Basis of Design.pdf

EPA CONTRACT NO. EP-S1-06-01

EPA TASK ORDER NO. 0014-RD-RD-01D5

Updated under:

EPA CONTRACT NO. 68HE0318D0002

TASK ORDER NO. 68HE0119F0023

EPA Project Officer: Heidi Horahan

EPA Task Order Project Officer: Ed Hathaway

BASIS OF DESIGN REPORT

for the

DMC STUDY AREA SOIL REMEDIAL DESIGN

Durham Meadows Superfund Site

Durham, Connecticut

REVISED FINAL

September 2016

Updated June 2022

AECOM

June 2022 i

Contents

1.0 Introduction .................................................................................................................... 1-1

2.0 Site Description and History......................................................................................... 2-1

3.0 Selected Remedy and Cleanup Goals ......................................................................... 3-1

3.1 Selected Remedy................................................................................................................. 3-1

3.2 Cleanup Levels and Soil Excavation Goals ........................................................................ 3-1

3.3 Potential Reuse Considerations .......................................................................................... 3-2

4.0 Distribution of Site Contaminants in Soil .................................................................... 4-1

4.1 Northwest Corner Area ........................................................................................................ 4-1

4.2 WS-20 Area .......................................................................................................................... 4-2

4.3 Eastern Area ........................................................................................................................ 4-3

5.0 Soil Excavation .............................................................................................................. 5-1

5.1 Estimated Volume of Soil to be Disposed of as RCRA Characteristic Waste ................... 5-2

5.2 Estimated Volume of Soil to be Disposed of as RCRA Listed Waste ................................ 5-2

5.3 Estimated Volume of Soil to be Disposed of as Non-RCRA Hazardous Material ............. 5-3

5.4 Confirming Limits of Excavation .......................................................................................... 5-3

5.5 Backfilling including Placement of Zero Valent Iron Reactive Backfill ............................... 5-3

5.6 Site Restoration ................................................................................................................... 5-4

6.0 Design Considerations ................................................................................................. 6-1

6.1 Geotechnical and Utility Considerations ............................................................................. 6-1

6.2 Conducting Excavation at an Active Manufacturing Facility............................................... 6-2

6.3 Dewatering during Excavation ............................................................................................. 6-2

6.4 Monitoring Wells and Former Extraction Wells ................................................................... 6-2

6.5 Perimeter Air Monitoring ...................................................................................................... 6-3

6.6 Excavation and Backfill Sequencing ................................................................................... 6-3

7.0 Environmental and Public Impacts .............................................................................. 7-1

7.1 Erosion and Sediment Control During Construction ........................................................... 7-1

7.2 Dust and Emissions Control ................................................................................................ 7-1 ii

7.3 Noise, Traffic ........................................................................................................................ 7-2

7.4 Impact on Abutting Residences........................................................................................... 7-2

8.0 Compliance with ARARs and Permits ......................................................................... 8-1

9.0 References ..................................................................................................................... 9-1

List of Attachments

Attachment A Draft Technical Memorandum for DMC Study Area Pre-Remedial Design Soil Data Evaluation

Attachment B List of Design Drawings and Specifications

List of Figures

Figure 2-1 Site Locus Map

Figure 2-2 Site Plan and Excavation Areas

Figure 2-3 Site Utility Plan

Figure 4-1 Historical and 2014 Soil Boring Locations – Northwest Corner Area

Figure 4-2 Historical and 2014 Soil Boring Locations – WS-20 Area

Figure 4-3 Historical and 2014 Soil Boring Locations – Eastern Area

Figure 5-1 Excavation Depths and Extent of Zero Valent Iron Backfill Placement

Figure 6-1 Utilities within Excavation Area

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Highlight Has this been checked against the final specs and plans? should we just delete this attachment?

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1-1

1.0 Introduction

The purpose of this Basis of Design Report (BODR) for the Durham Meadows Superfund Site, Durham Manufacturing Company (DMC) Study Area, located in Durham, Connecticut, is to define the technical parameters used to design the soil excavation component of the remedy for the DMC Study Area. The rationale for the selected remedy is presented in the Record of Decision (ROD) for the Durham Meadows Superfund Site (USEPA, 2005).

The BODR was prepared by AECOM under the EPA Response Action Contract 2 (RAC 2), EP-S1- 06-01, Task Order #0014-RDRD-01D5 and updated in 2022 to address comments from the USACE.

This final version of the BODR reflects the development of the design to the 100% design phase.

Pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), 42 U.S.C. § 9601 et seq., a Remedial Investigation (RI) and Feasibility Study (FS) were originally prepared for the Site in 2005. EPA issued a Record of Decision (ROD) in September 2005 (USEPA, 2005) that selected remedial actions for all areas of the Site, based on the results of the 2005 RI and FS.

Included in this report are the Site history and background, a brief summary of the results of the additional investigations, the remedial action objectives and cleanup goals, various design considerations, and identification of the drawings and technical specifications for implementation of the remedial action. Also, the Pre-Remedial Design Soil Data Evaluation Technical Memorandum for the DMC Study Area (AECOM, 2015) is included as Attachment A to this report. This memorandum was prepared in advance of the DMC Study Area soil design in order to present and evaluate the results of pre-remedial design sampling and related field activities that were conducted in 2014 to support the design. It should be noted that the discussion of extent of contaminated soils to be remediated and associated information have been superseded by the discussion in this report.

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2.0 Site Description and History

The Durham Meadows Superfund Site (the Site) is located in the southern Connecticut town of Durham in Middlesex County (Figure 2-1). The Site encompasses an area of groundwater contamination generally centered along Main Street in Durham and includes industrial and residential properties. The Site is generally bounded by Talcott Lane to the north; Brick Lane, Ball Brook and Allyn Brook to the East; wetlands west of Maple Avenue to the west; and based on recent sampling, the intersections of Maple Avenue and Fowler Avenue with Main Street to the south. Additionally, the RSD13 School District and the Durham Fairgrounds are within the Site boundary.

The site is centered around the former Merriam Manufacturing Company at 281 Main Street and a currently operating manufacturing facility, DMC, located at 201 Main Street. The “DMC Study Area” includes the property on which DMC currently operates at 201 Main Street, excluding the portion of the property east of Ball Brook, and a portion of the abutting residential property at 215 Main Street (Korn property) (Figure 2-2).

As summarized from the ROD for the site (USEPA, 2005), DMC was established in 1922 at 201 and 203R Main Street. DMC manufactures metal boxes and displays and has used various solvents during its operations. The ROD described an area of soil and overburden groundwater impacts with trichloroethene (TCE) and tetrachloroethene (PCE) around a former solvent storage tank on the north side of the main manufacturing building, as well as an area of non-chlorinated volatile organic compound (VOC) contaminated soil and overburden groundwater to the east of the main building, in area where former tanks that stored ethylbenzene, toluene, and xylene for use as paint solvents may have been maintained. A potential additional contaminant source area was described as being located near the former leach field to the northeast of the main manufacturing building, based on a high historical detection of TCE in that area. These three areas have been referred to more recently as the “Northwest Corner Area”, the “WS-20 Area”, and the “Eastern Area.” See Figure 2-2 for the location of these three areas.

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3.0 Selected Remedy and Cleanup Goals

The selected remedy and the cleanup goals for the DMC Study Area, as identified in the ROD, are described in this section, along with the potential reuse considerations.

3.1 Selected Remedy

The remedy for the DMC Study Area includes excavation and off-site disposal of soil hot spot areas (including DNAPL if encountered) at the DMC Study Area along with institutional controls, in order to address risks to human health from VOC contamination in overburden (shallow) groundwater and to address source contamination. Long-term monitoring of groundwater will be performed to demonstrate the effectiveness and protectiveness of the remedy. The remedy also includes further delineation of areas posing potential indoor air risks on and outside of the DMC Study Area along with further action to address any unacceptable risks that may be identified.

3.2 Cleanup Levels and Soil Excavation Goals

Overburden groundwater was identified as the medium requiring the development of cleanup levels at the DMC Study Area. Interim cleanup levels for groundwater at the DMC Study Area were established in the ROD for seven chemicals of concern, including TCE, PCE, vinyl chloride, 1,1,1-trichloroethane, ethylbenzene, toluene, and xylenes.

The remedial action objectives (RAOs) for the DMC Study Area, as identified in the ROD, include:

To reduce the potential exposure of future construction workers at the DMC Study Area to trichloroethene in shallow (overburden) groundwater via dermal contact that may present a human health target organ HI>1 such that the non-cancer risk attributable to this medium is a HI which does not exceed one for the protection of human health.

To reduce direct contact and inhalation exposures to 1,1,1-trichloroethane, tetrachloroethene, and toluene in overburden groundwater at the DMC Study Area by complying with the ARARs (MCLs and CT RSR GWPC and GWVC). (These groundwater ARARs are waived pursuant to the technical impracticability discussion in Section I of this ROD).

If it is determined, after further investigation, there are areas posing an unacceptable risk, actions will be taken to reduce the potential for ethylbenzene, trichloroethene, vinyl chloride, and xylene present in shallow groundwater at the DMC Study Area to volatilize into buildings.

The goal of the soil excavation component of the remedy for the DMC Study Area is to (1) remove source areas to the maximum extent practicable (with the goal of meeting Interim Cleanup Levels for groundwater in the DMC Study Area), and (2) remove any soil exceeding direct exposure criteria (DEC) and pollutant mobility criteria (PMC) under the Connecticut Remediation Standard Regulations (CT RSRs). Since the DMC Study Area is within an area with a groundwater classification currently designated as GA or GAA, but that may not meet current standards, the GA/GAA PMC will be used to guide the extent of soil excavation.

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3.3 Potential Reuse Considerations

Potential future uses for the DMC Study Area were considered during development of the remedial action cleanup objectives. The ROD indicated that property associated with the Superfund site was expected to continue to be used for its current purpose and it was assumed that DMC would continue to operate its business at this location.

Under existing zoning, residential homes could also be built on the property; however, an Environmental Land Use Restriction (ELUR) is planned that once in place, will restrict residential activities on the DMC property. Potential future residential use of this property was considered in the Remedial Investigation/Feasibility Study and Human Health Risk Assessment as a conservative, worst-case scenario with respect to exposure.

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4.0 Distribution of Site Contaminants in Soil

The distribution of Site contaminants in soil across the DMC Study Area is summarized in the following subsections for each of the three identified source areas, including the “Northwest Corner Area”, the “WS-20 Area”, and the “Eastern Area”.

The distribution of VOC contamination in soil has been evaluated with respect to the CT RSR DECs and PMCs to determine the extent of soil that will require excavation under the selected remedy for the DMC Study Area. VOC concentrations in soil are compared to the Industrial/Commercial (I/C) DECs, as well as the GA/GAA PMC. Additionally, SPLP or TCLP analysis for VOCs has been conducted on many soil samples and those results are compared to groundwater protection criteria (GWPC) in the CT RSRs. This comparison is done because the CT RSRs allow for pollutant mobility to be addressed for soil in a GA area, that is located above the seasonal low water table, by remediating to at least a concentration at which the results of a TCLP or SPLP analysis of the soil does not exceed the GWPC. The GA/GAA PMC do not apply to soils located below the seasonal low water table. The I/C DEC do not apply to soils located greater than 15 feet below the ground surface.

The distribution of VOC contamination (particularly TCE concentrations) in deeper soils, where the CT RSR DECs and PMCs do not apply, was also evaluated to assess locations where deeper soil excavation down to bedrock should be conducted to remove source areas that may serve as a continuing source for groundwater contamination.

In order to determine the Seasonal Low Water Table in each of the three investigation areas, GZA conducted a monthly water level monitoring program over periods from November 2008 through October 2009 and January 2011 through August 2011. The water level data is presented and evaluated in the Third Interim Soil Data Report (GZA, 2013). To summarize, the following ranges were determined for the Seasonal Low Water Table:

Area Depth (feet below grade) Elevation (feet above MSL)

Northwest Corner 12.0 (west end, OW-2R) to 8.4 (east end, OW-3-08)

201.8 (west end, OW-2R) to 195.0 (east end, OW-3-08)

WS-20 10.4 (central, OW-19-09) to 10.5 (east end, OW-20-09)

192.5 (central, OW-19-09) to 189.8 (east end, OW-20-09)

Eastern 6.9 (OW-6R-08) to 10.1 (northeast corner, OW-7R-08)

194.3 (OW-6R-08) to 190.7 (northeast corner, OW-7R-08)

4.1 Northwest Corner Area

Both surface (0 to 4 feet) and subsurface (greater than 4 feet) soil in the area along the north side of the main manufacturing building (Figure 4-1) are impacted by VOCs, primarily TCE and PCE, at concentrations that exceed CT RSR criteria. In general, VOCs impacts in soil extend from sample location R5C1, eastward along the driveway on the north side of the building, and extend just north of the driveway and onto the Korn property at a few sample locations. The highest concentrations of TCE were detected in subsurface soil samples from depths between 9 to 12.5 feet below the ground

4-2 surface that were located along the driveway adjacent to a former interior solvent storage tank and vapor degreaser. Other VOCs detected at concentrations exceeding CT RSR criteria included vinyl chloride, 1,2-dichloroethane, 1,2-dichloropropane, methylene chloride, hexachlorobutadiene, xylenes, benzene, and naphthalene. Benzene and naphthalene are included based on leachable benzene and naphthalene concentrations that exceeded the groundwater protection criteria (GWPC) in a sample located on the Korn property (NWC-15; 6 to 7 feet), well to the north of the other soil impacts above CT RSR criteria, and proximate to the leachfield for the Korn property. These detections are assumed to not be site-related given the absence of benzene and naphthalene in nearby borings.

Total VOC analytical results were compared to the CT RSR Industrial/Commercial (I/C) DECs. Within the 0 to 7 foot depth below the ground surface, none of the soil sample results exceeded CT RSR I/C DECs for VOCs. Based on samples collected from deeper than 7 feet below the ground surface, the I/C DEC for TCE was exceeded in two samples: R5C60 (11 to 12 feet) and R5C90 (9 to 10 feet).

Both of these soil samples are from borings clustered in the general area of the former interior solvent storage tank and vapor degreaser along the driveway.

Total VOC analytical results were also evaluated with respect to the CT RSR GA/GAA PMC and SPLP and TCLP VOC analytical results were evaluated with respect to the GWPC. The extent of soil impacts above these criteria are more widespread than the DEC exceedances and drive the overall extent of soil requiring excavation in the Northwest Corner Area. The extent includes several locations within surface and subsurface soil down to the seasonal low water table. Note that the PMC do not apply below the seasonal low water table.

TCE analytical results were also evaluated at depths below the seasonal low water table, and where the I/C DECs were not exceeded, to determine areas to require soil excavation down to bedrock to remove additional source contamination. Soil samples with TCE concentrations greater than 1,000 ug/L were generally used to guide the extent of these additional areas of soil to be excavated down to bedrock. In the Northwest Corner Area, an area has been identified for excavation to bedrock that extends along the edge of the building and encompasses several deep soil samples: R5C45 (11 to 12 feet), R10C60 (11 to 12 feet), R20C60 (11 to 12 and 12 to 13 feet), R10C75 (11.5 to 12.5 feet), R5C90 (13 to 14 feet), R10C90 (11 to 12 feet), R20C90 (11 to 12 feet), R5C105 (12.5 to 13.5 feet), R5C120 (13.5 to 14.5 feet), R20C120 (11.5 to 12.5 feet), R22C120 (9 to 10 feet), R5C150 (9 to 10 and 10 to 11 feet), R20C150 (9 to 10 and 13.5 to 14.5 feet), R22C150 (9 to 10 feet), and R20C180 (14 to 15 feet), A-NWC-12 (8 to 12 feet), and A-NWC-13 (8 to 12 feet). A separate area has been identified near the northeast corner of the building along the driveway and encompasses deep soil samples EA-1-09 (10 to 11 feet), EA-2-09 (10 to 11 feet), and EA-3-09 (10 to 11 feet). EA-1-09 (10 to 11 feet) is included because of the high 1,1,1-TCA concentration of 39,000 ug/L (and elevated reporting limit for TCE).

4.2 WS-20 Area

Both surface (0 to 4 feet) and subsurface (greater than 4 feet) soil in the area south of the drying shed located between the two main DMC buildings (Figure 4-2) are impacted by non-chlorinated VOCs, including primarily toluene, ethylbenzene, and xylenes, which were used as paint solvents.

Additionally, surface and subsurface soil across a broader area including the northwest, west, south, and east sides of the drying shed are impacted by chlorinated VOCs, primarily TCE, PCE, and methylene chloride. Other VOCs detected at concentrations exceeding CT RSR criteria included benzene, naphthalene, isopropylbenzene, cis-1,2-dichloroethene, 1,2-dichloroethane, and vinyl chloride. The highest concentrations of toluene, ethylbenzene, and xylenes were detected in soil samples from within the 4 to 7 foot interval below the ground surface, with concentrations decreasing

4-3 significantly deeper than 7 feet below the ground surface. On the other hand, concentrations of chlorinated VOCs appear to increase with depth.

Total VOC analytical results were compared to the CT RSR I/C DECs. Within the 0 to 4 foot depth below the ground surface, none of the soil sample results exceeded CT RSR I/C DECs for VOCs.

Within the 4 to 7 foot depth below the ground surface, I/C DECs were exceeded in four soil samples, including N-1 (4-5 feet) (but not its field duplicate), S-1 (4 to 5 feet), E-1 (4 to 5 feet), and E-2 (4 to 5 feet). Ethylbenzene and xylenes exceeded the I/C DECs in all four samples and toluene exceeded the I/C DEC in two out of four samples. In sample N-1 (4 to 5 feet), cis-1,2-dichloroethene (cis-1,2- DCE), TCE, and PCE also exceeded the I/C DEC. All of these samples are from locations just south of the existing shed in the WS-20 Area.

Total VOC analytical results were also evaluated with respect to the CT RSR GA/GAA PMC and SPLP and TCLP VOC analytical results were evaluated with respect to the GWPC. The extent of soil impacts above these criteria are more widespread than the DEC exceedances and drive the overall extent of soil requiring excavation in the WS-20 Area. The extent includes several locations within surface and subsurface soil down to the seasonal low water table. For the non-chlorinated VOCs, the extent of impacts is limited, with two exceptions, to a contiguous area just south and southwest of the existing shed in this area. Two soil samples, including E-7 (3-4) and S-4 (3-4), contained leachable benzene at concentrations above the GWPC. These appear to be isolated occurrences, since leachable benzene was not detected in other samples in this area, and may be related to impacts from automobiles parking in this area. As noted above, the extent of chlorinated VOC impacts covers a broader area of surface and subsurface soil including the northwest, west, south, and east sides of the drying shed.

TCE analytical results were also evaluated at depths below the seasonal low water table, and where the I/C DECs were not exceeded, to determine areas to require soil excavation down to bedrock to remove additional source contamination. Soil samples with TCE concentrations greater than 1,000 ug/L were generally used to guide the extent of these additional areas of soil to be excavated down to bedrock. In the WS-20 Area, an area has been identified for excavation to bedrock that includes the area of the drying shed and extends to the south and west. This area encompasses several deep soil samples: N-1 (15 to 16 feet), N-2 (13.5 to 14.5 feet), W-2 (16 to 17 feet), E-1 (16 to 17 feet), NW-1 (15.5 to 16.5 feet), and NE-1 (14 to 15 feet). The drying shed footprint is also included because of the lack of soil data within the footprint and the elevated TCE concentrations in the closest borings to the west and southwest.

4.3 Eastern Area

VOC impacts to surface (0 to 4 feet) and subsurface (greater than 4 feet) soil have also been detected in an area to the northeast of the main manufacturing building (Figure 4-3) referred to as the Eastern Area, where an industrial wastewater leaching gallery and two sludge settling lagoons were historically located. TCE and methylene chloride are the primary VOCs detected in this area and are the only VOCs that exceeded CT RSR criteria. None of the soil samples from the Eastern Area contained VOCs above the I/C DEC. Within the 0 to 4 foot depth, only two soil samples, including EA- 1C-08 (o to 2 feet) and EA-4D-09 (0 to 2 feet), exceeded the GWPC for leachable TCE. Within the 4 to 7 foot depth, the number of exceedances was larger and included both TCE and methylene chloride. Below the 7 foot depth, soil samples were either located below the seasonal low water table or did not contain VOCs above the CT RSR criteria. Overall, the extent of soil impacts is well defined in the Eastern Area.

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In this area, TCE analytical results were also evaluated at depths below the seasonal low water table, to determine areas to require soil excavation down to bedrock to remove additional source contamination. In general, TCE concentrations below the seasonal low water table in the Eastern Area are low compared to the Northwest Corner Area and WS-20 Areas; however, one location with a TCE concentration greater than 1,000 ug/L was identified within the current excavation footprint. The deep soil sample EA-2D-09 (7 to 8 feet) and the area immediately surrounding this location will be targeted for soil excavation down to bedrock.

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5.0 Soil Excavation

As described in Section 4.0, DMC Study Area surface and subsurface soils from the Northwest Corner Area, WS-20 Area, and Eastern Area are impacted by VOCs that exceed CT RSR DECs and GA/GAA PMCs. For the most part, the CT RSR PMC or GWPC (for SPLP or TCLP analysis) determine the extent of soil to be excavated. However, there are a small number of samples from below or partially below the seasonal low water table, but above 15 feet below the ground surface, that contain VOCs that exceed the I/C DEC and therefore, require excavation. The two soil samples (R5C60 [11 to 12 ft] and R5C90 [9 to 10 ft]), which contain TCE above the I/C DEC, are clustered in the same portion of the Northwest Corner Area along the driveway adjacent to a former interior solvent storage tank and vapor degreaser. Additionally, elevated concentrations of TCE (generally greater than 1,000 ug/L) are located in subsurface soils below the limits of where the CT RSR criteria apply in certain portions of the Northwest Corner Area, WS-20, and Eastern Area and will require excavation down to bedrock to remove additional source contamination. See Figure 5-1 for the extent and depth of soil excavation.

The lateral extent of soil to be excavated has been generally delineated using compliant samples to bound the limits of excavation. The limit of excavation next to the DMC building (Phase 01A) is fixed.

There are a few exceptions where the remediation contractor will be required to collect samples for analysis prior to excavation to provide confirmation of the excavation limits. At the eastern edge of the WS-20 Area, a sample will be needed to the east of boring E7 to provide lateral confirmation that the benzene concentration in the 3-4 foot depth at E7 has been bounded. Where the Northwest Corner Area and Eastern Area merge, two soil borings will be needed. Samples will be needed north of EA-3- 09 to provide lateral confirmation that the TCE and cis-1,2-DCE concentrations at the 0-4 foot depth and 4-9 foot depth at EA-3-09 have been bounded. A sample will be needed west of EA-5 to provide lateral confirmation that the TCE concentration at the 6-7 foot depth at EA-5 has been bounded.

With the exception of the areas targeted for excavation down to bedrock, the vertical extent of soil to be excavated has been generally defined using either a deeper compliant sample or the seasonal low water table, whichever is shallower.

For the purpose of estimating the extent and volume of soil to be excavated, assumptions were made in the areas where uncertainty exists in order to establish excavation limits. The excavation estimate assumes that the two main DMC buildings will remain in place, but the drying shed will be demolished prior to excavation and replaced as part of the site restoration.

Based on the excavation extent developed for the 100% design drawings, the total volume of soil to be excavated is estimated at 10,745 cubic yards.

The Contractor will be required to conduct a soil pre-characterization program for the purpose of obtaining necessary analytical data needed for disposal facility approval and also to define areas of soil to be excavated and managed and disposed as RCRA characteristic waste. As discussed below in Section 5.2, it appears unlikely that any excavated soil will need to be managed and disposed as RCRA listed waste. During excavation activities, the Contractor will be required to segregate RCRA characteristic waste from non-RCRA waste for handling and off-site disposal. The determination of what soil requires handling as RCRA characteristic waste would be made based on the results of the

5-2 pre-characterization program. The analytical basis for the manifests will be the pre-characterization data obtained by the Contractor and supplemented with existing soil data as appropriate.

5.1 Estimated Volume of Soil to be Disposed of as RCRA Characteristic Waste

As part of the 2014 supplemental soil sampling conducted by AECOM, certain soil samples from each of the Northwest Corner, WS-20 Area, and Eastern Area were collected and analyzed for a larger suite of analysis in order to assess soils that may require disposal as RCRA listed or characteristic waste. The additional analyses included total metals, TCLP metals, pesticides, polychlorinated biphenyls (PCBs), extractable total petroleum hydrocarbons (ETPH), herbicides, and waste characteristics (ignitability, reactivity, corrosivity). In addition, TCLP VOC analysis was performed on those samples when total VOC concentrations were above the “twenty-times rule” concentrations.

The twenty-times rule concentrations are those below which, even if 100 percent extraction occurred during the TCLP, the sample could not exceed RCRA toxicity characteristic maximum concentrations.

None of these waste characterization samples exceeded RCRA characteristic limits. However, based on review of the much larger set of available SPLP VOC results, certain SPLP VOC results do exceed the RCRA toxicity characteristic limits and therefore, it is expected that some excavated soil will require disposal as RCRA characteristic waste. SPLP TCE and/or PCE concentrations in samples N-1 (4 to 5 feet), E-2 (4 to 5 feet), and E-3 (4 to 5 feet) from the WS-20 Area exceeded RCRA toxicity characteristic limits. In addition, SPLP TCE, and/or 1,2-dichloroethane results in samples R10C90 (4 to 5 feet and 9 to 10 feet), R22C90 (3 to 4 feet and 9 to 10 feet), R5C90 (4 to 5 feet), R22C150 (4 to 5 feet), R5C105 (4 to 5 feet and 9 to 10 feet), R22C120 (9 to 10 feet), and R20C90 (9 to 10 feet) from the Northwestern Corner Area exceed RCRA toxicity characteristic limits.

For the purpose of estimating soil disposal costs, these samples were used to estimate a volume of soil to be disposed of as RCRA characteristic waste. The estimated soil volume is 1,000 cubic yards for the Northwest Corner Area and WS-20 Area combined.

5.2 Estimated Volume of Soil to be Disposed of as RCRA Listed Waste

Consideration was given to whether any of the excavated soil would require disposal as RCRA listed waste. The 2005 ROD stated that “Based on analytical data from an extraction well "EX-6" on the DMC property, it appears that a methylene chloride spill may have occurred in the area sometime in the mid-1990's. Analytical data provided in a [1997] draft work plan for remedial investigation work by DMC's contractor Leggette, Brashears & Graham (LB&G) indicates that methylene chloride detections in EX-6 increased from 168 parts per billion (ppb, or ug/L) on May 3, 1995, to 2,977,000 ppb on August 15, 1995.” Well EX-6 is located in the Northwestern Corner Area adjacent to the main building. Based on this information, EPA is assuming that a methylene chloride spill occurred at that location and that the spilled methylene chloride would be considered RCRA listed waste using waste code F001. No indication of documentation of spills of other degreasing solvents such as TCE and 1,1,1-TCA or paint solvents such as xylenes, ethylbenzene, and toluene are provided in the ROD, so it is assumed that these other solvents would not be RCRA listed waste.

Methylene chloride was detected in several soil samples from the site. This soil would be considered contaminated by RCRA listed hazardous waste (waste code F001) as defined under 40 CFR 261.31.

If soils containing methylene chloride were excavated, then the soil may be required to be disposed of in a RCRA hazardous waste landfill. Based on EPA’s “contained-in” policy, the soil is therefore also considered RCRA-listed hazardous waste unless the concentrations of the listed hazardous wastes are below health-based levels (USEPA, 1998). EPA recommends that the “contained-in

5-3 determination be made based on direct exposure using a reasonable maximum exposure scenario and that conservative, health-based standards be used to develop the site-specific health-based levels of hazardous constituents below which contaminated environmental media would be considered to no longer contain hazardous waste” (USEPA, 1998).

Site-specific risk-based cleanup levels are not available for soil at the DMC Study Area. Instead, EPA Regional Screening Levels (RSL) for methylene chloride for Industrial Soil (1,000 mg/kg) or Residential Soil (57 mg/kg) (based on the May 2014 update) could be used as health-based levels.

Alternatively, the Connecticut Department of Energy and Environmental Protection (CT DEEP) has a RCRA “Contained-In” Policy for contaminated soil and groundwater that is managed in Connecticut.

Following that policy, soil containing methylene chloride would be considered listed hazardous waste if the concentration is above the lower of the Industrial/Commercial Direct Exposure Criterion (760 mg/kg) and 100 x GA Pollutant Mobility Criterion (10 mg/kg). Results of a leachate analysis can also be considered when available. In summary, if Connecticut’s RCRA “Contained-in” Policy is followed, soil containing greater than 10 mg/kg methylene chloride would be considered RCRA listed waste. If we use only EPA’s RSL, soil containing greater than either 57 mg/kg or 1,000 mg/kg methylene chloride (depending on whether a residential or industrial value is appropriate) would be considered RCRA listed waste.

The maximum detected concentration of methylene chloride in soil at the DMC Study Area based on historical total VOC analysis is 1.1 mg/kg (sample S-1 [4 to 5 feet] in the WS-20 Area). In the Northwest Corner Area near well EX-6, the maximum concentration is 0.14 mg/kg. Based on these results, it seems unlikely that excavated contaminated soils will contain methylene chloride above any of the health based levels indicated in the previous paragraph and therefore would not be subject to RCRA requirements for listed waste.

5.3 Estimated Volume of Soil to be Disposed of as Non-RCRA Hazardous Material

Aside from the soil described in the previous sections, which will likely require disposal as RCRA characteristic waste, the majority of soil to be excavated from the DMC Study Area is expected to be acceptable for disposal as non-RCRA hazardous material. The estimated volume of soil to be disposed of as non-RCRA hazardous material is approximately 9,745 cubic yards.

5.4 Confirming Limits of Excavation

As described in detail in Section 5.0, there are a small number of locations where sampling will be needed prior to conducting soil excavation in order to confirm that the excavation limits as designed, will bound the full lateral extent of soil exceeding CT RSR criteria in the Northwest Corner Area, Eastern Area, and WS-20 Area..

5.5 Backfilling including Placement of Zero Valent Iron Reactive Backfill

Backfilling will involve placement of clean fill to return the excavated areas generally to the pre-excavation grades. Excavation and backfilling will be conducted in stages in order to minimize the area of open excavation. Granular backfill will be placed in lifts and compacted in accordance with the specifications. Bank or crushed gravel will be placed in the excavation abutting the main building and will not be compacted with vibratory roller to ensure there is no damage to the building walls or foundation. Along the excavation limit sidewalls, a demarcation layer consisting of geotextile or snow fencing will be installed to mark the final limits of excavation.

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In certain areas designated for soil excavation down to bedrock, zero valent iron (ZVI) aggregate shall be mixed ex-situ with the clean fill material at a 10%:90% ratio for placement between the seasonal low water table and bedrock. For each area, the design drawings will specify the top elevation for the ZVI backfill based on the estimated shallowest seasonal low water table elevation for each area. The goal of placing reactive backfill between the seasonal low water table and bedrock is to provide passive treatment of residual VOCs not removed through excavation. ZVI can react directly with chlorinated VOCs and would also stimulate anaerobic biodegradation.

For each source of backfill materials that are identified, the Contractor will be required to make best efforts to identify virgin fill material. If virgin material is not available, any fill to be used must comply with the definition of “Natural Soil” as defined in RSR 22a-133k-2(h)(4). Additionally, the Contractor will be required to provide certifications that the materials obtained are free of organic and inorganic contaminants above CT RSR criteria. The specifications will include a provision that EPA and CTDEEP will review and approve the fill to be used. Minimum analytical data requirements will include one representative composite sample per 2,000 cubic yards of material from each source and analysis for VOCs, SVOCs, ETPH, PCBs, pesticides, and metals.

5.6 Site Restoration

Upon completion of the soil excavation and backfilling, the entire excavation area will be graded and restored similar to the existing conditions (i.e. bituminous asphalt or loam and seeding).

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6.0 Design Considerations

A number of technical issues were considered during development of the design. These include geotechnical considerations relative to excavation in close proximity to the manufacturing facility buildings, the presence of numerous underground utility lines within the excavation areas, concerns relative to conducting construction work at an active manufacturing facility, and the presence of existing monitoring and extraction wells within the excavation areas.

6.1 Geotechnical and Utility Considerations

The limits of excavation to the north and east of the main manufacturing facility building coincide with the location of many of the facility’s utility lines. See Figure 6-1 for identified utilities that fall within excavations areas. The contractor is responsible for confirming the location of utilities through hand digging prior to starting excavation activities. If electric or gas utilities are present, the Contractor will need to identify them through hand digging and meet with public utility maintenance personnel to verify if they are active or not. If gas is present, work needs to be coordinated in advance. As the DMC manufacturing facility will remain in operation during site remediation, the Contractor will be responsible for developing a plan to protect or temporarily relocate underground utilities and above-ground utilities in a manner that will allow uninterrupted operation, or will limit facility shutdown to weekend or off-hours to the greatest extent possible. At the start of each phase of subsurface work, subsurface power lines in the work area will be de-energized, and temporary electrical service will be provided to the DMC Facility through a 480V, 3-phase generator system. The DMC electrical transformer, located in an alcove adjacent to the NWC Area driveway, will remain in place. No excavation will occur in the alcove. Once excavation has been completed and backfilling has commenced, new electrical conduit will be installed. This work will be coordinated with DMC and with the Utility Company.

The Contractor shall be responsible for the excavation work in accordance with the Excavation, Backfill and Grading, Excavation Support Systems, and Underpinning Specifications and applicable federal and state laws and regulations, including OSHA. Open excavation may be considered for areas outside the Exclusion Envelope defined by a 2H to 1V line drawn from the outside, bottom edge of the excavation to ground surface. Foundations within the Exclusion Envelope will require underpinning or earth retention systems. Underpinning and temporary earth retention systems shall be designed by a Professional Engineer registered in the State of Connecticut for a 0.5 inch maximum lateral or vertical deflection. The underpinning system is to be designed by the Contractor and submitted for review. The Contractor must demonstrate that the underpinning design will provide adequate foundation support and meet the settlement criteria. The following types may be considered:

Underpinning when excavating closer than 3 feet of foundations for existing structures.

Temporary earth retention systems when excavating more than 3 feet away from existing foundations.

o Steel H-piles and steel plate lagging, with the soldier piles installed by auguring and encased in concrete. The steel plate lagging shall be advanced ahead of the excavation.

o Trench box with steel plates pushed ahead of the excavation along the trench box open face on the side of the foundation. The excavation shall be conducted perpendicular to the existing foundation in 6 to 8 foot wide slots. Each excavation slot shall be backfilled and compacted as specified before continuing

6-2 with the excavation of adjacent areas.

For the excavated portions of the existing structure/pipelines that will be affected by the work, the Contractor shall install deformation monitoring points (DMPs) 25 feet on center and at locations that change direction along the existing structure/pipelines. The Contractor shall take and record readings not less than once per day during the work and take weekly readings for a period of 4 weeks, or longer if movement persists, after completion of the work.

6.2 Conducting Excavation at an Active Manufacturing Facility

To ensure that the manufacturing building is able to continue normal operations, minimizing impact from remediation activities, the excavation has been broken into two phases. This will maximize the amount of parking that will be open to the workers during excavation activities, as well as limit the impacts of construction related traffic on daily manufacturing operations. Temporary site fencing and erosion controls would be installed around a Phase 1 excavation in the parking area north of the buildings (Eastern Area). Access to the remaining site would be unimpeded. The Phase 1 area would be excavated and fully restored before proceeding to isolate and excavate the Phase 2 (remaining excavation areas in the Northwest Corner and WS-20 Areas) to install temporary site fence.

As discussed in Section 5.0, the Contractor will be required to pre-characterize the soil to be excavated and obtain disposal facility approvals in advance of commencing soil excavation work in order to minimize the need for stockpiling, although there would still be temporary stockpiles inside the excavation areas.

6.3 Dewatering during Excavation

In most areas, the excavation will either extend below the seasonal low water table to bedrock or will stop at the seasonal low water table. Note that the water table fluctuates by several feet throughout a typical year. The Contractor will be required to manage any water encountered during excavation. For small quantities of water, the Contractor will pump the water to onsite storage tanks for shipment offsite. If this becomes cost prohibited due to excessive quantities of water encountered during excavation, the Contractor will treat the water using an onsite water treatment facility and will then discharge the water to a storm drain on the DMC property. Under CERCLA, no discharge permit would be required to discharge to a storm drain (see Section 8.0) for more detail. The contractor will be required to submit a Construction Water Management Plan, which will describe the proposed treatment system. In addition, any water generated from decontamination activities will also need to be contained and treated in the same manner as for excavation water.

6.4 Monitoring Wells and Former Extraction Wells

A total of seven overburden monitoring wells (MW-2, OW-2R, OW-3-08, OW-6R-08, OW-7R-08, OW- 8R-08, OW-19-09A) and seven former extraction wells (EX-1, EX-1R, EX-2, EX-3, EX-5, EX-6, EX-7) are located with the boundary of the area to be remediated. With the exception of OW-3-08 in the Northwest Corner Area and OW-8R-08 in the Eastern Area, these wells will be removed during excavation and will not be replaced. Wells OW-3-08 and OW-8R-08 have been identified as part of a long-term monitoring program and will be replaced as part of the site restoration. One additional well, OW-20-09, located in the WS-20 Area, just beyond the limit of excavation, is also included in the Long-term Monitoring Program, and will be protected from damage during remediation work.

Although all are overburden wells, most of the monitoring wells are deeper than the bottom of the excavation. Therefore, to prevent contaminated soil from falling into the portion of the well below the

6-3 bottom of the excavation, the monitoring wells that are located within the excavation footprint will be backfilled with bentonite prior to starting excavation.

6.5 Perimeter Air Monitoring

Continuous perimeter air monitoring will be required during all activities within active work areas.

Monitoring will be required for particulates and VOCs to document levels that may leave the Site, compare to action levels, and assess when additional measures may be needed to control emissions.

The contractor will be required to make every effort to limit the generation of dust and vapors through covering stockpiles, limiting areas of open excavation, water spraying, and other measures.

6.6 Excavation and Backfill Sequencing

The Remedial Action Contractor will be required to prepare a Technical Execution Plan that will address the means and methods of completing the soil excavation. The excavation and backfill will need to be phased in order to limit the impacts to DMC workers by maximizing the available parking areas during work. Phasing will also limit the generation of nuisance odors and minimize any water that might accumulate within the excavation. The contractor’s excavation sequence and temporary excavation support system will need to allow for visual inspection of the excavation limits.

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7.0 Environmental and Public Impacts

Several measures will need to be taken to minimize environmental and public impacts during the implementation of the remedy. These include monitoring and exposure control procedures, traffic and noise mitigation, and measures to be taken to minimize impacts on abutting residences. Excavation activities will require abandonment or removal of all wells within the excavation areas. Well OW-3-08 is planned to be included in the post excavation groundwater monitoring. The contractor will be required to protect or abandon and replace this well during excavation activities.

7.1 Erosion and Sediment Control During Construction

The Contractor will be responsible for:

A. Prevention of soil erosion due to construction activities;

B. Prevention of sedimentation of wetlands and waterways due to construction activities;

C. Restoration of areas and controls eroded due to insufficient preventive measures;

D. Prevention of storm water run-on into work areas; and

E. Compensation of EPA and/or Engineer for fines levied by authorities having jurisdiction due to non-compliance by Contractor.

The Contractor will be required to implement erosion and sediment control measures including installing and maintaining perimeter silt fence and straw bales, covering of soil stockpiles, temporary mulching of exposed areas, and use of sediment traps. The Contractor will also be responsible for monitoring Main Street and DMC driveways/parking areas for deposition of materials, and street sweeping as needed. Trucks leaving the site with excavated soils will be required to be lined and properly covered to avoid spillage. Truck decontamination will be required prior to departure.

7.2 Dust and Emissions Control

The contractor will be required to make every effort to limit the generation of dust and vapors through covering stockpiles, limiting areas of open excavation, water spraying, and other measures.

The contractor will be required to mitigate odors that are released during excavation of impacted material. Odor suppressant foam has been successfully utilized on similar sites. It is presented in this plan as an option. Odor suppressant foam can provide immediate, localized control of VOC and odor emissions. Foam is a short term remedy and can be actively used to control VOC and odor emissions from active excavations/stockpiles, and during the loading of trucks. Soil-intrusive activities may be stopped based on air monitoring results until the source of VOCs is identified and actions taken to reduce the VOC concentrations in the worker’s breathing zone or at the perimeter or on residential property.

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7.3 Noise, Traffic

A large volume of truck traffic may occur on Main Street as excavated soil and other waste materials are loaded and transported for off-site disposal. The Contractor will be required to provide traffic flagmen or police details as needed to control traffic. The Contractor will also be required to not close or obstruct any portion of Main Street. Regular work hours will be limited to 7 AM to 5 PM, Monday through Friday. To minimize impacts during the Durham Fair in later September, no trucking will be allowed in and out of the Site over the four day period that the fair is in operation.

7.4 Impact on Abutting Residences

The extent of soil to be excavated extends onto southeastern portions of the residence at 215 Main Street (the Korn property). In this area, the excavation while require a vertical cut using trench box rather than sloping in order to minimize the impact to the Korn property.