ms. addie walker · 2017. 7. 31. · arcadis.com ms. addie walker july 31, 2017 page: 3/3 the...

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Ms. Addie Walker July 31, 2017

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shallow vadose zone soils (0-2 ft) are Industrial RSLs. The established media clean-up standards for deeper vadose zone soils are the Protection of Groundwater MCL-based soil screening levels (SSLs) (USEPA 2017). Also, Table 5-1 has been revised to include vadose zone soil for each alternative.

The language in Section 2.2.2 has been modified to clarify the presence of 1,1,1-TCA in vadose zone soils at locations WCSS-1 and WCSS-2 at concentrations above the applicable Protection of Groundwater MCL-based SSL. Additionally, it is noted that 1,1,1-TCA is generally not present in groundwater downgradient of the former MHA, the FFS process was implemented assuming that an ongoing source to groundwater exists in this area. Specifically, implementation of the ERD remedy in the Plant 1 area as described in the FFS uses an adaptive design approach, allowing modification based on conditions observed.

The text in Section 5.1.3 has been revised to include the No Action component for vadose zone soil.

Comment: The proposed cost ranges for each alternative are too broad. Please revise to give more specific cost analyses.

Response: The comparative analysis process described in the FFS and summarized on Tables 5-1 and 5-2 evaluates the complete implementation program and entire life cycle cost for each remedial alternative. Each alternative is composed of multiple components, either implemented concurrently or in separate phases, and represents a timeframe of activities spanning multiple decades. Arcadis’ strategy is to design and implement remedial actions with a dynamic and flexible approach to most effectively and efficiently respond to changing conditions encountered during remedy implementation. Utilizing a dynamic approach and allowing for some uncertainties and data gaps, it is very difficult to accurately predict life cycle costs with detailed precision for activities spanning multiple decades. For these reasons, relative costs are presented in $500,000 increments, which we believe is a meaningful framework for evaluation of options at this scale. In order to provide more detail for the alternatives presented in Tables 5-1 and 5-2, costs are presented for both the short-term action and long-term monitoring components.

Comment: Presentation of 3M's preferred alternative should not be included in the FFS itself but may be included in the cover letter to the report. Please revise.

Response: Section 6 has been revised to present a comparative evaluation of the alternatives for Plant 1 and Plant 2. Recommendations for a preferred alternative are not presented.

Comment: The remedial technology considered for each media should be clearly listed on the evaluation table.

Response: The media addressed by each remedial technology has been added to Tables 5-1 and 5-2.

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Ms. Addie Walker July 31, 2017

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The comment letter also states that the revised FFS should be submitted on or before August 1, 2017.

If you have any questions, please call me at (864) 987-3918 or email me at [email protected].

Sincerely,

Arcadis U.S., Inc.

Thomas Darby II, P.G. Senior Hydrogeologist

Copies:

Jeannie Martin – 3M (electronic) James Kotsmith – 3M (electronic) Lance Hauer – GE

Arcadis U.S., Inc.

10 Patewood Drive

Suite 375

Greenville

South Carolina 29615

Tel 864 987 3900

Fax 864 987 1609

www.arcadis.com

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Ms. Addie Walker South Carolina Department of Health and Environmental Control Bureau of Land and Waste Management 2600 Bull Street Columbia, South Carolina 29201

Subject:

Focused Feasibility Study – Revision 1 Laurens CeramTec Site: ID #5094

Dear Ms. Walker:

Arcadis U.S., Inc. (Arcadis), on behalf of 3M Company (3M), is submitting this Focused Feasibility Study Report (FFS) for the Laurens CeramTec Site (ID #5094) located in Laurens, South Carolina. The FFS presents a comparative analysis of alternatives for Plants 1 and 2. The highest-ranking alternative for Plant #1 includes a combination of No Action for vadose soil, Enhanced Reductive Dechlorination (ERD) and Monitoring Natural Attenuation (MNA) for groundwater and Institutional Controls. The highest-ranking alternative for Plant 2 includes ERD, Soil Vapor Extraction (SVE), Biosparging, MNA and Institutional Controls. Arcadis recommends the implementation of these highest-ranking alternatives for Plants 1 and 2.

Should you have any further questions regarding this document, please contact me at (864) 987-3918 or email me at [email protected].

Sincerely,

Arcadis U.S., Inc.

Thomas Darby II, P.G. Senior Hydrogeologist

Copies:

Jeannie Martin – 3M James Kotsmith – 3M Lance Hauer – GE

ENVIRONMENT Date:

July 31, 2017 Contact:

Thomas Darby II, P.G. Phone:

864-987-3918 Email:

[email protected] Our ref:

WI001459.0005.00001

3M Company

FOCUSED FEASIBILITY STUDY Laurens CeramTec Site: ID #5094

September 2016

July 2017 – Revision 1

FOCUSED FEASIBILITY STUDY

arcadis.com FFS_3M Laurens_Rev 1_Final 073117.docx i

CONTENTS Acronyms and Abbreviations ........................................................................................................................ iv

1 Introduction ............................................................................................................................................. 1

2 Site Background ...................................................................................................................................... 1

2.1 Previous Remedial Actions ............................................................................................................. 2

2.1.1 Plants 1 and 2 Wastewater Pond Closure .......................................................................... 2

2.1.2 Materials Handling Area Closure ......................................................................................... 3

2.1.3 Landfill Closure .................................................................................................................... 3

2.1.4 In-Situ Chemical Oxidation Pilot Test .................................................................................. 3

2.1.5 Air Sparge System ............................................................................................................... 4

2.2 Conceptual Site Model .................................................................................................................... 4

2.2.1 Geology and Hydrogeology ................................................................................................. 4

2.2.1.1 Site Geology and Hydrogeology ................................................................................ 5

2.2.1.2 Saprolite Hydrostratigraphic Units ............................................................................. 5

2.2.1.3 Partially Weathered Rock Hydrostratigraphic Units .................................................. 6

2.2.1.4 Bedrock Hydrostratigraphic Units .............................................................................. 7

2.2.1.5 Groundwater Flow ..................................................................................................... 7

2.2.2 Sources ............................................................................................................................... 8

2.2.3 Contaminant Distribution ..................................................................................................... 9

2.2.4 Impacted Media ................................................................................................................. 10

3 Remedial Action Objectives .................................................................................................................. 11

4 Remedial Technologies ........................................................................................................................ 11

4.1 Remedial Technologies ................................................................................................................ 11

4.1.1 No Action ........................................................................................................................... 11

4.1.2 Monitored Natural Attenuation ........................................................................................... 12

4.1.3 Soil Vapor Extraction ......................................................................................................... 12

4.1.4 Air Sparge/Biosparge ........................................................................................................ 12

4.1.5 Enhanced Reductive Dechlorination ................................................................................. 12

4.1.6 In-Situ Thermal Treatment ................................................................................................ 13

4.1.7 Institutional Controls or Land Use Controls ....................................................................... 13


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4.2 Remedial Alternatives ................................................................................................................... 13

4.2.1 Plant 1 ............................................................................................................................... 13

4.2.2 Plant 2 ............................................................................................................................... 14

4.3 Remedial Alternative Screening ................................................................................................... 14

5 Remedial Alternatives Evaluation ......................................................................................................... 15

5.1 Plant 1 ........................................................................................................................................... 15

5.1.1 Alternative #1 ..................................................................................................................... 15

5.1.2 Alternative #2 ..................................................................................................................... 15

5.1.3 Alternative #3 ..................................................................................................................... 15

5.1.4 Alternative #4 ..................................................................................................................... 16

5.2 Plant 2 ........................................................................................................................................... 16

5.2.1 Alternative #1 ..................................................................................................................... 16

5.2.2 Alternative #2 ..................................................................................................................... 16

5.2.3 Alternative #3 ..................................................................................................................... 17

5.2.4 Alternative #4 ..................................................................................................................... 17

5.2.5 Alternative #5 ..................................................................................................................... 18

6 Evaluation Summary ............................................................................................................................. 19

6.1 Plant 1 ........................................................................................................................................... 19

6.2 Plant 2 ........................................................................................................................................... 19

6.3 Institutional Controls ..................................................................................................................... 20

7 References ............................................................................................................................................ 21

TABLES Table 5-1 Comparative Analysis of Alternatives for Plant 1

Table 5-2 Comparative Analysis of Alternatives for Plant 2

FIGURES Figure 2-1 Historical Site Layout

Figure 2-2 Conceptual Groundwater Flow in the Piedmont

Figure 2-3 Potentiometric Surface of the Saprolite HSU, May 2015

Figure 2-4 Potentiometric Surface of the Partially Weathered Rock HSU, May 2015


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Figure 2-5 Potentiometric Surface of the Bedrock HSU, May 2015

Figure 2-6 Investigation Summary

Figure 2-7 Investigation Results, Plant 1 Area

Figure 2-8 Investigation Results, Plant 2 Area

Figure 2-9 Saprolite Concentration Contours for Tetrachloroethene, Trichloroethene, cis-1,2-Dichloroethene, and Vinyl Chloride

Figure 2-10 Partially Weathered Rock Concentration Contours for Tetrachloroethene, Trichloroethene, cis-1,2-Dichloroethene, and Vinyl Chloride

Figure 2-11 Bedrock Concentration Contours for Tetrachloroethene, Trichloroethene, cis-1,2-Dichloroethene, and Vinyl Chloride

Figure 2-12 Saprolite Concentration Contours for 1,1,1-Trichloroethane, 1,1-Dichloroethane, and 1,1-Dichloroethene

Figure 2-13 Partially Weathered Rock Concentration Contours for 1,1,1-Trichloroethane, 1,1-Dichloroethane, and 1,1-Dichloroethene

Figure 2-14 Bedrock Concentration Contours for 1,1,1-Trichloroethane, 1,1-Dichloroethane, and 1,1-Dichloroethene

Figure 5-1 Conceptual Layout for Alternatives #3 and #4

Figure 5-2 Conceptual Layout for Alternative #3



Figure 5-5 Alternatives #2, #3, #4 and #5 Upgraded Biosparge System Layout


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ACRONYMS AND ABBREVIATIONS 1,1-DCA 1,1-dichloroethane

1,1-DCE 1,1-dichloroethane

1,1,1-TCA 1,1,1-trichloroethane

3M 3M Company

Arcadis Arcadis U.S., Inc.

bgs below ground surface

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

cis-1,2-DCE cis-1,2-dichloroethene

cm/sec centimeters per second

COC constituent of concern

CSM conceptual site model

ERD enhanced reductive dechlorination

FFS Focused Feasibility Study

ft foot/feet

ft/day feet per day

GCL geosynthetic clay liner

GE General Electric Ceramics Inc.

HSU hydrostratigraphic unit

ISCO in-situ chemical oxidation

ISTT in-situ thermal treatment

LUC land use control

MCL maximum contaminant level

MNA monitored natural attenuation

NA no action

PCE tetrachloroethene

POTW publicly owned treatment works

PVC polyvinyl chloride

PWR partially weathered rock

RAO remedial action objective


arcadis.com FFS_3M Laurens_Rev 1_Final 073117.docx v

RQD Rock Quality Designation

RSL regional screening level

SCDHEC South Carolina Department of Health and Environmental Control

site Laurens CeramTec Site (File #5094), located in Laurens, South Carolina

SSL soil screening level

SVE soil vapor extraction

µg/kg micrograms per kilogram

USEPA United States Environmental Protection Agency

VOC volatile organic compound

WCSS wholecore soil sampling

Weston Weston Solutions


arcadis.com FFS_3M Laurens_Rev 1_Final 073117.docx 1

1 INTRODUCTION On behalf of 3M Company (3M), Arcadis U.S., Inc. (Arcadis) has prepared this Focused Feasibility Study (FFS) to evaluate potential remedial technologies for implementation at the Laurens CeramTec Site (File #5094), located in Laurens, South Carolina (site). This FFS is being developed at the request of the South Carolina Department of Health and Environmental Control (SCDHEC) in its letter dated August 22, 2013 (SCDHEC 2013). This FFS has been developed with the remedial technologies and applicable screening criteria outlined in the Focused Feasibility Study Work Plan (Arcadis 2016b).

This FFS presents a summary of the site background, current conceptual site model (CSM), and information on the alternatives evaluated. The evaluation included:

Definition of the remedial action objectives (RAOs) and applicable regulatory criteria

Description of remedial technologies included in this FFS

Screening of remedial alternatives

Summary of the screening results

2 SITE BACKGROUND The site is located approximately 2 miles northwest of the Town of Laurens, South Carolina. Operations at the facility include two Plants. Plant 1 was constructed between 1960 and 1961, which began operations in 1961. Plant 2 began operation in the mid-1960s. Both Plants are shown on Figure 2-1. A timeline of the operations at the site is as follows:

1960 – American Lava Company, a subsidiary of 3M acquired the property for construction of the facility. Plant 2 was expanded in the 1970s.

1983 – General Electric Ceramics Inc. (GE) purchased the facility.

1988 – GE sold the facility to Great American Industrial Group, which transferred the facility to Eagle Industries.

1996 – Eagle Industries sold the facility to AlSiMag Technical Ceramics, Inc. (now known as CeramTec).

2006 – CeramTec sold the Plant 1 building and associated grounds to ACI Industries, LLC. CeramTec retained Plant 2.

2013 – CeramTec was acquired by Cinven.

Currently, ACI Industries, LLC owns Plant 1 and CeramTec owns Plant 2 and the associated property (Figure 2-1).

From 1961 to 1988, the facility primarily produced textile guides, wear products, and some ceramic electrical substrates used in electrical circuitry, microprocessors, wrist watches, and computers. The manufacturing process that occurred at the facility included ceramic preparation, extrusion mixing, dry pressing, tape casting, glazing, grinding, and post-fire tumbling (Weston Solutions [Weston] 1998).



The site has been investigated through multiple phases of work, including the following:

1988: Phase I Preliminary Environmental Assessment (Law Environmental)

1988 to 1990: Phase II Assessment (Law Environmental)

1991 to 2002: Supplemental Investigations (Weston)

In addition to the historical investigations, Arcadis completed a Data Gap Investigation in 2016 to provide source characterization near Plants 1 and 2 and of the downgradient plume delineation at Plant 2. Results from this additional investigation were included in the Semi-Annual Progress Report (Arcadis 2016c). Data from the historical and current investigations are discussed in Section 2.2.

2.1 Previous Remedial Actions Multiple remedial actions and closure activities have been completed at the site, including wastewater pond closure, materials handling area closure, landfill closure, in-situ chemical oxidation (ISCO) pilot testing, and air sparge system installation and operation. A summary of these activities is included in the following subsections.

Also, in 2005 an Easement Agreement was recorded on the deed which restricts the extraction and use of groundwater, the use of surface water and restricts interference and disturbance of the closed areas and the elements of the remedy (Laurens County 2005). The restrictive covenants shall remain until such time as all appropriate government agencies have determined that (i) no further remediation or monitoring is required for the land or groundwater and (ii) no further restrictions on the use of groundwater or the land are required for the protection of human health or the environment.

2.1.1 Plants 1 and 2 Wastewater Pond Closure Three wastewater settling ponds were used as part of the former processing operations at the site to remove particulate fines from operation-related wastewater. Wastewater was then discharged from the ponds to the Laurens County publicly owned treatment works (POTW). Plant 1 contained one wastewater settling pond and was constructed in the early 1960s. The Plant 1 pond was rectangular in shape and measured approximately 70 feet (ft) by 40 ft by 5 ft deep. Operations at Plant 2 included two wastewater settling ponds, Pond 1 and Pond 2. Pond 1 at Plant 2 operated from the 1960s until 1988, and Pond 2 at Plant 2 operated from 1975 to 1994. Both Plant 2 ponds measured approximately 75 ft by 45 ft by 9 ft deep.

The use of wastewater settling ponds was discontinued at the site after installation of a pre-treatment solids removal system. Closure of all three wastewater settling ponds was completed in 1995. The closure of the Plant 2 ponds included pond liquid removal, solids removal, and clean soil backfill placement. The solids from the two ponds at Plant 2 were moved to the Plant 1 pond where they were combined, stabilized in place, and covered. Land use controls (LUCs), as discussed in Section 6.3, are in place to eliminate the disturbance of these consolidated and stabilized solids residing on the former Plant 1 footprint.



2.1.2 Materials Handling Area Closure As part of the 1994 investigation activities in the Plant 1 area, volatile organic compounds (VOCs) were discovered at the Materials Handling Area. Supplemental sampling was conducted in November 2003 to determine the level and extent of VOC contamination. Results of the supplemental investigation determined that a removal action was warranted to mitigate exposure to VOC-impacted soils. In February 2006, the asphalt pavement was removed from the Materials Handling Area, exposing an approximately 324-square ft structure that extended approximately 2.7 ft deep. VOC-impacted soil was excavated from the concrete structure, placed in roll-off containers, and shipped off site for proper disposal. Following the excavation, an inspection of the concrete structure identified no cracks and there was no evidence of groundwater exposure pathways (cracks, piping, or drains) within the structure. After the inspection, it was determined that the concrete structure would remain in place following VOC soil removal. The concrete structure was backfilled with gravel and the surface was repaved. A chain-link fence with a locking gate was installed around the area in May 2006.

2.1.3 Landfill Closure A landfill operated at the site from 1961 through 1983 and was located to the southwest of Plant 1 (Figure 2-1). This landfill was permitted to accept industrial wastes from the facility. Disposal activities ceased in December 1983 and then initial landfill closure activities were conducted. The initial activities at the landfill included constructing a fence around the footprint, completing a landfill cover assessment, and soil and groundwater sampling to evaluate the potential of the landfill as a source of VOCs and metals. Based on the results of these characterization activities, the landfill was not determined to be a source of constituent migration to groundwater or surface water. The investigation did determine that improvements to the landfill cover were needed to minimize maintenance, improve the drainage, and reduce infiltration (Weston 1999).

In 1998, improvements were made to the landfill cover. These improvements included consolidating areas of waste materials to the central portion of the landfill to promote drainage, optimize cover of the cap, and create a smaller, more uniform footprint with improved slope stability. The slope stability was addressed by mixing approximately 900 cubic yards of fines from within the landfill with 238 tons of Portland cement to enhance long-term stability. Following the stability improvements, the landfill was regraded to improve drainage. A final cover consisting of a geosynthetic clay liner (GCL) cap, an 18-inch layer of compacted soil, and a 6-inch layer of soil for the establishment of vegetative cover were installed. Swales were added along the perimeter of the landfill to drain stormwater. Six passive vents were also installed to prevent accumulation of potential vapor under the GCL. The perimeter wells are sampled annually to monitor groundwater quality around the landfill.

2.1.4 In-Situ Chemical Oxidation Pilot Test An ISCO pilot test study was conducted downgradient of Plant 2 as part of a Source Control Alternative Analysis that evaluated potential technologies to address residual VOCs, primarily tetrachloroethene (PCE), found in the groundwater. In January 1999, two injection wells and several injection monitoring wells were installed adjacent to monitoring well MW-36 as part of the pilot study. The pilot study consisted of an application of an oxidant to evaluate the effectiveness in destruction of the VOCs. Two injection events were conducted in April and May 1999 using mobile equipment. A total reagent volume of 160



gallons of 80% acetic acid, 790 gallons of ferrous sulfate, and 6,425 gallons of hydrogen peroxide were injected over the two events. Following the ISCO pilot test study, extensive groundwater monitoring was conducted from May through September 1999 to monitor the effectiveness of the two events. Results of the monitoring indicated the constituent of concern (COC) reduction was minimal and it was recommended that ISCO not be considered as a full-scale remedy in Plant 2.

2.1.5 Air Sparge System An air sparge system was constructed from February through June 2002 to limit the migration of downgradient COCs into the surface water and to address surface water of the small creek adjacent to the air sparge system. Eight air sparge wells (AW-1 through AW-8) were installed approximately 10 ft below the groundwater table, with total depths ranging from 12 to 20 ft below ground surface (ft bgs). Each air sparge well was constructed with 2 ft of 1.5-inch prepacked screen connected to a 1.5-inch polyvinyl chloride (PVC) riser. The air sparge wells are connected in two zones: Zone 1, consisting of even-numbered air sparge wells (AW-2, AW-4, AW-6, and AW-8), and Zone 2, consisting of odd-numbered air sparge wells (AW-1, AW-3, AW-5, and AW-7). The locations of these wells are included on Figure 2-1.

In addition to the wells, a creek diffuser was also installed to provide additional treatment of the surface water. This diffuser consists of a horizontally installed 5-ft screen, anchored to the stream bed. The air sparge compressor, heat exchanger, and manifolds are housed in a small shed adjacent to the air sparge wells. The air sparge system currently remains in operation.

2.2 Conceptual Site Model A CSM has been developed for the site using historical investigation data (collected prior to 2015) and recent data collected as part of the Data Gap Investigation. Results of the Data Gap Investigation were originally reported in the Semi-Annual Progress Report (Arcadis 2016c). A summary of these results, including historical data, are presented below to provide a collective understanding of the geologic and hydrogeologic framework and the processes that control the fate and transport of the contaminants within the hydrostratigraphic framework. Additional information pertaining to the CSM was included in the Data Gap Investigation Work Plan (Arcadis 2015).

2.2.1 Geology and Hydrogeology Laurens, South Carolina is located within the Piedmont physiographic province. The Piedmont is characterized by a series of thrust sheets between the Brevard fault zone to the west and the Carolina terrain to the east (Garihan 2001). The Piedmont is composed of crystalline metamorphic rocks, with the most abundant rock types including gneiss, schist, and metamorphosed granitic rocks. Other lithologies present in the Piedmont that are less widely distributed include quartzite, slate, phyllite, argillite, marble, and igneous rocks, such as granite, diorite, and gabbro (Ranson and Garihan 2001; LeGrand 2004).

The hydrogeology of the Piedmont hydrogeologic province is summarized by LeGrand (LeGrand 1954, 1967, 2004) and Heath (Heath 1984, 1988). Figure 2-2 illustrates a typical groundwater flow system in the Piedmont (LeGrand 2004). The generalized groundwater system in the Piedmont is a two-part aquifer



system. The unconsolidated saprolite composes the upper or surficial aquifer, which overlies the bedrock aquifer. The saprolite aquifer serves as the principal storage reservoir for the bedrock aquifer.

This hydrogeologic system possesses unique features that control groundwater flow. Groundwater flow in the Piedmont typically mimics surface water drainage. Topographic highs (the upland ridges) act as the principal areas of groundwater recharge. Perennial streams represent discharge boundaries where groundwater flows to the surface, as diffuse seepage or from springs. Groundwater in the Piedmont flows from hilltop areas to the nearest streams, marshes, or wetlands within the same drainage basin. Each upland ridge bounded by permanent streams is a separate groundwater flow system that functions as a “hydraulic island”.

Within the Piedmont, groundwater discharges to the closest local perennial stream within the same drainage basin. Perennial Piedmont streams can be shown to be discharge barriers that capture all local groundwater based on three mechanisms. First, the streams will usually gain flow downstream, as streams within the Piedmont typically do not recharge groundwater. Second, groundwater flows to the stream from both sides of the valley. Third, there is an upward hydraulic gradient into the streams, further illustrating that the streams typically capture the deeper groundwater from both sides of the valley. Via the above mechanisms, each perennial stream acts as a drain for all groundwater from the two adjacent hydraulic islands.

2.2.1.1 Site Geology and Hydrogeology

The site is located on the Laurens Thrust Sheet, approximately 8 miles west of the mapped fault that separates the Six Mile and Laurens Thrust Sheets. The geology of the bedrock near the site, more specifically the Laurens North quadrangle, consists primarily of biotite gneiss and amphibolite with sparse occurrences of schist, metagabbro, and metagranite. Based on the published Geologic Map (Niewendorp 1995), the predominant rock types near the site are biotite gneiss and amphibolite. Mapped areas also suggest that metagranite is also present in proximity to Plant 2; however, site-specific boring logs indicate bedrock lithologies are consistent with the published descriptions for biotite gneiss and amphibolite.

Characteristics of the saprolite, partially weathered rock (PWR), and bedrock hydrostratigraphic units (HSUs) were reviewed to support an evaluation of the extensive boring log records available for the site. The general characteristics of the HSUs are summarized below.

2.2.1.2 Saprolite Hydrostratigraphic Units

Saprolite is formed by the in-situ chemical weathering of the underlying metamorphic bedrock. The saprolite at the site is characterized as clay-rich soils and grades to a sandier soil with more pronounced relic rock structure at depth. The base of the saprolite HSU has been defined as the stratigraphic interval where the lithology transitions from fine-grained soils, high in silt and clay-sized grains, to a lithology dominated by coarser-grained sands and fragments of PWR, with a low percentage or absence of fine-grained materials. Additionally, the saprolite HSU can be further identified using blow counts, which range from 5 to 20 blow counts per ft. Blow counts within the saprolite gradually increase with depth as the HSU becomes sandier. Contact between the saprolite and PWR HSUs was established during the review of the lithologic descriptions on historical boring logs.



The fine-grained nature of the saprolite suggests the HSU will have a lower permeability at shallower intervals with an increase in permeability with greater depth as the grain size transitions from clay and silt to sandier soils. Slug testing was completed on 12 wells screened in the saprolite HSU (Weston 1998). Results of this testing indicates the horizontal hydraulic conductivity (K) values for the saprolite HSU range from 10-4 to 10-5 centimeters per second (cm/sec) (5.4 to 8.0 x 10-2 ft per day [ft/day]). Where paired, saprolite wells have historically been tested (MW-1 and MW-2, MW-3 and MW-4, MW-11 and MW-12), the shallow saprolite well exhibits a K value generally one order of magnitude lower than the deeper saprolite. The average K values for the PWR are generally higher than but within an order of magnitude of the overlying saprolite. The vertical variability in saprolite K values results in increased hydraulic interaction between the lower saprolite and the underlying PWR HSUs. The result is a contaminant transport tendency that involves the lower-permeability saprolite materials serving as shallow mass storage, which then discharges vertically downward from the source areas to the PWR where primary advective lateral mass transport is observed. These transport concepts are supported by the observed VOC mass distribution at the site, which is further discussed in Section 2.2.3.

2.2.1.3 Partially Weathered Rock Hydrostratigraphic Units

The PWR exhibits a range of physical characteristics that are indicative of its formation through the weathering process. The PWR is formed by the same processes that eventually result in saprolite, but the PWR represents an earlier stage of the bedrock weathering process. At the site, the PWR HSU is composed of a mix of two units with different physical characteristics that function as one HSU. The upper portion of the PWR, near the saprolite/PWR interface, is composed of medium to coarse sand and larger weathered rock fragments. The percentage of rock present in the HSU increases with depth until it reaches a point where it is composed entirely of highly fractured and weathered bedrock. Within the weathered bedrock, the relative degree of weathering declines with depth until the top of the competent bedrock is encountered.

The top of the PWR is characterized by split-spoon refusal (i.e., 50 blows over less than 6 inches); this data was available for approximately 75% of the boring logs reviewed. Concurrent with split-spoon refusal, hollow-stem auger refusal, if applicable, was also observed at the saprolite/PWR interface. At this interface, the visual characteristics include key descriptors, such as weathered rock fragments and/or medium to coarse sand. The key descriptors were used to distinguish between the saprolite and PWR where split-spoon/hollow-stem auger refusal data were not available.

The base of the PWR HSU is defined as the transition from highly fractured/weathered bedrock to competent bedrock. The borings that were advanced through the PWR HSU were generally drilled with rock coring methods to allow lithologic characterization. The base of the PWR is defined by the Rock Quality Designation (RQD) and the core recovery. The PWR HSU was characterized by poor core recovery and an RQD less than 75%. These PWR benchmark recovery and RQD classifications are consistent with the descriptions identified in the boring logs, which include “moderate to severe weathering” or “highly weathered zones with little recovery”.

Limited hydraulic data is available for the PWR. Slug test results were available for four wells, and the K values at these locations range from 10-4 to 10-5 cm/sec (5.4 to 8.0 x 10-2 ft/day), similar to the saprolite. This is anticipated because all four data points were collected from wells screened in the shallow portion of the PWR, which is similar in permeability to the deeper saprolite as the soil transitions with depth. In



the absence of a robust hydrogeologic data set, evaluation of the PWR can be completed using the relative distribution of VOC mass to make inferences and understand site groundwater transport. As further discussed in Section 2.2.3, the PWR is responsible for the majority of groundwater transport across the site.

2.2.1.4 Bedrock Hydrostratigraphic Units

Biotite gneiss comprises the majority of the bedrock encountered across the site. This bedrock type has been identified in the multiple borings that have completely penetrated the PWR HSU. In addition, sparse occurrences of mica schist have been mentioned in previously collected boring logs; however, the mica schist does not appear to be vertically or laterally extensive and is not considered a primary component of the bedrock system. Previous reports also mention an area of metagranite that has been historically mapped southeast of Plant 2 (Niewendorp 1995), but metagranite was not identified within the historical site boring logs.

The bedrock interface is variable with depth and is identified based on recovery and RQD classifications within the PWR. This transition is defined by an RQD of greater than 75%. In most of the bedrock boring logs evaluated, the transition from PWR to bedrock is rather distinct, where conditions change from highly weathered to very competent rock over a short vertical interval. Where fractures were observed in the bedrock, the boring log descriptions were typically presented as “little weathering or fresh”. In addition, the fracture density decreased with depth.

Hydraulic data were available for three bedrock locations distributed across the site. Near Plant 1, the hydraulic data indicate very low K values, with an average of 10-7 cm/sec observed at test location C-1. Downgradient of Plant 1 and near the landfill, the observed K values were also in the 10-7 cm/sec range (test location C-3). These values are two to three orders of magnitude lower than the observed K values in the saprolite and PWR HSUs.

An additional set of K data were available for the bedrock downgradient of Plant 2 (test location C-2). In this area, the average K value in the bedrock was in the 10-6 cm/sec range. The bedrock in this area does have higher permeability compared to the bedrock downgradient of Plant 2; however, these results are still one to two orders of magnitude lower than the K observed in the saprolite and PWR HSUs.

2.2.1.5 Groundwater Flow

The groundwater flow system of the Piedmont has been widely studied and, in general, provides a good framework for CSM development. Review of the available historical data in the context of typical Piedmont conditions has allowed refinement of the CSM and an improvement in the hydrogeologic framework that controls contaminant transport at the site. In general, the hydrogeology at the site conforms to the LeGrand model.

Groundwater flow at the site mimics surface water drainage. The topographic high along Church Street serves as a drainage divide for the site. Groundwater flow, similar to topography, slopes away from the ridge toward the small tributaries on site. This flow condition is evident in the groundwater potentiometric surface data collected at the site. Figures 2-3 through 2-5 include potentiometric maps for the saprolite, PWR, and bedrock HSUs, respectively, from the May 2015 sampling event.



Groundwater flow near Plants 1 and 2 have two distinct flow patterns toward different tributaries. Near Plant 1, and more specifically the area of the former pond at Plant 1, groundwater flow is to the southwest toward the tributary near monitoring well MW-100 (Figure 2-9). Plant 2 is located upgradient of the eastern tributary onsite. Groundwater flow from the eastern edge of Plant 2 is to the southeast.

The vertical groundwater flow path along the site also conforms to the LeGrand model for groundwater flow in the Piedmont. The upland portion of the site, near the drainage divide, acts as an area for groundwater recharge. This is confirmed by the presence of a downward vertical gradient observed in paired saprolite/PWR wells (i.e., MW-82/MW-83, MW-93/MW-94, and MW-96/MW-97). As groundwater nears the discharge boundaries, the gradients transition from downward to upward, indicating a discharge condition. This is supported by the upward vertical gradients observed in well pairs along the two tributaries (i.e., MW-101/MW-102, MW-84/MW-97, and MW-73/MW-74).

2.2.2 Sources Prior to implementing the Data Gap Investigation, potential sources were identified based on the knowledge of past operations at the site and identified groundwater impacts downgradient of these potential sources. The list of potential sources included:

Former Materials Handling Area

Former Wastewater Pond – Plant 1

Former Wastewater Ponds – Plant 2

Area beneath Plant 2

A summary of each area is included in the Data Gap Investigation Work Plan (Arcadis 2015). The boring locations completed during the investigation are shown on Figure 2-6. Results for Plants 1 and 2 are shown on Figures 2-7 and 2-8, respectively.

Investigation activities completed in 2016 focused on data collected around these potential sources. The data collected during this investigation included high resolution soil samples collected from both the vadose and saturated zones. This approach was used because it provided a bulk measure of soil and groundwater concentrations, where saturated. This provided a consistent data set for evaluating potential sources and migration pathways between borings along the vertical profile.

Results of the investigation concluded that the primary source remaining near Plant 1 is the former Materials Handling Area, and the borings adjacent to the former Plant 1 pond did not indicate this was an ongoing source area. The mass distribution identified as part of the investigation shows the impacts are present in both the vadose and saturated saprolite near the former Materials Handling Area, but quickly migrate into the deeper saprolite and PWR away from the source. The impacts present in the vadose zone are relatively low, and only two locations showed COC concentrations above the applicable Protection of Groundwater Maximum Contaminant Level (MCL)-based Soil Screening Level (MCL-based SSL) (Arcadis 2016c). Locations WCSS-1 and WCSS-2, located near the materials handling area, contained concentrations of 1,1,1-trichloroethane (1,1,1-TCA) above the MCL-based SSL of 70 micrograms per kilogram (g/kg) (Figure 2-7). These low-level impacts in the vadose zone are consistent with the data collected prior to the materials handling area closure when borings were collected through the bottom of the concrete containment (Weston 2006). Monitoring data also indicate an overall lack of



1,1,1-TCA in the groundwater plume. The presence of 1,1-dichloroethene (1,1-DCE) and 1,1-dichloroethane (1,1-DCA) in the PWR zone groundwater confirms ongoing degradation of 1,1,1-TCA, and trends in downgradient wells confirm that the plume is stable and not increasing. While the available data indicate soil concentrations in the vadose zone were slightly above the MCL-based SSL and leaching to groundwater appears to be minimal, as a conservative measure consideration in this FFS will be given to this area as an ongoing source to groundwater through leaching.

Results of the investigation around Plant 2 identified a source area, that is not attributed to the former Plant 2 ponds or the area beneath Plant 2, which was the location of the historical sumps and process lines. The data collected around Plant 2 indicate that the source is upgradient of the former Plant 2 ponds, near the eastern exterior wall (near WCSS-8). Similar to the mass distribution observed in Plant 1, the boring closest to the source area (i.e., WCSS-8) has impacts in both the vadose zone and shallow saprolite. The borings farther downgradient (i.e., WCSS-11) shows the mass in the saturated saprolite. Farther downgradient at borings WCSS-13 through WCSS-15, the borings were below laboratory detection in the saprolite. This mass distribution is consistent with the migration pathway from the saprolite to PWR where the dominant flow path is downward through the less permeable saprolite until it reaches the PWR where the mass will migrate laterally. Additional information on distribution in groundwater at Plant 2 is presented in Section 2.2.3.

2.2.3 Contaminant Distribution The distribution of VOCs in groundwater is consistent with the sources identified as part of the Data Gap Investigation. Isoconcentration figures for PCE and its degradation products are shown for the saprolite, PWR, and bedrock HSUs on Figures 2-9 through 2-11, respectively. 1,1,1-TCA and its degradation products are shown on Figures 2-12 through 2-14, respectively. These panel figures provide an improved representation of individual VOC distribution and the correlated relationships between parent compounds and degradation products. The relationship between the saprolite, PWR, and bedrock HSUs observed on the figures reflects the geologic and hydrogeologic classifications discussed in previous sections.

The VOC extents shown on Figures 2-9 through 2-14 indicate two general areas of groundwater impacts. The area of elevated groundwater concentrations southwest of Plant 1 are consistent with the identified source at the former Materials Handling Area. Additionally, the groundwater data is consistent with the mass distribution observed in the wholecore soil sampling (WCSS) results (Figure 2-7). Near the source zone, the mass is present in the saprolite but quickly migrates vertically towards the PWR HSU. With the groundwater data, the majority of the mass and highest concentrations are observed in the PWR HSU, downgradient of the former Materials Handling Area (MW-62). Only a small portion of the bedrock is responsible for the migration of dissolved VOCs as shown on Figures 2-11 and 2-14. This is consistent with the bedrock aquifer testing previously completed in this portion of the site, as the bedrock has very low-permeability and does not represent a significant portion of the groundwater flow system.

The identified source of the groundwater impacts associated with Plant 2 is along the eastern edge of the building, near WCSS-8. The mass distribution near the source zone is consistent with the distribution observed at Plant 1 where the mass migrates downward along the flow direction to the southeast. The observed groundwater impacts associated with Plant 2 differ from those in Plant 1, with the primary difference being the proximity and location of the source related to the surface water body. In addition, the



concentrations present in the vadose zone soil and saturated saprolite are two orders of magnitude higher than the concentrations observed in Plant 1.

In Plant 2, the plume originates upgradient of the headwaters of the tributary and flows parallel to the stream instead of perpendicular as observed in Plant 1. The resulting plume is distributed on both sides of the tributary, with migration along the surface water feature. The saprolite impacts are persistent farther downgradient (i.e., PZ wells: Figure 2-1) at concentrations within an order of magnitude of those observed in the PWR. This is due to the presence of the stream and the upward hydraulic gradient promoting discharge to the stream. Additionally, the Plant 2 bedrock in this portion of the site is more permeable compared to the bedrock near the Plant 1 plume; however, K values are still one to two orders of magnitude less than the overlying PWR and saprolite. This permeability contrast is reflected in the mass distribution, as the concentrations in bedrock are generally one order of magnitude lower than the overlying PWR.

The current distribution of mass for both Plants 1 and 2 is controlled by the ongoing natural degradation occurring in both areas. Data collected during the 2015 annual sampling (Arcadis 2016a) indicates that the groundwater in Plant 1 is suboxic or anaerobic and that naturally present organic carbon and localized toluene are both contributing to reductive dehalogenation along the plume length. This is evidenced by the observation of sequential breakdown products of both PCE (cis-1,2-dichloroethene [cis-1,2-DCE], vinyl chloride, and ethene) and 1,1,1-TCA (1,1-dichloroethane, ethane) and an overall disappearance in parent species with increased distance from the source. As a result of these ongoing processes, the Plant 1 plume is relatively stable with COCs depleted at the groundwater discharge boundary.

In Plant 2, the data suggests there is evidence of reductive dechlorination with the presence of elevated levels of daughter products cis-1,2-DCE and vinyl chloride, but the geochemical data indicate only mildly reducing conditions. While the COCs decrease along the groundwater flow path, the absence of available organic carbon results in only partial dehalogenation within the plume under current conditions.

2.2.4 Impacted Media Investigation activities completed to date have been successful in identifying the ongoing sources to groundwater and the migration pathways of the contaminants from the source zone, through the groundwater flow system, and ultimately towards discharge points at the surface water bodies. Based on the data available, the following table outlines the media that is addressed in this FFS for both Plants 1 and 2. The list of media includes soil, groundwater, and surface water where the concentrations of site COCs are present above the applicable regulatory standards.

Media Plant 1 Plant 2

Vadose Zone X X

Groundwater X X

Surface Water -- X Notes: X = denotes media to be considered in this FFS. Note: The available data for Plant 1 indicates soil concentrations are below Regional Screening Levels (RSLs), but will evaluated in the FFS as a potential ongoing source to groundwater through leaching. -- = denotes media that will not be included in this FFS



3 REMEDIAL ACTION OBJECTIVES The primary goal of the remedial actions is protection of human health and the environment. The existing restrictive covenants provide an administrative control to eliminate exposure and protect human health. However, based on the current conditions and the impacted media identified for Plant 1 and Plant 2 in Section 2, if the covenants were not in place, potential exposure pathways include vadose zone soil, and groundwater. Also, surface water could allow potential exposure to the environment (Plant 2 only). On this basis, the RAOs at this site are focused on:

Reducing ongoing sources to groundwater from the vadose zone

Mitigating discharges of impacted groundwater to surface water

Managing groundwater and surface water to applicable state and federal criteria

In accordance with South Carolina Regulation R.61-68 (SCDHEC 2012), the established media clean-up objectives for groundwater and surface water will include applicable state regulations. These clean-up objectives for groundwater are the MCLs (United States Environmental Protection Agency [USEPA] 2009). If a constituent is detected at the site where an MCL has not been established, the RSL for tap water (USEPA 2017) will be used. The surface water goals will include the criteria outlined in South Carolina Regulation R.61-68 (Appendix: Water Quality Numeric Criteria for the Protection of Aquatic Life and Human Health; SCDHEC 2012).

The media clean-up objectives for soil are based on an industrial land use, which is consistent with the current and projected future land use of the property. Based on these site-specific characteristics, the established media clean-up objectives for shallow vadose zone soils (0-2 ft) are Industrial RSLs (USEPA 2017). The established media clean-up standards for deeper vadose zone soils are the Protection of Groundwater MCL-based SSLs (USEPA 2017).

4 REMEDIAL TECHNOLOGIES

4.1 Remedial Technologies This section identifies and screens remedial technologies for both Plant 1 and Plant 2. Potentially applicable remedial technologies were identified as part of the Focused Feasibility Study Work Plan (Arcadis 2016b). This section describes each of the technologies and their application to specific media. It is anticipated that the technologies presented below will be coupled together to address each media in both Plant 1 and Plant 2. A summary of each of the most applicable remedial technologies is included in the following sections.

4.1.1 No Action No action (NA) has been carried forward as a means of evaluating site conditions if allowed to remain unattended. Under this general response, no efforts would be taken to monitor, remove, treat, or otherwise mitigate site COCs. In addition, NAs would be taken to minimize the potential for human or ecological exposure to COCs. This alternative would rely solely on natural attenuation to reduce the COCs present; however, because monitoring is not included as part of this alternative, there is no way to



verify the remedy is working and if clean-up levels are achieved. This technology is applicable to all impacted media.

4.1.2 Monitored Natural Attenuation Monitored natural attenuation (MNA) has been identified as the reliance on natural attenuation processes, within the context of a controlled and monitored site clean-up approach, to achieve site-specific remediation objectives within a timeframe that is reasonable compared to that of other more active remedial methods. The natural processes at work include a variety physical, chemical, and/or biological processes that, under favourable conditions, act to reduce the mass, toxicity, mobility, volume, or concentration of COCs in soil and/or groundwater. This technology is applicable to all impacted media at the site.

4.1.3 Soil Vapor Extraction Soil vapor extraction (SVE) has been carried forward as a means of capturing vadose zone COCs in-situ for above-grade treatment. Mass removal is achieved via direct COC volatilization by applying a vacuum to an extraction well located in the unsaturated contaminated media and drawing out the contaminated soil gas using a vacuum blower/pump. Recovered vapors are then routed to an above-grade vapor treatment unit, if required. The key to a successful SVE system is to place the wells and equipment so that when the system is in operation, an air flow pattern is created across the entire area of contaminant distribution within the unsaturated zone. The use of SVE is effective in reducing the overall contaminant source mass; however, the method is limited to unsaturated vadose zone soils and does not address COCs currently in the dissolved-phase.

4.1.4 Air Sparge/Biosparge Air sparge/biosparge has been identified as a means of providing oxygen into the subsurface to promote in-situ bioremediation and to facilitate volatilization of dissolved-phase COCs. Air is injected through an air sparge/biosparge well network using an air compressor. Air bubbles injected from the well network migrate laterally and upward through the aquifer, allowing the partitioning of oxygen into groundwater. The COCs present in groundwater also partition into the sparge bubbles and are volatilized and carried up and out of the groundwater. Air sparge/biosparge consideration at the site is limited to the groundwater in the capillary fringe and saprolite, and surface water COCs. This alternative is less applicable and not considered for deeper impacts in PWR groundwater.

4.1.5 Enhanced Reductive Dechlorination Enhanced reductive dechlorination (ERD) is a process in which indigenous or augmented micro-organisms (i.e., fungi, bacteria, and other microbes) degrade (metabolize) organic contaminates found in soil and/or groundwater, converting them to innocuous end products. ERD for halogenated organics is typically implemented using an injection well network to perform periodic injection of a suitable organic carbon source. Sustained organic carbon is then fermented to yield a usable electron donor (e.g., dissolved hydrogen) for use by the microbial population to deplete naturally occurring electron acceptors (e.g., oxygen, nitrate, ferric iron, and sulfate) in addition to the target contaminants in the treatment zone.



ERD is well-suited for treatment of chlorinated COCs, which are the COCs for the site groundwater within each of the primary impacted geologic units (saprolite and PWR).

4.1.6 In-Situ Thermal Treatment Thermal remediation technology involves the application of energy to increase the temperature of soil and groundwater to mobilize subsurface contaminant and increase their recoverability, and/or to facilitate in-situ destruction of the COCs. Implementation of in-situ thermal treatment (ISTT) is typically completed using a network of thermal electrodes that apply the energy (heat) and vapor extraction wells to recover the steam and vapors in which the mass is partitioned. The objectives of most thermal remediation projects are the attainment of a certain level of mass removal (typically 90% or higher, as appropriate) and/or the removal of accessible nonaqueous-phase liquids. Given the costs associated with ISTT and the robust surface infrastructure required, these remedies are often focused on smaller remedial footprints and then combined with complementary remedial technologies that work to either contain or reduce the remaining contaminant mass. ISTT treats both vadose zone soil COCs and dissolved-phase groundwater COCs.

4.1.7 Institutional Controls or Land Use Controls Institutional controls or LUCs include any type of physical, legal, or administrative mechanisms that restrict the use of the property in accordance with a remedial decision, including the existing restrictive covenants. As applied, this technology refers to any restriction or control that limits the use of any portion of the property, including water resources, arising from the need to protect human health and the environment. Institution controls or LUCs are used to mitigate risks associated with exposure to in-place residual contamination instead of eliminating those risks through execution of removal actions or implementation of other remedial measures. The technology applies to all media on site.

4.2 Remedial Alternatives This section identifies the remedial alternatives that will be evaluated for Plant 1 and Plant 2. The remedial alternatives include a combination of the technologies outlined in Section 4.1 to meet the remedial action objectives within the variable media and COC levels in both Plants 1 and 2. The proposed alternatives for Plant 1 and Plant 2 are included below.

4.2.1 Plant 1 The alternatives considered for Plant 1 were developed to address vadose zone soil and groundwater. The Plant 1 alternatives are intended to be implemented in a phased approach to allow for flexibilities to account for conditions observed in the field. MNA is included in each alternative to take advantage of the existing natural attenuation processes currently ongoing at Plant 1. The alternatives evaluated for Plant 1 are listed below:

NA

MNA (ongoing remedy)

ERD Source Treatment and MNA within the Plume Footprint



SVE and ERD Source Treatment and MNA within the Plume Footprint

4.2.2 Plant 2 The alternatives considered for Plant 2 were developed to address vadose zone soil, groundwater, and surface water impacts. Multiple alternatives were identified as potential remedies to address the affected media in Plant 2 to meet the remedial action objectives listed in Section 3. The alternatives evaluated for Plant 2 are listed below:

NA

MNA and Biosparge Barrier System (ongoing remedy)

Air Sparge/SVE in the Source Area, Dissolved-Plume ERD, and Biosparge Barrier System

Source Area SVE and ERD, Dissolved-Plume ERD, and Biosparge Barrier System

Thermal Source Area Treatment, Dissolved-Plume ERD, and Biosparge Barrier System

4.3 Remedial Alternative Screening This section identifies and screens each of the remedial alternatives for Plants 1 and 2 using the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) nine evaluation criteria. Specifically, these criteria include:

Threshold Criteria o Protection of human health and the environment o Compliance with applicable or relevant and appropriate standards

Balancing Criteria o Long-term effectiveness o Reduction of toxicity, mobility, or volume o Short-term effectiveness o Implementability o Cost

Modifying Criteria o Regulatory acceptance o Community acceptance

The alternatives have been evaluated with a clear set of remedial action objectives in mind. The overall objective of the site-wide remedy is to reduce toxicity, mobility, and volume of contaminants through implementation and operation of the appropriate remedial alternatives. Remedies will target mass removal to lower the migration potential of contaminants in the vadose zone soils, groundwater, and surface water. Short-term enhancements may be implemented to reduce the duration or the remedies. Each Plant will include different alternatives designed to target vadose zone soil, groundwater, and surface water.



5 REMEDIAL ALTERNATIVES EVALUATION As summarized in Section 2, the impacted media consists of vadose zone soil, groundwater, and surface water (Plant 2 only), where the concentrations of site COCs are present above the applicable regulatory standards. As directed by the SCDHEC, this alternatives evaluation has been developed in accordance with the general guidelines under CERCLA as detailed in the Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (USEPA 1988). The screening evaluation and a ranking system for each of the remedial alternatives is presented in Table 5-1 for Plant 1 and Table 5-2 for Plant 2. The following subsections include a brief summary of the site-specific considerations.

5.1 Plant 1 The four alternatives for Plant 1 were selected to address residual vadose zone source material and groundwater impacts. Each of the alternatives described below are also discussed and evaluated in Table 5-1. The conceptual layouts for Alternatives #3 and #4 are presented on Figure 5-1. Each of the selected alternative evaluations are summarized below.

5.1.1 Alternative #1 No Action

Site conditions indicate that natural attenuation is currently ongoing along the natural groundwater flow path and work to reduce COC concentrations prior to surface water discharge. While the NA alternative would likely be effective in controlling plume transport due to ongoing natural attenuation, this alternative does not include a monitoring component; therefore, there would be no way to verify the remedy is working and if/when clean-up levels are achieved.

5.1.2 Alternative #2 Monitored Natural Attenuation

Site conditions indicate that MNA is ongoing along the natural groundwater flow path. The existing site controls limit contact with the source area vadose zone soils and groundwater, and this represents the current alternative at Plant 1. While currently effective in controlling COC transport towards potential receptors, this mechanism will require an extended monitoring period to achieve the remedial action objectives. The vadose mass would be treated through natural flushing (NA) to groundwater where it would be attenuated with the ongoing processes. MNA may be implemented as a stand-alone remedy or in combination with other potential active remedies considered to address vadose zone soil and groundwater impacts.

5.1.3 Alternative #3 No Action and ERD Source Treatment and MNA

This combined alternative would address the soil and groundwater in Plant 1. This approach consists of NA in vadose zone soils combined with ERD treatment in the saturated saprolite present in the vicinity of the materials handling area. The reducing conditions already present would be further enhanced by ERD



using this alternative, which would result in an overall reduction in toxicity in groundwater. While vadose zone impacts in this area appear to be limited, any remaining mass would be treated through flushing (NA) to groundwater where it would be treated as part of the saturated zone remedy. This alternative would be minimally invasive with a mobile ERD unit and can be customized based on substrate delivery (injection) and monitoring results. The conceptual layout of this alternative is shown on Figure 5-1.

5.1.4 Alternative #4 SVE and ERD Source Treatment and MNA

This alternative represents the most aggressive residual source removal/reduction. Mass present within the residual vadose zone soils would be addressed with SVE, volume and toxicity of the source area groundwater would be reduced with ERD, and the timeframe in which natural attenuation can be used to achieve clean-up goals would be reduced via the reduction in source mass. The conceptual layout of this alternative is shown on Figure 5-1. A phased approach would be applied during implementation of SVE and ERD for an adaptive remedy based upon conditions observed through the MNA program. This remedy would address all remedial action objectives for Plant 1.

5.2 Plant 2 The five alternatives for Plant 2 were selected to address residual vadose zone soil, dissolved-phase groundwater, and surface water impacts. Each of the alternatives described below are also discussed and evaluated in Table 5-2. The conceptual layouts for Alternatives #3, #4, and #5 are presented on Figures 5-2, 5-3, and 5-4. Each of the selected alternative evaluations are summarized below.

5.2.1 Alternative #1 No Action

The current levels of COCs within the source area and within the surface water of Plant 2 are currently above the MCLs to allow for NA. Additionally, the absence of a monitoring program would prevent verification that the alternative was working.

5.2.2 Alternative #2 Biosparge Barrier System and MNA

The elevated contaminant levels within the source area of Plant 2 are currently contributing to downgradient plume transport and surface water discharge, and natural attenuation processes are not significantly contributing to reductions within the plume. A biosparge barrier system is currently implemented at the site to address the groundwater to surface water interface, and this alternative would include modifications to the existing biosparge system (new biosparge wells, location of well network, depth of wells, and infrastructure) to make the network more robust, increase airflow to the subsurface, and improve volatilization of dissolved-phase COCs from groundwater and surface water (Figure 5-4). This alternative would address the groundwater and surface water media but not the meet the RAO for the vadose zone soils. Given the elevated COC concentrations observed in the source area and upgradient plume and their limited natural degradation, the anticipated timeframe for operation of the



current biosparge system and associated MNA program is likely decades in length. MNA is viable as a secondary remedy for dilute areas of the plume and as part of the long-term site management program in conjunction with other considered active remedial actions.

5.2.3 Alternative #3 AS/SVE in the Source Area, Dissolved-Plume ERD, Biosparge Barrier System, MNA

The combined remedial technologies provide COC removal from the vadose zone saprolite, saturated saprolite near the source area, and in saprolite/PWR groundwater along the length of the plume. Within the source area, saprolite soils and groundwater would be addressed via air sparge/SVE, which would entail installation of an air sparge and SVE recovery well network and placement of an on-site mobile treatment unit (Figure 5-2). Downgradient of the air sparge/SVE treatment network, supplemental COC treatment would be achieved for saprolite/PWR groundwater via an ERD injection program. As shown on Figure 5-2, a network of injection wells would be installed perpendicular to the plume to intersect COCs prior to downgradient discharge at the surface water tributary. These wells would be installed as part of a phased implementation program following initiation and operation of the source area air sparge/SVE program (Figure 5-2). Data collected during the onset of air sparge/SVE treatment would be reviewed to assess remedial performance and changes in groundwater concentrations within and outside the air sparge/SVE treatment area. This data would then be used to inform placement and orientation of the ERD injection wells, as appropriate. The biosparge barrier would remain in operation to continue facilitating COC volatilization near the point of discharge. While natural geochemical controls are expected to eliminate any secondary by products of the ERD program prior to surface water discharge (e.g., iron, manganese), the biosparge system would serve as an additional, redundant control mechanism to limit any discharge of these species to the tributary. This alternative meets the RAOs for all site media and can be completed in phases to tailor the remedy to site conditions. Implementation of this alternative would be classified as moderate due to the proximity of the air sparge/SVE wells and piping adjacent to the existing manufacturing building, but sufficient area exists for staging of this equipment. This alternative would include the relevant air sparge/SVE treatment and conveyance equipment; remediation wells for air sparge, SVE, and ERD treatment purposes; a mobile ERD injection system; and replacement or upgrade of the biosparge system wells and infrastructure.

5.2.4 Alternative #4 Source Area SVE and ERD, Dissolved Plume ERD, and Biosparge Barrier System

Similar to Alternative #3, this alternative would be effective in addressing COC mass in all impacted media at Plant 2. SVE would recover vadose zone soil impacts from the saprolite, ERD would address source area and dissolved plume groundwater impacts within the saprolite and PWR, and the biosparge barrier system would address the surface water concerns as described in Alternative #3. The ERD component of the source area treatment would target COC distribution within the saprolite and also address the transition interval between the saprolite and PWR to eliminate downgradient transport.

Implementation of this alternative would include an above-grade SVE and associated conveyance piping, remediation wells for SVE and ERD treatment, a mobile ERD system, and replacement or upgrade of the biosparge system wells and infrastructure. This alternative would require a relatively small footprint in the



source area when compared to the other alternatives due to the mobile ERD system. The small footprint reduces overall impacts on facility operations and associated risk during implementation and operation of the alternative. This alternative would meet all of the remedial action objectives for Plant 2. The conceptual layout of this alternative is shown on Figure 5-3.

As shown on Figure 5-3, implementation of this alternative would also entail a phased approach, with ERD source treatment initiated first and subsequent injection wells installed as appropriate based on observed changes in COCs and the observed distribution of organic carbon substrate beyond the radial injection area. Collectively, this step-wise program enables the ideal placement of injection wells relative to performance monitoring data and observed site conditions. The Phase II row of seven injection wells is provided for conceptual purposes on Figure 5-3.

The SVE well network proposed as part of Alternative #4 would consist of three total wells and an above-grade treatment system. The wells would be placed to address observed vadose zone concentrations identified during the Data Gap Investigation. The SVE well network is smaller in Alternative #4 compared to Alternative #3, as this network does not need to capture sparged air from the saturated saprolite interval. SVE operations in Alternative #4 would be completed concurrent with initial implementation of the ERD source treatment program (Phase I).

Alternatives #4 also includes the continued operation of the biosparge barrier system. It is anticipated that this system would be improved or augmented with additional biosparge wells and a new stream diffuser, as appropriate. This system would continue to provide point of discharge control for COCs migrating at the groundwater to surface water interface. The existing air compressor, heat exchanger, and shed will remain in place.

5.2.5 Alternative #5 ISTT Source Treatment, Dissolved-Plume ERD, and Biosparge Barrier System

The ISTT source treatment program provides a robust form of treatment for vadose zone and saturated saprolite. The available footprint for ISTT implementation is presented on Figure 5-4, which would cover the primary source material identified during the Data Gap Investigation. ISTT implementation would consist of a heating element and vapor recovery well installation throughout the approximately 10,000-square-ft area, above-grade vapor cover installation, above-grade power supply lines, and the necessary above-grade treatment system for both vapor and dissolved-phase COC treatment. In conjunction with the ISTT program, Alternative #5 also includes downgradient ERD treatment for control of COC mass in saprolite/PWR groundwater along the length of the plume. Similar to Alternatives #2, #3, and #4, (Figure 5-5) an ongoing biosparge system operation would be used to provide plume and surface water treatment at the point of plume discharge. Due to the elevated temperatures achieved during ISTT operation (e.g., 100 degrees Celsius), implementation of the ERD program would be initiated following ISTT operation and subsurface cool down periods. While the ISTT program is considered a robust form of source control, implementability concerns associated with the proximity of the ISTT network to Plant 2, detrimental impacts on ongoing Plant 2 operations, and the associated costs of treatment are considerable.



6 COMPARATIVE ANALYSIS OF ALTERNATIVES This section provides a comparative evaluation for the alternatives for Plant 1 and Plant 2, as presented in Tables 5-1 and 5-2.

6.1 Plant 1 The current remedial approach at Plant 1 is MNA, which relies on natural attenuation mechanisms to minimize COC flux and support COC treatment in saprolite and PWR units along the groundwater flow path. Coupled with current site property controls, COC attenuation effectively eliminates any potential exposure pathways. While currently effective for COC treatment, an MNA-only program (Alternative #2) has an extended timeframe to achieve overall remedial goals, which results in a lower ranking for reduction of toxicity, mobility, or volume as part of the comparative alternative analysis. Comparatively, Alternatives #3 and #4 also include direct-source treatment using ERD to take advantage of the already present anaerobic conditions in site groundwater and to enhance the natural biodegradation that is already ongoing. The ability to treat remaining mass in the vicinity of the materials handling area while remaining protective of human health and the environment are the primary rationale that contribute to the rankings of Alternatives #3 and #4 in the comparative analysis (Table 5-1).

Under Alternatives #3 and #4, injection wells would be installed at two different vertical intervals within the saprolite to address the thickness of primary COC mass observed during site characterization activities (Figure 5-1). A reduction in dissolved-phase saprolite mass would minimize downgradient COC transport within both the saprolite and PWR units. Influence from ERD treatment activities and clean water migration downgradient would then serve to expedite ongoing MNA processes. In conjunction with development of an ERD work plan, ERD and MNA performance monitoring programs would be developed to track the progress and attenuating parameters within the Plant 1 plume groundwater.

Compared to Alternative #4, Alternative #3 achieves the same overall dissolved-phase treatment benefit and reduction in remedial timeframe at a lower overall project cost. While Alternative #4 includes a supplemental SVE component to address any COCs in vadose zone soils, should that be necessary, historical data collected from the former materials handling area demonstrate that the presence of COCs above the applicable standards in unsaturated soils are very limited, and thus direct treatment in the vadose zone may not be needed. As a result, Alternatives #3 and #4 are generally equivalent in their ability to improve site conditions and reduce the overall monitoring duration. As calculated in Table 5-1, Alternative #3 scored a 34 out of a possible 35 while maintaining a low overall remedial cost. Alternative #2 scored a 33 out of a possible 35 and ranked below Alternative #3 based on the estimated reduction in timeframe to achieve reductions in toxicity, mobility and volume of contaminants.

6.2 Plant 2 As presented in Table 5-2, Alternatives #3 and #4 had the highest score in the comparative ranking and effectively balance source reduction, short-term and long-term effectiveness, implementability, and cost. Both alternatives utilize a combined remedial strategy to achieve RAOs related to vadose zone soil, groundwater, and surface water at Plant 2. Alternative #5 represents the most aggressive technology for source treatment but would require extensive surficial improvements and site access during operation,



which would be detrimental to current Plant 2 operations. Comparatively, while Alternative #5 achieves the overall remedial objectives faster than Alternatives #3 and #4, the latter two remedies still achieve comparable remedial endpoints at a significant lower overall cost.

From a technical standpoint, the ERD component of Alternative #4 for treatment of saprolite COC mass is considered to be more technically effective than the air sparge/SVE component in Alternative #3 for several key reasons. First, aqueous-phase injections completed during the ERD program will migrate through the saprolite and any more permeable flow pathways to perpetuate and sustain enhanced biological treatment. Dissolved-phase organic carbon materials can diffuse and permeate the finer-grained saprolite materials, which will enable more direct treatment of COC impacts that have had considerable residence time in the subsurface. Comparatively, air bubbles delivered via an air sparge/SVE program may exhibit increased tendency to remain in the most permeable channels and migrate upwards towards the SVE capture network, thereby limiting physical volatilization from diffuse COC source mass. A second advantage of Alternative #4 relative to Alternative #3 is the uniform geochemistry established in both the source area and along the plume length. Once injected, the soluble organic carbon electron donor would be anticipated to migrate through similar pathways as the site COCs, and utilization of these materials will foster development of highly reducing groundwater conditions (i.e., methanogenic) that are required for ERD. Operation of the ERD program along the plume length will, therefore, establish reducing conditions throughout the target treatment area and improve overall remedial efficiency. Comparatively, air sparge/SVE operation upgradient of an existing ERD injection transect would likely foster a sustained supply of dissolved oxygen that would need to be then reduced via ERD in advance of COC utilization as an electron acceptor. A final advantage of the ERD treatment remedy at Plant 2 is its ability to leverage existing degradation mechanisms already underway. While dechlorination at Plant 2 is not as complete as that observed at Plant 1, the observations of cis-1,2-DCE and vinyl chloride concentrations in Plant 2 groundwater demonstrate that a suitable microbial population is already in place. Air sparge/SVE operations would limit these naturally occurring activities and would rely on physical removal alone.

As calculated in Table 5-2, Alternative #4 scored a 29 out of a possible 35. Alternative #3 also scored a 29 out of a possible 35 but is considered less technically applicable to addressing residual VOC mass present within the saprolite and would be more difficult to implement based on the current site conditions.

6.3 Institutional Controls In addition to the alternatives discussed in the previous sections, institutional controls will be utilized as part of the remedial alternative to mitigate risks associated with potential exposure to in-place residual contamination. A number of physical and administrative LUCs are in place and are summarized below.

Restrictive covenant on the use of groundwater and creek water

Restrictive covenants limiting the potential for disturbance of the Closed Landfill Area, the Materials Handling Area, and the Closed Pond Areas

Fencing around the site with access available to authorized personnel only

The asphalt cover and capped footprint of the former materials handling area

The capped area marked with signage identifying the consolidation area at the former Plant 1 Pond



The fencing and cover at the former landfill

No additional institutional controls are proposed at this time. If conditions change and warrant reconsideration, additional institutional controls will be evaluated at that time.

7 REFERENCES Arcadis. 2015. Data Gap Investigation Work Plan. 3M Company, Laurens CeramTec Site: ID #5094.

August.

Arcadis. 2016a. 2015 Annual Monitoring Report. 3M Company, Laurens CeramTec Site: ID #5094. February.

Arcadis. 2016b. Focused Feasibility Study Work Plan – Revision 1. 3M Company, Laurens CeramTec Site: ID #5094. August 16.

Arcadis. 2016c. Semi-Annual Progress Report. 3M Company, Laurens CeramTec Site: ID #5094. July 28.

Garihan. 2001. Bedrock Geology of the Hickory Tavern 7.5 Minute Quadrangle, Southeastern Inner Piedmont, Laurens and Greenville Counties, South Carolina, South Carolina Geology, V. 42, p 1-15.

Heath. 1984. Groundwater Regions of the United States, U.S. Geological Survey Water Supply Paper, no 2242, 78 p.

Heath. 1988. Hydrogeologic Setting of Regions, in Back, W., Rosensheim, J.S., and Seaber, P.R., eds. Hydrogeology, Boulder, Colorado, Geological Society of America, The Geology of North America, vol. 0-2.

Laurens County. 2005. Easement Agreement between 3M Company and CeramTec North American Corporation, Document #500504584. May 23.

LeGrand. 1954. Geology and Groundwater in the Statesville Area, North Carolina, North Carolina Department of Conservation and Development Bulletin, no. 68.

LeGrand. 1967. Groundwater of the Piedmont and Blue Ridge Provinces in the Southeastern States, U.S. Geological Survey Circular, no 538, 11p.

LeGrand. 2004. A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina, North Carolina Department of Environment and Natural Resources, Division of Water Quality, Groundwater Section.

Niewendrop. 1995. Geology of the Laurens North 7.5-Minute Quadrangle, South Carolina: 1:24,000. South Carolina Department of Natural Resources, Open File Report 89.

Ranson and Garihan. 2001. Geology of the Inner Piedmont in the Caesars Head and Table Rock State Parks Area, Northwestern South Carolina: 2001 Carolina Geological Society Field Trip, South Carolina Geology, vol. 43, p 73-86.

SCDHEC. 2012. R.61-68, Water Classifications and Standards. Bureau of Water, SCDHEC. June 22.

SCDHEC. 2013. Focused Feasibility Study Request Letter. 3M Company, Laurens CeramTec Site: ID #5094. August 22.



USEPA. 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA. EPA/540/G-89/004. OSWER Directive 9355.3-01. October.

USEPA. 2009. Drinking Water Standards and Health Advisories Table. November.

USEPA. 2017. Regional Screening Levels (RSLs) Summary Table. USEPA. June.

Weston. 1998. Plant 2 Remedial Options Evaluation and Implementation Plan. Laurens Ceramics Site. Laurens, South Carolina. January 29.

Weston. 1999. Landfill Closure Report. Laurens Ceramics Site Landfill. Laurens, South Carolina. June.

Weston. 2006. Closure Report. Former Materials Handling Area. Laurens Ceramics Site. Site ID No, 00172. May 10.

TABLES

Focused Feasibility Study Ceramtec Site

Laurens, South Carolina

Overall Protection of Human Health and the Environment 3

Existing site controls limit contact with residual vadose zone and saturated zone VOC impacts. Combined natural attenuation processes eliminate discharge to surface water and potable water supply pathways while promoting destruction of VOCs along primary plume flow path. Without monitoring no way to track progress to ensure remedy effectively achieving objectives

5

Existing site controls limit contact with residual vadose zone and saturated zone VOC impacts. Combined natural attenuation processes eliminate discharge to surface water and potable water supply pathways while promoting destruction of VOCs along primary plume flow path.

5

Provides protection of human health and environment through reduction of COC mass. ERD would provide treatment of groundwater in both the source area (direct injection) and downgradient plume (via transport of carbon substrates and generation of in-situ reactive zone).

5

Provides protection of human health and environment through removal of VOCs from source area soils/groundwater. SVE provides treatment of source area soils and ERD provides source area groundwater treatment to eliminate ongoing contributions to downgradient plume. MNA to monitorin

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