considered to be more applicable for use in the Perched Zone than EISB. Similar to EISB, ISCO may not be an economically justifiable treatment technology for the relatively low COC concentrations in the Perched Zone. In addition, ISCO would not be effective for treating the free product in well PD-04 and continued operation of HVDPE in this area would be required;

• HVDPE has reduced COC concentrations in the Perched Zone by an average of 99%. The HVDPE system has been retrofitted with a variable frequency drive to reduce energy consumption; nevertheless, the system is energy intensive and requires long-term operations and maintenance. Implementation of an alternative treatment that would reduce the duration of HVDPE operation will reduce long-term costs and improve the sustainability of the remedy. EISB, ISCO, and Optimized HVDPE treatment alternatives require capital investment costs and would be initially more expensive than continued operation of the current HVDPE system;

• Optimized HVDPE will not accelerate reduction of COC concentrations in the vicinity of well PC-06. However, Optimized HVDPE is the only alternative which would accelerate cleanup of persistent free product in well PD-04 and potentially reduce the long-term operation of the HVDPE system; and

• MNA is a viable long-term remedy if it can be verified that there are no potential receptors and that beneficial uses will not become impaired over the planned timeframe of the remedy. However, significant additional research would be required to assure these conditions can be met. Under these two conditions, MNA is the least costly and most sustainable alternative. MNA is not an applicable remedy for treatment of free product and continued operation of HVDPE in the vicinity of well PD-04 would be required.

Treatment of the free product in well PD-04 is the limiting factor for accelerating remediation of Perched Zone groundwater. Optimized HVDPE is the only treatment alternative capable of addressing the PD-04 free product. Consequently, Optimized HVDPE is the treatment alternative with the highest probability of reducing the overall duration of HVDPE operation, reducing long-term costs, and improving the sustainability of the remedy.

U.S. EPA will turn over operation of the remedy to the State of California in August 2018. This administrative boundary condition establishes a minimum period of time, roughly 1.5 years, in order to install and/or implement the Optimized HVDPE or another treatment alternative for this zone.

6.0 REFERENCES Li, M., J. Mathieu, Y. Yang, S. Fiorenza, Y. Deng, Z. He, J. Zhou, and P.J.J. Alvarez (Li et al.). 2013.

Widespread Distribution of Soluble Di-Iron Monooxygenase (SDIMO) Genes in Arctic Groundwater Impacted by 1,4-dioxane, Environmental Science and Technology, ACS Publications, August 2.

Mahendra, S., Alvarez-Cohen, L., (Mahendra and Alvarez-Cohen). 2005. Pseudonocardia dioxanivorans sp. nov., a novel actinomycete that grows on 1,4-Dioxane. Int. J. Syst. Evol. Microbiol. 55.



Mohr, Thomas K.G., Julie A. Stickney, and William H. DiGuiseppi (Mohr et al.). 2010. Environmental Investigation and Remediation: 1,4-Dioxane and Other Solvent Stabilizers. CRC Press.

Oneida Total Integrated Enterprises, LLC. (OTIE). 2015. Semiannual Groundwater Monitoring Report, December 2014 Monitoring Event for Pemaco Superfund Site, Maywood, California. December.

_____. 2016a. 2015 Annual Operations Report for Pemaco Superfund Site, Maywood, California. August.

_____. 2016b. Semiannual Groundwater Monitoring Report, July 2016 Monitoring Event for Pemaco Superfund Site, Maywood, California. October 13.

T N & Associates, Inc. (TN&A). 2003. Technical Memorandum, Pemaco Data Evaluation for Natural Attenuation and Biodegradation of Chlorinated Ethenes. January.

United States Environmental Protection Agency (U.S. EPA) Office of Solid Waste and Emergency Response (OSWER). 1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites. OSWER Directive 9200.4-17P.

_____. 2014. Technical Fact Sheet – 1,4-Dioxane. January.

_____. 2005. Record of Decision for Pemaco Maywood Superfund Site, Maywood, California. U.S. EPA ID: CAD980737092. January 13.

FIGURES Figure 1 Site Location Map

Figure 2 Chemicals of Concern in Groundwater, Perched Zone, July 2016

TABLES (AFTER TEXT) Table 2 Comparison of Treatment Alternatives for Perched Zone Groundwater

GRAPHS Graph 1 Perched Zone Well PC-06 Concentrations of COCs in Groundwater 2012 to 2016

FIGURES

CAUFORNIA

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~ Maywood Riverfront Part< Boundary

~ Former Pemaco Property

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B-10

B-11

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B-29

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B-25

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PD-08PD-09

PA-01PA-02

PA-03

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PA-05

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PB-02PB-03PB-04

PB-05PB-06

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1. This groundwater gradient map represents dynamicconditions during DPE.

2. Five DPE wells were operating during Q4 2013,including PB-01, PB-02, PC-06, PD-04, and PD-08.Four DPE wells, PB-01, PB-02, PC-06, and PD-04,werepumping during groundwater level collection. Thesewells were not used for contouring.

3. Wells screened in intervals below the perched zone arenot shown in this figure.

4. All groundwater elevations are expressed in feet abovemean sea level.

DPE = dual phase extractionNS = not surveyed as a value engineering option during June 2013 re-survey effortU.S. EPA = United States Environmental Protection Agency,

Region 9

PA-02

PB-01

DA-1

50 μg/L TCE Isoconcentration Contour, 'A' Zone(Dashed Where Inferred)

50 μg/L TCE Isoconcentration Contour, 'B' Zone(Dashed Where Inferred)

500 μg/L TCE Isoconcentration Contour, 'B' Zone(Dashed Where Inferred)

Groundwater Flow Direction(December 2013)

Date:

File:

Pemaco Superfund SiteMaywood, California

Figure 2Chemicals of Concern in Groundwater

Perched Zone, July 2016

November 2016

Pem_Site_COC_JulySA16.dwg

NOTES:

1. All analyte concentrations are expressed in μg/L.2. Wells without a chembox were not sampled during the July

2016 groundwater monitoring event.3. Red highlighting indicates a result that exceeds the SSRL.4. Bold font indicates an anlytical detection.5. Groundwater SSRLs (μg/L):

1,1-DCA: 5 1,1-DCE: 6 Benzene: 1 cis-1,2-DCE: 6 Naphthalene: 6.2 PCE: 5 TCE: 5 VC: 0.5

CA Department of Public Health Notification Levels (μg/L): 1,4-Dioxane: 1

FP = free product in wellU.S. EPA = United States Environmental Protection Agency,

Region 9SSRL = Site Specific Remediation Levelμg/L = micrograms per liter1,1-DCA = 1,1-Dichloroethane1,1-DCE = 1,1-Dichloroethenecis-1,2-DCE = cis-1,2-DichloroethenePCE = TetrachloroetheneTCE = TrichloroetheneVC = Vinyl ChlorideN = normal sampleU = not detected above laboratory detection limitJ = estimated value

Grayed Wells indicate Abandoned orInaccessable

Dry

B-33

Former Pemaco Property

Maywood Riverfront Park Boundary

Site Fencing

Dry Indicates less than six inches of water in wellWells have a 6 inch sump

PC-05

B-38 U.S. EPA, Monitoring Well, Exposition Aquifer

U.S. EPA, Extraction Well, Individual Screensfor the 'Perched' Zone

PB-03 U.S. EPA, Normally Active Extraction Well,Individual Screens for the 'Perched' Zone

FP

TABLES

Table 2 – Comparison of Treatment Alternatives for Perched Zone Groundwater Pemaco Superfund Site, Maywood, California

Oneida Total Integrated Enterprises Table 2 Comparison of Treatment Alternatives for Perched Zone Groundwater

Pemaco Superfund Site, Maywood, California Page 1 of 2

Treatment Alternative

Conceptual Design / Description Effectiveness Implementability Key Advantages Key Disadvantages

Estimated Time to Reach RAOs Relative Cost Sustainability

Enhanced In Situ Bioremediation (EISB)

• Implemented at well PC-06 due to highest Perched Zone chlorinated VOC concentrations

• Injection of substrate mixture via 2 injection wells located near PC-06

• Monitoring for a minimum of 2 additional years after achieving RAOs

• HVDPE must continue to operate at well PD-04 to remove free-product

• Traditional EISB targeted for chlorinated ethenes is not effective for 1,4-dioxane. Biodegradation of 1,4-dioxane through co-metabolic processes is relatively new development and would require an additional pilot study

• Not applicable to free-product at well PD-04

• Recent decreases in VOC concentrations suggest EISB may not be economically justifiable

• CA WDR permit required • Coordination with City of

Maywood due to impacts on Maywood Riverfront Park

• Hollow-stem auger drilling technology proven

• The Pemaco EISB Pilot Study conclusions indicate EISB would be effective at the Site

• Decreased HVDPE operating cost (assumes fewer active extraction wells)

• Probable longer-term treatment and less rebound than w/ ISCO

• Potential for incomplete dechlorination of chlorinated ethenes to VC, a more toxic and mobile breakdown product

• Physical limitations of substrate delivery in heterogeneous subsurface; potential for post-treatment residual contamination in less permeable areas

• Would continue to operate HVDPE at well PD-04

2 - 3 years

• Design/Capital: Medium

• Long-Term Operation / Monitoring: Medium

• Decreased energy demand from HVDPE treatment system

• Decreased waste generated from GAC

• Increased IDW and materials for drilling/installation of injection wells

In Situ Chemical Oxidation (ISCO)

• Implemented at well PC-06 due to highest Perched Zone COC concentrations

• Injection of oxidant using direct push points near well PC-06

• Monitoring for a minimum of 2 additional years after achieving RAOs

• HVDPE must continue to operate at well PD-04 to remove free-product

• Highly effective for all Perched Zone COCs after baseline oxidant demand is met

• CA WDR permit required • The oxidant demand is

unknown; high concentrations of certain metals and other organic carbon could consume a considerable amount of chemical oxidant

• Coordination with City of Maywood due to impacts on Maywood Riverfront Park

• Direct push method proven

• Near immediate reduction in concentrations

• Direct push method would not leave permanent structures in the Park, unlike EISB

• Potentially high oxidant demand for resident soil

• Requires handling of hazardous chemicals

• Physical limitations of oxidant delivery in heterogeneous subsurface; potential for post-treatment residual contamination in less permeable areas

• Not considered cost-effective for free-product removal at PD-04

< 1 year

• Design/Capital: Medium

• Long-Term Operation / Monitoring: Medium

• Decreased energy demand from HVDPE treatment system

• Decreased waste generated from GAC

• Decreased IDW and materials from direct push method, compared to EISB

High Vacuum Dual-Phase Extraction (HVDPE)

• Utilizes existing wells and infrastructure

• Timeframe based on forecasted concentrations at PC-06 (Graph 1)

• Effective removal of all Perched Zone COCs

• GAC is not an effective method of treatment for low molecular weight VOCs or COCs with low adsorptive capacity, such as 1,4-dioxane

• Maintain existing LACSD discharge permit

• Nothing new to implement

• Proven technology • Reliable method to reduce

COC mass and prevent offsite migration

• Known limitations

• Current GAC system does not effectively treat 1,4-dioxane

• Diminishing returns; increasingly expensive to remove diffuse groundwater concentrations

• Energy demand • O&M requirement (personnel,

utilities, security, etc. to maintain treatment plant)

4 - 8 years • Design/Capital: None

• Long-Term Operation / Monitoring: High

• High energy demand to operate HVDPE wells and treatment system

• Discharge water to sanitary sewer system (requiring additional energy demand for treatment)

Table 2 – Comparison of Treatment Alternatives for Perched Zone Groundwater Pemaco Superfund Site, Maywood, California

Oneida Total Integrated Enterprises Table 2 Comparison of Treatment Alternatives for Perched Zone Groundwater

Pemaco Superfund Site, Maywood, California Page 2 of 2

Treatment Alternative

Conceptual Design / Description Effectiveness Implementability Key Advantages Key Disadvantages

Estimated Time to Reach RAOs Relative Cost Sustainability

Optimized HVDPE

• Install additional two additional HVDPE wells in the vicinity of the free product in PD-04

• Extend infrastructure to join wells with existing treatment plant

• Optimized design differs from current HVDPE in that it more aggressively remediates free product removal from PD-04

• Increased effectiveness of free product removal compared to current HVDPE due to increased radius of influence

• Coordinate with City of Maywood for park encroachment

• Decreased time to remove free product from Perched Zone, accelerating cleanup

• No permitting required

• Park disruption • Energy demand • O&M requirement (personnel,

utilities, security, etc. to maintain treatment plant)

• Would not accelerate cleanup of COCs in PC-06

2 – 4 years* *time for free product removal from Perched Zone, allowing for transition to MNA

• Design/Capital: Medium-High

• Long-Term Operation / Monitoring: Medium-High

• Increased IDW and materials for well drilling and installation

• Higher energy demand in the short-term; reduced energy demand long-term

• Initial increased GAC and IDW waste

Monitored Natural Attenuation (MNA)

• Reliance on natural attenuation processes to achieve RAOs

• Assumes cessation of current HVDPE

• Evidence of biodegradation of 1,4-dioxane lacking; assumed attenuation primarily based on dilution and dispersion

• Assumed long term effectiveness for chlorinated ethenes in Perched Zone based on previous study (TN&A, 2003)

• Requires determination of applicability and confirmation that there are no currently exposed receptors and that beneficial uses will not become impaired over the planned timeframe of the MNA

• Would not be implemented in areas containing free product

• No permitting requirements • Potentially smaller

environmental footprint (less generated waste, surface disturbance, and energy use)

• Low cost

• Potentially longer remediation timeframes compared to more “active” technologies

• Does not address free product at PD-04

10+ years • Design/Capital: None

• Long-Term Operation / Monitoring: Low

• Lowest energy used • Lowest IDW and

materials required • Minimized disturbance

Notes: Acronyms: CA WDR = California State Water Resources Control Board Waste Discharge Requirements; COC = contaminant of concern; GAC = granular activated carbon; IDW = investigation-derived waste; LACSD = Sanitation Districts of Los Angeles County; O&M = operation and maintenance; RAOs = remedial action objectives; VOC = volatile organic compound. References: T N & Associates, Inc. (TN&A). 2003. Technical Memorandum, Pemaco Data Evaluation for Natural Attenuation and Biodegradation of Chlorinated Ethenes. January.

GRAPHS

0

50

100

150

200

250

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3504/1/20

12

8/1/20

12

12/1/201

2

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13

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4/1/20

14

8/1/20

14

12/1/201

4

4/1/20

15

8/1/20

15

12/1/201

5

4/1/20

16

8/1/20

16

12/1/201

6

4/1/20

17

8/1/20

17

12/1/201

7

4/1/20

18

8/1/20

18

12/1/201

8

4/1/20

19

8/1/20

19

12/1/201

9

4/1/20

20

8/1/20

20

12/1/202

0

4/1/20

21

8/1/20

21

12/1/202

1

4/1/20

22

Concen

tration (µg/L)

Date

Graph 1Perched Zone Well PC-06

Concentrations of COCs in Groundwater 2012 to 2016 Pemaco Superfund Site, Maywood, California

Benzene PCE TCE Cis‐1,2‐DCE1,1‐DCE 1,1‐DCA VC 1,4‐DioxaneND PCE trendline TCE Trendline 1,1‐DCE Trendline

1,4‐Dioxane Trendline PCE Trendline

COC = contaminant of concernND = Not Detected at the detection limitDCA = dichloroethaneDCE = dichloroetheneTCE = trichloroethenePCE = tetrachloroethene

technical memo: comparison of perched zone treatment alternatives at site, w… · ·...

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