B.08 GFI JB CHS PBR_SA036 (SWMU 36)_2023 OES Report.pdf

DRAFT

Solid Waste Management Unit 36 (SA036)

Optimized Exit Strategy

Implementation Completion Report

PERFORMANCE-BASED REMEDIATION

Joint Base Charleston Weapons

SOUTH CAROLINA

Contract FA8903-15-C-0016

February 2023 Revision 01

Prepared for:

AFCEC/CZRW

Prepared by:

With Teaming Partners:

Bay West LLC 5 Empire Drive

St. Paul, Minnesota 55103

U.S. Air Force Civil Engineer Center

SWMU 36 Optimized Exit Strategy Implementation Report Joint Base Charleston, South Carolina

Contract FA8903-15-C-0016 i BWJ140078

Table of Contents

1.0 INTRODUCTION ........................................................................................................ 1-1

1.1 Basic Project Information ........................................................................................... 1-2

1.2 Objectives................................................................................................................... 1-3

1.2.1 Awarded Performance Objective ............................................................................ 1-3

1.2.2 Technical Objectives .............................................................................................. 1-5

2.0 OVERVIEW OF REMEDIAL PROGRESS AND STATUS ......................................... 2-1

2.1 Overview of Site Advancement .................................................................................. 2-1

2.2 Performance Model Update ....................................................................................... 2-2

2.2.1 Baseline Performance Indicator Projection ............................................................ 2-2

2.2.2 Actual Performance Indicator Values ..................................................................... 2-2

2.3 Continual Improvement Efforts ................................................................................... 2-2

2.3.1 Optimization, Corrective Actions, Contingencies ................................................... 2-3

2.3.2 Compliance with Decision Documents and Plans .................................................. 2-3

2.3.3 Periodic Review Deficiencies Corrected ................................................................ 2-3

3.0 DISCUSSION OF PERFORMANCE .......................................................................... 3-1

4.0 REFERENCES ........................................................................................................... 4-1

List of Figures

Figure 1-1 SWMU 36 Site Location Map Figure 1-2 SWMU 36 Site Map Figure 2-1 SWMU 36 Performance Model Figure 2-2 SWMU 36 Thiessen Polygon Network, April 2022

List of Tables

Table 1-1 OES Report Checklist .......................................................................................... 1-1 Table 1-2 Milestones ............................................................................................................ 1-4

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LIST OF ACRONYMS

μg/L ................. micrograms per liter AFCEC ............ Air Force Civil Engineer

Center AFLOA ............ Air Force Legal Operations

Agency Bay West ......... Bay West LLC BEHP .............. bis(2-ethylhexyl)phthalate BHC ................ alpha-benzene hexachloride CLIN ................ contract line item number CMI ................. Corrective Measures

Implementation CMO ................ corrective measures objective CMS ................ Corrective Measures Study COC ................ contaminant of concern CSM ................ conceptual site model DD ................... decision document ERP ................. Environmental Restoration

Program ISCR ............... in situ chemical reduction JBC ................. Joint Base Charleston LCC ................. life cycle cost LTM ................. long-term management LUC ................. land use control MCS ................ media cleanup standard MCL ................ maximum contaminant level MNA ................ monitored natural attenuation OES ................ Optimized Exit Strategy

O&M ............... operations and maintenance PAL ................. project action level PCE ................ tetrachloroethene PDI .................. pre-design investigation POP ................ period of performance RAO ................ remedial action objective RA-O ............... remedial action – operations RC .................. response complete RCRA ............. Resource Conservation and

Recovery Act RCRA Permit .. RCRA Hazardous Waste

Permit No. SC8 170 022

RFI .................. RCRA Facility Investigation RIP .................. remedy in place SC ................... site closeout SCDHEC ........ South Carolina Department of Health and Environmental Control

SoB ................. Statement of Basis SOO ................ Statement of Objectives SWMU ............ solid waste management unit TCE ................ trichloroethene TtNUS ............. Tetra Tech NUS, Inc.

USEPA ........... United States Environmental

Protection Agency VOC ................ volatile organic compound

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1.0 INTRODUCTION

The following is an Optimized Exit Strategy (OES) Implementation Completion Report for the Solid Waste Management Unit (SWMU) 36 (SA036) Facility at Joint Base Charleston (JBC) Weapons, South Carolina (Figure 1-1). This document was prepared by Bay West LLC (Bay West) under Contract FA8903-15-C-0016 for the United States Air Force Civil Engineer Center (AFCEC), in support of the Environmental Restoration Program (ERP) at JBC Weapons. The work at JBC Weapons is being conducted under Resource Conservation and Recovery Act (RCRA) Part B permit number SC8 170 022 620, effective 22 September 2011 through 22 September 2021 (RCRA Permit; Modified 23 October 2019).

The performance objective for SWMU 36 is to achieve response complete (RC) for tetrachloroethene (PCE) and its degradation products within the period of performance (POP), as defined under Contract FA8903-15-C-0016.

The purpose of an OES Implementation Completion Report is to demonstrate performance along the path to achieve site closeout (SC), or as close to SC as practical, while maximizing effectiveness and efficiencies, and minimizing life cycle costs (LCCs), as developed in the Final SWMU 36 OES Plan (Bay West, 2020a). This OES Implementation Completion Report was developed in accordance with the Final OES Compendium for Performance-Based Remediation (OES Compendium; AFCEC, 2014) and is the second OES Implementation Completion Report for SWMU 36. The first OES Implementation Completion Report was developed in 2021 (Bay West, 2021).

The OES Compendium checklist of required OES Report elements and locations within this document is provided in Table 1-1.

Table 1-1 OES Report Checklist

Check Location in OES

Report OES Element

Does the OES Report:

✓ Section 1.1 Include description of remedial strategies that have been implemented?

✓ Section 2.3.1 Include description of remedial strategies that remain to be implemented?

✓ Section 2.2 Include documentation of any modifications to the OES Plan arising from performance to date?

✓ Section 2.2.2 Use quantitative evidence to demonstrate whether or not the remedial approach is performing in accordance with the performance model?

✓ Section 2.3.1 Indicate whether or not corrective or contingency actions have been triggered?

According to the OES Compendium, OES Reports must meet the following objectives:

• Reporting current site conditions and summary of progression toward SC over time;

• Update the performance model by reporting and plotting actual performance indicator values and their relation to proposed performance goals;

• Report continual improvement efforts; and

• Performance monitoring data must meet the standard of being optimized (best achievable given the approved OES). Evidence should confirm that actual results are at least as good as expected results. If actual results fall short, the report must document activation of corrective action measures (process improvement) or contingency actions (process failure).

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The following sections describe basic project information and objectives.

1.1 Basic Project Information

JBC Weapons is located in Berkeley and Charleston Counties, approximately 10 miles northwest of Charleston, South Carolina (Figure 1-1). JBC Weapons comprises 16,868 acres of contiguous property with a base population of approximately 9,300. SWMU 36 – Old Southside Hazardous Waste Storage Facility is in the east-central portion of JBC Weapons, south of the main facility entrance and northeast of the railroad tracks that transect the central portion of JBC Weapons (Figure 1-2). SWMU 36 is located off Red Bank Road and abuts the motor vehicle pool area and the current Part B-permitted Hazardous Waste Storage Facility (Building 2332). The site supports few structures and has several different ground surfaces, including gravel, asphalt pavement, and grass. During its operation, SWMU 36 was an unpaved site serving as the accumulation point for wastes generated throughout JBC Weapons. SWMU 36 operated from the 1940s until 1980, when an Interim Status Hazardous Waste Storage Facility was constructed.

Several investigations have been conducted at SWMU 36. The RCRA facility investigation (RFI) was conducted in several stages from 1998 through 2001 (Tetra Tech NUS, Inc. [TtNUS], 2002).

PCE and its degradation products present in groundwater represent the greatest potential risk drivers at SWMU 36. Pesticides are also present in groundwater.

In 2003, a Corrective Measures Study (CMS) was completed for SWMU 36 (TtNUS, 2003). The recommended alternative presented in the CMS Report was monitored natural attenuation (MNA) and land use controls (LUCs). A Statement of Basis (SoB) was not completed at that time.

Between December 2005 and February 2006, additional field investigations were conducted at the site, including collection of groundwater elevations and a surface water sample. Updated monitoring recommendations were based on the results of this investigation. Groundwater monitoring was conducted at SWMU 36 during the period of 2008–2012; the South Carolina Department of Health and Environmental Control (SCDHEC) requested that a CMS Work Plan be submitted to address further delineation of PCE at SWMU 36 to support a reevaluation of corrective measures alternatives (C. Pickett, 2013) prior to finalizing an SoB and modification of the RCRA Permit.

Annual groundwater monitoring resumed in 2016, and a data gap investigation was also completed in 2016 under the CMS Work Plan (Bay West, 2016) to support preparation of a revised CMS Report. This included delineation of the extent of pesticides detected at the northern boundary of the site. Following the completion of the 2016 groundwater monitoring and data gap investigation, the SWMU 36 2016 Annual Monitoring Report recommended to continue annual groundwater monitoring for volatile organic compounds (VOCs) and pesticides at select monitoring wells only while the CMS Report and SoB were being finalized (Bay West, 2017a). Six monitoring wells were sampled for VOCs and pesticides in 2017 and 2018.

The data collected from the 2016 monitoring and data gap activities was used to update the conceptual site model (CSM) and reevaluate corrective measures alternatives for the site. The proposed remedy decision for SWMU 36 is enhanced reductive dechlorination, groundwater monitoring, and LUCs, as selected through a CMS Report (Bay West, 2017b).The CMS Report was approved by SCDHEC in a letter dated 9 June 2017 (C. Pickett, 2017). A detailed investigation history is presented in the CMS Report (Bay West, 2017b). An SoB was approved on 9 February 2018 (C. Pickett, 2018), and the remedy selected for SWMU 36 was finalized and added to Appendix A-8 by the 2018 permit modification on 14 October 2018. The CMS Report (Bay West, 2017b) and the SoB (SCDHEC, 2018) presented the following corrective measures objectives (CMOs) for SWMU 36:

Contract FA8903-15-C-0016 1-3 BWJ140078

• CMO 1: Prevent unacceptable risks for potential future human exposure (i.e., hypothetical future resident) to contaminated site groundwater; and

• CMO 2: Attain media cleanup standards (MCSs) for PCE and its degradation products for groundwater.

The medium of concern at SWMU 36 is groundwater. The final MCSs as stated in the SoB are the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) for PCE and its degradation products as follows:

• PCE: 5 micrograms per liter (µg/L)

• Trichloroethene (TCE): 5 µg/L

• cis-1,2-dichloroethane: 70 µg/L

• Vinyl chloride: 2 µg/L

A Corrective Measures Implementation (CMI) Work Plan was developed for implementation of corrective measures to address the groundwater contaminant plume exceeding cleanup goals (Bay West, 2019). Corrective measures were completed at the site between November 5 and December 17, 2019. A total of 160 direct push technology injection points were advanced, with each point receiving a slurry of EHC® in situ chemical reduction (ISCR) reagent, magnesium hydroxide pH buffer, and water. Forty-seven of the 160 injection points also received a predetermined amount of SDC-9TM, a microbial consortium, to accelerate and promote complete biodegradation of PCE to its end-products. Injections were conducted across four transects designed to act as treatment barriers to contaminant migration. Each transect consisted of a series of double-row points oriented roughly perpendicular to the groundwater flow direction, unless utilities or other obstructions required points to be moved. Additional details are included in the Injection Completion Report (Bay West, 2020b) and the CMI Report (Bay West, 2020c).

An additional corrective measures event was completed at the site between February 2 and March 4, 2022. A total of 70 additional DPT injection points were advanced at SWMU 36 to target areas of the PCE plume not adequately addressed by the 2019 injections. Each point received a slurry of EHC® reagent, magnesium hydroxide pH buffer, and water. Additional details are included in the Injection Completion Report (Bay West, 2022b).

A performance monitoring program has been implemented at the site to track progress of the corrective measures. LUCs have also been implemented to restrict the use of site groundwater until cleanup objectives are achieved, and to require further evaluation of vapor intrusion risks if construction activities are planned at the site in the future. Because pesticide concentrations currently exceed Project Action Levels (PALs), the corrective measures include ongoing long-term monitoring of pesticides in groundwater as requested by SCDHEC.

1.2 Objectives

1.2.1 Awarded Performance Objective

The performance objective for the site is to achieve RC within the contract POP and move the site towards SC by documenting that PCE and its degradation products reduce to and remain below USEPA MCLs. The RC endpoint performance objective includes completion of CMI, remedial action – operations (RA-O, including long-term monitoring [LTM]), and LUCs. The milestones under sub-Contract Line Item Numbers (CLINs) for SWMU 36 are provided in Table 1-2.

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Table 1-2 Milestones

CLIN Milestone Status

0022 SA036 (SWMU 36), Old Southside Hazardous Waste Storage Site

0022AA

Mobilize and develop an optimized exit strategy/plan to achieve SC while maintaining compliance with current regulatory and binding agreements at SA036 and achieve Final Decision Document (DD)/Statement of Basis (SoB).

0022AA.01 AF Approval of Final OES Plan Completed

0022AA.02

AF Approval of Draft 2016 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AA.03

AF and Regulatory Written Notice of Approval of Final 2016 Annual RA-O Report

Completed

0022AA.04

AF Approval of Draft 2017 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AA.05

AF and Regulatory Written Notice of Approval of Final 2017 Annual RA-O Report

Completed

0022AA.06

AF Approval of Draft 2018 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AA.07

AF and Regulatory Written Notice of Approval of Final 2018 Annual RA-O Report

Completed

0022AA.08

AF Approval of Draft pre-design investigation (PDI) Work Plan (Submit Draft to Regulators)

Completed

0022AA.09 AF and Regulatory Written Notice of Approval of Final PDI Work Plan Completed

0022AA.10 AF Approval of Draft CMS Work Plan (Submit Draft to Regulators) Completed

0022AA.11

AF and Regulatory Written Notice of Approval of Final CMS Work Plan

Completed

0022AA.12 AF Approval of Draft CMS (Submit Draft to Regulators) Completed

0022AA.13 AF and Regulatory Written Notice of Approval of Final CMS Completed

0022AA.14

AFCEC and Air Force Legal Operations Authority (AFLOA) Approval of Draft SA036 SoB

Completed

0022AA.15

AF and Regulatory Written Notice of Approval of Final SA036 SoB - Achievement of DD

Completed

0022AB

Achieve Remedy-in-Place (RIP) while maintaining compliance with current regulatory and binding agreements at SA036.

0022AB.01

AF Approval of Draft 2019 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AB.02

AF and Regulatory Written Notice of Approval of Final 2019 Annual RA-O Report

Completed

0022AB.03

AF Approval of Draft SA036 CMI Work Plan (Submit Draft to Regulators)

Completed

0022AB.04

AF and Regulatory Written Notice of Approval of Final SA036 CMI Work Plan

Completed

0022AB.05

AF Approval of Draft Injection Completion Report (Submit Draft to Regulators)

Completed

0022AB.06

AF and Regulatory Written Notice of Approval of Final Injection Completion Report

Completed

0022AB.07 AF Approval of Draft SA036 CMI Report (Submit Draft to Regulators) Completed

0022AB.08

AF and Regulatory Written Notice of Approval of Final SA036 CMI Report - Achievement of RIP

Completed

0022AB.09 AF Approval of Final OES Implementation Completion Report Completed

0022AC

Implement OES Strategy and Deliver a Final OES Implementation Completion Plan Report while maintaining compliance with current regulatory and binding agreements at SA036.

0022AC.01

AF Approval of Draft 2020 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AC.02

AF and Regulatory Written Notice of Approval of Final 2020 Annual RA-O Report

Completed

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Table 1-2 Milestones

CLIN Milestone Status

0022AC.03

AF Approval of Draft 2021 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AC.04

AF and Regulatory Written Notice of Approval of Final 2021 Annual RA-O Report

Completed

0022AC.05

AF Approval of Draft 2022 Annual RA-O Report (Submit Draft to Regulators)

Completed

0022AC.06

AF and Regulatory Written Notice of Approval of Final 2022 Annual RA-O Report

Completed

0022AC.07 AF Approval of Final OES Implementation Completion Report In review (this document)

0022AD

Achieve Response Complete (RC) in accordance with Table 1 of the Statement of Objectives (SOO) and deliver Final OES Effectiveness Report to achieve SC while maintaining compliance with current regulatory and binding agreements at SA036.

0022AD.01

AF Approval of Draft 2023 Annual RA-O Report (Submit Draft to Regulators)

To be prepared 2023

0022AD.02

AF and Regulatory Written Notice of Approval of Final 2023 Annual RA-O Report

To be prepared 2023

0022AD.03

AF Approval of Draft 2024 Annual RA-O Report Documenting Achievement of Remedial Action Objectives (RAOs) (Submit Draft to Regulators)

To be prepared 2024

0022AD.04

AF and Regulatory Written Notice of Approval of Final 2024 Annual RA-O Report Documenting Achievement of RAOs - Achievement of

RC

To be prepared 2024

0022AD.05 AF Approval of Final OES Effectiveness Report To be prepared 2024

1.2.2 Technical Objectives

Based on the OES Plan (Bay West, 2020a), the selected remedial alternative for OES is enhanced reductive dechlorination, groundwater monitoring, and LUCs as presented in the SoB (SCDHEC, 2018). Following implementation of the corrective measures described above, groundwater contaminant concentrations will be tracked against the performance model. If groundwater concentrations fall outside the acceptable range according to the performance model, evaluation and implementation of a contingency action will be performed. The actions needed for the selected remedial alternative are:

1. Complete CMI Work Plan and OES Plan (completed: Bay West, 2019; Bay West, 2020a).

2. Implement corrective measures injection activities and submit an Injection Completion Report following completion of each injection event (completed: Bay West, 2020b).

3. Submit CMI Report demonstrating achievement of remedy in place (RIP; completed: Bay West, 2020c).

4. Complete RA-O activities with groundwater performance monitoring, and track groundwater trends against performance model (current document).

5. Submit annual operations and maintenance (O&M) reports with recommendations for additional injections and/or reduction in sampling scope and/or frequency.

6. If groundwater trends are outside the performance objectives, evaluate the need for a second injection event; perform second injection event if warranted.

7. Upon achieving all contaminants of concern (COCs) below USEPA MCLs, submit RA-O report documenting achievement of CMOs (RC).

8. Support RCRA Permit Modification Request.

9. Submit O&M or LTM reports for the duration of the POP, depending on when RC is achieved.

10. Provide five-year review support for the duration of the POP.

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11. Submit an OES Effectiveness Report near the end of the POP.

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2.0 OVERVIEW OF REMEDIAL PROGRESS AND STATUS

The following sections provide an overview of site advancement, a performance model update, and continual improvement efforts.

2.1 Overview of Site Advancement

The decision process for data collected at SWMU 36 is focused on confirming that the selected remedial approach is on track to meet the contract performance goal of achieving RC by the POP end date of 20 July 2025.The project decisions as presented in the OES Plan (Bay West, 2020a) are:

1. Does groundwater meet USEPA MCLs at any or all selected performance monitoring locations? Monitoring wells that have met the USEPA MCLs may have sampling discontinued or the frequency decreased. Groundwater monitoring program changes will be proposed in annual monitoring reports, and page revisions to the Closure Certification Report will be submitted with a request for RCRA Permit modification.

2. Once all performance monitoring locations have met and remain below USEPA MCLs for at least three consecutive annual monitoring events, the monitoring wells will be recommended for decommissioning and reported on in annual monitoring reports.

Data used to guide the above decisions will consist of groundwater monitoring analytical results and LUC inspection findings. The SWMU 36 remedy described in Section 1.2 is currently protective of human health and the environment. LUC inspections will monitor for potential unacceptable risks of hypothetical future resident exposure to contaminated site groundwater.

Groundwater monitoring will continue to be conducted at the site as outlined in the CMI Work Plan (Bay West, 2019) and will include monitoring for pesticides at a subset of wells as requested by SCDHEC until pesticide concentrations achieve and remain at or below the pesticide PAL (the USEPA MCL, or if a USEPA MCL is not established, the USEPA Regional Screening Level for tap water) for at least three consecutive annual monitoring events.

Progress towards achievement of milestones (Section 1.2.1) is summarized below:

• Milestones under sub-CLIN 0022AA (Mobilize and develop an OES/plan to achieve SC while maintaining compliance with current regulatory and binding agreements at SA036 and achieve Final DD/SoB) have been achieved including the OES Plan, 2016 Annual Monitoring Report, 2017 Annual Monitoring Report, 2018 Annual Monitoring Report, PDI Work Plan, CMS Work Plan, CMS Report, and SoB (DD).

• Milestones under sub-CLIN 0022AB (Achieve RIP while maintaining compliance with current regulatory and binding agreements at SA036) have been completed or are underway. The 2019 Annual Monitoring Report, CMI Work Plan, Injection Completion Report, CMI Report (documenting RIP) are completed. This OES Implementation Completion Report is in review.

• Milestones under sub-CLIN 0022AC (Implement OES Strategy and Deliver a Final OES Implementation Completion Plan Report while maintaining compliance with current regulatory and binding agreements at SA036) are underway. The 2020 Annual Monitoring Report, 2021 Annual Monitoring Report, and 2022 Annual Monitoring Report are complete. The update to the OES Implementation Completion Report is in review (this document).

• Milestones under sub-CLIN 0022AD (Achieve RC in accordance with Table 1 of the Statement of Objectives (SOO) and deliver Final OES Effectiveness Report to achieve SC while maintaining compliance with current regulatory and binding agreements at SA036)

Contract FA8903-15-C-0016 2-2 BWJ140078 are scheduled and include the 2023 Annual Monitoring Report, 2024 Annual Monitoring Report, and OES Effectiveness Report.

2.2 Performance Model Update

The performance model for SWMU 36 models the sitewide average PCE trend and includes an optimization approach with trigger levels to achieve RC within the POP. The trigger levels shown are associated with contingency implementation approaches when monitoring data indicate the baseline technical approach is at risk of not achieving the USEPA MCLs by the POP end date.

The performance model is included as Figure 2-1.

In addition to the performance model presented in Figure 2-1, the April 2022 PCE data and existing monitoring well network have been used to generate a Thiessen Polygon network (Figure 2-2), from which an estimate for total contaminant mass at the site can be generated. The Thiessen Polygon method (Thiessen, A.H., 1911) was originally developed as a method to estimate total precipitation volume over large areas, but the same principles can be applied to estimate total contaminant mass in groundwater. The method divides the site up into a network of polygons, with one monitoring well per polygon. The PCE concentration at each well is assigned to the entire polygon area and, when multiplied by an assumed consistent plume thickness and effective porosity, can be used to determine total contaminant mass per polygon. The contaminant mass for all polygons across the site can then be added together to generate a total contaminant mass estimate. To differentiate between contaminant mass reduction due to reductive dechlorination and mass reduction due to contaminant migration off-site, the site should be bounded by “clean” polygons, where PCE concentrations for the representative well in each polygon are below the MCL.

Data from future annual and performance monitoring events will be used to update the site contaminant mass derived from the Thiessen Polygon method and will provide a more accurate means of tracking contaminant mass reduction across the site over time. Assessment of contaminant mass reduction at SWMU 36 will be included in future Annual RA-O Reports.

2.2.1 Baseline Performance Indicator Projection

The projected average PCE concentration is based on the anticipated reduction in PCE concentrations due to the corrective measures injections. It is anticipated that RC will be achieved by the POP end date of 20 July 2025 and that groundwater monitoring will need to be completed for an additional three years to support SC.

2.2.2 Actual Performance Indicator Values

Performance monitoring data are reported and evaluated in the SWMU 36 CMI Report (Bay West, 2020c) and 2022 Annual Monitoring Report (Bay West, 2022a). Remedial performance was assessed using the geometric mean for the PCE plume as shown in the performance model, which was calculated using data from all wells that are currently monitored for PCE.

The geometric mean values for the PCE plume from the October 2020, March 2021, and April 2022 performance monitoring data are 6.02, 4.13, and 2.27 µg/L, respectively, each within the ideal performance range shown on the performance model. Performance monitoring data to date indicate that the USEPA MCLs will be achieved by the POP end date.

2.3 Continual Improvement Efforts

The following sections describe optimization, corrective actions, contingencies, compliance with decision documents and plans, and Period Review deficiencies corrected, as applicable.

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2.3.1 Optimization, Corrective Actions, Contingencies

RA-O activities are grouped with other similar activities at the base, such as annual LUC inspections and RA-O sampling, minimizing mobilization costs and thus providing continual optimization. Additionally, as of November 2019, RA-O activities are performed by a local employee, thus further reducing mobilization costs and providing continual optimization.

The groundwater monitoring network is evaluated on an annual basis throughout the POP to identify opportunities to optimize the program. Monitoring wells that have met the USEPA MCLs may have sampling discontinued or the frequency decreased. Groundwater monitoring program changes will be proposed in the annual monitoring reports, and page revisions to the Closure Certification Report will be submitted with a request for RCRA Permit modification.

If groundwater trends fall outside the ideal performance range according to the performance model, evaluation and implementation of a corrective and/or contingency action will be performed.

Corrective and/or contingency actions may include in-situ polishing of the implemented remedy (i.e., additional injections) to maintain performance within the ideal performance range.

After implementing corrective measures, concentration trends indicate that PCE and its daughter products are on track to meet performance objectives by the POP end date under current conditions based on the performance model.

2.3.2 Compliance with Decision Documents and Plans

According to the Final Performance of a Periodic Review (13 Sites) at Joint Base Charleston Weapons (2014 Periodic Review; Aerostar Environmental Services, Inc., 2014), which includes SWMU 36, the remedy of LTM was functioning as intended in the RCRA Permit and the remedy is protective of human health and the environment. It should be noted that the 2014 Periodic Review is the most recent periodic review and was written before the SoB was developed.

The selected remedy presented in the SoB is enhanced reductive dechlorination, groundwater monitoring, and LUCs to ensure progress towards CMOs (Section 1.1). The status of the selected remedy is described below:

• Corrective measures injection activities were conducted in 2019 and 2022, consisting of injections to promote enhanced reductive dechlorination. The corrective measures activities are summarized in the CMI Report (Bay West, 2020c) and the Injection Completion Report (Bay West, 2022b), respectively.

• Groundwater monitoring is ongoing. The most recent groundwater monitoring results are summarized and evaluated in the SWMU 36 2022 Annual Monitoring Report (Bay West, 2022a).

• LUCs were implemented at SWMU 36 in accordance with the CMS Report (Bay West, 2017b). The third annual LUC inspection was conducted on 15 April 2022. The findings of the annual LUC inspection as well as the completed LUC inspection checklist and photographic log are included in the 2022 Annual Monitoring Report (Bay West, 2022a).

No deficiencies or violations were reported during this inspection event.

Based on the post-remedy implementation performance monitoring results and the LUC inspection results, the corrective measures have been successfully implemented at the site in accordance with the CMS Report (Bay West, 2017b), SoB (SCDHEC, 2018), and CMI Work Plan (Bay West, 2019) and are functioning as designed.

2.3.3 Periodic Review Deficiencies Corrected

The following issue was noted for SWMU 36 in the Periodic Review (Aerostar Environmental Services, Inc., 2014) followed by corrective actions:

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• There are no data to confirm or deny the migration of trichloroethene (TCE), PCE, bis(2-ethylhexyl)phthalate (BEHP), alpha-benzene hexachloride (BHC), beta-BHC and lindane downgradient at SWMU 36. Monitoring wells 36MW22D, 36MW16D, 39MW21D, 39MW25D and 36MW20D have consistently shown concentrations of COCs above USEPA MCLs and the estimated direction of groundwater flow beneath the site is north.

Without monitor wells north of 36MW22D, 36MW16D, 39MW21D, 39MW25D and 36MW20D, the downgradient edge of the contaminant plume cannot be fully delineated.

• Downgradient monitoring wells 36MW26D through 36MW30D were installed in 2016 and downgradient wells 36MW31D through 36MW33D were installed in 2019. Groundwater monitoring results are summarized and evaluated in the SWMU 36 2020 Annual Monitoring Report (Bay West, 2020d).

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3.0 DISCUSSION OF PERFORMANCE

Geometric mean values for the PCE plume from the 2022 performance monitoring event is in the ideal performance range as shown in Figure 2-1. Additionally, groundwater monitoring and LUCs meet the standard for optimization.

After implementing corrective measures, concentration trends indicate that PCE and its daughter products are on track to meet performance objectives by the POP end date under current conditions based on the performance model.

Groundwater monitoring results are summarized and evaluated in the SWMU 36 2022 Annual Monitoring Report (Bay West, 2022a) and will continue to be evaluated in future annual monitoring reports. Additional corrective and/or contingency actions will be recommended in future annual monitoring reports as applicable.

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4.0 REFERENCES

Air Force Civil Engineer Center (AFCEC), 2014. Optimized Exit Strategy (OES) Compendium for Performance-Based Remediation. Version 1.0. October.

Aerostar Environmental Services, Inc., 2014. Performance of a Periodic Review (13 Sites) at Joint Base Charleston Weapons, Charleston, South Carolina. Final. June.

Bay West, 2016. Uniform Federal Policy Quality Assurance Project Plan, Work Plan for Corrective Measures Study at SWMU 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final. February.

Bay West, 2017a. 2016 Annual Monitoring Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final.

March.

Bay West, 2017b. Corrective Measures Study Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final.

May.

Bay West, 2019. Corrective Measures Implementation Work Plan, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final. October.

Bay West, 2020a. Solid Waste Management Unit 36 (SA036) OES Plan, Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final. July.

Bay West, 2020b. Injection Completion Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final.

February.

Bay West, 2020c. Corrective Measures Implementation Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final. November.

Bay West, 2020d. 2020 Annual Monitoring Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Draft.

December.

Bay West, 2021. Solid Waste Management Unit 36 Optimized Exit Strategy Implementation Completion Report, Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final. February.

Bay West, 2022a. 2022 Annual Monitoring Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Draft Final. October.

Bay West, 2022b. Injection Completion Report, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Draft Final. April.

Pickett, C., 2013. Subject: Approval, SWMU 36 2012 Groundwater Monitoring Report. Letter correspondence to H. Patterson. 26 August.

Pickett, C., 2017. Subject: Approval, Draft Final Corrective Measures Study for Change Pages and Response to Comments (RTCs) for SWMU 36. Letter Correspondence to H. Patterson.

9 June.

Pickett, C., 2018. Subject: Approval, SWMU 36 – Draft Final Statement of Basis (SoB). Letter Correspondence to H. Patterson. 9 February.

Contract FA8903-15-C-0016 4-2 BW140078

SCDHEC, 2018. Statement of Basis for Enhanced Reductive Dechlorination, Groundwater Monitoring, and Land Use Controls, Solid Waste Management Unit 36 (SA036), Performance-Based Remediation, Joint Base Charleston Weapons, South Carolina. Final.

February.

Thiessen, A.H., 1911. Precipitation for large areas, Monthly Weather Review, 39, 1082–1084.

Tetra Tech NUS, Inc. (TtNUS), 2002. RCRA Facilities Investigation Report, SWMU 36 – Old Southside Hazardous Waste Facility. June.

TtNUS, 2003. Corrective Measures Study (CMS) Report for SWMU 36 – Old Southside Hazardous Waste Facility. April.

Contract FA8903-15-C-0016 BW140078

Figures

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SWMU 62

SWMU 77

SWMU 18

TU933

TU929

SWMU 17

SWMU 20

SWMU 79

AOC-G

SWMU 84

SWMU 12

TU925

SWMU 22

TU926

SWMU 85

AOC-L

SWMU 82

SWMU 78

SWMU 80

SWMU 72

SWMU 10

AOC-Q

SWMU 75

SWMU 47

SWMU 83

SWMU 67

SWMU 66

SWMU 69

SWMU 14

SWMU 10

SWMU 36

SWMU 34

SWMU 32

SWMU 57

SWMU 55

SWMU 56

SWMU 60D

SWMU 11

SWMU 39

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SWMU 38

SWMU 13

SWMU 15

AOC B-3 (TU939)

SWMU 9

SWMU 44

SWMU 37

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SWMU 12

SWMU 35

SWMU 14

0 4,750 9,500 Feet

Map Projection: NAD 1983 StatePlane South Carolina FIPS 3900 Feet Basemap: World Street Map WMS (ESRI 2016)

Figure 1-1 SWMU 36 Site Location Map

Drawn By: Project No.

µJoint Base Charleston !

SOUTH CAROLINA

CEN J140078Date Drawn/Revised: 12/2/2019

Joint Base Charleston Weapons Charleston, South Carolina

0 800 1,600 Feet

SWMU Boundary

Joint Base Charleston Boundary

SWMU 36 Boundary

Map Projection: NAD 1983 StatePlane South Carolina FIPS 3900 Feet Basemap: ESRI Imagery WMS Imagery Date Accessed: 09/2016

Drawn By: Project No.

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SWMU 9

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SWMU 13

(former)

SWMU 44

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SWMU 37

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NWS-930-02

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10MW13

10MW17

36MW30D

36MW29D36MW28D

36MW27D

36MW26D

36MW25D

36MW24D

36MW23S

36MW23D36MW22D

36MW21D

36MW20S

36MW20D

36MW19D

36MW18S

36MW18D

36MW17D

36MW16D

36MW15D

36MW14D

36MW13D

36MW12S

36MW12D

36MW11S 36MW11D

36MW10S

36MW10D

36MW09S

36MW09D

36MW08S

36MW08D

36MW07D

36MW07S

36MW06S

36MW05S

36MW04S

36MW03S

36MW02S

36MW02D

36MW01S

36MW01D

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NWS-9MW-01

NWS-9MW-03S

NWS-9MW-03D

36MW33D

36MW32D

36MW31D

µJoint Base Charleston

SOUTH CAROLINA

CEN J140078Date Drawn/Revised: 12/15/2020

Figure 1-2 SWMU 36 Site Map

Joint Base Charleston Weapons Charleston, South Carolina

0 150 300 Feet

0 50 100 Meters

!A Monitoring Well SWMU 36 Site Boundary/LUC Boundary Other Site Boundary

Note:

"Former" refers to sites that are listed as No Further Action in the RCRA permit

130.77 months from present 96.49411 months from present

10.89734 years from present 8.041176 years from present

0.40

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(µ g/

L) Figure 2-1 SWMU 36 Performance Model

Ideal Performance

Range

Risk Mitigation Range (2nd round injections)

End of POP

PCE MCL = 5 µg/L

Failure Range (contingency action required)

EHC®

Injection #2

Map Projection: NAD 1983 StatePlane South Carolina FIPS 3900 Feet Basemap: ESRI World Imagery WMS, 5/2/2017

Figure 2-2 SWMU 36 Thiessen Polygon

Network, April 2022

Project No.

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Sandlapper Ln

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SWMU 36

36MW22D

39,511 sqft

1.42 ug/L

36MW26D

101,354 sqft

ND

36MW07D

28,424 sqft

3.63 ug/L

36MW15D

37,326 sqft 0.70J ug/L

36MW24D

19,333 sqft 2.56J ug/L

36MW32D

101,372 sqft 0.682J ug/L

36MW21D

49,504 sqft

7.52 ug/L

36MW27D

45,278 sqft

5.23 ug/L

36MW29D

237,838 sqft

ND

10MW09

74,042 sqft

ND

10MW13

64,111 sqft

2.34 ug/L

36MW16D

41,401 sqft

7.58 ug/L

10MW17

102,621 sqft

ND

36MW11D

31,978 sqft 0.974J ug/L

36MW09D

24,414 sqft

2.45 ug/L 36MW17D

36,383 sqft

2.72 ug/L

36MW18D

23,057 sqft

ND

36MW30D

191,169 sqft

1.47 ug/L

36MW14D

27,765 sqft

ND

36MW08D

28,035 sqft

7.94 ug/L

36MW13D

21,264 sqft 0.977J ug/L

36MW31D

61,182 sqft

ND

36MW20D

120,840 sqft

4.34 ug/L

36MW19D

49,091 sqft

ND

36MW28D

83,776 sqft

1.29 ug/L

36MW23D

46,888 sqft

11.3 ug/L

36MW25D

75,309 sqft 0.836J ug/L

36MW33D

50,491 sqft 0.846J ug/L µJoint Base Charleston

SOUTH CAROLINA

J140078Date Drawn/Revised: 1/27/2023

Joint Base Charleston Weapons Charleston, South Carolina

0 200 400 Feet

0 50 100 Meters

Tetrachloroethene Plume, 2022 5 - 10 µg/L 10 - 25 µg/L Site Boundary

!A Monitoring Well, VOCs detected !A Monitoring Well,Not Sampled

Thiessen Polygon

Tetrachloroethene (PCE) 5 Trichloroethene (TCE) 5 Dichloroethene (DCE) 70

PAL (µg/L)

Groundwater Flow Direction

Notes:

ND = Analyte not detected µg/L = micrograms per liter *Results for 10MW13 included to provide downgradient delineation of PCE plume