B.08 GFI SWMU 55 FT003 - 2022 LTM Report DRAFT for GFI (2).pdf

DRAFT

2022 ANNUAL LONG TERM GROUNDWATER MONITORING REPORT

SWMU 55 (FT003) - FIRE PROTECTION TRAINING AREA NO. 3

JOINT BASE CHARLESTON-AIR

NORTH CHARLESTON, SOUTH CAROLINA

FACILITY ID SC3570024460

Performance-Based Remediation Contract Number: FA8903-13-C-0006

Prepared for

AIR FORCE CIVIL ENGINEER CENTER

2261 Hughes Ave., Suite 163

Joint Base San Antonio Lackland, Texas 78236-9853

March 2023

Prepared by:

FPM Remediations, Inc.

An Olgoonik Company 181 Kenwood Avenue

Oneida, NY 13421

2022 Annual LTM Report SWMU 55 (FT003) - Fire Protection Training Area No. 3 Joint Base Charleston - Air

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2022 Annual Long Term Groundwater Monitoring Report for SWMU 55 (FT003) – Fire Protection Training Area No. 3

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 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.

Site:

SWMU 55 (FT003) –

Fire Protection Training Area No. 3 Joint Base Charleston-Air North Charleston, South Carolina

Submitted to:

South Carolina Department of Health and Environmental Control (SCDHEC) 2600 Bull Street Columbia, South Carolina 29201

Prepared for:

Air Force Civil Engineer Center (AFCEC) 2261 Hughes Ave., Suite 163 Joint Base San Antonio Lackland, Texas 78236-9853

Prepared by:

FPM Remediations, Inc.

181 Kenwood Avenue Oneida, New York 13421

Author:

Margaret Milman-Barris FPM Remediations, Inc.

Title: Site Lead

Date:

Reviewer:

Lisa Coffey FPM Remediations, Inc.

Title: Project Manager

Gaby Atik, PE FPM Remediations, Inc.

Title: Program Manager

Laura Powers

Title: JBCA Remedial Project Manager

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TABLE OF CONTENTS

LIST OF ACRONYMS

EXECUTIVE SUMMARY

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

1.1 Report Organization ................................................................................. 1-1

2 SITE BACKGROUND ...................................................................................... 2-1

2.1 Facility Information ................................................................................. 2-1

2.2 Site Description ........................................................................................ 2-1

2.3 Site History .............................................................................................. 2-1

2.4 Site Hydrology, Geology, and Hydrogeology ......................................... 2-2

2.5 Previous Investigation and Remediation Activities ................................. 2-4

2.6 Current LTM Requirements ................................................................... 2-10

3 GROUNDWATER AND SURFACE WATER MONITORING

ACTIVITIES .................................................................................................... 2-12

3.1 LTM Groundwater Monitoring Procedures ............................................. 3-1

3.2 LTM Surface Water Monitoring Procedures ........................................... 3-1

3.3 Quality Control Samples .......................................................................... 3-2

3.4 Sample Analysis....................................................................................... 3-2

3.5 Data Validation ........................................................................................ 3-2

3.6 Investigation-Derived Waste ................................................................... 3-3

4 GROUNDWATER AND SURFACE WATER MONITORING

RESULTS ........................................................................................................... 3-4

4.1 Annual Groundwater and Surface Water LTM Event ............................. 4-1

4.1.1 Groundwater Elevation Monitoring Results ................................ 4-1

4.1.2 LTM Groundwater Sampling Results .......................................... 4-1

4.1.3 LTM Surface Water Sampling Results ........................................ 4-3

4.2 Historical Groundwater and Surface Water Monitoring Trends .............. 4-3

5 REMEDIAL PROCESS OPTIMIZATION .................................................... 5-1

6 SITE PERFORMANCE MODEL .................................................................... 6-1

7 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .................. 7-1

7.1 Summary .................................................................................................. 7-1

7.2 Conclusions .............................................................................................. 7-1

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7.3 Recommendations .................................................................................... 7-1

8 REFERENCES ................................................................................................... 8-1

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TABLES

Table 1 Monitoring Well Construction Details and Groundwater Level Measurements, November 2022

Table 2 Historical Groundwater Elevations, December 1996 to November 2022

Table 3 Historical Field Parameter Measurements in Groundwater, December 1996 to November 2022

Table 4 Groundwater Sample Analytical Results, November 2022

Table 5 Historical Field Parameter Measurements in Surface Water, December 2016 to November 2022

Table 6 Surface Water Sample Analytical Results, November 2022

Table 7 Historical Groundwater COC Monitoring Analytical Results, December 1996 to November 2022

Table 8 Historical Surface Water COC Monitoring Analytical Results, December 2016 to November 2022

FIGURES

Figure 1 Site Location

Figure 2 Historical Site Features

Figure 3 Groundwater (Water Table) Elevation Contours, Shallow Wells, November 2022

Figure 4 Groundwater Elevation Contours, Deep Wells, November 2022

Figure 5 Groundwater and Surface Water Sampling Results, November 2022

Figure 6 Historical COC Concentrations in Groundwater at Monitoring Wells MW-P-11S and 55MW-25

Figure 7 Site Performance Model

APPENDICES

Appendix A Field Notes

Appendix B Daily Field Reports

Appendix C Equipment Calibration Forms

Appendix D Monitoring Well Gauging Form

Appendix E Groundwater Sampling Forms

Appendix F Surface Water Sampling Forms

Appendix G Chain of Custody

Appendix H Laboratory Analytical Reports

Appendix I Data Validation Reports

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LIST OF ACRONYMS

% percent

%D percent difference µg/L micrograms per liter

Aerostar Aerostar SES LLC

AFCEC Air Force Civil Engineer Center

Air Force United States Department of the Air Force amsl above mean sea level

AS/SVE air sparging/soil vapor extraction bgs below ground surface

CAO corrective action objective

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act cis-1,2-DCE cis-1,2-dichloroethene

CMS corrective measures study

COC contaminant of concern

CSM conceptual site model

DO dissolved oxygen

DOD U.S. Department of Defense

Earth Tech Earth Tech, Inc.

ELAP Environmental Laboratory Accreditation Program eV electron-volt

FPM FPM Remediations, Inc.

gal gallons

Halliburton Halliburton NUS Corporation

IDW investigation-derived waste

IM interim measure

ISCO in situ chemical oxidation

ITRC Interstate Technology and Regulatory Council

J estimated concentration (analytical data qualifier)

JBCA Joint Base Charleston-Air ka kiloannum

LCS laboratory control sample

LTM long term monitoring

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LUC land use control

MCL Maximum Contaminant Level

MFR Modified Fenton’s Reagent mg/L milligrams per liter

MNA monitored natural attenuation

MS/MSD matrix spike/matrix spike duplicate mV millivolts

NFA no further action

No. number

NTU nephelometric turbidity unit

ORP oxidation-reduction potential

PAH polynuclear aromatic hydrocarbon, also known as polycyclic aromatic hydrocarbon

PARCCS precision, accuracy, representativeness, completeness, comparability, and sensitivity

PBR performance-based remediation

PCE tetrachloroethene, also known as perchloroethylene

PFAS per- and polyfluoroalkyl substances

PG Professional Geologist

PID photoionization detector

QC quality control

RCRA Resource Conservation and Recovery Act

RFI RCRA facility investigation

RI remedial investigation

SAIC Science Applications International Corporation, Inc.

SCDHEC South Carolina Department of Health and Environmental Control

SGS SGS North America, Inc.

SoB statement of basis

SU standard unit (pH)

SWMU solid waste management unit

TCE trichloroethene, also known as trichloroethylene

Tetra Tech Tetra Tech NUS, Inc.

trans-1,2-DCE trans-1,2-dichloroethene

UFP-QAPP Uniform Federal Policy Quality Assurance Project Plan

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URS URS Group, Inc.

U.S. United States

USEPA United States Environmental Protection Agency

USGS United States Geological Survey

Versar Versar, Inc.

VOC volatile organic compound

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EXECUTIVE SUMMARY

This report presents the results of annual long term monitoring (LTM) conducted in November 2022 at Solid Waste Management Unit (SWMU) 55 (Site FT003), Joint Base Charleston-Air (JBCA). The site is a former fire protection training area used from 1971 to 1983, located in a wooded area at the southeast corner of JBCA. Site contaminants of concern (COCs) are trichloroethene, also known as trichloroethylene, (TCE) and tetrachloroethene, also known as perchloroethylene, (PCE) in groundwater.

The LTM results indicate that TCE in groundwater continues to exceed its Federal drinking water Maximum Contaminant Level (MCL) at monitoring well MW-P-11S. Site COCs were detected in surface water samples collected during LTM.

Contamination at SWMU 55 has been investigated extensively (e.g., Versar, Inc. [Versar], 1990, 1992; URS Group, Inc. [URS]/Radian International, 2001; Tetra Tech NUS, Inc. [Tetra Tech], 2004). Two interim measures (IMs) were conducted historically to address soil and groundwater contamination at the site: a bioventing system was installed in 1992 in the former fire pit to address fuel-impacted soils (Engineering-Science, Inc., 1993), and an air sparge/soil vapor extraction (AS/SVE) system was installed in 2002 in the southern part of the site to address a groundwater plume of dissolved TCE, PCE, and benzene (IT Corporation, 2002a, 2002b).

A focused corrective measures study (CMS) (Earth Tech, Inc. [Earth Tech], 2006) and a Statement of Basis (SoB) (Earth Tech, 2007) formalized the selection of the bioventing and AS/SVE IMs as the final remedy for the site. The site remedy also included LTM of groundwater. The final corrective action objectives (CAOs) set forth by the SoB were the MCLs of 5 micrograms per liter (µg/L) for TCE and PCE in groundwater (United States [U.S.] Environmental Protection Agency [USEPA], 2009). Operation of the bioventing and AS/SVE systems ceased in 2006 because the IMs had successfully removed contamination to the CAOs.

Post-remediation phase LTM began in the fourth quarter of 2006.

Rebound of TCE and PCE in groundwater above MCLs in the southern part of the site was observed during subsequent LTM. A supplemental investigation in 2015 determined that natural attenuation was occurring at low rates and recommended additional groundwater treatment (FPM Remediations, Inc. [FPM], 2016a). An off-Base supplemental investigation in 2016 determined that TCE and PCE contamination in groundwater did not extend beyond the JBCA boundary or to surface water in a ditch on the south side of the property boundary (FPM, 2017b). On May 26, 2017, South Carolina Department of Health and Environmental Control (SCDHEC) requested the addition of surface water monitoring to the LTM program to monitor potential migration of site COCs from groundwater to the ditch (SCDHEC, 2017b).

In June 2017, FPM conducted an additional IM consisting of in situ chemical oxidation (ISCO) by injection of Modified Fenton’s Reagent (MFR) (catalyzed hydrogen peroxide) into the

FPM Remediations, Inc. xii Contract No. FA8903-13-C-0006 shallow aquifer in the southern part of the site (FPM, 2017a). Initial decreases in groundwater COC concentrations in July 2017 were followed by rebound to pre-injection levels by September 2017. In August 2018, an additional investigation found that, contrary to expectation, a narrow plume of impacted groundwater was entering the treatment area from the north, between two existing groundwater sampling locations that were previously thought to define the upgradient edge of groundwater contamination. In February 2019, FPM conducted additional groundwater sampling to investigate the upgradient plume extent as far north as the 1996-1997 plume boundary. TCE and PCE concentrations in the northernmost row of temporary wells exceeded their respective MCLs, indicating that the source of contamination remained north of the investigation area (FPM, 2021b).

An additional groundwater investigation was conducted in 2022 to investigate the upgradient extent of impacted groundwater across the site (FPM, 2022). Groundwater samples were collected along three east-west transects: between the former fire pit and the 1996-1997 plume boundary, through the former fire pit, and north of the former fire pit.

As a result of this investigation, the plume of shallow groundwater impacted by TCE and PCE that was previously known in the southern area of the site, near monitoring well MW-P-11S, has been determined to continue to the north (hydraulically upgradient) as far as Transect A. In this plume, the ratio of PCE to TCE decreases in the downgradient direction from Transect A to the southern ditch, likely due to biodegradation of PCE to TCE. PCE and TCE were not detected in groundwater samples from Transect B-2, indicating that the source of the southern plume is located between Transect A and Transect B-2. An additional mixed plume of dissolved benzene and vinyl chloride is present at Transect B-2 near the fire pit. The source of this plume must be between Transect B-2 and Transect C-2. Hydrocarbon odor and sheen in the boring logs from the per- and polyfluoroalkyl substances (PFAS) Phase I Remedial Investigation (RI), conducted under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Aerostar, 2021) suggest that a hydrocarbon source may remain in the top ten feet of the subsurface near the fire pit. This is a possible source for dissolved benzene in the northern groundwater plume. No specific sources for the chlorinated VOCs in the northern plume or the southern plume are known in the site history.

LTM was conducted in November 2022 at five existing site monitoring wells and three surface water monitoring locations. TCE concentrations in groundwater remained above the MCL at MW-P-11S and below the MCL at well 55MW-25. PCE concentrations in groundwater were below its MCL at all LTM wells. TCE and PCE continue to be non-detect in groundwater from the other LTM wells (3-14, 3-15, and MW-P-12D). TCE was not detected in surface water samples from the drainage ditch, although cis-1,2-DCE was detected below its South Carolina Surface Water Standard at surface water location 55SW11A.

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Site Performance Model

The performance model graphic depicting SWMU 55 (FT003) analytical results in the timeframe of this performance-based remediation (PBR) contract (July 2013 to July 2023) is shown below.

The original PBR performance objective was site closeout, which the Air Force defines as occurring when cleanup goals have been achieved in accordance with the site decision documents that allow unrestricted use of a property, with regulatory concurrence. An IM consisting of ISCO injections was conducted in June 2017. Performance monitoring events to assess the efficacy of the groundwater injections were conducted from July 2017 through August 2018. The June 2017 injection did not result in a decrease in TCE and PCE concentrations to below MCLs. Due to the discovery in 2019 of upgradient groundwater impacts, the Air Force modified the contract, changing the site objective to Achieve Supplemental Investigation. A supplemental groundwater investigation was completed in March, April, and June 2022 and delineated the upgradient extent of the plume of impacted groundwater.

Recommendations

Installation of two additional shallow groundwater monitoring wells has been recommended based on the results of the supplemental groundwater investigation (FPM, 2023a): one located at Transect A and the other at Transect B-2 at locations corresponding to the highest detected concentrations of Site COCs. A work plan (FPM, 2023b) describing installation of the two wells has been submitted to SCDHEC for review. Upon installation, it is recommended that these wells be added to the LTM program.

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Additional treatment activity is recommended to address remaining COCs in groundwater at the site. Any additional treatment should be designed in a manner that considers the 2022 conceptual site model (CSM) update incorporating knowledge of the entire plume.

Groundwater and surface water LTM will continue on an annual basis until additional groundwater treatment is completed. The next planned monitoring event will be an annual LTM sampling event in fall 2023.

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1 INTRODUCTION

FPM Remediations, Inc. (FPM), in association with URS Group, Inc. (URS) under a performance-based remediation (PBR) contract with the United States (U.S.) Department of the Air Force (Air Force) Civil Engineer Center (AFCEC), is conducting environmental remediation activities at Solid Waste Management Unit (SWMU) 55 (Site FT003), Fire Protection Training Area Number (No.) 3 (the “site”), located at Joint Base Charleston-Air (JBCA) (Figure 1). The original PBR performance objective was site closeout, which the Air Force defines as occurring when cleanup goals have been achieved in accordance with the site decision documents that allow unrestricted use of a property, with regulatory concurrence. However, due to the discovery in 2019 of upgradient groundwater impacts, the Air Force modified the contract, changing the site objective to Achieve Supplemental Investigation.

The site was used from 1971 to 1983 for fire training exercises that resulted in soil and groundwater contamination. The site is being regulated under the Resource Conservation and Recovery Act (RCRA), as amended. Regulation is pursuant to RCRA Part B Permit SC3 570 024 460, dated October 4, 2010, as modified April 18, 2018, issued by the South Carolina Department of Health and Environmental Control (SCDHEC). SCDHEC has been delegated authority by the U.S. Environmental Protection Agency (USEPA) for RCRA Corrective Actions.

This report presents the results of the annual long-term monitoring (LTM) event, conducted November 15 and 16, 2022. The LTM was conducted in accordance with the following work plan:

Revised Draft/Final Long-Term Monitoring and Supplemental Investigation Uniform Federal Policy Quality Assurance Project Plan (UFP-QAPP) (FPM, 2015), which was approved by SCDHEC Division of Waste Management in a letter dated March 10, 2015

(SCDHEC, 2015).

The following deviation from the approved work plan occurred during this field event:

Groundwater and surface water samples were analyzed for VOCs by USEPA SW846 Method 8060D. The LTM UFP-QAPP specified USEPA SW846 Method 8060B (FPM, 2015). USEPA SW846 Method 8060D is an updated version of USEPA SW846 Method 8060B.

Beginning in 2018, one surface water sampling location was shifted east to location 55SW11A to accommodate property access permissions, which is a deviation from the SCDHEC-approved recommendation for surface water sampling at location 55SW11 (FPM, 2017b; SCDHEC, 2017b).

1.1 Report Organization

The report has been organized into the following sections:

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Section 1.0 Introduction

Section 2.0 Site Background

Section 3.0 Groundwater and Surface Water Monitoring Activities

Section 4.0 Groundwater and Surface Water Monitoring Results

Section 5.0 Remedial Process Optimization

Section 6.0 Site Performance Model

Section 7.0 Summary, Conclusions, and Recommendations

Section 8.0 References

Tabulated data generated for the site is included in Tables, and maps and graphs for the site are included in Figures. Field notes are provided in Appendix A, Daily Field Reports are provided in Appendix B, equipment calibration logs are provided in Appendix C, groundwater elevation measurement logs are provided in Appendix D, groundwater sampling logs are available in Appendix E, surface water sampling logs are provided in Appendix F; chain-of-custody forms are provided in Appendix G, laboratory reports are included as Appendix H, and data validation reports are provided in Appendix I.

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2 SITE BACKGROUND

2.1 Facility Information

JBCA lies approximately 10 miles northwest of the City of Charleston and is 3,731 acres in area with an approximate population of 5,500 (Figure 1). The population changes periodically as military operations vary from year to year and from mission to mission. The facility is highly developed, with most land used for military operations and housing, including airfield runways and taxiways that are shared with the Charleston International Airport. JBCA is surrounded by industrial, commercial, and residential properties that are part of the City of North Charleston, South Carolina.

2.2 Site Description

The site is located in the southeasternmost portion of JBCA along South Aviation Avenue, directly opposite and east of Building 2035 (Figure 2). The site consists of approximately 9 acres of wooded, undeveloped land. Currently, the only structures located at the site are the inactive bioventing system blower equipment and the inactive air sparge/soil vapor extraction (AS/SVE) system. The site is enclosed by a chain-link fence with a locked gate. The land use type for the site is Open Space, within an Enhanced Use Lease parcel (Zapata International, 2009; D. Holsclaw, personal communication, 2014). The former Aero Club is located to the west of the site, commercial land is located to the north, wooded land is located to the east, and off- Base residential land (Celestial Court in the Joppa Way subdivision) is located to the south.

Norfolk Southern Railway Company maintains an active railway along the northeast side of the site. An unnamed drainage ditch borders the southern side of the site, within a Homeowners Association drainage easement on the off-Base residential properties.

2.3 Site History

The site was used for fire training exercises from 1971 to 1983. The exercises were conducted in a pit with an earthen berm and a limestone base containing an empty rail tank car (used as a mock aircraft) (Figure 2). A two-story cinder block building was located approximately 150 feet southwest of the pit and berm. The rail tank car was sprayed with JP-4 fuel, ignited, and then extinguished during routine fire training exercises. During the initial establishment of the fire protection training area, some other flammable industrial wastes may have been burned as well (Engineering-Science, Inc., 1983). The fuel was sprayed directly onto the ground, the rail tank car, and/or the cinder block building. Extinguishing agents included aqueous film forming foam, dry chemicals, and halon. These agents contain sodium bicarbonate, potassium chloride, ammonium phosphates, sodium chloride, halogenated hydrocarbons, or per- and polyfluoroalkyl substances (PFAS). The fuel was transported to the site by a tanker truck and may have been stored in two aboveground tanks that were located northwest and southeast of the burn pit. An oil/water separator was also present, as well as piping associated with the tank southeast of the berm area. In 2001, the rail car, cinder block building, and tanks and associated piping were

FPM Remediations, Inc. 2-2 Contract No. FA8903-13-C-0006 demolished, the oil/water separator was excavated and removed, materials were disposed of offsite, and fencing was installed around the site perimeter (Tetra Tech, 2001).

The off-Base residential properties adjacent to the south side of the site are part of the Joppa Way subdivision. A private landowner donated the property in 2003 to The Charleston Bank Consortium, a non-profit consortium of local mortgage lenders founded in 1994 to create affordable housing for low- to moderate-income families (Parks, 2003). Construction of the residential houses on Celestial Court began in 2005. In early 2008, the remaining undeveloped parcels were purchased by a new developer, Nice Joppa LLC, who continued residential construction (Parker, 2008). Undeveloped parcels have transferred ownership subsequently, and residential construction continued through 2020.

2.4 Site Hydrology, Geology, and Hydrogeology

JBCA is situated on the Lower Coastal Plain physiographic province of South Carolina, between two major rivers, the Ashley River and the Cooper River. The Ashley River is approximately one mile to the west, and the Cooper River is approximately three miles to the east. SWMU 55 lies within the Cooper River watershed.

Historically, surface water drainage at SWMU 55 consisted of an intermittent creek that followed a path through the interior of the site, exited the site at the middle of the south edge, and turned west approximately 200 feet south of the property boundary into a gully (Figure 2). The creek was approximately 5½ feet wide and filled with roots, leaves, and organic debris (Radian International, 1997). A small runoff drainage ditch or swale exited the southeast corner of the berm area and led to the creek (Science Applications International Corporation, Inc. [SAIC], 1986, 1989; Versar, 1989, 1990). Surface water runoff from the berm area was evident during a site visit in 1982 (Engineering-Science, Inc., 1983). The historical creek location is shown on a 1958 U.S. Geological Survey (USGS) topographic map and in figures from historical site reports as late as 1992 (e.g., Engineering-Science, Inc., 1993). At some date after that, the off-Base property south of the site was apparently re-graded, creating the ditch along the southern site boundary (Figure 2). FPM field staff have also observed that trees along the JBCA southern property boundary have soil piled above the natural root crown of the tree. The former creek and gully ran approximately beneath Celestial Court and the residential housing. Both the historical creek and gully and the present-day ditch eventually discharge to Filbin Creek, which flows east to the Cooper River.

The Lower Coastal Plain consists of a series of unconsolidated to partially consolidated sediments laid down from Late Cretaceous to Quaternary times. These formations strike northeast (parallel to the coast), dip to the southeast, and thicken seaward. Because of this geometry, successively younger formations outcrop closer to the coast. Terrace deposits were laid down in the Pleistocene (2 million to 10,000 years ago) during a series of sea level encroachments and recessions.

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The surficial geologic units at JBCA have been identified in the past as the Ladson Formation at the ground surface, underlain by the Cooper Formation (e.g., Park, 1985; Halliburton NUS Corporation [Halliburton], 1995). Recent geologic mapping by the USGS has identified the surficial deposits in the vicinity of the site as the barrier sand and barrier-island sand facies of the Ten-Mile Hill Formation (middle Pleistocene, 70 to 130 kiloannum [ka]), which is younger than the Ladson Formation (middle Pleistocene, 240-730 ka) (Weems et al., 2014). However, for simplicity, this report continues to use the older nomenclature of Ladson and Cooper Formations.

The Ladson Formation soils observed at the site comprise poorly graded fine to medium sands with intermittent layers of sandy clay. In the southern part of the site, a soft, dark greenish gray, fat clay is present at depths varying from 13 to 20 feet below ground surface (bgs) (7 to 11 feet above mean sea level [amsl]) down to the top of the Cooper Formation (FPM, 2017b, 2021b).

The Cooper Formation (sometimes referred to as the Cooper Marl) consists of a thick, olive green, stiff clay with some silt and fine sand. At the site, in borings located near the berm area, the top of the Cooper Formation was encountered at depths ranging from 35 to 56.5 feet bgs, with a slope to the north of approximately 0.17 feet per foot (Halliburton, 1995). In the southern portion of the site, the top of the Cooper Formation was encountered at depths of 20 to 25 feet bgs (IT Corporation, 2002a; FPM, 2017b). A stratum of silty calcareous clay containing phosphate nodules from ¼-inch to 2-inch diameter was encountered immediately on top of the Cooper Formation and ranged in thickness from 2.6 to 4.0 feet (Earth Tech, Inc. [Earth Tech], 2006; FPM, 2017b, 2021b).

An unconfined surficial aquifer is present within the Ladson Formation at the site at a depth of approximately 3 to 6 feet bgs (20 to 33 feet amsl). The hydraulic gradient is to the south-southeast in the northern part of the site, near and north of the berm area, and to the south in the southern part of the site, near the Base boundary (URS/Radian International, 2001). South of the Base boundary, the direction of the hydraulic gradient is to the north-northwest, towards the ditch, as shown by groundwater elevation measurements from temporary wells in December 2016 (FPM, 2017b). The fluctuation in depth to water is approximately 1 to 2 feet; there does not appear to be a consistent correlation of depth to groundwater with season (Halliburton, 1995).

Groundwater in this surficial aquifer typically has a low pH, below 6.0 standard units (SU) (SAIC, 1986, 1989). Historical reports at JBCA have said that infiltration of precipitation is the primary recharge mechanism, and that the Cooper Formation acts as a low-permeability confining unit, impeding downward groundwater flow at the base of the Ladson Formation (Halliburton, 1995). However, in the southern portion of SWMU 55 an upward vertical component to the hydraulic gradient is present, observed in shallow/deep monitoring well pairs (e.g., FPM, 2014b). It is not known whether this is a local feature or extends throughout the site.

Regionally, the underlying aquifer systems (in Tertiary and Cretaceous units) present throughout most of the coastal plain are under artesian conditions, confined by the Cooper Formation; these aquifers are recharged by precipitation in inland, up-dip outcrop locations (Park, 1985).

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Shallow groundwater at the site discharges to the ditch. Low levels of TCE and cis-1,2-DCE were detected in surface water from the ditch during the Phase II RCRA Facility Investigation (RFI) Addendum (Tetra Tech, 2003) and the Supplemental Investigation (FPM, 2017b), as well as in ongoing LTM. Measured water table elevations at monitoring well MW-P-11S have ranged from 19.94 to 22.87 feet amsl, above the elevation of the base of the ditch (approximately 18.5 feet amsl). Groundwater elevations measured in off-Base temporary wells in December 2016 during the Supplemental Investigation confirmed that south of the ditch, the direction of the hydraulic gradient is to the north-northwest, towards the ditch, thus confirming that the ditch is a local groundwater discharge feature (FPM, 2017b).

2.5 Previous Investigation and Remediation Activities

A brief summary of historical site investigations and activities is provided below. More complete details were provided in the On-Base Groundwater Supplemental Investigation Report (FPM, 2016a) and the historical reports referenced herein.

Previous Investigations

SWMU 55 has been extensively investigated, dating back to 1983 with an initial Phase I Records Search (Engineering-Science, Inc., 1983), followed by several phases of investigations from 1985 through 2016 (SAIC, 1986, 1989; Versar, 1990, 1992; Halliburton, 1995; Radian International, 1997; Parsons Engineering Science Inc., 1999; URS/Radian International, 2001;

Tetra Tech, 2003, 2004; FPM, 2016a) and groundwater monitoring beginning in 2000 (URS, 2001). These investigations detected volatile organic compound (VOC) and polynuclear aromatic hydrocarbon, also known as polycyclic aromatic hydrocarbon, (PAH) contamination in soil in the northern portion of the site near the fire pit, interpreted as residual or weathered components of burned fuels and waste solvents, and groundwater contamination. The groundwater contamination consisted of dissolved benzene above the Federal drinking water Maximum Contaminant Level (MCL) delineated in a plume extending from the fire pit towards the south (hydraulically downgradient); and dissolved TCE, PCE, and vinyl chloride above MCLs delineated in plumes north of the fire pit and near the southern Base boundary, as shown in Figure 2. The source of groundwater contamination was concluded to be JP-4 and, potentially, flammable industrial wastes that were burned at the site during fire training activities (URS/Radian International, 2001).

Previous IMs

The first Interim Measure (IM) at the site addressed fuel-impacted soils in the former fire pit. A pilot test bioventing system was installed in the fire pit area at the location shown on Figure 2 in October 1992 (Engineering-Science, Inc., 1993). The bioventing system was expanded in 1996 and operated until 2006.

FPM Remediations, Inc. 2-5 Contract No. FA8903-13-C-0006

The second IM at the site was an AS/SVE system installed in 2001-2002, which operated until 2006. The AS/SVE system was installed across the entire southern edge of the site, as shown on Figure 2. The purpose of the AS/SVE system was to intercept and prevent further migration of a groundwater plume containing dissolved TCE, PCE, and benzene exceeding the MCL of 5 micrograms per liter (μg/L), as well as to provide in situ treatment. Activities were described in the Closeout Report (IT Corporation, 2002a) and the AS/SVE IM Report (IT Corporation, 2002b). The system consisted of 23 vertical AS wells that injected air at a depth of approximately 18 to 20 feet bgs, and 25 horizontal trenched SVE wells. These wells and associated piping are still in place, but are no longer operational. At that time, 23 additional groundwater monitoring wells were installed in the southern portion of the site; these wells are still in use.

In March 2005, soil samples from the area surrounding the bioventing system demonstrated that a significant benzene source was no longer present at the site, and that risk from PAHs in soil was below the USEPA target risk range (Tetra Tech, 2005). By early 2006, the only groundwater contaminant of concern (COC) that occasionally exceeded its MCL was TCE in the southern part of the site (Earth Tech, 2006).

Focused CMS and SoB

In July 2006, a Focused CMS was prepared for the site (Earth Tech, 2006). Since two IMs had already been conducted at the site (bioventing and AS/SVE), the Focused CMS evaluated those IMs to address the residual TCE in groundwater in the southern part of the site. By early 2006, it appeared that soils at the fire pit had been adequately remediated, and groundwater monitoring results showed that the only groundwater COC that occasionally exceeded its MCL was TCE.

The CMS recommended that the AS/SVE system be shut down and the site enter post-remediation monitoring. The site remedy also included groundwater LTM to ensure that the source area did not deliver a continued release (Earth Tech, 2006).

On August 24, 2006, lightning struck the power pole that supplied electricity to the AS/SVE and bioventing systems. Because concentrations of COCs in groundwater had already decreased to below MCLs, JBCA and SCDHEC jointly decided during the August 29, 2006, Tier I Meeting to shut down both systems and begin post-remediation monitoring (TEAM Integrated Engineering, Inc., 2006).

SCDHEC approved the Focused CMS in a letter dated February 13, 2007 (SCDHEC, 2007). The approval letter required land use controls (LUCs) to be implemented at the site to limit exposure pathways to contaminated constituents. A Statement of Basis (SoB) was issued for the site stating that the IMs already conducted (bioventing and AS/SVE) were considered the Final Corrective Measures for the site (Earth Tech, 2007). The SoB stated that the source area had been addressed through the bioventing IM in the former fire pit. The CAOs were to achieve MCLs. The SoB estimated that the Corrective Action Objectives (CAOs) would be achieved

FPM Remediations, Inc. 2-6 Contract No. FA8903-13-C-0006 within 0.5 years via natural attenuation, and anticipated that the site would be monitored for three years, after which time a No Further Action (NFA) status would be requested.

Post-Remediation LTM and Supplemental Investigation

Post-remediation phase LTM began in the fourth quarter of 2006. After termination of the AS/SVE system, TCE and PCE in groundwater rebounded to concentrations above their respective MCLs at monitoring wells MW-P-11S and 3-14. These wells are located in the southern part of the site and are screened across the water table (Figure 2). Subsequently, at monitoring well 3-14, TCE concentrations in groundwater decreased again, and have been below the MCL since May 2013 (PCE concentrations in groundwater at this well exceeded its MCL only in one sampling event, in May 2009). PCE and TCE in shallow groundwater remained above their respective MCLs at monitoring well MW-P-11S (screened from 4 to 14 feet bgs).

PCE and TCE have been non-detect or below MCLs in deeper groundwater at monitoring well MW-P-12D since monitoring began at that well in May 2001. Monitoring well MW-P-12D is located adjacent to well MW-P-11S, and screened from 20 to 25 feet bgs and across the soft clay, phosphate gravel zone, and into the top of the Cooper Formation clay.

On December 11, 2007, with the approval of SCDHEC, the groundwater monitoring wells associated with the bioventing system in the northern part of the site were abandoned, because the bioventing system was no longer in operation and groundwater sampling was no longer required. This included groundwater monitoring wells 3-1, 3-2, 3-3, 3-4, 3-5, 3-6, 3-7, 3-8, 3-9, 3-10, 3-11, 3-12, and 3-13 (Earth Tech, 2008).

The on-Base portion of a groundwater Supplemental Investigation was conducted in 2015 (FPM, 2016a). The objectives were to provide data to evaluate the potential for natural attenuation of site COCs in groundwater, and to provide data to support the design of possible future groundwater treatments. Groundwater samples were collected from nine shallow temporary wells surrounding existing monitoring well MW-P-11S and analyzed for VOCs, microbial parameters, and monitored natural attenuation (MNA) parameters. Groundwater PCE and TCE contamination was more precisely delineated to the north, west, and east at a depth range of 5 to 10 feet bgs. Populations of Dehalococcoides microbes were detected at low levels (14.7 to 85 cells per milliliter), and groundwater geochemistry conditions were mildly oxidizing with low pH (4.5 to 6.5), indicating that existing aerobic geochemical groundwater conditions were not conducive to biodegradation via reductive dechlorination of PCE and TCE (FPM, 2016a).

In December 2016, subsurface soil samples were collected from on-Base locations near well MW-P-11S to help delineate any areas of residual PCE and TCE contamination. Subsurface soil samples were collected roughly every five feet in three borings down to 25 feet bgs. TCE and PCE were detected only in one subsurface soil sample (below regulatory standards), at a depth of

8.0 feet bgs (FPM, 2017b).

FPM Remediations, Inc. 2-7 Contract No. FA8903-13-C-0006

In addition, the off-Base portion of the Supplemental Investigation was conducted in December 2016 (FPM, 2017b). The objective was to determine whether site COCs in groundwater were potentially migrating downgradient of monitoring well MW-P-11S and beyond the JBCA property boundary. Groundwater samples were collected from eight temporary wells installed on private property south of the site, and surface water samples were collected from four locations along the drainage ditch south of the site. Groundwater elevation measurements from the off- Base temporary wells showed that south of the ditch, the direction of hydraulic gradient is to the north-northwest, towards the ditch. PCE and TCE were not detected in groundwater samples from any of the off-Base temporary wells. TCE and cis-1,2-DCE were detected in one surface water sample downstream of monitoring well MW-P-11S, but both analytes were below their respective MCLs and South Carolina surface water standards. The results of the off-Base portion of the Supplemental Investigation indicated that the on-Base TCE and PCE groundwater plume does not continue beneath the off-Base private properties south of the ditch, and any contamination infiltrating the ditch is either quickly volatilized or diluted (FPM, 2017b).

An additional groundwater monitoring well (55MW-25) was installed on May 19, 2017, near the Base boundary downgradient of MW-P-11S, per an earlier SCDHEC request (SCDHEC, 2014b).

SCDHEC requested monitoring of groundwater in monitoring well 55MW-25 (FPM, 2015, 2017a), and on May 26, 2017, SCDHEC requested surface water monitoring at three of the locations in the drainage ditch south of the site (SCDHEC, 2017b). TCE concentrations in surface water samples from the drainage ditch remained below criteria through 2021, indicating that there has been no downgradient migration of the plume.

On-Site ISCO IM

In June 2017, an additional IM for groundwater treatment by in-situ chemical oxidation (ISCO) was performed in the southernmost on-Base area in order to address the remaining groundwater contamination above MCLs (FPM, 2017c). A total of 6,233 gallons (gal) of Modified Fenton’s Reagent (MFR) (catalyzed hydrogen peroxide) was injected into the aquifer from 5 to 15 feet bgs at a grid of 13 injection points covering the area of impacted groundwater that was known at the time (FPM, 2017a, 2017c). Groundwater samples collected for 30-day post-treatment performance monitoring from monitoring wells MW-P-11S and 55MW-25 showed that PCE and TCE had decreased at both wells, although they remained above their MCLs of 5 μg/L (FPM, 2017c). However, during the September 2017, November 2017, March 2018, and June 2018 sampling events, PCE and TCE groundwater concentrations and dissolved oxygen (DO) and oxidation-reduction potential (ORP) measurements returned to levels within the range of observed historical fluctuations. The Fourth Quarter 2017 LTM Report concluded that the ISCO injection conducted in June 2017 was not effective in permanently decreasing COC concentrations to below CAOs (FPM, 2018a). The Second Quarter 2018 LTM Report recommended additional groundwater treatment to address remaining COCs in groundwater at the site.

FPM Remediations, Inc. 2-8 Contract No. FA8903-13-C-0006

PFAS Investigations

In 2017, Aerostar SES LLC (Aerostar) conducted a site inspection under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) for firefighting foam usage at the site (Aerostar, 2018). Three soil borings were advanced near the fire training pit in the center of the site and converted to temporary groundwater wells screened from 5 to 15 feet bgs (CHRTN01-001, CHRTN01-002, and CHRTN01-003) (Figure 2). The temporary wells were sampled and then abandoned. PFAS compounds were detected above screening levels in surface soil, subsurface soil, and groundwater samples, and the site was recommended for an RI.

From October 2021 through January 2022, Aerostar conducted a Phase I Remedial Investigation (RI) for PFAS under CERCLA (Aerostar, 2021). Aerostar installed four new groundwater monitoring wells, one north of the site (CHRTN01-MW005) and three near the fire training pit in the center of the site (CHRTN01-MW006, CHRTN01-MW007, and CHRTN01-MW008) (Figure 2). All four of the new PFAS wells were screened from approximately 14 to 24 feet bgs, at a depth intermediate between the shallow and deep wells in the LTM program. In addition, soil borings were advanced to 10 feet bgs in six locations (CHRTN01-SB014 through CHRTN01- SB019). Near the former fire pit, boring logs noted several indications of the presence of hydrocarbons near the water table, noting hydrocarbon odor, sheen, and/or “saturated with hydrocarbons” at locations CHRTN01-007, CHRTN01-008, CHRTN01-SB014, CHRTN01- SB017, CHRTN01-SB018, and CHRTN01-SB019.

Additional Groundwater Investigations

In May 2018, FPM submitted an addendum to the IM Work Plan (FPM, 2018b) proposing PersulfOx® application to the aquifer by soil mixing to augment the 2017 IM. The work plan was approved by SCDHEC in a letter dated June 26, 2018 (SCDHEC, 2018). Although delineation of the TCE- and PCE-impacted area was considered to be complete based on the 2015-2016 supplemental investigations, in an effort to explore all possible reasons for the ineffectiveness of the 2017 injections, FPM considered it prudent to rule out the unlikely scenario of a narrow contaminant plume coming from the north between monitoring well 3-14 and former temporary well 55T05, and proposed conducting additional site characterization prior to the soil mixing activities.

This additional site characterization was conducted in August 2018. Groundwater and soil samples were collected at four locations north of the planned soil mixing area (55T18 through 55T21) and analyzed for VOCs. Three of the four groundwater samples contained TCE and PCE above the MCL of 5 µg/L, at concentrations up to 43 µg/L of TCE and 17.1 µg/L of PCE (FPM, 2019b). These results indicated that, contrary to expectation, a narrow plume of impacted groundwater was entering the planned soil mixing area from the north. The plume appeared to have an east-west width as narrow as 10 feet and a vertical thickness of approximately 5 feet.

The Fourth Quarter 2018 LTM Report (FPM, 2019b) concluded that the ongoing contamination

FPM Remediations, Inc. 2-9 Contract No. FA8903-13-C-0006 at MW-P-11S was likely caused by advection of dissolved TCE and PCE borne by the plume of impacted groundwater coming from the north. It recommended further site characterization prior to implementing any additional groundwater treatment in order to determine the northern extent of impacted groundwater. The proposed PersulfOx® application was not conducted.

In February 2019, FPM conducted an additional groundwater Supplemental Investigation farther north (locations 55T22 through 55T59) (FPM, 2019a, 2021b; SCDHEC, 2019a). Groundwater samples were collected from a line of 16 locations at the northern (upgradient) edge of the 1996- 1997 plume boundary (URS/Radian International, 2001) (Figure 2) to determine whether or not contaminated groundwater was entering from a source upgradient of that boundary. Additional groundwater samples were collected from 22 locations within the 1996-1997 plume boundary to refine the area of any future planned soil mixing zone. Soil borings were advanced by direct-push drilling to the bottom of the sand unit, and the lithology was logged. Soil lithologies encountered during drilling conformed with earlier observations. At each location, two temporary wells were installed, screened at discrete shallow and deeper depths within the sand unit, because observations to date had suggested that the vertical thickness of the plume was small, five to ten feet. Groundwater samples were collected from the temporary wells and analyzed for VOCs.

TCE and PCE were detected above their respective MCLs in groundwater samples from a contiguous area in the center of the sampling grid (Figure 2). TCE was detected at concentrations up to 87.5 µg/L, and PCE was detected at concentrations up to 69.7 µg/L. The detections were bounded on the eastern and western ends of each row of temporary wells by samples in which TCE and PCE were not detected. TCE and PCE concentrations in the northernmost row of temporary wells exceeded their respective MCLs, indicating that the source of contamination remained north of the investigation area. Cis-1,2-DCE, a degradation daughter product of TCE, was detected below its MCL of 70 µg/L in 61 of the 76 groundwater samples.

Benzene, carbon disulfide, ethylbenzene, isopropylbenzene, 1,4-dioxane, methyl chloride, trans- 1,2-DCE, vinyl chloride, and xylenes were also detected in groundwater samples below their respective MCLs or SCDHEC risk-based screening level (RBSLs), or no MCLs or SCDHEC RBSLs are established. Trans-1,2-DCE and vinyl chloride are also degradation daughter products of TCE. Carbon disulfide is a common laboratory contaminant and is also naturally produced in soils, marshes and oceans by metabolic action of soil bacteria and plants. Measured geochemical conditions indicated generally anaerobic and moderately reducing conditions, with pH ranging from 4.87 to 6.72, and ORP values higher in the shallower samples than in the deeper samples, consistent with observations from LTM.

Additional features observed in this part of the site included a ditch trending southwards along the west side of the investigation area; a three-foot-high berm trending ESE-WNW north of the investigation site; debris in the…