KGS_2018e_2017_Annual_Long-Term_Monitoring_and_Maintenance_Report_AOC_50_Devens.pdf

DECEMBER 2018

Prepared for:

U.S. Army Corps of Engineers

New England District Concord, Massachusetts

Prepared by:

KOMAN Government Solutions, LLC

293 Boston Post Road West, Suite 100 Marlborough, MA 01752

Contract No.: W912WJ-15-C-0002

2017 ANNUAL

OPERATION & MAINTENANCE (O&M)

AND MONITORING REPORT

AREA OF CONTAMINATION 50

FORMER FORT DEVENS ARMY INSTALLATION, DEVENS, MA

NOTICE

The United States Department of Defense, Department of Army, funded wholly or in part the preparation of this document and work described herein under Contract No. W912WJ-15-C- 0002. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

2017 ANNUAL

OPERATION & MAINTENANCE (O&M)

AND MONITORING REPORT

AREA OF CONTAMINATION 50

Devens, Massachusetts

December 2018

CERTIFICATION:

I hereby certify that the enclosed Report, shown and marked in this submittal, is that proposed to be incorporated with Contract Number W912WJ-15-C-0002. This document was prepared in accordance with the U.S. Army Corps of Engineers (USACE) Scope of Work and is hereby submitted for Government approval.

Reviewed By:

12/19/18

KGS Project Manager Date

Received By:

USACE Project Manager Date

This page is intentionally left blank.

TABLE OF CONTENTS

Section Page i

1.0 INTRODUCTION ...................................................................................................................... 1-1 PURPOSE AND OBJECTIVES .................................................................................... 1-1 SITE DESCRIPTION AND HISTORY ........................................................................ 1-1 SITE HYDROGEOLOGY ............................................................................................. 1-4

REMEDIAL SYSTEM OPERATIONS AND MODIFICATIONS ............................ 1-4

2.0 REMEDIAL SYSTEM ................................................................................................................. 2-1

ENHANCED REDUCTIVE DECHLORINATION (ERD) SYSTEM ...................... 2-1

Area 1 ............................................................................................................... 2-1 Area 3 ............................................................................................................... 2-2 Area 4 ............................................................................................................... 2-2 Area 4/5 ............................................................................................................ 2-2 Area 5 ............................................................................................................... 2-2

IN-WELL STRIPPING SYSTEM .................................................................................. 2-3

3.0 LONG-TERM MONITORING EVENT METHODOLOGY ................................................. 3-1 GROUNDWATER SAMPLING AND ANALYSIS .................................................. 3-1 DECONTAMINATION PROCEDURES ................................................................... 3-1 INVESTIGATIVE-DERIVED WASTE HANDLING ................................................ 3-2 LONG-TERM MONITORING EVENTS .................................................................... 3-2

Monitoring Well Inspection ............................................................................ 3-2 Water Level Measurements ............................................................................ 3-2

WELL MAINTENANCE ACTIVITIES ...................................................................... 3-3

4.0 GROUNDWATER MONITORING RESULTS ....................................................................... 4-1

GROUNDWATER CHEMISTRY FOR MONITORING EVENTS .......................... 4-1

Field Parameters ............................................................................................... 4-1 Volatile Organic Compounds ........................................................................ 4-2 Inorganic Metals ............................................................................................... 4-4 Other Analytes ................................................................................................. 4-6 Data Evaluation Summary ............................................................................. 4-7

QUALITY ASSURANCE/QUALITY CONTROL .................................................... 4-8 LABORATORY AND FIELD CORRECTIVE ACTIONS ......................................... 4-8

5.0 LAND-USE CONTROL MONITORING ................................................................................ 5-1 ON-SITE INSPECTIONS.............................................................................................. 5-2 LAND-USE CONTROL INTERVIEW ........................................................................ 5-2 LAND-USE CONTROL MONITORING SUMMARY ............................................. 5-3

6.0 SUMMARY ................................................................................................................................. 6-1

7.0 REFERENCES ............................................................................................................................. 7-1 ii

FIGURES

Figure 1-1 Site Location, AOC 50 Figure 1-2 Site Layout, AOC 50 Figure 1-3 Site Layout, Source Area, AOC 50 Figure 2-1 ERD Injection Locations, July 2017 Figure 3-1 Groundwater Contour Map, AOC 50, May 15, 2017 Figure 3-2 Groundwater Contour Map, AOC 50, October 2, 2017 Figure 4-1 Dissolved Oxygen and Oxidation Reduction Potential Trend Graphs Figure 4-2 Tetrachloroethene Concentrations in Groundwater, 2004, AOC 50 Figure 4-3 Tetrachloroethene Concentrations in Groundwater, 2010, AOC 50 Figure 4-4 Tetrachloroethene Concentrations in Groundwater, October 2015, AOC 50 Figure 4-5 Tetrachloroethene Concentrations in Groundwater, October 2017, AOC 50 Figure 4-6 Cross-Section Plan View, AOC 50 Figure 4-7 Cross-Section Plan View, AOC 50, Area 1 Figure 4-8 Tetrachloroethene Plume in Groundwater - Cross Section, A-A’ AOC 50, October 2017 Figure 4-9 Tetrachloroethene Plume in Groundwater Cross Section, B-B’ AOC 50, October 2017 Figure 4-10 Tetrachloroethene Plume in Groundwater Cross Section, C-C’ AOC 50, October 2017 Figure 4-11 Area 1 PCE Concentration Trend Graphs Figure 4-12 Area 2 PCE Concentration Trend Graph Figure 4-13 Area 3 PCE Concentration Trend Graph Figure 4-14 Areas 4 and 5 PCE Concentration Trend Graphs Figure 4-15 Dissolved Arsenic in Groundwater AOC 50, 2017 Figure 4-16 Methane Concentrations in Groundwater AOC 50, October 2017

TABLES

Table 1-1 AOC 50 Cleanup Levels Table 2-1 AOC 50 2017 ERD Injection Program Table 3-1 Sample Preparation and Analysis Methods, Containers, Preservatives and Holding

Times Table 3-2 Groundwater Level Data, Spring 2017 Table 3-3 Groundwater Level Data, Fall 2017 Table 4-1 Monitoring Wells Selected for 2017 Sampling Events Table 4-2 Groundwater Analytical Results Spring 2017 Table 4-3 Groundwater Analytical Results Fall 2017 iii

APPENDICES

APPENDIX A GROUNDWATER FIELD ANALYSIS FORMS

A.1: Spring 2017 LTM Event

A.2: Fall 2017 LTM Event

APPENDIX B LABORATORY ANALYTICAL REPORTS (on CD)

B.1: Spring 2017 LTM Event

B.2: Fall 2017 LTM Event

APPENDIX C ANALYTICAL DATA VALIDATION REPORTS (on CD)

C.1: Data Validation Reports – Spring 2017 LTM Event

C.2: Data Validation Reports – Fall 2017 LTM Event

APPENDIX D HISTORICAL GROUNDWATER RESULTS

APPENDIX E ANNUAL LAND USE CONTROL PLAN CHECKLIST

APPENDIX F RESPONSES TO COMMENTS

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ACRONYMS AND ABBREVIATIONS

ABC® Anaerobic BioChem®

ABC® Ole’ Anaerobic BioChem® + Oleic Acid ABC® Ole’+ Anaerobic BioChem® + Oleic Acid + Zero Valent Iron amsl above mean sea level AOC area of contamination ARCADIS ARCADIS U.S., Inc./G&M, Inc.

Army U.S. Army bgs below ground surface BCT Base Realignment and Closure Cleanup Team BRAC Base Realignment and Closure °C degrees Celsius CERCLA Comprehensive Environmental Response, Compensation, and Liability Act cis-1,2-DCE cis-1,2-dichloroethene COC contaminant of concern CVOC chlorinated volatile organic compound CY calendar year 1,2-DCA 1,2-dichloroethane 1,1-DCE 1,1-dichloroethene 1,2-DCP 1,2-dichloropropane DTW depth-to-water DO dissolved oxygen DoD Department of Defense DPT direct push technology DRFTA Devens Reserve Forces Training Area ELAP Environmental Laboratory Accreditation Program ERD enhanced reductive dechlorination FDSA Former Drum Storage Area ft feet ft/day feet per day HGL HydroGeoLogic, Inc.

IDW investigation-derived waste IRZ in-situ reactive zone IWS in-well stripping J estimated result KGS KOMAN Government Solutions, LLC LTM long-term monitoring LTMMP Long-Term Monitoring and Maintenance Plan LUC land-use control MCL Maximum Contaminant Level mg/L milligrams per liter MAAF former Moore Army Airfield MassDevelopment Massachusetts Development and Finance Agency MiHPT Membrane Interface Probe-Hydraulic Profiling Tool MS matrix spike MSD matrix spike duplicate v

NELAP National Environmental Laboratory Accreditation Program O&M operation and maintenance ORP oxidation-reduction potential PARCCS precision, accuracy, representativeness, comparability, completeness, and sensitivity PCE tetrachloroethene QA quality assurance QAPP Quality Assurance Project Plan QC quality control QSM Quality Systems Manual RAWP Remedial Action Work Plan TCE trichloroethene trans-1,2-DCE trans-1,2-dichloroethene µg/L micrograms per liter USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency USFWS U.S. Fish and Wildlife Service VC vinyl chloride VOC volatile organic compound ZVI zero valent iron

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1.0 INTRODUCTION

This 2017 Annual Operation & Maintenance (O&M) and Monitoring Report was prepared by KOMAN Government Solutions, LLC (KGS) for the U.S. Army Corps of Engineers (USACE) under contract number W912WJ-15-C-0002, to detail the operation and performance of on-going remediation activities and groundwater monitoring results at Area of Contamination (AOC) 50 at the former Fort Devens Army Installation (Devens), Devens, Massachusetts. Remediation activities were performed in accordance with the Final Long-Term Monitoring and Maintenance Program AOC 50 (LTMMP) [HydroGeoLogic, Inc. (HGL), 2012] and the Area of Contamination 50, 2017 Injection Program Summary (KGS, 2017b).

Purpose and Objectives

The purpose of this Annual O&M and Monitoring Report is to document the O&M activities conducted at AOC 50 and to summarize the results of the long-term monitoring (LTM) for groundwater conducted during 2017. The Annual Report for AOC 50 also includes information regarding remedial actions performed at the site. The Army conducted groundwater monitoring events during the spring and fall of 2017 and completed an enhanced reductive dechlorination (ERD) injection event in July 2017.

Site Description and History

The AOC 50 site is located on the northeastern boundary of the former Moore Army Airfield (MAAF), within the former North Post of the former Fort Devens Army Installation, in the town of Ayer, Massachusetts (Figure 1-1). Fort Devens was identified for cessation of operations and closure under Public Law 101-510, the Defense Base Realignment and Closure (BRAC) Act of 1990, and was officially closed in March 1996. Portions of the property formerly occupied by Fort Devens were retained by the U.S. Army (Army) for reserve forces training and was renamed the Devens Reserve Forces Training Area (DRFTA). Areas not retained as part of the DRFTA were transferred to new owners (the Massachusetts Development and Finance Agency [MassDevelopment] and the U.S. Fish and Wildlife Service [USFWS]) for reuse and redevelopment. In 2009, the DRFTA was renamed the U.S. Army Garrison Fort Devens.

All but approximately 14 acres of the former MAAF (approximately 246 acres total) were transferred to MassDevelopment for reuse in 1997. Currently, the airfield is closed to aircraft traffic and is used by the Massachusetts State Police for training purposes and vehicle storage. The former MAAF is zoned for Special Use II and Innovation and Technology Business. Under the Devens Reuse Plan dated 14 November 1994, Special Use II and Innovation and Technology Business includes a broad range of industrial, light industrial, office, and research and development uses. MassDevelopment is considering repairs and upgrades for the Massachusetts State Police’s use of the airfield, but the plans are still under development. The Devens Army Installation retained approximately nine acres of the former airfield for vehicle storage and maintenance and approximately four acres in and around the AOC 50 Source Area for remediation activities.

The primary area of groundwater contamination at AOC 50 is referred to as the Southwest Plume, which extends from the Source Area approximately 3,000 feet (ft) downgradient towards the Nashua River. Sources of groundwater contamination at AOC 50 include two World War II fueling systems, a drywell formerly connected to the parachute shakeout tower, and the tetrachloroethene (PCE) Former Drum Storage Area (FDSA); these sources are collectively referred to as the AOC 50 Source Area. The AOC 50 Source Area is comprised of less than two acres and surrounds

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Building 3803 (the former parachute shop), Building 3840 (the former parachute shakeout tower), Building 3824 (a gazebo), and Building 3801 (the former 10th Special Forces airplane parachute simulation building). Although these sources have been removed or taken out of commission, groundwater underlying AOC 50 contains elevated concentrations of VOCs, most notably PCE.

The AOC 50 site layout with existing monitoring wells is depicted in Figures 1-2 and 1-3.

The Final Record of Decision, AOC 50 (ARCADIS, 2004) identified the groundwater contaminants of concern (COCs) and their interim cleanup levels (Table 1-1).

Table 1-1 AOC 50 Cleanup Levels

Chemical Cleanup Level

(µg/L)

Arsenic 10

Benzene 5

1,2-dichloroethane (1,2-DCA) 5

1,1-dichloroethene (1,1-DCE) 7 cis-1,2-dichloroethene (cis-1,2-DCE) 70

1,2-dichloropropane (1,2-DCP) 5

Iron 3,129

Lead 15

Manganese 1,460

Methylene Chloride 5

Nitrate 10,000

PCE 5

Trichloroethene (TCE) 5

Vinyl Chloride (VC) 2

Some of the contaminants were designated COCs because they were present at concentrations above the applicable maximum contaminant level (MCL) or state groundwater quality standard (i.e., cis-1,2-DCE, iron, methylene chloride, and 1,2-DCP). Benzene was designated as a COC due to past releases. Cis-1,2-DCE and nitrate were identified as COCs due to their contribution to risk.

Lead was identified as a COC due to its potential to pose ecological risks. Arsenic was designated as a COC because it may be solubilized (mobilized) by the selected remediation technology, even though it was not predicted to pose significant risks under baseline conditions.

The selected remedy for AOC 50, documented in the ROD (ARCADIS, 2004), was Alternative 6:

Soil Vapor Extraction, ERD (with solubilized inorganic controls), In-Well Striping/Aerobic Bioremediation, Monitoring, and Institutional Controls. In addition, Geochemical additives and In-situ Chemical Oxidation were included as contingencies to address inorganics and volatile

1-3 organic compounds, respectively, in the event that monitoring data indicate that implementation of these contingencies was warranted. It was estimated that ERD injections was expected to be phased out after approximately 10 to 15 years. Approximately 27 years were estimated as the amount of time necessary to achieve the goals consistent with unrestricted land use and potable use of groundwater for the entire site (ARCADIS, 2004).

Summary of Past Groundwater Treatment at AOC 50

In September 2004, ARCADIS U.S., Inc./G&M, Inc. (ARCADIS) implemented a full-scale remedial action at AOC 50 that included soil vapor extraction in the source area, ERD throughout the plume, and an in-well stripping (IWS) system at the western edge of the plume. The first ERD injection event was conducted in October 2004 utilizing molasses as the ERD substrate. ARCADIS discontinued the soil vapor extraction system in November 2005, as the monitoring program indicated that the recoverable mass of chlorinated volatile organic compounds (CVOCs) was removed from the vadose zone. The IWS was shut off in March 2013 once it was clear that it was not needed to treat dissolved arsenic or to “polish” the CVOC plume (Sovereign Consulting, Inc., 2013).

HydroGeoLogic, Inc. (HGL) revised the ERD injection program in November 2008 by changing the substrate from molasses to a product called Anaerobic BioChem® (ABC®). Semi-annual injections of ABC® continued in Areas 1 through 5 of the AOC 50 plume through 2014.

Throughout most of the plume, CVOC concentrations were reduced substantially in response to the ERD injections. However, some areas did not respond as well to the remedy, so in 2013 and 2014 investigations were performed within the source area and at locations within the plume to support remedy optimization. In calendar year (CY) 2013 vertical profiling using direct push technology (DPT) probing was performed in the source area of AOC 50 (“Area 1”) as well as in several of the other Areas of the plume (Sovereign Consulting, Inc., 2015). Based on the results of the vertical profiling in Area 1 a Membrane Interface Probe Hydraulic Profiling Tool (MiHPT) investigation was conducted in 2014 to further assess potential residual source(s). Specifically, the MiHPT investigation was intended to improve the overall understanding of the location/source of residual CVOC contamination both vertically and laterally in the saturated soils in the source area where elevated concentrations of PCE (over 1,000 µg/L1) remained, as well as to better understand the relative permeability of those soils. Those data were used to recommend modifications of the existing remedy to more effectively treat the source area.

In 2015, the substrate injection strategy was optimized based on review of the historical data and MiHPT results (Sovereign Consulting, Inc., 2015). The 14th ERD injection event using ABC® was performed in July 2015. Modified substrates Anaerobic BioChem® + Oleic Acid (ABC® Ole’) and Anaerobic BioChem® + Oleic Acid + Zero Valent Iron (ABC® Ole’+) were also added to the 14th event. ABC® Ole’ includes oleic acids, which are long-chained compounds that persist for a longer period of time in the aquifer formation, and therefore may improve the effectiveness of the injections. ABC® Ole’+ includes the oleic acids plus zero valent iron (ZVI) which is intended to enhance the rate of degradation in the less permeable impacted source area soils. Substrate injections using ABC® Ole’ were injected into existing injection wells in Areas 1, 2, and 3. ABC® was injected into existing injection wells in Areas 4 and 5. ABC® Ole’+ was directly injected using DPT via a Geoprobe® into targeted locations in Area 1.

1 1 µg/L = 1 part per billion

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The 15th ERD injection event was performed in July 2017. During this injection event the ERD substrate was a combination of ABC® Ole’\ and ABC® Ole’+. Injection wells in Areas 3 and 4 received ABC® Ole’. To treat contamination that was not readily affected by the existing permanent injection wells, ABC® Ole’+ was injected directly into soils using a Geoprobe® in Areas 1, 3, 4, 4/5, and 5. The details of the 2017 injection event are presented in Section 2.0 of this Annual Report.

Site Hydrogeology

A single groundwater aquifer is present within the overburden deposits at the former MAAF and AOC 50. Restrictions to vertical groundwater flow, such as silty clay layers, are present, but are not prevalent or continuous in soil borings conducted within the kame glacial deposit or along the Nashua River. Some silty clay layers were encountered within the aquifer in the AOC 50 Source Area. These thin, silty clay layers appear to reduce the vertical permeability, contribute to a slight increase in the water table elevation, and increase the difference between shallow and deep water levels.

Depth to groundwater measurements have been collected from a network of monitoring wells and sampling points on a regular basis since 1997. Groundwater is encountered at approximately 3 ft below ground surface (bgs) in the AOC 50 Source Area and at approximately 64 ft bgs at the southwestern end of the former MAAF. Groundwater elevations within deeper wells and to the north of AOC 50 typically have lower total heads than wells screened at shallower depths, indicating that there is a downward hydraulic gradient within this area.

The Nashua River is the controlling hydrologic feature of AOC 50 and the former MAAF area. As groundwater beneath AOC 50 moves downgradient in a southwesterly direction toward the Nashua River (Figure 1-2), vertical gradients become neutral. Vertical gradients reverse and become upward along the Nashua River, as would be expected near such a discharge feature. These changes in gradient indicate that groundwater is recharged near the AOC 50 Source Area, travels below the former MAAF, and discharges to the Nashua River.

Hydraulic conductivities at the site range from 1 to over 50 ft per day (ft/day), with seepage velocities ranging from 0.024 to 1.19 ft/day.

Remedial System Operations and Modifications

The overall O&M approach and remedial system configuration at AOC 50 is adjusted over time to achieve optimum remedial performance. During the 2017 reporting period, the Army conducted the following routine activities and modifications:

Collected semi-annual water level measurements (spring and fall);

Conducted semi-annual and annual LTM groundwater monitoring events in May 2017 (spring) and October 2017 (fall).

System modifications/updates performed during the 2017 reporting period included:

Modified the ERD substrate injection strategy based on an evaluation of groundwater and VOC trends observed in groundwater, and

Performed ERD substrate injection event using six injection wells (IW) and 41 Geoprobe direction push soil injection locations (GP) in July 2017.

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2.0 REMEDIAL SYSTEM

The current remedial system consists of ERD. The IWS was turned off in March 2013 and is currently non-functional.

Enhanced Reductive Dechlorination (ERD) System

The 2017 ERD injections at AOC 50 were implemented by Redox Tech, LLC and monitored by KGS. The 2017 injection event occurred from July 10-25, 2017 and was performed in accordance with Area of Contamination 50, 2017 Injection Program Summary (KGS, 2017b), with exceptions described in the subsections below. ABC® Ole’ was injected into injection wells in Areas 3 and 4 to increase persistence and prolong treatment of VOCs. ABC® Ole’+ was injected to enhance VOC reduction and stimulate long-term release of the components for bioremediation and create a more reductive environment. This combination was injected directly into soils using a Geoprobe® in Areas 1, 3, 4, 4/5, and 5.

The 2017 injection strategy was adjusted based on the historical LTM data, the MiHPT results (Sovereign Consulting, Inc., 2015), and the 2015 ERD injection event. The strategy consisted of performing injections into existing injection wells and using direct push injections via a Geoprobe® to reach deeper impacted zones. The direct injections were conducted by directly injecting the ERD substrate through 1.5-inch diameter grouting rods. Injections were performed at:

five Area 1 direct push injection locations in the FDSA, 16 Area 1 direct push injection locations adjacent to Building 3803/3840, three Area 3 direct push injection locations, three Area 3 injection wells, three Area 4 injection wells, five direct push locations southwest of Area 4 injection wells, at five direct push locations west of Area 4/5 injection wells; and at seven direct push locations southwest of Area 5 injection wells.

An injection log provided in Table 2-1 identifies each injection location (DPT injection point or existing injection well), quantity and type of injected product, and measured field parameters (i.e., flame ionization detection and photoionization detector measurements of headspace for the injection wells as indicators of biodegradation processes). Injection locations are presented on Figure 2-1.

Area 1

The Area 1 injection program consisted of direct injection locations at the FDSA and near Building 3803/3840. Figure 2-1 shows the injections locations. A concentration of 20 wt% solution of ABC®-Ole’+ was directly injected into each of the locations in Area 1. At the 16 locations near Building 3803/3840, the injections were planned to be conducted starting at approximately 40 feet below ground surface (bgs) (GP-22 to GP-37). An estimated 125 gallons of ABC® Ole'+ solution was injected at 4 ft intervals from approximately 40 to 64 ft bgs, for an approximate total of 875 gallons per location. At seven of the locations in this area, refusal occurred at five to seven feet shallower than the planned injection depth, which are specified in Table 2-1. Each location

2-2 received the full volume of ABC®-Ole’+ that was planned. The volume of substrate that was planned for the depth that was not reached was injected into the deepest interval that was reached.

The locations where the planned injection depth was not achieved are in the western portion of the Area near G6M-13-05X (Figure 2-1). It is likely that the target depths were not achieved due to fine-grained sediments at depth. The Geoprobe® refusal depths of the seven locations were similar with the MiHPT Investigation (Sovereign Consulting, Inc., 2015), which encountered refusal depths ranging from approximately 47 ft to 65 ft bgs in the same area.

At the FDSA, five injections were conducted (GP-17 to GP-21). Approximately 125 gallons of ABC®-Ole'+ solution was injected at 4 ft intervals from approximately 23 to 47 ft bgs, for an approximate total of 875 gallons per location (Table 2-1).

Area 3

The 2017 injections in Area 3 were conducted at three existing injection wells in Area 3 (IW-25 to IW-27) and three direct injection locations. The volume of ERD solution injected at existing Area 3 injection wells was approximately 450 gallons of a ABC® Ole’ mixture at 20 wt% solution.

ZVI was not used in the existing injection wells due to potential of clogging the well screens.

Three direct injections were conducted upgradient of G6M-04-02X, just east of Bldg. 3813 (GP-38 to GP-40). A concentration of 15 wt% solution of ABC® Ole’+ was directly injected.

Approximately 133 gallons of ABC® Ole'+ solution was injected across six intervals from approximately 70 to 95 ft bgs, for an approximate total of 800 gallons per location.

Area 4

The 2017 injections in Area 4 were conducted at three existing injection wells in Area 4 (IW-35, IW-36, and G6M-06-01X) and five direct injection locations. The volume of ERD solution injected at existing Area 4 injection wells was approximately 450 gallons of a ABC® Ole’ mixture at 20 wt% solution. ZVI was not used in the existing injection wells due to potential of clogging the well screens.

Five direct injections were conducted upgradient of G6M-13-02X (GP-41 to GP-45).

A concentration of 15 wt% solution of ABC® Ole’+ was directly injected. Approximately 130 gallons of ABC® Ole'+ solution was injected across five intervals from approximately 105 to 125 ft bgs, for an approximate total of 650 gallons per location.

Area 4/5

The 2017 injections were conducted at five direct injection locations (GP-46 to GP-50) west of Area 4/5 injection wells. A concentration of 15 wt% solution of ABC® Ole’+ was directly injected.

Approximately 130 gallons of ABC® Ole'+ solution was injected across five intervals from approximately 110 to 130 ft bgs, for an approximate total of 650 gallons per location.

Area 5

The 2017 injections were conducted at seven direct injection locations southwest of Area 5 injection wells, upgradient of G6M-97-05B and adjacent to G6M-13-01X (GP-51 to GP-57).

A concentration of 15 wt% solution of ABC® Ole’+ was directly injected. Approximately 130 gallons of ABC® Ole'+ solution was injected across five intervals from approximately 120 to 135 ft bgs, for an approximate total of 650 gallons per location.

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In-Well Stripping System

The Army operated the IWS system from 2004 to March 2013. Operation of the system was discontinued in 2013 with regulatory concurrence (Sovereign, 2013) and has not been fully operational since that time. In 2017, an assessment of the system was performed. The assessment was limited due to the lack of functionality. Visual inspection of system components revealed corrosion of pumps and blowers. In order for the IWS system to be returned to full functionality, it is likely the central processing unit along with various pumps, blowers, and other system components will need to be replaced. At the BCT meeting on January 18, 2018, the Army and EPA agreed that the system could be repaired in the future if it was found to be needed again.

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3.0 LONG-TERM MONITORING EVENT METHODOLOGY

The LTM program at AOC 50 was conducted in accordance with the Final Long-Term Monitoring Plan, AOC 50 (HGL, 2012) to monitor COC trends over time in groundwater. Modifications have been made to the LTM monitoring network based on ongoing remedial actions and historical results and the Final Long-Term Monitoring and Maintenance Plan (LTMMP) Area of Contamination 50 (KGS, 2017a) will be implemented in 2018. KGS performed semi-annual LTM groundwater sampling events in spring (May) and fall (October) 2017. The AOC 50 site layout, showing the Southwest Plume area, ERD injection well transects, and LTM monitoring wells is depicted on Figure 1-2. The layout of the AOC 50 Source Area is presented on Figure 1-3.

Groundwater Sampling and Analysis

The groundwater sampling events were performed in accordance with the low-flow procedures documented in Low Stress (low flow) Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells [U.S. Environmental Protection Agency (USEPA) Region 1, 2010], and included the following activities:

A combination of dedicated and non-dedicated, stainless steel bladder pumps and peristaltic pumps were used for groundwater purging and sampling. The bladder pump intake screens were placed approximately in the center, or slightly below the center, of the submerged well screen interval. The pump intakes were placed a minimum of 2 feet above the bottom of the monitoring wells.

Previously installed, dedicated, dual bonded, ¼-inch Teflon-lined polyethylene sample tubing was used in each LTM well.

Each monitoring well was purged at a rate between 100 and 500 milliliters per minute. The purge rate was established to maintain a stable depth-to-water (DTW) and/or total draw down less than 0.3 ft (about 3.6 inches).

The pump discharge was monitored for field parameters [pH, specific conductivity, dissolved oxygen (DO), oxidation-reduction potential (ORP), temperature, and turbidity].

The DTW was measured every five minutes during purging. The purging of the monitoring well was determined to be complete when field parameters stabilized.

Turbidity samples were collected via a “Y” or “T” connector with a shut-off valve located after the pump, but before the flow-through cell.

Dissolved metals samples were field-filtered using 0.45-micron filters.

Investigation-derived waste (IDW) was handled following established procedures in place at AOC 50.

Groundwater samples were collected from the monitoring wells for the analytical parameters discussed in Section 4 of this report. Details on analytical sample container and preservation requirements are presented in Table 3-1. Completed groundwater low flow sampling forms for the 2017 events are presented in Appendix A.

Decontamination Procedures

Bladder pumps were decontaminated between wells by using the following five-step process:

1) rinse with potable water, 2) wash with a non-phosphate detergent solution, 3) rinse with potable

3-2 water, 4) rinse again with isopropyl alcohol, and 5) rinse with distilled water. The bladder pumps were disassembled prior to decontamination. The single use bladder was also removed from the bladder pump and replaced during the decontamination process. The same five-step process was used to decontaminate other non-dedicated sampling equipment.

Investigative-Derived Waste Handling

Investigative-derived waste (i.e., low-flow purge water and decontamination water) was containerized at each wellhead during groundwater sampling events. During sampling events, purge water from monitoring wells was discharged back to the ground at the site of generation after sampling was completed, as per the 2003 Waste Management Plan (ARCADIS, 2003) and the May 1995 Project Operations Plan (ABB Environmental Services, Inc. 1995).

Long-term Monitoring Events

A summary of the methodology used during the 2017 sampling events is outlined below.

Monitoring Well Inspection

Prior to sampling, the following procedures were used to inspect the LTM wells at AOC 50:

The monitoring well location was identified, and the well identification number was confirmed;

The wellhead was inspected for signs of damage and any damage noted, as warranted; and, The monitoring well gripper seal was removed, and the wellhead was allowed to vent prior to well inspection.

No tampering of the wells was apparent during the 2017 sampling events. Several wells had missing protective casing locks and plugs that were subsequently replaced in July 2017 (Section 3.5).

Water Level Measurements

The depth to water in the AOC 50 monitoring wells was measured and recorded within a 24-hour period as part of the spring and fall LTM events. A summary of the water level measurements and the corresponding water elevation data is presented in Table 3-2 for spring event, and Table 3-3 for fall event. Groundwater elevation contours are presented on Figure 3-1 (May 2017) and Figure 3-2 (October 2017).

Consistent with previous LTM event, the groundwater flow direction was observed to be toward the southwest during the spring and fall sampling events. Groundwater was encountered at approximately 9 to 11 ft bgs in Area 1 (at wells G6M-04-10X/A) and approximately 51 to 53 ft bgs at the southwestern end of the former MAAF (at well G6M-03-08X).

The groundwater hydraulic gradient between Area 1 well G6M-04-10A and downgradient well G6M-03-08X (southeast edge of plume) was calculated to be 0.0029 ft/ft in May 2017 and

0.0037 ft/ft in October 2017.

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Well Maintenance Activities

On July 5 and 6, 2017, locks were added to unsecured wells and monitoring well plugs were added where necessary based on the spring inspection results. At the same time, flush mount monitoring well pads were replaced at G6M-92-03X and G6M-13-03X based on the spring inspection results.

On September 26 and 27, 2017, accumulated sediment was removed from the bottom of MicroWells® XSA-12-95X, -96X, -97X, -98X, and monitoring well G6M02-07X. The sediment was removed from the wells using an inertial pump.

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4.0 GROUNDWATER MONITORING RESULTS

Sampling was conducted for the continued monitoring of chemical and geochemical parameters in AOC 50 groundwater in accordance with the LTMMP (HGL, 2012). Laboratory analytical results for the groundwater samples collected during LTM events in the spring (May) and fall (October) 2017 are discussed in the following subsections. The laboratory analytical reports are in Appendix B. Analytical results judged to be laboratory contaminants originating in the sampling and analytical processes are not considered representative of site conditions. The effects of contamination in the laboratory and field blanks, as well as the effects of other quality control (QC) issues associated with the analytical results, are reported in the data validation reports for the 2017 sampling events (Appendix C).

Groundwater Chemistry for Monitoring Events

The spring 2017 LTM event included the sampling of 19 wells. The fall 2017 LTM event included the sampling of 45 wells.

The frequency, sampling locations, and analytical parameters for the two LTM sampling events conducted in 2017 are summarized in Table 4-1. The spring and fall 2017 LTM analytical results and field parameters are presented in Tables 4-2 and 4-3, respectively. Historical laboratory analytical results and groundwater field parameters, including the 2017 sampling results, are presented in Appendix D.

Field Parameters

Field parameter measurements collected during the 2017 LTM sampling events are summarized below.

Observed pH levels ranged from 5.51 to 6.85 in May 2017 and from 5.56 to 7.88 in October 2017, which is suitable to support the ERD process. Five of wells sampled in May 2017 had unusually high pH values (pH>10): G6M-03-01X (12.52), G6M-13-05X (11.40), G6M-02-08X (12.31), IW-17D (11.10), and IW-18D (11.00). Even though the instrument measuring pH was appropriately calibrated each morning and the afternoon calibration check was within 1 percent of the three pH references, the pH values are suspicious and were eliminated from the evaluation.

During previous and subsequent sampling events at the same monitoring wells pH values ranged from 5.27 to 6.66 suggesting that the high pH values are a result of a faulty pH probe. The other water quality parameters measured using the same instrument were consistent with previous and subsequent measurements at the same wells.

The wells with lower pH were present within and downgradient of in-situ reactive zones (IRZ), especially in the FDSA/Area 1 and Former Dry Well Area/Area 1. IRZs are formed as a result of the ERD treatment, the placement of which is shown on Figure 2-1. Reduced pH is expected due to ERD treatment; pH reduction occurs due to generation of carbonic and supplementary acid (e.g., fatty acids, propionic acid) from organic carbon fermentation that occurs in the ERD processes.

In general, low DO levels and negative ORP values were recorded downgradient and within the IRZs formed as a result of the ERD treatment. Low DO [less than 1 milligram per liter (mg/L)] and negative ORP values (reducing conditions) are indicators of the anaerobic breakdown of CVOCs. Reducing conditions are present throughout most of Area 1 where ERD injections have occurred or downgradient of injections. The impact of the ERD injections is clearly seen by an

4-2 increase of anaerobic biodegradation evidenced by a decrease in DO to below 1 mg/L and a decrease of ORP to negative values at G6M-13-05X (near Building 3840) and G6M-07-02X (FDSA) in October 2017. Both of these locations were the focus of direct injections of the ERD substrate in July 2017. Reducing conditions in the FDSA are also present at G6M-04-10A but are not present at nearby locations G6M-04-10X and G6M-04-13X.

Upgradient of the Former Dry well, where numerous rounds of injections occurred in previous years, reducing conditions persist at G6M-02-08X. The DO levels at G6M-03-01X continue to fluctuate between aerobic and anaerobic conditions. At G6M-03-02X DO levels increased in October 2017 indicating a return to aerobic conditions. Downgradient of the Former Dry Well reducing conditions continue to persist at G6M-04-09X, G6M-13-06X, and G6M-04-31X.

In Area 2, reducing conditions persist at G6M-04-03X, G6M-04-01X and G6M-02-01X in 2017 in the IRZ. In Area 3, reducing conditions persist at G6M-03-07X and G6M-04-04X in 2017.

Within the small portion of the plume remaining at Area 3 (G6M-04-02X), aerobic conditions were present in May 2017 after reducing conditions were observed in 2016. After the ERD injections in July 2017 directly upgradient of G6M-04-02X, reducing conditions were observed at G6M-04-02X in October 2017. The flame ionization detector measurements from the headspace of the Area 3 injection wells measured prior to the injections (Table 2-1) indicate the presence of organic compounds in the air (including methane), which is a result of anaerobic biodegradation.

Anaerobic conditions persist in most of Areas 4 and 5 where ERD injections have occurred in the eastern portion of the plume. Anaerobic biodegradation occurring in this area is evident by the high FID results from headspace monitoring of the Area 4 injection wells (Table 2-1). The FID results are indicative of methane produced from fermentation of the injected substrate. Within the western portion of the plume in Areas 4 and 5 there are some areas of low DO (i.e., G6M-13-02X, G6M-13-01X, G6M-97-05B) but reducing conditions are not consistently present. It is anticipated reducing conditions will become more prevalent as the injected substrate migrates through the aquifer. In the most downgradient portion of the plume, a similar condition is observed, area of low DO but reducing conditions are not consistently present. DO and ORP trend graphs for select locations are presented on Figure 4-1. The date of 2017 injections was added to trend graphs with locations that were directly affected by the 2017 injections.

Specific conductivity data above 2.0 milliSiemens per centimeter (mS/cm) were generally recorded for wells southwest of Route 2A and in the gravel parking lot for Area 1, which may be the result of the introduction of de-icing salt applied to roadways during snow removal activities.

Volatile Organic Compounds

Groundwater samples were collected from 19 monitoring wells during the spring 2017 sampling event and 45 monitoring wells during the fall 2017 sampling event and submitted for VOC analyses. Figures 4-2 through 4-5 present PCE concentration contours over time and demonstrate continued cleanup of PCE in AOC 50 groundwater. However, it should be noted that the interpretation of plume contours is affected by the distribution of data used to construct the contours, which changes over time, specifically the monitoring well network has changed from 2004 (Figure 4-2) to 2017 (Figure 4-5). The remediation of the groundwater plume at AOC 50 will continue to be monitored over time to verify that remedial goals are being achieved across the site.

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Figure 4-2 shows a continuous PCE plume across AOC 50 in 2004, extending from the AOC 50 Source Area to downgradient Area 5, with the highest detected PCE concentrations, up to 17,000 µg/L at location G6M-94-18X, in the AOC 50 Source Area. These data were collected prior to full-scale remedy implementation. Location G6M-94-18X has since been converted to an injection well (IW-38).

Figure 4-3 shows PCE concentrations in 2010, after six years of the remedial action. The PCE plume decreased substantially over all areas at AOC 50, and was no longer continuous over the area. Residual pockets of PCE levels remained around the ERD injection transects. The highest concentrations continued to be present at the AOC 50 Source Area, with PCE detected at 1,000 µg/L at location G6M-04-09X.

Figure 4-4 shows PCE concentrations from the fall 2015 LTM sampling event. These samples were collected following an ERD injection in July 2015. The PCE concentrations continued to be highest in the AOC 50 Source Area with a maximum of 1,120 µg/L at location G6M-13-05X. PCE concentrations in Areas 2 and 3 continued to decrease. The PCE concentrations, west of the Areas 4 and 5 injection well transects, were the highest in well G6M-97-05B (117 µg/L).

Figure 4-5 shows PCE concentrations from the fall 2017 LTM sampling event. The plume contours are based on current and historic data presented in previous annual reports, groundwater flow patterns, and groundwater fate and transport processes. The PCE concentrations are also shown in cross-sections (Figures 4-6, 4-7, 4-8, 4-9, and 4-10). The cross-sections also show vertical profiling results from 2013; the profiling results are for informational purposes only and were not directly used in contouring 2017 PCE concentrations.

PCE concentrations in the source area (Area 1) have decreased in many of the wells;

however, PCE concentrations continue to be the highest in Area 1 at locations G6M-13- 05X and G6M-07-02X. PCE decreases were evident following the July 2017 ERD injections, from 1,300 µg/L (May 2017) to 280 µg/L (October 2017) at G6M-13-05X and from 1,800 µg/L (May 2017) to 910 µg/L (October 2017) at G6M-07-02X (Figure 4-11).

PCE concentrations in Area 2, both upgradient and downgradient of the injections wells remained non-detect in 2017 (Figure 4-12).

In Area 3, PCE concentrations at G6M-04-02X decreased from 280 µg/L (May 2017) to 97 µg/L (October 2017) after the July 2017 ERD injections conducted upgradient of G6M-04-02X. PCE concentrations remain non-detect in monitoring wells downgradient of the injection wells (Figure 4-13).

Downgradient of most of the Area 4 and Area 5 injection wells, specifically at G6M-02-

13X, MW-7, MW-3, G6M-02-11X, G6M-02-12X, G6M-04-05X, G6M-03-08X, G6M-03-

09X, and G6M-03-10X, the PCE concentrations were non-detect or below the 5 µg/L cleanup goal in 2017. There was an increase of PCE concentrations at G6M-13-04X to 40 µg/L (October 2017) from non-detect (May 2017). PCE concentrations at G6M-13- 04X have previously fluctuated between non-detect (May 2017, June 2015) to a maximum concentration of 41 µg/L (January 2014) (Figure 4-14).

West of the Areas 4 and 5 injection wells, the plume has not changed significantly from 2016 and PCE concentrations continue to persist at low levels. The PCE concentrations in this portion of the plume have decreased in 2017 in G6M-13-02X from 84 µg/L (November 2016) to 79 µg/L (May 2017) and to 65 µg/L (October 2017) (Figure 4-14). The highest

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PCE concentrations in this portion of the plume at G6M-97-05B increased slightly from November 2016 (140 µg/L) to May 2017 (190 µg/L) and then decreased in October 2017 (140 µg/L). There was a decrease in PCE concentrations at G6M-04-07X from 78 µg/L (November 2016) to 38 µg/L (October 2017) and a slight increase in PCE concentrations at XSA12-95X from 23 µg/L (November 2016) to 36 µg/L (October 2017), however these concentrations have decreased from 290 µg/L (October 2012). Most of the other wells had steady PCE concentrations in the furthest downgradient portion of the plume including PCE concentrations at G6M-04-06X [set 16 feet shallower, 168.07 to 158.07 ft above mean sea level (amsl), than G6M-04-07X (142.68 to 132.68 ft amsl)] where PCE concentrations have remained below 5 µg/L since 2014.

TCE concentrations have decreased below the MCL (5 µg/L) in most of the plume, but there are some remaining areas where TCE concentrations are above the MCL. All of the areas with TCE above the MCL are areas where PCE is currently or previously above the MCL.

In Area 1, TCE concentrations have decreased but are present above the MCL at G6M-03- 01X [9.7J (estimated result) µg/L, October 2017] and IW-17D (6.1 µg/L, May 2017), both of which are areas where PCE was previously above the MCL and current methane and TOC concentrations suggest biodegradation is occurring. At G6M-13-05X, TCE increased from 7.2J µg/L (November 2016) to 69 µg/L (October 2017), which is likely an indication of PCE degradation due to the July 2017 injections immediately surrounding the monitoring well. The cis-1,2-DCE concentrations at G6M-13-05X also increased from 31 µg/L (November 2016) to 750 µg/L (October 2017), indicating the degradation of TCE.

In Area 3, TCE is present above the MCL at G6M-04-02X (26 µg/L, October 2017), and variation in the TCE concentration is approximately commensurate with the fluctuations in PCE concentration (Appendix D).

Downgradient of the Area 4 injection wells at G6M-02-13X, TCE concentrations have increased above the MCL since February 2016 to the current concentration of 21 µg/L (October 2017). At the same time cis-1,2-DCE and vinyl chloride (VC) concentrations have also gradually increased from below 1 µg/L in 2012 to 57 µg/L and 17 µg/L, respectively, in October 2017, indicating degradation is occurring. Reducing conditions are present at G6M-02-13X but the methane concentrations are low (1,500 µg/L, October 2017) and TOC concentrations are low (1.8 mg/L, October 2017). The results suggest incomplete degradation of the VOC compounds, and although reducing conditions are favorable for degradation, it appears there is minimal degradation occurring potentially due to a lack of carbon to support degradation. The last injection in Area 4 injection wells upgradient of G6M-02-13X was completed in July 2015.

TCE is also present above the MCL in wells west of the Areas 4 and 5 injection wells, co-located with elevated PCE concentrations, specifically at G6M-13-02X, G6M-13-04X, G6M-97-05B, XSA-12-96X, XSA-12-95X, and G6M-04-07X.

Inorganic Metals

Groundwater samples were collected from 19 wells during spring 2017 sampling event and from 45 wells during the fall 2017 sampling event. The samples were submitted for dissolved metals (arsenic, iron, and manganese) analysis; except for wells G6M-04-22X and G6M-04-31X, which were submitted for dissolved arsenic analysis only.

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Metals solubilization associated with the ERD process, particularly arsenic and manganese which are mobilized under reducing groundwater conditions, appears to be occurring within the IRZs across AOC 50. The resulting desorption naturally occurring metals from aquifer soils is directly correlated with the geochemically reducing conditions within the IRZ for each injection area. This relationship is observed throughout the AOC 50 treatment area and was an expected by-product of the selected remedial action.

The dissolved metals concentrations will likely continue to fluctuate within an IRZ and are not anticipated to significantly diminish until the IRZ reverts to an oxidizing state. As the aquifer becomes oxic (i.e., has a positive ORP) the geochemical conditions will promote the oxidation and precipitation of the dissolved metals. Metal hydroxides form and precipitate out of solution; in such areas, dissolved arsenic sorbs to metal hydroxides and is immobilized.

Areas with dissolved arsenic concentrations above the MCL of 10 ug/L are primarily in areas where ERD injections have occurred and downgradient of ERD injection areas, specifically in Areas 1, 2, 3, and in the eastern portion of Areas 4 and 5.