2021_April_16_Removal_Action_Workplan___Engineer_s_Opinion_of_Probable_Costs_BBJ.pdf

BBJ Group, LLC www.bbjgroup.com

April 16, 2021

Fred Pinkney, Ph.D.

United States Fish & Wildlife Service Chesapeake Bay Field Office Environmental Contaminants Program 177 Admiral Cochrane Dr.

Annapolis, MD 21401

Re: Removal Action Workplan and Engineer’s Opinion of Probable Costs – Lead Shot Site

Prime Hook National Wildlife Refuge Milton, Delaware Contract Order No.: 140F0420P0137

BBJ Group Project No.: R2012075

Dear Dr. Pinkney:

BBJ Group, LLC (BBJ Group) is pleased to provide the United States Fish & Wildlife Service (FWS) with this Removal Action Workplan and Engineer’s Opinion of Probable Costs (RAWP) for the Lead Shot Site located at the Prime Hook National Wildlife Refuge, Milton, Delaware. This RAWP was prepared in accordance with the requirements of Contract Order No. 140F0420P0137 dated June 8, 2020.

We appreciate the opportunity to provide the FWS with our environmental services. If you have any questions or require additional information, please contact Mr. Nick Dufficy at (773-982-0009) or ndufficy@bbjgroup.com.

Sincerely, BBJ GROUP, LLC

Nicholas Dufficy John Tanaka, P.E.

Project Manager Senior Engineer

J. Tim Bradburne, P.G.

Principal

Attachment: Removal Action Workplan and Engineer’s Opinion of Probable Costs – Lead Shot Site http://www.bbjgroup.com/ mailto:ndufficy@bbjgroup.com

Removal Action Workplan and Engineer’s Opinion of Probable Costs – Lead Shot Site

Prime Hook National Wildlife Refuge Milton, Delaware

Contract Order No.: 140F0420P0137

Submitted to:

United States Fish & Wildlife Service

Prepared by:

BBJ GROUP, LLC

April 16, 2021

Prepared by: Reviewed by:

4.16.2021 4.16.2021 Nick Dufficy Date BBJ Group, LLC

John Tanaka, P.E. Date BBJ Group, LLC

Reviewed by: Approved by:

4.16.2021 Tim Bradburne, P.G. Date BBJ Group, LLC

Fred Pinkney Date U.S. Fish and Wildlife Service

4-19-2021

U.S. Fish and Wildlife Service / Milton, DE Project No. R2012075

April 16, 2021 Page i

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 SITE DESCRIPTION AND BACKGROUND

2.1 Previous Environmental Investigations and Remediation

2.2 Site Geology and Hydrogeology

2.3 EE/CA

2.4 2017 DNREC BSC Trap Shooting Range Site Investigation Report

2.5 Analysis of Fate and Transport

3.0 BENCH-SCALE AND PILOT-SCALE TREATABILITY STUDIES

4.0 REMOVAL ACTION PLANNING

4.1 Substantive Requirements of ARARs

4.2 Health and Safety

4.3 Utility Clearances

4.4 Wetlands Delineation and Limited Site Boundary and Topographical Survey

4.5 Tree Species and Diameter at Breast Height Survey

4.6 Supplemental Lead Soil Screening Event to Delineate Northern Removal Action

Extents

4.7 Groundwater and Surface Water Quality Testing

4.8 Monitoring Well Decommissioning

4.9 Site Preparation

4.10 Waste Characterization and Solid Waste Disposal Facility Approval

4.11 Clean Fill Source Identification and Evaluation

5.0 REMOVAL ACTION IMPLEMENTATION

5.1 In-situ Stabilization Overview

5.2 ISS Mix Design and Procedures

5.3 Confirmation Sampling

5.4 Excavation Procedures

5.5 Backfill and Topsoil

5.6 Site Restoration

5.7 Contaminated Materials Management Plan

5.8 Long-Term Stewardship Plan

5.9 Removal Action Completion Report

6.0 ESTIMATED REMOVAL ACTION SCHEDULE

7.0 ENGINEER’S OPINION OF PROBABLE COSTS

8.0 REFERENCES

TABLES

Table 1 Applicable or Relevant and Appropriate Requirements Table 2 Engineer’s Opinion of Probable Costs

FIGURES

Figure 1 Site Location Map Figure 2 Site Plan Figure 3 Site Plan with Removal Action Extents and Depths

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APPENDICES

Appendix A BBJ Group Bench Scale and Pilot Scale Treatability Study Technical Memoranda

April 16, 2021 Page 1

1.0 INTRODUCTION

BBJ Group, LLC (BBJ Group) prepared this Removal Action Workplan and Engineer’s Opinion of Probable Costs (RAWP) for United States Fish & Wildlife Service (FWS) for a portion of land which straddles the property boundary between the Prime Hook National Wildlife Refuge (Prime Hook NWR) and the former Broadkiln Sportsman’s Club (BSC) trap shooting range (Subject Property). Following completion of bench-scale and pilot-scale treatability studies described further herein, this RAWP describes preparation and remediation activities necessary to implement excavation, in-situ treatment and off-site disposal of lead-contaminated soil (as non-hazardous waste), a non-time-critical removal action (NTCRA) alternative (Alternative 3) previously recommended in the Engineering Evaluation/Cost Analysis (EE/CA) (Geosyntec Consultants, Inc., 2017) prepared for the Subject Property.

2.0 SITE DESCRIPTION AND BACKGROUND

The Prime Hook NWR is a 9,700-acre area on the southeast coast of Delaware (Figure 1) that provides habitats for numerous species of birds, fish, reptiles, amphibians, mammals, insects, and plants. Between 1962 and 1998, the BSC trap shooting range operated on adjacent land, which resulted in contamination of certain areas of the Prime Hook NWR from lead shot deposition.

2.1 Previous Environmental Investigations and Remediation

In 2000, the trap shooting range closed, and between 2000 and 2017, environmental investigations and remediation were conducted at the Subject Property, including a Preliminary Assessment (PA) (Harding ESE, 2001), groundwater investigations (Pinkney & Callahan, 2017; Soeder & Miller, 2003), interim Remedial Action, and a Supplemental Site Investigation (SSI). These activities are summarized chronologically below.

In 2000 and 2001, the U.S. Geological Survey (USGS) investigated groundwater impacts at the Subject Property using a network of 19 monitoring wells installed from about 2.0 to 11.5 feet below ground surface (bgs) in the forested area with a high concentration of shotgun pellets (the drop zone); and upgradient and downgradient from the drop zone. USGS concluded that lead pellets in the drop zone leached into groundwater due to acidic water conditions and the existence of a sandy, shallow saturated zone. The highest detected concentration of lead in groundwater monitoring wells was 1,000 micrograms per liter (µg/L) (Soeder & Miller, 2003).

In 2000, FWS placed a geotextile over the trap shooting range drop zone to prevent waterfowl and birds from coming into direct contact with shotgun pellets. From 2002 to 2003, the geotextile was removed and the upper eight inches of soil beneath the geotextile was excavated and disposed off-site. An 8-inch layer of soil beneath the excavation was stabilized using Portland cement and the area was backfilled with clean soil and re-seeded.

In 2004, the FWS conducted an ecological risk assessment (ERA) to evaluate potential threats to ecological receptors from exposure to lead contaminated soil and sediment and ingestion of lead

April 16, 2021 Page 2 shot (Guy et al., 2004). Based on the ERA, lead Preliminary Remediation Goals (PRGs) for soil [421 milligrams per kilogram (mg/kg)] and sediment (312 mg/kg) were established.

From 2007 to 2015, FWS monitored lead concentrations in groundwater and surface water (Pinkney & Callahan, 2017). The ten years of sampling show that only trace amounts of lead are detectable in the groundwater samples, and usually in only one of the three wells on the remediated area. Lead was only detected once in the upgradient well (3.2 µg/L in October 2008) and twice in the downgradient well (3.2 µg/L in January 2008 and 3.0 µg/L in October 2008). In the most recent round, May 2017, no detectable lead was reported in any well samples. Surface water concentrations were frequently well in excess of the state standard of 0.93 µg/L. In the most recent sampling (December 2017) filtered concentrations ranged from 43.9 to 292 µg/L.

FWS also monitored the bioaccumulation and effects of lead in southern leopard frog (Lithobates sphenocephalus) tadpoles exposed in situ in two locations in the wetlands and an on-refuge reference location (Fred’s Pond) about 6 km away (Krest et al., 2017). The Krest et al. (2017) study recommended the preliminary remediation goal of 312 ppm in wetland sediments for protection of amphibians.

In 2017, the FWS conducted an SSI to evaluate the nature and extent of impacts from the trap shooting range. Soil, sediment, and surface water samples were collected and analyzed for metals and other analytes, and the results were compared to PRGs for soil and sediment developed in the ERA. The SSI concluded that lead was the primary chemical of concern and that it was delineated to the PRGs.

2.2 Site Geology and Hydrogeology

Based on soil sampling completed in 2000, the surface and subsurface soil (up to two feet bgs) contains an average of about 14% and 22% silt and clay, respectively, with the balance consisting of sand. The lead-impacted portion of the Prime Hook NWR consists of a forested wetland along an unnamed tributary or slough comprised of a series of small, shallow ponds or pools separated by saturated hummocks of mud, fallen trees, and organic matter (Figure 2). Surface water in the slough is nearly stagnant with slow drainage to Primehook Creek (Soeder & Miller, 2003). Seasonal variation in the water table elevation influences the size and shape of the slough, which occasionally may dry up completely. Numerous small mammals, birds, amphibians, and insects are common in and around the slough and use it as a water supply.

Historic water level gauging data conducted between 2000 and 2001 indicates that the water table is highest (approximately 2.6 feet above mean sea level1) in the upland areas near the BSC shooting range and decreases gradually toward the wetland areas to the east at an average gradient of

0.0013 feet/feet (ft/ft) (Soeder & Miller, 2003). Groundwater also generally flows eastward from the shooting range to the wetland and slough. Lead in shotgun pellets leaches to groundwater and downgradient surface water bodies from acidic water conditions and a transmissive, sandy, shallow unconfined aquifer (Soeder & Miller, 2003).

1 Around two feet bgs.

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A 2003 report by the USGS (Soeder & Miller, 2003) concluded that the geology of the Subject Property is complex and the uppermost layers of soil and sediment predominantly consist of Holocene-aged fine sandy, silty clays.

2.3 EE/CA

In 2017, FWS completed an EE/CA following regulatory criteria established by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The objectives of the EE/CA were to:

• Characterize the nature and extent of soil exceeding PRGs;

• Evaluate human health and environmental risks;

• Identify goals for a NTCRA;

• Evaluate NTCRA alternatives; and

• Recommend a NTCRA alternative.

Based on prior investigations, the area of lead above PRGs was estimated to be approximately 5.5 acres and up to approximately two feet bgs (Figure 3). An estimated 11,600 tons of lead impacted soil above PRGs were present at the Subject Property. The Removal Action Objectives (RAOs) presented in the EE/CA were to:

• Prevent potential exposure of ecological and human receptors to unacceptable concentrations of lead in soil and sediment; and

• Attain all applicable or relevant and appropriate requirements (ARARs).2

As described in Section 2.1 the EE/CA proposed the following PRGs for lead:

• 312 mg/kg in wetland sediment; and

• 421 mg/kg in soil.

The EE/CA evaluated several NTCRA alternatives to address areas impacted above PRGs, including:

• Excavation with Off-Site Disposal (Alternative 2);

2 Compliance with ARARs is a requirement of removal actions conducted pursuant to the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) and CERCLA.

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• Excavation, In-situ Treatment and Off-Site Disposal of Non-Hazardous Waste (Alternative 3);

and

• A combination of Alternatives 2 and 3.

To implement Alternative 3, the EE/CA recommended application of a chemical lead stabilization reagent in-situ to reduce leachable lead concentrations to below Resource Conservation and Recovery Act (RCRA) hazardous waste levels [i.e., the Toxicity Characteristic Leaching Procedure (TCLP) Regulatory Level of 5 milligrams per liter (mg/L)]. An evaluation of a specific stabilization reagent was conducted in 2020 and detailed in Section 3.0.

The EE/CA evaluated removal alternatives only for soil and sediment. The EE/CA assumed that groundwater and surface water impacts would be addressed through Monitored Natural Attenuation (MNA) by periodically sampling the existing groundwater monitoring well network and eight surface water sample locations for up to 20 years.

2.4 2017 DNREC BSC Trap Shooting Range Site Investigation Report

BBJ Group reviewed the Broadkiln Sportsman Club Site: DE-1371 - Site Inspection Report, prepared by Delaware Department of Natural Resources and Environmental Control (DNREC) for United States Environmental Protection Agency (USEPA) Region 3, dated November 2017 (Department of Natural Resources and Environmental Control, Site Investigation and Restoration Section, 2017) (BSC SIR) to evaluate if residual contamination at the BSC trap shooting range has the potential to influence the long-term effectiveness of the selected Removal Action (Alternative 3). The stated purpose of the BSC SIR was “to determine if [BSC] site activities have contaminated groundwater, surface water, sediment, and/or soil on [the BSC property] and into the surrounding area.” Notable findings from the May 2017 trap shooting range area investigation are summarized below.3

Soil:

• One hundred soil samples were collected from 40 soil borings to characterize the nature and extent of soil impacts. Borings were advanced via hand auger or direct-push technology to a maximum depth of 2 feet bgs. Up to three soil samples were collected from each boring consisting of a “shallow”, “intermediate”, and “deep” sampling interval.

• All 100 samples were initially field screened via the use an XRF analyzer and photoionization detector (PID). Preliminary laboratory screening was conducted at the DNREC laboratory in New Castle, Delaware, prior to submitting 28 samples to TestAmerica, of Edison, New Jersey for confirmation laboratory analysis.

3 Other areas of the BSC property were investigated as part of the BSC SIR including the former pistol range area and a man-made pond located near the western BSC parcel boundary; however, BBJ Group notes the potential for residual contamination from these areas to impact the Subject Property is remote due to the lack of complete exposure pathways and/or transport mechanisms (i.e., overland flow from the pond to the onsite wetland areas is unlikely to occur on a routine basis, and there is a topographic drainage divide near the trap shooting houses which inhibits the migration of surface water and groundwater from these areas towards the Subject Property).

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• Thirteen analytes (primarily metals and polynuclear aromatic hydrocarbons [PAHs]) were detected at concentrations above Delaware Hazardous Substance Cleanup Act (HSCA) Soil Screening Levels (October 2017), USEPA June 2017 Residential Soil Regional Screening Levels (RSLs), and/or USEPA June 2017 Industrial Soil RSLs: Antimony, Arsenic, Lead, Thallium, Benz[a]anthracene, Benzo[a]Pyrene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Chrysene, Dibenz[a,h]anthracene, Dibenzofuran, Indeno[1,2,3-cd]pyrene, and Naphthalene.

• The maximum reported concentration of lead was 128,000 mg/kg in soil sample BSCSO-34s, located near the eastern portion of the BSC parcel boundary and west-adjacent to the former drop zone at the Subject Property. In general, soil samples collected closest to western boundary of the Subject Property contained the highest concentrations of lead.

Exceedances of PAHs were not observed in soil samples collected closest to the Subject Property and were confined to areas closer to the trap shooting houses.

• A human health risk assessment (HHRA) was conducted to evaluate if soil impacts (and groundwater impacts, described below) posed unacceptable cancer or non-cancer risks to various receptors. The HHRA results are discussed further below.

Groundwater:

• Groundwater samples were collected from three monitoring wells (BSC-GW-47, BSC-GW-48, and BSC-GW-49) installed in the trap shooting range during the soil sampling event described above. The 1-inch diameter wells were set within the shallow groundwater bearing zone with 10-foot, Geoprobe® prepacked screens. The wells were screened to a maximum depth of 15 feet bgs. Groundwater samples were collected from the wells approximately two weeks after installation following development and purging and submitted to TestAmerica, of Edison, New Jersey for laboratory analysis.

• Total lead (12.1 µg/L) and dissolved lead (9.3 µg/L) were detected in one monitoring well (BSC-GW-47) above the DNREC HSCA Screening Level for tap water (5 µg/L), but below the USEPA RSL for tap water (15 µg/L). One shallow soil sample was obtained from BSC-GW-47 during well installation and submitted for laboratory analysis with lead reported at a concentration of 2,680 mg/kg.

• Except as noted above, lead was not detected above the aforementioned screening levels in any other wells at the BSC property. Cobalt, manganese, and/or cyanide were detected in the three wells above applicable screening levels. BBJ Group notes that the reported concentrations for cobalt and cyanide were estimated4 and concentrations of manganese were reported approximately 10 µg/L above the most stringent screening level (43 µg/L).5

4 I.e., reported above the method detection limit (MDL) but below the associated laboratory reporting limit (RL).

5 The screening levels for manganese are additionally not human health-based.

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• A HHRA was conducted (results detailed below) to evaluate if the groundwater impacts posed unacceptable cancer and non-cancer risks to various receptors.

DNREC BSC SIR Conclusions and Recommendations:

• According to the results of the HHRA, soil impacts at all intervals (shallow, intermediate, and deep) posed unacceptable cancer and non-cancer risks (primarily via the ingestion and direct-contact exposure routes) for the following exposure scenarios: Resident, Recreator, Trespasser, Outdoor Worker, and Excavator.

• Groundwater (as tap water) was determined to pose an unacceptable non-cancer risk to the

Residential receptor only, however the cancer risk was determined to be acceptable. The cumulative cancer and non-cancer risks were acceptable for all other exposure scenarios evaluated.

• In accordance with applicable DNREC and USEPA Risk Assessment Guidance, lead was evaluated separately from the other constituents of potential concern as it does not affect the cumulative cancer risk or non-cancer risk (hazard index). BBJ Group notes that the calculated 95th Upper Confidence Level (95 UCL) of the mean for lead across all intervals from 0 to 2 feet bgs (shallow, intermediate and deep) at the trap shooting range was 6,722 mg/kg, which exceeds the calculated lead PRGs for the Subject Property, the USEPA Protection of Groundwater Soil Screening Level (14 mg/kg), and the USEPA non-residential screening level (SL) of 800 mg/kg. Based on the groundwater results, the maximum observed concentration (MOC) of 12.1 µg/L, exceeds the HSCA tap water screening level, but does not exceed the USEPA RSL for tap water.

• Based on the results of the HHRA, DNREC recommended that the trap shooting range “be remediated.”6 DNREC further recommended that “the degree and extent of remediation should be determined by performing a feasibility study and an ecological risk assessment.”

BBJ Group is unaware if those activities have been completed to date.

BBJ Group’s conclusions as they relate to the recommended removal action alternative are as follows:

• The three monitoring wells installed as part of the BSC SIR are insufficient to: (1) fully characterize groundwater quality (including lead) at the BSC property or (2) evaluate the potential for off-site migration onto the Subject Property since monitoring wells were not installed hydraulically downgradient of the areas containing the highest lead concentrations in soil.

• The BSC SIR did not directly evaluate the leachability of lead in soil (e.g., through TCLP or Synthetic Precipitation Leaching Procedure (SPLP) analysis) to derive a site-specific soil concentration that is protective of groundwater.

6 DNREC also recommended that the pistol shooting range be remediated.

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• Historic water gauging data, geologic cross-sections, and a conceptual site model of groundwater flow and contaminant transport developed for the BSC property and Subject Property in 2003 (Soeder & Miller, 2003) indicates that groundwater underlying the trap shooting range flows eastward (downgradient) towards the Subject Property in a shallow, sandy unconfined aquifer. Regionally acidic groundwater conditions may further contribute to the mobility of lead into groundwater (Soeder & Miller, 2003).

• Given the hydrogeological conditions noted above and reported total lead concentrations ranging from about 10,000 mg/kg to 100,000 mg/kg, the potential for residual soil contamination at the BSC property to impact groundwater and surface water at the Subject Property following implementation of the Removal Action cannot be ruled out (see Section

2.5 for further details and analysis).

2.5 Analysis of Fate and Transport

BBJ Group reviewed an Analysis of Fate and Transport of Soil Contamination from the Broadkiln Sportsman’s Club to the Prime Hook National Wildlife Refuge, Milton, Delaware (Geosyntec Consultants, Inc., 2019), prepared by Geosyntec Consultants for the FWS, dated March 2019 (2019 Fate and Transport Study). The stated objectives of the 2019 Fate and Transport Study were to:

1. Evaluate the fate and transport of lead from the Broadkiln Sportsman Club (BSC) to the Refuge property;

2. Assess whether further remediation on Refuge property would be successful without remediation of the BSC property; and

3. Identify options for preventing contamination from entering the Refuge from the

BSC.

Notable findings from the study are summarized below:

• Using lead pellet density data from prior soil investigations and estimates of lead mass (in grams) per pellet, the total estimated lead pellet mass in 2019 on the Subject Property and west-adjacent BSC property was 9,542 kg and 26,921 kg, respectively. Prior to the 2002 interim removal action at the Subject Property (see Section 2.1), an estimated total lead pellet mass of 30,013 kg was calculated.

• Due to limited site-specific hydrological data, a detailed surface water transport model could not be completed. Instead, the 2019 Fate and Transport Study incorporated the previous total lead pellet mass calculations and precipitation data to derive mass dissolution rates of lead into groundwater and surface water (results in kilograms of lead per gallon of water).

Based on the calculations, between 1,950 and 7,800 kg of lead were estimated to have leached to approximately 153 million gallons of groundwater over 50 years and approximately 4,500 to 18,200 kg of lead were estimated to have dissolved into approximately 360 million gallons of surface water run-off over 50 years. The resultant long-

April 16, 2021 Page 8 term average concentration of lead in surface water to have contacted impacted soils was 3,300 to 13,500 ug/L, which is reported to be similar to unpublished 2015 FWS data obtained from a downgradient unnamed tributary.

• Lead mobility in soil and groundwater was modeled as a function of site-specific pH and oxidation-reduction potential (Eh) values. Based on site-specific pH values (generally ranging between 5 to 6) and Eh values (0.25 to 0.75 volts), equilibrium modeling of lead speciation indicates that lead likely remains dissolved in groundwater in the form of aqueous cationic lead (lead 2+) and/or neutrally charged lead carbonate. The aforementioned site-specific geochemical conditions suggest a mobile environment for lead transport via groundwater and surface water.

• Using a 1-dimensional advection-dispersion equation from Domenico and Schwartz, default and site-specific chemical, aquifer, and physical property data were used to model predicted groundwater lead concentrations along the plume centerline as a function of distance from a fixed source area (defined as a 9.4-acre portion of impacted land encompassing both the BSC property and Subject Property and shown on Figure 2 of the 2019 Fate and Transport Study). A sensitivity analysis for certain sensitive model parameters was conducted to provide a range of predicted lead concentrations as a function of distance from the fixed source area. Geosyntec concluded that lead concentrations would decrease to below 2 µg/L at a maximum distance of approximately 300 feet from any point of the fixed source area.

• Predicted groundwater concentrations were modeled as a function of time at a fixed distance of 150 feet from the source area, which was selected as a representative average distance from the centroid of the source area to monitoring wells DG-8 and DG-9 and also representative of the distance of the highest soil concentrations on the BSC property to the westernmost Subject Property boundary. The results of the modeling indicate that lead from the BSC property is likely to have leached to groundwater at the Subject Property over a 50-year span (the approximate period during which the BSC was open) and will continue to be a potential source of lead in groundwater and surface water at the Subject Property if not removed. The 2019 Fate and Transport Study further concluded that removal of lead-contaminated soils at the Subject Property “will reduce but not eliminate the source of lead to groundwater and surface water downgradient of the BSC property.”

Based on the FWS groundwater monitoring conducted between 2007 and 2015 (Pinkney & Callahan, 2017), there were few detections of lead in the upland, wetland, and background monitoring wells on the Refuge. The highest detected concentration in the entire monitoring period was 15.5 µg/L in an upland well in 2010 and most subsequent detections were less than 6 µg/L. Based on these data, it does not appear that transport of highly contaminated groundwater from the Broadkiln Sportsman’s Club to the refuge is occurring.

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3.0 BENCH-SCALE AND PILOT-SCALE TREATABILITY STUDIES

Bench-scale and pilot-scale treatability studies were conducted at the Subject Property in September 2020 and December 2020, respectively to evaluate the implementability of in-situ stabilization (ISS).

Specific data quality objectives (DQOs) for the treatability studies were as follows:

• Identify and confirm whether a lead stabilization reagent can stabilize concentrations of leachable lead in bench and pilot-scale testing to below the TCLP Regulatory Level of 5 mg/L;

• Identify dose(s) of the lead stabilization reagent capable of stabilizing leachable lead to below 5 mg/L;

• Identify an in-situ mixing methodology that is capable of stabilizing leachable lead in both aboveground and submerged areas of the Subject Property;

• Understand performance characteristics of the lead stabilization reagent on different matrices (e.g., soil and sediment);

• Understand the leachability characteristics of active ingredients in the stabilization reagent;

and,

• Identify and confirm whether the chemical and physical nature of impacted soils and sediment meet additional acceptance criteria for non-hazardous waste disposal at a permitted off-site facility.

The findings of the bench-scale treatability study related to the above DQOs were as follows:

• A 4% dosage rate (weight of reagent/wet weight of soil) of Enviroblend® CS, a proprietary magnesium oxide and hydroxide-based stabilization reagent, was the minimum dosage rate required to stabilize lead leachate to below the TCLP Regulatory Level of 5 mg/L in all soil and sediment samples analyzed during the bench-scale and pilot-scale treatability studies.

Further, a 4% dose of EnviroBlend® CS was able to effectively stabilize lead leachate in soil and sediment containing concentrations of total lead on the order of 1,000 mg/kg to 10,000 mg/kg.

• A rotary (end-over-end) soil mixing head was an effective large-scale in-situ mixing technique for stabilizing leachable lead in soil and sediment.

• Differences in matrices (e.g., soil and sediment) did not appear to alter the performance of the reagent.

• Active ingredients in the reagent did not appear to present a significant human health or ecological concern once applied, as measured by concentrations of total and leachable iron and magnesium; total phosphorous and orthophosphate; and nitrate and nitrite.

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• Stabilized material was capable of meeting the Delaware Solid Waste Authority’s (DWSA) non-hazardous solid waste disposal criteria (Delaware Solid Waste Authority, 2005) [i.e., a RCRA Subtitle D non-hazardous solid waste disposal facility (SWDF)] if effectively stabilized in-situ.

Based on the above findings, BBJ Group recommended the application of a 4% dose of EnviroBlend® CS combined with the use of a rotary soil mixing head across the entire remediation extents at field scale. Detailed treatability testing methodologies, sampling locations and procedures, laboratory analytical results, and findings and recommendations were summarized in Technical Memoranda submitted to the FWS on October 22, 2020 and January 19, 2021 (Appendix A).

4.0 REMOVAL ACTION PLANNING

Required activities prior to beginning ISS, off-site transportation and disposal, and related field work are discussed below.

4.1 Substantive Requirements of ARARs

Prior to implementation of the Removal Action, compliance with certain permit conditions and obtaining approvals for response actions will be required, which are summarized in Table 1.

Obtaining permits for on-site actions conducted under CERCLA area is not required, but the substantive requirements of such permits are considered ARARs. Also, off-site disposal facilities must be permitted for the type of waste disposed from the Subject Property. The requirements in Table 1 will be adjusted as necessary after specific discussions with the identified regulatory agencies and stakeholders.

4.2 Health and Safety

A site-specific Health and Safety Plan (HASP) in accordance with 26 CFR 1910 (OSHA Laws and Regulations) will be required for all contractors and subcontractors to manage known and potential risks posed by COCs; establish standard operating procedures (SOPs) for mitigating site and work-related hazards (e.g., decontamination procedures); and additional health and safety issues such as the establishment of Work Zones (i.e., Support, Contamination Reduction/Decontamination, and Exclusion Zones). Based on known concentrations of lead and the potential for fugitive dust generation during implementation of the Removal Action, an air monitoring plan may be needed.

4.3 Utility Clearances

Prior to intrusive activities, Delaware’s Call-Before-You-Dig services (Miss Utility of Delmarva [811]) will be contacted to clear and mark public utilities. A private utility locate service will also be required to mark underground utilities and structures that may be present in the remediation area and not part of a public utility system. Overhead or subsurface utility lines are not anticipated to be encountered in the project area; however, should utility lines have the potential to interfere with the proposed remedial activities, appropriate measures will need to be taken (e.g., contacting the utility

April 16, 2021 Page 11 company and implementing hazard mitigation controls) in accordance with the HASP to safely eliminate potential threats.

4.4 Wetlands Delineation and Limited Site Boundary and Topographical Survey

Removal Action preparation activities will require a wetlands delineation and a limited site boundary and topographical survey7. Based on the timeframe to secure approvals or complete consultations as identified in Table 1, BBJ Group recommends completing these tasks at least 90 days prior to Removal Action implementation. Completion of these tasks will require qualified or licensed professionals in the state of Delaware.

During the treatability studies, BBJ Group identified discrepancies in the absolute locations of historically surveyed monuments (e.g., monitoring wells) and their positioning on previously prepared site plans that depict the nature and extent of lead contaminated soils. The completion of a limited site boundary and topographical survey will rectify locational discrepancies that may affect Removal Action preparation and implementation activities.

4.5 Tree Species and Diameter at Breast Height Survey

Removal of selected vegetation and trees is required as part of the Removal Action. Prior to the start of the work, a tree species survey and diameter at breast height (DBH) survey will be conducted by qualified professionals in conjunction with the selected remediation contractor to identify and mark trees to be preserved. Many trees that are less than 10 inches in diameter are anticipated to require removal to implement the Removal Action in an efficient manner; however, a site-specific diameter may be determined during the course of the DBH survey upon consultation with the FWS.

4.6 Supplemental Lead Soil Screening Event to Delineate Northern Removal Action Extents

As described in the EE/CA, additional lead in soil or sediment may be present at concentrations above the PRGs along the northern portion of the projected removal extents (Figure 3) as one historical soil sample contained lead at 710 mg/kg. Sampling activities (as part of the EE/CA) to fully define the Removal Action extents in this area were unable to be completed, which was identified as a “potential data gap.”

Using a portable x-ray fluorescence (XRF) analyzer, BBJ Group recommends screening soil and/or sediment to demonstrate compliance with the site-specific PRGs around the historical sampling location and fully define the northern Removal Action extents. XRF soil screening should be conducted in accordance with USEPA Method 6200 to extent practicable, which involves submitting a limited number of sample surrogates for chemical laboratory analysis at an accredited laboratory to verify the accuracy of the field screening results. Actual sample locations and frequencies will be dependent on field conditions at the time of the event.

7 Given the size of the NWR relative to the projected removal action extents, BBJ Group recommends a “limited” land survey comprising the areas of potential disturbance and potentially affected surface water bodies.

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4.7 Groundwater and Surface Water Quality Testing

Technical requirements of certain permits (but not acquiring permits themselves) and other Removal Action activities will require groundwater quality and surface water quality testing prior to Removal Action implementation. Specific analytical parameters for sampling before and during the onsite activities should be determined in cooperation with the DNREC Division of Watershed Stewardship. During the removal action, water quality objectives must be met to protect beneficial uses under Title 7, Delaware Administrative Codes 7401 and 7418 for the Broadkiln River Watershed (which includes the Prime Hook watershed) and to regulate discharges of fill and dredged material under CWA Section 401.

Sampling groundwater and surface water prior to the Removal Action will also establish baseline conditions for the MNA evaluation.

4.8 Monitoring Well Decommissioning

Several monitoring wells were observed within the Removal Action extents projected in the EE/CA and at least eight monitoring wells (DG-1, DG-4, DG-5, DG-7, DG-8, DG-9, DG-10, and UG-2) may require decommissioning by a state of Delaware licensed well driller based on locations of monitoring wells depicted in 2003 (Soeder & Miller, 2003). Well decommissioning will occur after sampling and analysis activities described in Section 4.7.

4.9 Site Preparation

Site preparation activities will follow site-specific requirements such as best management practices (BMPs) in a Stormwater Pollution Prevent Plan (SWPPP), Sediment and Stormwater Management Plan, and other permit-specific requirements related to wetland disturbances or surface water discharges. These activities will generally specify: the overall construction site layout and associated activities that are to take place in designated areas; construction sequencing; stormwater, erosion, surface water, and site security controls that will be used; site stabilization BMPs (pre- and post-construction); BMP operation and maintenance requirements; drainage and dewatering plans and procedures; clearing and grading plans; clean fill criteria for backfilling; design criteria for stabilized construction roads and entrances; and detailed site restoration details.

4.10 Waste Characterization and Solid Waste Disposal Facility Approval

Waste disposal activities will be performed in accordance with applicable state and federal regulations and guidance. Preliminary waste characterization data conducted during the bench and pilot scale treatability studies indicated that onsite soil and sediment meets DWSA non-hazardous solid waste disposal criteria (Delaware Solid Waste Authority, 2005) (i.e., can be disposed at a RCRA Subtitle D non-hazardous solid waste disposal facility) if effectively stabilized in-situ with a 4% dose of EnviroBlend® CS.

Based on the volume of total material that will require disposal at a licensed offsite solid waste disposal facility (SWDF), additional waste characterization testing will likely be required to (1) identify, April 16, 2021 Page 13

(2) coordinate, and (3) obtain SWDF approval for disposal of stabilized soil and sediment. Waste characterization testing procedures, analyses, and approval criteria will be SWDF-specific.

BBJ Group recommends conducting additional waste characterization testing at least 30 to 60 days prior to the proposed scheduling of hauling stabilized material off-site.

4.11 Clean Fill Source Identification and Evaluation

A source of clean fill and topsoil (Department of Natural Resources and Environmental Control, Division of Air and Waste Management, Site Investigation & Restoration Branch, 2010) will be identified prior to implementation of the Removal Action. Prior to bringing fill material to the Subject Property, a thorough review of the source history and operations and supplemental analytical testing (if needed) will be conducted.

Imported fill will have similar properties to native soils. In addition, fill material will comply with site-specific lead PRGs and applicable HSCA soil and freshwater sediment screening levels (Department of Natural Resources and Environmental Control, Division of Waste and Hazardous Substances, 2019).

5.0 REMOVAL ACTION IMPLEMENTATION

The following sections outline the Removal Action implementation activities to execute Alternative 3 (Excavation, In-situ Treatment and Off-Site Disposal of Non-Hazardous Waste). To satisfy regulatory and permitting obligations and increase the overall productivity of the Removal Action, preparation activities outlined in Section 4.0 should be completed to the maximum extent practicable prior to the start of the implementation activities described below.

5.1 In-situ Stabilization Overview

Impacted soils will be stabilized in-situ via dry mixing performed by an excavator with a soil rotary mixing head. The projected removal extents as determined from the EE/CA will be surveyed and marked with flags or stakes. A 4% dose of EnviroBlend® CS will be introduced during soil mixing to pre-determined depths and locations where PRGs are exceeded. Once thoroughly mixed, the stabilized material will be excavated and hauled offsite for disposal. Confirmation soil sampling and XRF soil screening (described further below) will be conducted concurrent with the Remedial Action to verify its effectiveness.

5.2 ISS Mix Design and Procedures

BBJ Group recommends subdividing the removal extents into predetermined grid cells (Interstate Technology & Regulatory Council, Solidification/ Stabilization Team, 2011). Prior to introducing EnviroBlend® CS, an excavator with a bucket will pre-excavate the grid cells to the desired removal depths as determined by the EE/CA and XRF soil screening conducted in the field. Dewatering of grid cells may be required during the mixing process in wet or submerged areas of the Subject Property.

If a significant volume of water needs to be contained, it will be tested and treated (if necessary)

April 16, 2021 Page 14 prior to 1) disposal at an off-site facility; or 2) infiltration into the ground in accordance with applicable discharge criteria. Excavated soils from each grid cell will be used to temporarily berm the perimeter of each grid cell and manage any spoils, stormwater, or surface water infiltration during ISS8. A 4% dose of EnviroBlend® CS will then be introduced into each grid cell as the excavated soils are simultaneously added back into the cell. The soil/reagent mixture will be thoroughly mixed with the soil rotary mixing head until the reagent is uniformly distributed throughout the grid cell. To screen for the uniformity of reagent distribution within each grid cell, the pH of the soil/reagent mixture will be measured at several different areas and depths of each grid cell to evaluate whether the mixture is close to the native pH range of the EnviroBlend® CS (10.0 to 11.0).

Grid cell sizing will be determined prior to mixing based on the following:

• Known or suspected depths of remediation;

• Site conditions;

• Number of TCLP lead confirmation samples required for chemical laboratory analysis or by the SWDF to verify Removal Action effectiveness;

• Limitations of the equipment used;

• Ability to efficiently measure, monitor, and record reagent performance; and

• A combination of the above.

5.3 Confirmation Sampling

Total Lead Confirmation Sampling

Total lead confirmation sampling will be conducted to confirm that soil remaining onsite is below the lead PRGs. The confirmation sampling procedure includes:9

• Select one sidewall sample location for every 50 linear feet of sidewall to demonstrate horizontal compliance with the PRGs and collect samples at the top and bottom of each sidewall to demonstrate vertical compliance with the PRGs; and,

• Collect one sample per 1,000 square feet of bottom area (i.e., the depth of the removal extents).

BBJ Group recommends using a portable XRF analyzer to screen selected sample locations prior to sample collection to evaluate initial compliance with the PRGs. Upon sample collection confirmatory

8 Spoils are not anticipated to occur based on BBJ Group’s previous experience and correspondence with the manufacturer.

9 BBJ Group notes that actual total lead sampling frequencies and locations may vary based on DNREC guidance or regulations, SWDF requirements, and/or site conditions.

April 16, 2021 Page 15 soil samples should be placed in a cooler with ice and analyzed for total lead via USEPA Method 6010 by an accredited laboratory to verify XRF screening results and compliance with the PRGs.

Quality Assurance/Quality Control (QA/QC) samples consisting of field duplicates and equipment blanks should also be collected at predetermined frequencies and/or in accordance with applicable DNREC guidance or regulations.

TCLP Lead Confirmation Sampling

After soil mixing, TCLP lead confirmation sampling should be conducted to verify that leachable lead in stabilized soil and sediment (destined for offsite disposal) is not characteristically hazardous (i.e., below the TCLP regulatory level of 5 mg/L). TCLP lead confirmation samples should be composited from various areas and depths. Sampling frequencies should adhere to applicable DNREC guidance or regulations and/or SWDF requirements. In BBJ Group’s experience, typical frequencies range between collecting one sample per every 250 to 500 tons of stabilized soil. As mentioned in Section

5.2 BBJ Group recommends sizing the grid cells to account for TCLP lead confirmation sampling frequencies. This allows for easier Removal Action performance monitoring and greater transparency in the results for DNREC and SWDF, if required or requested.

Upon sample collection TCLP lead samples should be placed in a cooler with ice and analyzed for TCLP lead via USEPA Method 1311/6010 by an accredited laboratory.

Under no circumstances should stabilized soils be excavated and hauled offsite until the respective TCLP lead analytical results demonstrate compliance with the TCLP Regulatory Level of 5 mg/L.

5.4 Excavation Procedures

Following soil/reagent mixing and confirmation sampling, mechanized equipment such as a backhoe or an excavator will be used to excavate soil and direct load end-dump semi-trailer dump trucks.

Excavation and loading procedures will be conducted to minimize spills.

Excavations greater than five feet below grade will comply with Occupational Safety and Health Administration (OSHA) requirements for excavation sloping and benching per 29 Code of Federal Regulations (CFR) 1926 Subpart P, Appendix B. Given the granular nature of the subsurface soil at this site, OSHA Type C soil (Methods Development Team, Industrial Hygiene Chemistry Division, OSHA Salt Lake Technical Center, 2019) is assumed and the excavation sidewall will be no steeper than 1.5 feet horizontal per 1 foot of depth (1:1.5). A competent person (as defined by the OSHA regulations) will determine whether surcharge loads from stored material or equipment, operating equipment, or traffic are present, and the degree to which the actual slope must be reduced below the maximum allowable slope to achieve the reductions.

Disposable liners may be required in the end-dump trailers to minimize contamination of the trailer and the potential for subsequent worker exposure. Loaded trucks leaving the Subject Property will be required to cover the trailers with a tarp to minimize loss of excavated material in transit to the landfill. An outbound-truck inspection station will be set up close to the Subject Property exit. Before exiting the Subject Property, trucks will be required to stop at the truck inspection station and will be

April 16, 2021 Page 16 examined for evidence of contaminated soil on the undercarriage, body, and wheels. Soil and debris will be removed using brooms and shovels, as necessary. The residual from cleaning the trucks will be stabilized; and periodically loaded into a truck and transported to the landfill with the excavated soil.

Excavation activities will proceed in a manner that avoids double handling of materials. Vehicular traffic and construction equipment will avoid movement over any areas where the Removal Action has already been implemented. Each load of impacted soil will be observed as it is placed into trucks to determine that no liquid wastes are present and no unexpected wastes are included. Suspect wastes, if encountered, will be individually inspected prior to addition to the impacted soil waste stream.

Copies of trucking tickets, weigh tickets, and waste manifests or bills of lading will be retained to document the quantity of material generated and transported off site for disposal.

5.5 Backfill and Topsoil

Excavated areas will be backfilled after (1) verifying that total and TCLP lead confirmation samples demonstrate compliance with the applicable standards, and (2) sources of imported clean fill and topsoil have been reviewed, identified and/or analyzed in accordance with Section 4.11.

Soft material or material that cannot be compacted should not be accepted; however, subgrade soils (to a depth of six inches) prior to the application of topsoil should be free of excessive compaction to enhance the establishment of permanent vegetative cover.

5.6 Site Restoration

The project will involve removal of vegetation and trees in the remediation area and other temporary land disturbance activities. Site restoration activities should proceed in accordance with:

(1) DNREC Sediment and Stormwater Regulations; (2) standards and specifications included in the Delaware Erosion and Sediment Control Handbook (Delaware Sediment & Stormwater Program, Division of Watershed Stewardship, 2013); and (3) specifications and procedures detailed in the site-specific SWPPP and Sediment and Stormwater Management Plan and will notably include:

• Backfill, grading, and compaction specifications;

• Temporary or permanent soil erosion and sediment stabilization specifications;

• Revegetation specifications, as necessary (i.e., flora type, locations, and densities; seeding, planting, mulching, fertilizing and vegetation establishment specifications);

• Removal of dewatering equipment and stormwater and surface water controls; and

• Installation of temporary or permanent fencing to restrict public access to disturbed areas.

Final restoration details will be reviewed by the FWS for consistency with future land use plans.

April 16, 2021 Page 17

5.7 Contaminated Materials Management Plan

Remedial activities and potential land disturbing activities following implementation of the Removal Action should proceed under a DNREC-approved Contaminated Materials Management Plan (CMMP), which typically requires submission to the DNREC within 60 days of issuance of the FPRA.

The objective of the CMMP will be to provide guidance to enable onsite workers and future workers to safely handle potentially impacted or unknown media at the Subject Property. Primary components of the CMMP will include the following:

• Site Background – Document the nature and extent of impacted media Subject Property.

• Materials Management – Document approaches for safely remediating, excavating, handling, and managing known or potentially impacted media, as well as non-native subsurface materials (e.g., debris material, buried pipes, asbestos, etc.). This includes soil screening procedures, backfilling and grading protocols, stockpile maintenance, dewatering and wastewater sampling procedures, equipment decontamination procedures and associated waste characterization requirements, and procedures for safely handling, transporting, and disposing non-hazardous and…