B.08 GFI JB CHS PBR SS042 (Zone 4) 2022 1Q-4Q Annual Monitoring Report #13-14 DRAFT for GFI.pdf

DRAFT

ANNUAL CORRECTIVE MEASURES IMPLEMENTATION

PROGRESS REPORT Nos. 13/14 (1st Quarter 2022 – 4th Quarter 2022)

Zone 4 (SS042)

PERFORMANCE-BASED REMEDIATION

Joint Base Charleston Air

SOUTH CAROLINA

Contract FA8903-15-C-0016 March 2023 Revision 00

Prepared for:

AFCEC/CZRE

US Air Force Civil Engineer Center 772nd ESS/PKS

2261 Hughes Avenue, Suite 155 JBSA Lackland, TX 78236-9853

Prepared by:

AECOM

4016 Salt Pointe Parkway

North Charleston, South Carolina 29405

With Teaming Partners:

Corrective Measures Implementation Annual Progress Report #13/14 Zone 4, Spill Site 42 (SS042)

Joint Base Charleston Air, South Carolina i

DOCUMENT CERTIFICATION

I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system, or those persons directly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for submitting false information, including the possibility of fine and imprisonment for knowing violations. This document is signed and certified in accordance with South Carolina Hazardous Waste Management Regulations R.61-79.270.11 and 270.30(K).

Eva Rasdal Moore, P.G. Date Registration Number 2462

Laura Powers Date JBCA Remedial Project Manager

Joint Base Charleston Air, South Carolina ii

TABLE OF CONTENTS

LIST OF FIGURES .................................................................................................................... III LIST OF TABLES ...................................................................................................................... III LIST OF APPENDICES ............................................................................................................ IV ACRONYMS AND ABBREVIATIONS ....................................................................................... V

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

1.1 Site Description ....................................................................................................... 1-1

1.2 CMI Monitoring, Operation and Maintenance ........................................................... 1-2

1.3 Report Organization................................................................................................. 1-2

2.0 GROUNDWATER COMPLIANCE MONITORING .....................................................2-1

2.1 Compliance Monitoring Points ................................................................................. 2-1

2.2 Sample Collection and Handling Procedures ........................................................... 2-2

2.3 Laboratory Analysis ................................................................................................. 2-2

2.4 Data Evaluation and Usability .................................................................................. 2-3

2.4.1 Groundwater and Surface water Data .................................................................. 2-3

2.4.2 Vapor Data .......................................................................................................... 2-3

2.5 Investigation Derived Waste .................................................................................... 2-3

2.6 Evaluation of Analytical Results ............................................................................... 2-3

2.6.1 Remedial System Evaluation Parameters ............................................................ 2-4

2.6.2 Plume 1 ............................................................................................................... 2-5

2.6.3 Plume 2 ............................................................................................................... 2-8

3.0 SURFACE WATER COMPLIANCE MONITORING ...................................................3-1

3.1 Compliance Monitoring Points ................................................................................. 3-1

3.2 Sample Collection and Handling Procedures ........................................................... 3-1

3.3 Laboratory Analysis ................................................................................................. 3-1

3.4 Evaluation of Analytical Results ............................................................................... 3-1

4.0 VAPOR EXTRACTION SYSTEM OPERATION AND MAINTENANCE .....................4-1

4.1 Air Permitting ........................................................................................................... 4-1

4.2 Summary of Operations and Maintenance ............................................................... 4-1

4.3 Data Evaluation ....................................................................................................... 4-2

4.3.1 Building 532 System ............................................................................................ 4-2

4.3.2 Building 543 East System .................................................................................... 4-2

4.3.3 Building 543 West System ................................................................................... 4-2

4.4 Soil Corrective Measures ......................................................................................... 4-2

5.0 CONCLUSIONS AND RECOMMENDATIONS ..........................................................5-1

5.1 Conclusions ............................................................................................................. 5-1

5.2 Recommendations ................................................................................................... 5-1

6.0 REFERENCES ..........................................................................................................6-1

Joint Base Charleston Air, South Carolina iii

List of Figures

Figure 1 Site Location Map Figure 2 Site Detail Map Figure 3 Compliance Points for Groundwater Figure 4 Groundwater Contours April 2022 (Shallow) Figure 5 Groundwater Contours April 2022 (Deep) Figure 6 Groundwater Contours October 2022 (Shallow) Figure 7 Groundwater Contours October 2022 (Deep) Figure 8 TCE Isoconcentration – April 2022 (Shallow) Figure 9 TCE Isoconcentration – April 2022 (Intermediate) Figure 10 TCE Isoconcentration – April 2022 (Deep) Figure 11 DCE Isoconcentration – April 2022 (Shallow) Figure 12 DCE Isoconcentration – April 2022 (Intermediate) Figure 13 DCE Isoconcentration – April 2022 (Deep) Figure 14 VC Isoconcentration – April 2022 (Shallow) Figure 15 VC Isoconcentration – April 2022 (Intermediate) Figure 16 VC Isoconcentration – April 2022 (Deep) Figure 17 TCE Isoconcentration – October 2022 (Shallow) Figure 18 TCE Isoconcentration – October 2022 (Intermediate) Figure 19 TCE Isoconcentration – October 2022 (Deep) Figure 20 DCE Isoconcentration – October 2022 (Shallow) Figure 21 DCE Isoconcentration – October 2022 (Intermediate) Figure 22 DCE Isoconcentration – October 2022 (Deep) Figure 23 VC Isoconcentration – October 2022 (Shallow) Figure 24 VC Isoconcentration – October 2022 (Intermediate) Figure 25 VC Isoconcentration – October 2022 (Deep) Figure 26 Compliance Points for Surface Water Figure 27 Building 532 Sub-Slab Depressurization System Layout Figure 28 Building 532 Sub-Slab Depressurization Flow Diagram Figure 29 Building 543 Extraction System Layout Figure 30 Building 543 - East Soil Vapor Extraction System Flow Diagram Figure 31 Building 543 - West Soil Vapor Extraction System Flow Diagram

List of Tables

Table 1 Well Construction Summary Table 2 Compliance Monitoring Matrix – Groundwater and Surface Water Table 3 Groundwater Elevation and Field Parameters Table 4 Constituents of Concern in Groundwater Table 5 Constituents of Concern in Surface Water Table 6 O&M Monitoring Matrix – Vapor Extraction Systems Table 7 Historical Results of Periodic Vapor Monitoring from System Outlet

Joint Base Charleston Air, South Carolina iv

List of Appendices

Appendix A Field Documentation Appendix B Laboratory Analytical Data Appendix C Historical COC Concentration Graphs - Groundwater Appendix D Historical COC Concentration Graphs - Surface Water Appendix E Vapor Extraction System O&M Field Documentation

Joint Base Charleston Air, South Carolina v

ACRONYMS AND ABBREVIATIONS

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

Center AOC .................. area of concern CCR .................. construction completion report cis-1,2-DCE ...... cis-1,2-dichloroethene CMI ................... corrective measures implementation CMO ................. corrective measures objective CMS .................. corrective measures study COC .................. constituent of concern CVOC ............... chlorinated volatile organic compound DNAPL .............. dense non-aqueous phase liquid DO .................... dissolved oxygen DoD .................. Department of Defense ERD .................. enhanced reductive dechlorination EVO .................. emulsified vegetable oil GAC .................. granular activated carbon JBC ................... Joint Base Charleston LCS ................... laboratory control sample LCSD ................ laboratory control sample duplicate MCL .................. maximum contaminant level MDL .................. method detection limit mg/L ................. milligrams per liter

MS ................... matrix spike MSD ................. matrix spike duplicate mV ................... millivolts NFA .................. no further action O&M ................. operations and maintenance ORP ................. oxidation reduction potential Pace ................. Pace Analytical Services, LLC ppb ................... parts per billion RCRA ............... Resource Conservation and Recovery Act RPD ................. relative percent difference SCDHEC .......... South Carolina Department of Health and Environmental Control

SVE .................. soil vapor extraction SWMU .............. solid waste management unit TCE .................. trichloroethene TOC ................ total organic carbon UFP-QAPP ....... uniform federal policy quality assurance project plan

USEPA ............. United States Environmental Protection Agency

VC .................... vinyl chloride VOC ................. volatile organic compound

Joint Base Charleston Air, South Carolina

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

1.0 INTRODUCTION

This Corrective Measures Implementation (CMI) Annual Progress Report for Zone 4 at Joint Base Charleston (JBC) Air, South Carolina, has been prepared in accordance with Section IV.I.6 of the Resource Conservation and Recovery Act (RCRA) Permit Number SC3 570 024 460 (South Carolina Department of Health and Environmental Control [SCDHEC], 2019) issued to JBC Air by SCDHEC in conjunction with Region 4 of the United States Environmental Protection Agency (USEPA). This document has been prepared under Air Force Civil Engineer Center (AFCEC) Contract Number FA8903-15-C-0016 in support of the JBC Air Environmental Restoration Program.

This Annual Progress Report presents the results from the semi-annual groundwater and surface water monitoring performed in April 2022 and October 2022, provides an assessment of the enhanced reductive dechlorination (ERD) remedial system, and summarizes the operations and maintenance (O&M) of sub-slab depressurization systems located at Buildings 532 (one system) and 543 (two systems, designated East and West). This report documents operation of the Building 543 East vapor system in support of approved corrective measures for soil, which includes soil vapor extraction (SVE).

Per the approved CMI Work Plan (AECOM, 2010b) the groundwater corrective measures were implemented sitewide in 2010. Continued operation of the remedial system includes injections performed in 2012 and December 2016, with additional gravity injections performed in March 2018 and December 2021. Per the approved CMI Work Plan Addendum (AECOM, 2012), implementation of soil corrective measures includes continued operation of the Building 543 East extraction system.

On June 28, 2019, SCDHEC approved the recommendation to change the frequency of reporting from semi-annually to annually. The recommendation is based on discussions at the November 2018 Tier I meeting and as recommended in the Semi-Annual CMI Progress Report No. 6 (4th Quarter 2018 – 1st Quarter 2019). On June 16, 2022, SCDHEC approved a portion of the compliance monitoring wells recommended for removal from the sampling program. This annual progress report covers the period from January 1 through December 31, 2022.

1.1 Site Description

JBC Air, located in Charleston County approximately 10 miles northwest of Charleston, South Carolina, comprises 3,731 acres of contiguous property. JBC Air is highly developed with most land used for military operations and dormitory and domestic housing. JBC Air is surrounded by industrial, commercial, and residential properties that are part of the City of North Charleston, South Carolina. Site location and site detail maps are presented as Figures 1 and 2, respectively.

Zone 4 is defined as the area encompassing solid waste management units (SWMUs) 29, 33, 86, 88, 89, 90, 103, 104, 121, 122, 149, and 151. Zone 4 occupies approximately 19.45 acres in an industrial area near the JBC Air flight line (ARCADIS, 2004). Activities performed in this area include engine maintenance, storage, and parts cleaning. The site is relatively flat with few trees and is primarily covered with grass with the exception of buildings, parking areas, and roads.

Surface water at the site consists of a concrete-lined drainage canal which lies along the western boundary of Zone 4 with a flow direction of northeast to southwest.

In a letter dated March 28, 2013, SCDHEC granted a No Further Action (NFA) status for Area of Concern (AOC) Q, a PD-680 solvent spill that occurred in 1978. An exact location for AOC Q was not determined, however based on interviews with JBC Air personnel the only place that PD-680 was used is Building 532. NFA was granted based on the high probability that any contamination that may have originated from AOC Q would be addressed by the ongoing remedial activities

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 1-2 BWJ140078 associated with SWMU 149. Therefore, future documentation referencing SWMU 149 in Zone 4 will include the history of AOC Q and its association with SWMU 149.

1.2 CMI Monitoring, Operation and Maintenance

The primary objective of the remedial action at Zone 4 is to reduce concentrations of constituents of concern (COC), specifically trichloroethene (TCE) and daughter products, in groundwater via in-situ enhanced anaerobic bioremediation. The goal of the CMI injection is to facilitate biogeochemical conditions conducive to the reductive dechlorination of TCE, effectively reducing source zone mass and decreasing the overall footprint of the contaminant plume. As summarized in the CMI Work Plan (AECOM, 2010b), emulsified vegetable oil (EVO) was selected as the injection material for the Zone 4 site based on the COCs, substrate characteristics, site specific hydraulics, and the successful application of EVO during the treatability study conducted at Plume

2. Monitoring COCs in groundwater is a critical portion of the CMI to evaluate the overall success of the remedy and to monitor contaminant reductions.

Groundwater monitoring is performed to monitor plume extent, overall decrease in parent compound concentrations, increase in daughter compound concentrations, and ultimately overall decrease in daughter compound concentrations. Surface water sampling is also performed as part of the overall evaluation of the corrective measures system since constituents detected in surface water are believed to be present due to contaminated groundwater seeping into the surface water canal adjacent to Zone 4.

The selected corrective measures for groundwater also include operation of sub-slab depressurization systems (also historically referred to as SVE) at Buildings 543 and 532 for the purposes of sub-slab depressurization to reduce or eliminate potential vapor intrusion of volatile organic compounds (VOCs) and methane generated from groundwater remediation activities.

The system operating parameters are monitored monthly, air samples are collected quarterly, and periodic maintenance is performed to ensure the effectiveness of the systems in providing sub-slab depressurization.

1.3 Report Organization

This CMI Semi-Annual Progress Report is organized into the following sections:

Section 1.0 Introduction: Presents the site description and the CMI monitoring, operation and maintenance.

Section 2.0 Groundwater Compliance Monitoring: Summarizes the groundwater monitoring procedures and presents the analytical results for this monitoring period and an evaluation of the in-situ groundwater bio-remediation system.

Section 3.0 Surface Water Compliance Monitoring: Summarizes the surface water monitoring procedures and presents the analytical results for this monitoring period.

Section 4.0 Vapor Extraction System Operation and Maintenance: Summarizes the O&M of the three operating vapor extraction systems and presents a summary of the analytical results for this monitoring period.

Section 5.0 Conclusions and Recommendations Section 6.0 References

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-1 BWJ140078

2.0 GROUNDWATER COMPLIANCE MONITORING

The following presents a summary of monitoring and injection activities related to CMI.

• September-October 2008: Baseline groundwater monitoring;

• August-September 2010: CMI injection;

• November 2010: Periodic compliance monitoring begins for groundwater and surface water. Compliance monitoring will continue throughout implementation of corrective measures;

• October-December 2012: CMI injection;

• Beginning with the November 2013 monitoring event, groundwater and surface water monitoring are performed semi-annually, during the 2nd and 4th quarters in April and October;

• December 2016: CMI injection;

• March-April 2018: Additional gravity injections at MW89-6 and MW89-7;

• October 2019: Modified groundwater monitoring is implemented, including elimination of select wells and reduced monitoring at select wells;

• December 2021-February 2022: Additional gravity injections were completed at select wells; and

• October 2022: Modified groundwater monitoring is implemented, including elimination of select wells.

Details associated with the implementation of corrective measures are presented in the CMI Construction Completion Report (CCR) (AECOM, 2010c), CCR Addendum (AECOM, 2013), and CCR 2016 Remedial Injections (AECOM, 2017). Table 1 presents a summary of the well construction data and Table 2 presents the groundwater compliance monitoring matrix.

2.1 Compliance Monitoring Points

The groundwater compliance points are used to monitor plume extent, overall decrease in parent compound concentrations, increase in daughter compound concentrations, and ultimately overall decrease in daughter compound concentrations. As compliance monitoring events are completed, each monitoring point is evaluated to ensure effective monitoring of changing plume conditions. As plume conditions change, the compliance monitoring system will be evaluated for the reduction, elimination, or addition of compliance points as appropriate.

As previously approved by SCDHEC in the Corrective Measures Study (CMS) Report (AECOM, 2010a), 32 compliance points were selected for Plume 1 (Figure 3), and 17 compliance points were selected for Plume 2 to provide adequate coverage throughout the shallow, intermediate, and deep portions of the surficial aquifer. The compliance monitoring points were modified per SCDHEC’s letters dated April 17, 2019, and June 16, 2022. These modifications were implemented during the October 2019 and October 2022 groundwater monitoring events, respectively. The current compliance monitoring program, presented on Figure 3, includes the wells listed below:

• Plume 1:

o Shallow Interval Wells – MW88-2, MW88-3, MW88-4, MW88-5, MW88-29, MW88-31, MW89-2, MW89-5, MW-9R

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-2 BWJ140078 o Intermediate Interval Wells – EW-1, MW88-41, MW88-42, MW88-40, MW89-6, MW89-7, SIW-5, SIW-15 o Deep Interval Wells - DIW-15, DIW-16, DIW-21, MW023, MW025, MW026, MW88-32, MW88-6, MW-8R, Z4-17, Z4-18.

• Plume 2:

o Shallow Interval Wells – MW29-2, MW29-6, MW29-7, MW29-8, MW29-10, MW29-14, MW29-15, MW29-21.

o Intermediate Interval Wells – IW29-30, MW29-22, MW29-26R.

o Deep Interval Wells – MW29-1, MW29-23, MW29-25R, MW29-36

All wells will be monitored semi-annually (April and October) except for wells, MW29-1, MW29- 10, MW29-23, MW88-3, MW88-4, MW88-29, MW88-32, and MW-9R (October only).

2.2 Sample Collection and Handling Procedures

Prior to collection of groundwater samples, the depth to groundwater was measured using an electronic water level meter. The water level meter was decontaminated between locations.

Calculated groundwater elevations are presented on Table 3. Contoured groundwater elevation maps depicting the shallow and deep intervals are provided as Figures 4 and 5 for April 2022 and Figures 6 and 7 for October 2022.

Groundwater samples were collected following low-flow purging methods. Purging of the monitoring wells was performed using a peristaltic pump with Teflon®-lined polyethylene tubing.

New disposable tubing was used at each well during sample collection to eliminate the potential for cross-contamination. Low-flow purging and sampling were performed as detailed in the USEPA publication Ground Water Issue: Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures (USEPA, 1996), the CMI Work Plan (AECOM, 2010b), and the Zone 4 Uniform Federal Policy Quality Assurance Project Plan (UFP-QAPP) (Zapata, 2014; updated by AECOM, 2016). Field parameters (dissolved oxygen [DO], pH, temperature, oxidation reduction potential [ORP], and specific conductivity) were measured with a YSI 556 (or equivalent) and recorded periodically during purging activities. Groundwater samples were collected following field parameter stabilization. Quality assurance/quality control samples were collected as specified in the UFP-QAPP (Zapata, 2014; updated by AECOM, 2016). Field parameters are presented on Table 3. Field documentation is provided as Appendix A. Sample collection is documented electronically. Therefore, there are no paper field forms generated during the groundwater and/or surface water monitoring.

All sample containers were supplied by the analytical laboratory, Pace Analytical Services, LLC in Columbia, South Carolina (Pace, formerly Shealy Environmental Services, Inc.), an approved Department of Defense (DoD) facility. Sample collection activities were coordinated with the analytical laboratory so that the proper containers, with appropriate preservatives, were provided that hold sufficient sample volumes. After preservation, all samples were stored in a cooler on ice until shipment to the laboratory. All samples were packaged for shipment in a controlled environment to ensure sample integrity. The samples were shipped on ice to maintain a temperature of approximately 4 degrees Celsius. Chain of custody forms were completed to document sample custody and allow traceability of the sample history. Copies of the chains of custody have been included in the laboratory analytical data packages provided electronically in Appendix B.

2.3 Laboratory Analysis

Groundwater samples were submitted for laboratory analyses for VOCs (USEPA Method 8260B, full suite), light hydrocarbon gases (methane, ethene, and ethane) (USEPA Method RSK-175), and total organic carbon (TOC) (USEPA Method SM5310B). Surface water samples were

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-3 BWJ140078 analyzed for VOCs only. All surface and groundwater samples were submitted to a South Carolina certified off-site fixed laboratory, in accordance with the Zone 4 UFP-QAPP (Zapata, 2014;

updated by AECOM, 2016). Laboratory analytical data is presented in Appendix B.

2.4 Data Evaluation and Usability

One hundred percent of the analytical data were reviewed based on USEPA National Functional Guidelines for Inorganic Superfund Methods Data Review (USEPA, 2017a), USEPA National Functional Guidelines for Organic Superfund Methods Data Review (USEPA, 2017b), DoD Consolidated Quality Systems Manual for Environmental Laboratories, version 5.3 (DoD, 2019) for the April 2022 data and version 5.4 (DoD, 2021) for the October 2022 data, and the Uniform Federal Policy – Quality Assurance Project Plan for Performance-Based Remediation, Basewide Groundwater, Surface Water, and Land Use Control Monitoring (Bay West, 2016). The data validation process included review of chains-of-custody, sample condition receipt forms, field duplicate sample relative percent differences (RPDs), surrogate recoveries, method/trip blanks, laboratory control sample/laboratory control sample duplicate (LCS/LCSD) recoveries and RPDs, and matrix spike/matrix spike duplicate (MS/MSD) RPDs. Data was evaluated to verify the achievement of precision, accuracy, representativeness, completeness, comparability, and sensitivity goals established to meet the project data quality objectives.

2.4.1 Groundwater and Surface water Data

Results of the evaluation suggest representative samples were collected and analyzed, and the results are representative of the media analyzed. The overall quality of the data collected is discussed in the Data Validation Reports provided in Appendix B. Data qualifiers were added to the data as a result of the validation process (holding time exceedances, field duplicate RPDs, surrogate recoveries, method blank contamination, LCS recovery, LCS/LCSD RPDs, MS recovery, and MS/MSD RPDs); however, the data reflect expected site conditions and should be considered compliant and adequate for their intended purpose.

2.4.2 Vapor Data

Results of the evaluation suggest representative samples were collected and analyzed, and the results are representative of the media analyzed. No qualifiers were added to the data as a result of the validation process. The data reflect expected site conditions and should be considered compliant and adequate for their intended purpose. The overall quality of the data collected is discussed in the Data Validation Reports provided in Appendix B.

2.5 Investigation Derived Waste

A total of two 55-gallon drums of liquid waste (purge water and decontamination water) were generated during the reporting period. All waste was managed under the supervision of the JBC Air Solid and Hazardous Waste Program Manager. All generated waste was properly managed, removed, transported, and disposed of following all applicable state and federal regulations. Since JBC Air directly disposed of the generated waste, appropriate documentation will be provided per their reporting requirements. Personal protective equipment and disposable sampling materials/equipment was disposed of in on-site dumpsters.

2.6 Evaluation of Analytical Results

The data collected from the baseline groundwater monitoring event (Earth Tech, 2008) in combination with the performance monitoring events conducted since November 2010 have been collectively used to evaluate whether the applied corrective measures are successfully remediating the COCs in groundwater beneath the site. The COCs include 1,1-dichloroethene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, chlorobenzene, cis-1,2-dichloroethene (cis-1,2-DCE), trans-1,2-dichlorethene, TCE, and vinyl chloride (VC). Table 4 presents historical compliance well

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-4 BWJ140078 analytical results for COCs in groundwater. Isoconcentration maps for TCE, cis-1,2-DCE, and VC at shallow, intermediate, and deep groundwater intervals for April and October 2022 are presented as Figures 8 through 25.

Graphs summarizing select VOCs and biogeochemical parameters in groundwater are provided in Appendix C. These trend graphs summarize the VOC mass balance of TCE and its degradation daughter products measured during CMI. This is discussed further below.

2.6.1 Remedial System Evaluation Parameters

CMI effectiveness has been evaluated using the indicators presented below. The data collected during groundwater monitoring has been compared to these indicators to evaluate the in-situ ERD system performance.

• Effectiveness of Amendment Following Injections-o TOC concentrations should increase following the EVO injections and should be maintained to enhance the reductive dechlorination. Increased TOC concentrations are required at the injection locations to maintain sufficient TOC concentrations throughout the treatment zone. TOC concentrations greater than 100 milligrams per liter (mg/L) are considered an indication of effectiveness in amending organic substrates (Parsons, 2004).

• Establishing Anaerobic/Reducing Conditions in Subsurface-o Anaerobic conditions are critical for reductive dechlorination. The EVO solution should be amended sufficiently to alter and maintain geochemical conditions conducive to reductive dechlorination. DO and ORP monitoring results can be used to determine if an anaerobic condition has been established effectively. The DO concentration should be less than 0.5 mg/L, and the ORP should be less than -50 millivolts (mV) as an indication of reducing conditions favorable for reductive dechlorination (AECOM, 2010b).

o Methane – “The presence of methane in groundwater is indicative of strongly reducing conditions… In addition, the presence of methane in groundwater contaminated with chlorinated solvents suggests that the geochemistry of the water is favorable for reductive dechlorination” (Wiedermeier and others, 1999).

Changes in methane concentrations inside the groundwater plume compared to background concentrations or compared to previous concentrations inside the plume can be used as an indicator for the amount of mass that has been biodegraded by methanogenesis.

• Contaminant Dechlorination -o As discussed above, the ultimate goal of the CMI is the reduction in concentration of groundwater COCs, specifically TCE and related daughter products. Under anaerobic conditions, TCE and its daughter products are degraded through reductive dechlorination. A decreasing trend in TCE concentrations or increasing trend in daughter product concentrations should be observed if the bioremediation system is performing efficiently. The daughter products will also ultimately degrade yielding a long-term decreasing trend as well.

The wells discussed in the following sections were selected to present results from multiple geographical areas and depth intervals across the site. In general, monitoring wells within both Plume 1 and Plume 2 have shown significant dechlorination, which is a strong indicator that ERD has been successfully stimulated as a result of the CMI activities. Any anomalies of concentrations of groundwater COCs will be discussed in Section 6.2.

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-5 BWJ140078

2.6.2 Plume 1

Overall Plume 1 showed a positive response to both initial and subsequent EVO injections. Some areas of elevated concentrations, or “hot-spots,” remain following the initial round of injections specifically the areas around MW89-6 and MW89-7, and high cis-1,2-DCE and VC concentration areas within Transect #3. The area surrounding wells MW89-6 and MW89-7 (Injection Grid #1) was not included in the previously installed interim measures; as a result, no injections were performed in this area prior to CMI (AECOM, 2010b). During the CMI injections in 2010, the total proposed injection volumes were not achieved due to extensive ‘daylighting’ of injectate into the storm drain system. As a result, Grid #1 did not receive the original proposed injectate volume per the remedial design. In 2012, a supplemental site wide injection was conducted at specific locations based on evaluation of the groundwater sampling results throughout post injection monitoring (AECOM, 2013). The injection activities at Grid #1 were nearly completed, with 97 percent of the goal volume of EVO injected into the subsurface, however a significant response to the injections (reduction in COCs) was not observed at wells MW89-6 and MW89-7. In 2016, a supplemental site wide injection was conducted (AECOM, 2017). This injection event included the use of five monitoring wells as injection points in areas where prior injections had not shown a significant response. In 2018, a small injection event was performed at MW89-6 and MW89-7.

In December 2021 through February 2022, gravity injections were performed at seven targeted wells. The grid and transect areas are presented in Figure 2.

The following presents a review of the groundwater analytical results for select compliance monitoring wells within Plume 1.

Injection Grid #1: Elevated groundwater contamination in the vicinity of SWMU 151, located near the northern end of Transect 1.

• MW89-7

o Intermediate zone monitoring well located immediately down gradient of injection Grid #1 and was originally located within the greater than (>) 50,000 micrograms per liter (µg/L) total chlorinated volatile organic compound (CVOC) concentration contour (CMI Work Plan; AECOM, 2010b). No injections were performed in the area immediately surrounding Grid #1 prior to CMI. This well received injectate via gravity feed during the 2016 injections and 2018/2022 gravity injection due to limited response following injections in 2010 and 2012.

o TCE concentrations at this location have fluctuated since 2008 with a peak concentration of 64,900 µg/L (May 2014). Following the 2016 injections and 2018 and 2022 gravity injections, concentrations decreased from 40,900 (October 2016) to a concentration of 280 µg/L (April 2022). TCE was not detected in October 2022, due to elevated detection limits. Cis-1,2-DCE and VC concentrations have increased following the decrease in TCE. Cis-1,2- DCE increased to a peak of 31,400 µg/L (October 2021), with a current concentration of 20,000 µg/L (October 2022). VC concentrations increased from 189 µg/L (October 2019), with a current concentration of 6,600 µg/L (October 2022). Concentrations of cis-1,2-DCE and VC have fluctuated as dechlorination occurs.

o TOC concentrations increased to 35,000 mg/L in April 2022 following the December 2021 – February 2022 gravity feed injections. Concentrations decreased to 13,000 mg/L in October 2022. Prior to 2017, TOC had remained below 30 mg/L. Methane concentrations observed at this location suggest strongly reducing conditions conducive to dechlorination are present.

Joint Base Charleston Air, South Carolina

Contract FA8903-15-C-0016 2-6 BWJ140078

Injection Grid #2: “Hot spot” area directly upgradient of surface water receptor located at the toe of Plume 1.

• MW88-31

o Shallow zone monitoring well located within injection Grid #2 and was originally located within the >10,000 µg/L total chlorinated volatile organic compound (CVOC) concentration contour (AECOM, 2010b). Historically ERD activities were performed upgradient of this area and elevated TOC and reducing conditions were present in the area during baseline sampling conducted in September and October 2008.

o Since the CMI, TCE concentrations at this location have remained below the laboratory method detection limit (MDL). Concentrations of cis-1,2-DCE have dropped from 7,600 µg/L (October 2008) and have remained below the maximum contaminant level (MCL) since August 2011. Concentrations of VC have dropped from 11,000 µg/L (October 2008) and have remained below the MCL since August 2013, with the exception of April and October 2018 where it was slightly above the MCL. Declining concentrations of late stage dechlorination products cis-1,2-DCE and VC combined with ethene generation provide strong evidence that complete dechlorination is occurring in this portion of the plume.

o TOC concentrations increased to a maximum of 1,090 mg/L in February 2013, following completion of injection activities in 2012. TOC concentrations at this location have shown a steady decline indicating consumption of the applied EVO substrate. Methane concentrations observed at this location suggest strongly reducing conditions conducive to continued degradation are present.

• EW-1

o Intermediate zone monitoring well located within injection Grid #2 and was originally located within the >1,000 µg/L total CVOC concentration contour (CMI Work Plan; AECOM, 2010b).

o TCE concentrations have remained below the MCL since baseline sampling in October 2008. Since the CMI, cis-1,2-DCE concentrations at this location have decreased from 990 µg/L (October 2008) and have remained below the MCL since August 2011. VC concentrations have also decreased from 2,000 µg/L (October 2008) to a current concentration of 6.8 µg/L (October 2022).

o The elevated methane concentrations observed at this location suggest strongly reducing conditions conducive to continued degradation are present.

Declining concentrations of late stage dechlorination products cis-1,2-DCE and VC combined with ethene generation provide strong evidence that complete dechlorination is occurring in this portion of the plume.

• MW88-6

o Deep zone monitoring well located within injection Grid #2 and was originally located within the >50,000 µg/L total CVOC concentration contour (AECOM, 2010b). Historically ERD activities were performed upgradient of this area and elevated TOC and reducing conditions were present in the area during baseline sampling in September and October 2008.

o Since the CMI, TCE concentrations at this location have decreased from 21 µg/L (October 2008) and have generally remained below the MCL since

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Contract FA8903-15-C-0016 2-7 BWJ140078

November 2010. The current concentration of TCE is 1.3 µg/L. Similarly, concentrations of cis-1,2-DCE have decreased from 38,000 µg/L (October 2008) and have generally remained below the MCL since November 2011, with a current concentration of 3.9 µg/L. VC has decreased from 42,000 µg/L (October 2008) with a current concentration of 3.4 µg/L (October 2022).

o The elevated methane concentrations observed at this location suggest strongly reducing conditions conducive to continued degradation are present.

Declining concentrations of late stage dechlorination products cis-1,2-DCE and VC provide strong evidence that complete dechlorination is occurring in this portion of the plume.

Transect #1: Plume 1 dense non-aqueous phase liquid (DNAPL) source zone.

• MW88-2

o Shallow zone monitoring well located approximately 20 feet from the nearest injection well at injection Transect #1 and was originally located within the >10,000 µg/L total CVOC concentration contour (AECOM, 2010b). Historically, ERD activities were performed upgradient of this area and elevated TOC (190 mg/L) and reducing conditions (-37.2 mV) were present in the area during baseline sampling in October 2008. This well received injectate via gravity feed during the 2016 injections.

o Since the CMI, TCE concentrations at this location have dropped from 1,300 µg/L (October 2008) to concentrations ranging from below the MDL to 398 µg/L. Currently, the TCE concentration is 8.8 µg/L (October 2022).

Concentrations of cis-1,2-DCE have decreased from 29,000 µg/L (October 2008) to a current concentration of 9.8 µg/L (October 2022). Concentrations of VC have fluctuated with a current concentration of 29 µg/L (October 2022).

o TOC concentrations increased to a peak concentration of 7,840 mg/L in April 2017, following the 2016 injections. The general decrease in TCE and cis-1,2- DCE coupled with subsequent increase in VC and ethene production indicate the progression of reductive dechlorination at this location. Elevated concentrations of methane suggest strongly reducing conditions conducive to continued degradation are present.

Transect #2: Across Plume 1 core, west of Building 543.

• Z4-17 o Deep zone monitoring well located approximately 10 feet from the nearest injection well along Injection Transect #2 and was originally located within the >50,000 µg/L total CVOC concentration contour (CMI Work Plan; AECOM, 2010b). Historically ERD activities were performed upgradient of this area and as a result reducing conditions were present in the area during baseline sampling in September/October 2008.

o Since the CMI, TCE concentrations at this location have decreased from 52,000 µg/L (October 2008) and have remained below the laboratory MDL since November 2010. Due to elevated concentrations of other compounds, the MDL has been as high as 100 µg/L. Concentrations of cis-1,2-DCE have decreased from 56,000 µg/L (October 2008) and remained below the MCL until April 2017. Currently, the concentration of cis-1,2-DCE is 50 µg/L. VC concentrations have increased from 1,800 µg/L in October 2008 to a maximum

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Contract FA8903-15-C-0016 2-8 BWJ140078 of 49,300 µg/L in November 2010, with a current concentration of 24,000 µg/L (October 2022).

o The decrease in TCE and cis-1,2-DCE has been accompanied by an increase in VC and ethene. Ethene concentrations have increased from 56 µg/L (October 2008) to a peak concentration of 12,400 µg/L (November 2011) with a current concentration of 3,300 µg/L, indicating that complete dechlorination is occurring within this area. Elevated concentrations of methane suggest strongly reducing conditions conducive to continued degradation are present.

Injection Grid #2 (formerly Transect #3): Across Plume 1 core, west of Building 543.

• MW026

o Deep zone monitoring well located 10 feet downgradient from the nearest injection well along injection Transect #3 and was originally located within the >50,000 µg/L total CVOC concentration contour (AECOM, 2010b). Direct push injections were performed in this area in 2016. Historically, ERD activities were performed upgradient of this area and elevated TOC and reducing conditions were present in the area during baseline sampling in September and October 2008.

o Since the CMI, TCE concentrations at this location have decreased from 290 µg/L (2008) and have remained below the laboratory MCL with the exception of April 2017 (200 µg/L). Concentrations of cis-1,2-DCE have fluctuated with concentration peaks following injection events, with a current concentration of 25 µg/L. VC concentrations have also fluctuated through historical monitoring with an overall decrease from 47,000 µg/L (2008) to 12,000 µg/L (October 2022).

o The decrease in TCE, cis-1,2-DCE, and VC has been accompanied by an increase in ethene concentration from 2,600 µg/L (October 2008) with peak concentrations of 23,000 µg/L (November 2010) and 22,800 µg/L (February 2013) following the primary and secondary injections, respectively, indicating that complete dechlorination is occurring within this area. TOC concentrations increased to 11,700 mg/L (April 2017) following EVO injections in 2016, with a current concentration of 61 mg/L (October 2022). Elevated concentrations of methane indicate that reducing conditions conducive to continued dechlorination are present in this area.

2.6.3 Plume 2

Similar to Plume 1, overall Plume 2 has shown a positive response to the EVO injections with some areas of elevated concentrations still remaining. The following presents a review of the groundwater analytical results for selected compliance monitoring wells within Plume 2:

Grid #3: Plume 2 DNAPL source zone (SWMU 149) and along plume core.

• MW29-15

o Shallow zone monitoring well located upgradient or side-gradient of injection

Grid #3. This monitoring well received injectate via gravity feed during the 2016 injections.

o TCE concentrations have fluctuated throughout monitoring with peak concentrations of 39,300 µg/L (August 2013) and 27,100 µg/L (October 2016).

The current concentration is below the MCL (October 2022). Cis-1,2-DCE concentrations have fluctuated with a current concentration of 210 µg/L

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(October 2022). VC concentrations have fluctuated, with increasing concentrations following decreases in parent compounds, with a current concentration of 75 µg/L (October 2022).

o TOC concentrations remained below 15 µg/L until April 2017, concentrations increased following both the 2016 and 2021 injections. Following the dramatic increase in TOC, dechlorination has been enhanced resulting in decreases in parent compounds and increases in daughter products. TOC concentrations are currently 3,300 mg/L (October 2022), following an increase to 8,600 mg/L as a result of the 2022 mini-injections. Elevated concentrations of methane indicate that reducing conditions conducive to dechlorination are present in this area.

• IW29-30

o Intermediate zone monitoring well located within injection Grid #3 at the Plume

2 source area. This well was originally utilized for the Treatability Study (AECOM, 2009), when injections were completed at this location in June and July 2008. During CMI, injections were completed approximately 25 feet downgradient (2010) and subsequent injections were completed at this location in 2012 and 2016.

o TCE concentrations have decreased from 18,200 µg/L (May 2008) and have remained below the MCL since April 2017. Cis-1,2-DCE concentrations have fluctuated with concentration peaks following injection events, with concentrations below the MCL since October 2018. VC concentrations have also fluctuated following injection events with a current concentration of 5.4 µg/L (October 2022).

o The overall decrease in TCE, cis-1,2-DCE, and VC has been accompanied by an increase in ethene concentrations from 10.5 µg/L (October 2008) to a maximum of 493 µg/L (November 2010), indicating that complete dechlorination is occurring within this area. TOC concentrations at this location have fluctuated with peaks following injection activities followed by a concentration decline indicating consumption of the applied EVO substrate in the period following the injection event.

• MW29-23

o Deep zone monitoring well located immediately down gradient of injection Grid

#3 and was originally located within the >1,000 µg/L total CVOC concentration contour (AECOM, 2010b). In 2005, injections were completed by ARCADIS in the shallow zone, approximately 15 feet upgradient of this location. During CMI, injections were completed approximately five feet upgradient during the 2010, 2012, and 2016 events.

o TCE concentrations have decreased from 5,900 µg/L (October 2008) and remained below the MCL since May 2011. Cis-1,2-DCE concentrations have decreased from a peak concentration of 4,600 µg/L (November 2010) and have remained below the MCL since February 2012. VC concentrations have decreased from a peak concentration of 320 µg/L (August 2011), with concentrations remaining below the MCL since November 2013.

o Ethene concentrations have increased from 0.82 µg/L (October 2008) to a maximum concentration of 181 µg/L (August 2011) indicating complete dechlorination has occurred in this area. A significant increase in TOC was

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Contract FA8903-15-C-0016 2-10 BWJ140078 observed at this well following EVO injection in 2010 followed by a concentration decline indicating consumption of the applied EVO substrate.

Residual organic carbon has promoted a reducing environment as indicated by elevated concentrations of methane.

• MW29-36

o Deep zone monitoring well located within injection Grid #3, approximately 10 feet down gradient of the nearest injection well. Injections were completed upgradient of this location in June and July 2008 as part of the Treatability Study (AECOM, 2009). During CMI, injections were completed approximately 25 feet downgradient (2010), and injections were completed approximately 10 feet upgradient in 2012 and 2016.

o TCE concentrations have dropped from a peak of 42,100 µg/L (February 2009) and have remained below the MCL since November 2010, with the exception of a detection of 40.5 µg/L in April 2020. Concentrations of cis-1,2-DCE increased from 103 µg/L (May 2008) to a maximum of 4,280 µg/L (November 2010) and have remained below the MCL since August 2011. Concentrations of VC increased from 21 µg/L (May 2008) to a maximum of 3,280 µg/L (November 2010) and is currently below the detection limit (October 2022).

o Ethene concentrations at this location increased from 5.69 µg/L (May 2008) to a maximum of 4,440 µg/L (November 2010) indicating that complete dechlorination is occurring in this area. An increase in TOC was observed at this well following the 2010 and 2016 injections, indicating good distribution of the injected substrate. A reducing environment is illustrated by the presence of elevated concentrations of methane. The observed decrease in concentrations of TCE and cis-1,2-DCE followed by a subsequent increase in concentrations of VC and ethene indicate effective dechlorination is occurring.

Grid #4: Located at the toe of Plume 2.

• MW29-6

o Shallow zone monitoring well located within injection Grid #4 and was originally located within the >100 µg/L total CVOC concentration contour (AECOM, 2010b). Historically, ERD activities were performed upgradient of this area.

During CMI, injections were completed approximately 5–10 feet upgradient in 2010, 2012, and 2016.

o TCE concentrations have remained below the MCL since baseline sampling (October 2008). Cis-1,2-DCE concentrations have decreased from 430 µg/L (October 2008) and have remained below the MCL since November 2014.