KGS 2017 Draft_Final_2017_Long-Term_Monitoring_and_Maintenance_Plan AOC 50 Devens.pdf

U

DRAFT FINAL

LONG-TERM MONITORING AND

MAINTENANCE PLAN

AREA OF CONTAMINATION 50

FORMER FORT DEVENS ARMY INSTALLATION

DEVENS, MASSACHUSETTS

OCTOBER 2017

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

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.

This page is intentionally left blank.

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TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 PURPOSE

1.2 BACKGROUND

2.0 REMEDIAL OPERATIONS

2.1 ENHANCED REDUCTIVE DECHLORINATION SUBSTRATE

2.2 INJECTION PLACEMENT

2.2.1 Area 1

2.2.2 Area 2

2.2.3 Area 3

2.2.4 Area 4

2.2.5 Area 5

2.3 ENHANCED REDUCTIVE DECHLORINATION INJECTION ACTIVITIES

2.3.1 Substrate Injection Quantities

2.3.2 Substrate Injection System

2.3.3 Substrate Injection Documentation

3.0 LONG-TERM MONITORING AND MAINTENANCE PROGRAM

3.1 HYDROGEOLOGIC CONDITIONS

3.2 GROUNDWATER MONITORING PROGRAM

3.2.1 North Plume

3.2.2 Area 1 (Source Area)

3.2.3 Area 2 (Southwest Plume)

3.2.4 Area 3 (Southwest Plume)

3.2.5 Area 4 (Southwest Plume)

3.2.6 Area 5 (Southwest Plume)

4.0 SAMPLING AND ANALYSIS PLAN FOR GROUNDWATER

4.1 ANALYTICAL METHODS AND ANALYTES

4.2 PRE-SAMPLING ACTIVITIES

4.2.1 Equipment and Supplies

4.2.2 Site Location, Security and Access

4.2.3 Initial Well Opening and Inspection

4.2.4 Water Level Measurements

4.3 SAMPLING PROCEDURES

4.3.1 Equipment Calibration

4.3.2 Low-Flow Well Purging

4.3.3 Sample Containers and Preservatives

4.4 SAMPLE COLLECTION

4.4.1 Sample Identification

4.4.2 Quality Assurance/Quality Control Samples

4.5 POST-SAMPLING ACTIVITIES

4.5.1 Total Well Depth Measurement

4.5.2 Chain of Custody

4.5.3 Sample Delivery/Shipment to Laboratory

4.5.4 Equipment Decontamination

4.5.5 Investigation-Derived Waste

4.5.6 Data Validation

4.6 FIELD DOCUMENTATION

4.6.1 Field Logbooks

4.6.2 Groundwater Sample Collection Sheets

4.6.3 Photographic Documentation

4.6.4 Project File

4.6.5 Reporting

5.0 REFERENCES

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LIST OF TABLES

1 Injection Well Construction Details

2 Historical Groundwater Concentrations AOC 50

3 Monitoring Wells Selected for Water Level Measurement

4 Monitoring Wells Selected for Long-Term Monitoring

5 Monitoring Well Construction Details

6 Sample Preparation and Analytical Methods, Containers, Holding Times, and

Preservation

LIST OF FIGURES

1 Site Location, AOC 50

2 Site Layout, AOC 50

3 Tetrachloroethene Concentrations in Groundwater, 2004, AOC 50

4 Tetrachloroethene Concentrations in Groundwater, 2010, AOC 50

5 Tetrachloroethene Concentrations in Groundwater, 2014, AOC 50

6 Tetrachloroethene Concentrations in Groundwater, 2015, AOC 50

7 Tetrachloroethene Concentrations in Groundwater, 2016, AOC 50

8 Cross-Section Plan View, AOC 50

9 Tetrachloroethene Plume in Groundwater - Cross Section, A-A’ AOC 50, November

10 Tetrachloroethene Plume in Groundwater Cross Section, B-B’ AOC 50, November 2016

11 Proposed Monitoring Network, AOC 50

LIST OF APPENDICES

Appendix A

Appendix B

Appendix C

Monitoring Well Low Flow Sampling Form

USEPA Low Stress (low flow) Purging and Sampling Procedure (2010)

Product Substrate Information

LIST OF ACRONYMS AND ABBREVIATIONS

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ABC® Anaerobic BioChem®

AOC area of contamination

ARCADIS ARCADIS U.S., Inc./G&M, Inc.

Army U.S. Army bgs below ground surface

BRAC Base Realignment and Closure

°C degrees Celsius cis-1,2-DCE cis-1,2-dichloroethene

COC contaminant of concern cVOC chlorinated volatile organic compound

DPT direct push technology

DO dissolved oxygen

DoD Department of Defense

DRFTA Devens Reserve Forces Training Area

ERD enhanced reductive dechlorination ft feet ft/day feet per day

FDSA Former Drum Storage Area

HGL HydroGeoLogic, Inc.

IRZ in situ reactive zone

IWS in-well stripping

KGS KOMAN Government Solutions, LLC.

LTM long-term monitoring

LTMMP Long-Term Monitoring and Maintenance Plan mg/L milligrams per liter mS/cm milliSiemens per centimeter

MAAF former Moore Army Airfield

MassDEP Massachusetts Department of Environmental Protection

MassDevelopment Massachusetts Development and Finance Agency

MiHPT Membrane Interface Probe-Hydraulic Profiling Tool

MS matrix spike

MSD matrix spike duplicate mV millivolt

NTU nephelometric turbidity unit

ORP oxidation-reduction potential

% percent

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

PCE tetrachloroethene

PID photoionization detector

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

ROD Record of Decision

Sovereign Sovereign Consulting Inc.

LIST OF ACRONYMS AND ABBREVIATIONS

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SU standard units

SVE soil vapor extraction trans-1,2-DCE trans-1,2-dichloroethene

TCE trichloroethene µg/L micrograms per liter µm micron

USACE U.S. Army Corps of Engineers

USEPA U.S. Environmental Protection Agency

VC vinyl chloride

VOC volatile organic compound

LONG-TERM MONITORING AND MAINTENANCE PLAN

AREA OF CONTAMINATION 50

AT FORMER FORT DEVENS ARMY INSTALLATION

DEVENS, MASSACHUSETTS

1.0 INTRODUCTION

1.1 Purpose

The purpose of this Long-Term Monitoring and Maintenance Plan (LTMMP) revision is to update the long-term monitoring (LTM) approach to account for changes in the plume and site’s geochemistry, and to present the revised approach for the Enhanced Reductive Dechlorination

(ERD) injection program. This revision updates the Final Long-Term Monitoring Plan, AOC 50, Devens, Massachusetts. (HydroGeoLogic Inc.[HGL], 2012) and the Enhanced Reductive

Dechlorination Operations and Maintenance Manual, Addendum I (HGL, 2009). This revision provides descriptions of the planned tasks, methodologies, and objectives to evaluate whether the site continues to make progress toward achieving site cleanup goals associated with remediation at Area of Contamination (AOC) 50, Devens, Massachusetts. KOMAN Government Solutions, LLC (KGS) prepared this LTMMP for the U.S. Army Corps of Engineers (USACE) under contract number W912WJ-15-C-0002.

1.2 Background

The AOC 50 site is located on the northeastern boundary of the former Moore Army Airfield

(MAAF), within the former North Post portion of the former Fort Devens Army Installation, Ayer, Massachusetts (Figure 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 renamed the Devens

Reserve Forces Training Area (DRFTA). Areas not retained as part of the DRFTA were transferred to new owners (Massachusetts Development and Finance Agency [MassDevelopment] and the

U.S. Fish and Wildlife Service) for reuse and redevelopment. The DRFTA was renamed the U.S.

Army Garrison Fort Devens in 2009.

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 and vehicle storage. The former

MAAF is zoned for Special Use II and Innovation and Technology Business. Under the Devens

Reuse Plan (November 14, 1994), Special Use II and Innovation and Technology Business includes a broad range of industrial, light industrial, office, and research and development uses.

There are currently no plans for development of the former MAAF, although the area can be developed if interested parties are identified. 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.

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) drum storage area; 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 Buildings 3803 (the former parachute shop), 3840 (the former parachute shakeout tower), 3824 (a gazebo), and 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 volatile organic compounds (VOCs), most notably the chlorinated volatile organic compound (cVOC) PCE. 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 toward the Nashua River.

Investigations performed in 1997, 1998, 2000, and 2005 defined the longitudinal and lateral extents of the plume. Supplemental investigations performed in 2014 confirmed the lateral extents of the plume, at that time, and demonstrated that the direction of the plume remains consistent with the direction of groundwater flow.

In 2014, Sovereign conducted a Membrane Interface Probe Hydraulic Profiling Tool (MiHPT)

Source Area Investigation in accordance with the Source Area Investigation Work Plan, Area of

Contamination 50 (Sovereign Consulting Inc. [Sovereign] and HGL, 2014). The study and its results, detailed in the AOC 50 Source Area MiHPT Investigation Summary Report (Sovereign, 2015), support the former dry well as a primary former source. The former floor drain in the parachute tower (connected to the former dry well) did not appear to be a secondary source based on the lack of shallow cVOC responses in the MiHPT points. In portions of the Source Area that did contain cVOCs, the higher concentrations were generally restricted to deeper depths.

The MiHPT study also evaluated the effectiveness of the current remedial strategy. The report concluded the fixed screen injection well network was effective in addressing cVOC concentrations in the shallow aquifer, but a more targeted approach for deeper impacts would be required. The study found denser, lower permeability deeper soils containing cVOC concentrations that were not being effectively treated at that time.

2.0 REMEDIAL OPERATIONS

Remedial options at AOC 50 were implemented to degrade contaminants of concern (COCs) found in the source area as well as in downgradient groundwater. ARCADIS U.S., Inc. /G&M, Inc.

(ARCADIS) conducted a pilot study to evaluate ERD and in-well stripping (IWS) in Area 5, at the downgradient portion of the plume. Based on the results of the pilot study, the full-scale remedy was implemented by ARCADIS in September 2004. The remedy was comprised of ERD in the source area and in a series of transects throughout the plume (Figure 2), IWS at the downgradient edge of the plume in Area 5, and soil vapor extraction (SVE) in the AOC 50 source area.

The SVE system was discontinued in 2005 as monitoring data indicated that recoverable compounds had been removed. The IWS was discontinued in 2013. An evaluation of the IWS central processing unit will be conducted in 2017 and a schedule for repair or replacement will be provided after the evaluation is complete. Full scale ERD injections were started in 2004 and the injections were initially conducted on a monthly basis. In 2009 the injections were decreased to a semiannual basis. The injections were decreased to an annual basis in 2015 and the approach was further modified at that time to utilize a longer lasting substrate and augment the fixed injection wells with direct injections of the substrate into the subsurface to target residual contamination.

The ERD remedy has significantly reduced the cVOC mass throughout the plume through use of substrate injections via injection wells and recent direct injections into the subsurface via direct push technology (DPT) (Figures 3, 4, 5, 6, 7, 8, 9, and 10). Evaluation of 2016 monitoring data after the 2015 injections indicates anaerobic biodegradation is occurring in the groundwater downgradient of many of the injection areas even though injections were not conducted in 2016

(KGS, 2017).

The need for injections will be evaluated annually. The timing, placement of injection, method of injection, specific substrate, percent weight of substrate, and volume of each injection will be designed prior to each injection event based on results of the ongoing long-term groundwater monitoring program. A brief memorandum detailing the specifics of injection plan will be provided to the regulatory agencies 60 days prior to the start of the injection event.

The record of decision (ROD) and 60% design estimated injections would be conducted for a period of a 10 to 15 years (USACE, 2004; ARCADIS, 2005). The total estimated time to achieve cleanup levels was 27 years. As cVOC mass continues to decrease throughout the plume, injections will be phased out and residual plume contaminants will be monitored until cleanup levels are attained.

2.1 Enhanced Reductive Dechlorination Substrate

ERD is bioremediation technology where organic substrate is injected into the subsurface to create reducing conditions and promote the growth of microorganisms that are capable of degrading chlorinated ethenes such as PCE. These microorganisms use the chlorinated ethenes as their respiration electron acceptors, thereby removing chlorine atoms and transforming PCE to trichloroethene (TCE), TCE to dichloroethene (DCE), DCE to vinyl chloride (VC), and VC to ethene. Hydrogen is the primary electron donor for the chlorinated ethene reducing microbes.

Hydrogen can be produced in-situ through the fermentation of readily degradable organic compounds such as sugars, molasses, vegetable oil, whey, and various lactates.

There are two basic requirements for complete reductive dechlorination:

• sufficient electron donor to achieve strongly reducing conditions, and

• bacteria capable of efficient dechlorination.

It is recognized that the establishment of reducing conditions can mobilize metals such as iron, manganese, and arsenic, which naturally occur in the aquifer formation at AOC 50. Elevated metals have been detected in monitoring wells near areas where injections have been completed.

The AOC 50 remedy includes injection of an organic carbon substrate into injection wells and direct injections of the substrate into the subsurface via DPT. Groundwater is treated as it flows through the injection areas. The initial design of the remedy included the use of injection wells installed in transects oriented perpendicular to groundwater flow along the plume. The use of injection transects allows the naturally occurring metals to precipitate out of solution in the regions between the transects. Monitoring is conducted to ensure that this approach is effective and that a large-scale plume of metals in groundwater is not being developed.

The injection of an organic substrate promotes the activity of naturally occurring microorganisms to reduce dissolved oxygen (DO) concentrations and generate the hydrogen electron donor supply.

The resulting effect is the development of reducing conditions in groundwater, as needed to support the reductive dechlorination process. Although metals are mobilized to some extent during this process, the degree of metals mobilization is similar to that previously observed. Groundwater sampling is performed to monitor metals mobilization, cVOC degradation, and the extent of reduced groundwater conditions.

The injections will use products called Anaerobic BioChem® (ABC®), ABC®-Ole', and ABC®-

Ole'+. ABC® is a patented mixture of lactates, fatty acids, and a phosphate buffer. ABC® contains soluble lactic acid as well as slow-and long-term releasing components. The phosphate buffer provides phosphates, which are a micronutrient for bioremediation. In addition, the buffer helps to maintain the pH in a range that is best suited for bacteria. The product, ABC®-Ole', consists of a modified blend of ABC® and a fatty acid (a kind of vegetable oil). The fatty acids absorb to the soil, providing longer residence time in the treated area. This process includes both short-term consumption of lactates in the product and long-term consumption of the fatty acids such that remediation will start quickly and the half-life will be longer. The product ABC®-Ole'+ includes zero valent iron (ZVI) in the mixture and is added to the direct injections to allows for the rapid and complete dechlorinating of target compounds. The degradation process via the ZVI is an abiotic reductive dichlorination process occurring on the surface of the granular iron. Degradation rates using ZVI are several orders of magnitude greater than under natural conditions. The Ole' component of the ABC®-Ole'+ provides a longer residence time of the ABC® component of the injected substrate in the treated area. ZVI is not used in injection wells due to the likelihood for clogging of the well screens. Additional information regarding the substrate is provided in

Appendix C.

The volume and percent weight of the specific substrate to be injected at specific locations will be designed prior to each injection event based on results of the ongoing long-term groundwater monitoring program. The injection plan for each event will be reported to the regulatory agencies in a brief memorandum prior to each injection event.

2.2 Injection Placement

The ERD remedy has significantly reduced the cVOC mass throughout the plume through use of substrate injections via injection wells and direct injections into the subsurface via DPT (Figures

3, 4, 5, 6, 7, 8, 9, and 10). The ERD remedy will continue with injection of the organic substrate described above. The placement of injections via existing injection wells and direct injections for each injection event will be designed to target residual contamination identified through ongoing groundwater monitoring. Areas where COC concentrations have achieved cleanup goals through prior treatment, and those exhibiting sufficiently reduced groundwater conditions [i.e., DO less than 0.5 milligrams per liter (mg/L), and a negative oxidation-reduction potential (ORP)], will not receive additional ERD substrate injections. The placement of injections will be designed prior to each injection event based on results of the ongoing long-term groundwater monitoring program.

The existing injection well network is described in the subsections below.

2.2.1 Area 1

A network of 21 injection wells is available in Area 1 (Source Area), as shown on Table 1 and

Figure 2. The injection wells in this area were installed within and downgradient of the former drywell and the former drum storage areas. In addition, direct injection of ERD via DPT has been conducted in areas immediately downgradient of the parachute tower and former dry well.

The aquifer materials within Area 1 are characterized by higher silt content and lower hydraulic conductivities than in the Southwest Plume. Hydraulic conductivities in the Area 1 are less than 5 feet per day as compared to hydraulic conductivities on the order of 25 to 50 feet per day in the area of the Southwest Plume.

2.2.2 Area 2

Area 2 is located approximately 450 feet downgradient of the Source Area (Figure 2). A line of four injection wells, IW-20 to IW-23, were installed with 30-foot spacing between each injection well measured perpendicular to groundwater flow. The injection well screens were set at approximately 75 to 95 feet below ground surface (bgs) corresponding to the depth interval exhibiting the highest historical PCE concentrations. An additional injection well, IW-37, was installed northwest of IW-20 with injection screens constructed at depth of approximately 79 to 99 feet bgs. Monitoring well G6M-07-01X (screened from 78 to 98 ft bgs) was converted to an injection well. No further ERD injections are planned for Area 2 because the current groundwater concentrations indicate groundwater in Area 2 has achieved the cleanup criteria (Table 2).

2.2.3 Area 3

Area 3 is located approximately 850 feet downgradient of the Source Area and approximately

450 feet downgradient of Area 2 (Figure 2). A line of five injection wells, IW-24 to IW-28, were installed with 30-foot spacing between each injection well measured perpendicular to groundwater flow. The injection well screens were set at 70 to 90 feet bgs, corresponding with the depth interval with the highest PCE concentration.

2.2.4 Area 4

Area 4 is located approximately 1,540 feet downgradient of the Source Area and 700 feet downgradient of Area 3 (Figure 2). A line of six injection wells, IW-29 to IW-34, were installed with 30-foot spacing between each injection well measured perpendicular to groundwater flow.

The injection well screens are set from approximately 95 to 115 feet bgs (IW-32, IW-33, IW-34), 100 to 120 ft bgs (IW-31), and 105 to 125 ft bgs (IW-29 and IW-30), corresponding with the depth with the highest PCE concentration. Monitoring wells G6M-05-02X (IW-35) (109 to 129 ft bgs) and G6M-06-01X (10 to 126 ft bgs) were converted to injection wells and IW-36 (106 to 126 ft bgs) was installed to provide greater plume coverage northwest of IW-34.

2.2.5 Area 5

Area 5 is located approximately 2,000 feet downgradient of the Source Area and approximately

420 feet downgradient of Area 4 (Figure 2). A line of six injection wells, IW-1 through 1W to

IW-6, were installed with 30-foot spacing between each injection well. The injection well screens are set approximately 115 to 135 feet bgs, an interval corresponding with the depth interval with the highest PCE concentration. Monitoring well G6M-02-05X was converted to an injection well

(120 to 135 ft bgs). Injection well 39 (125 to 145 ft bgs) was installed just northwest of the Area

5 transect.

2.3 Enhanced Reductive Dechlorination Injection Activities

The first full scale ERD injection event was conducted in October 2004 utilizing molasses as the

ERD substrate. HGL revised the ERD injection program in November 2008 by changing the substrate utilized from molasses to ABC®.

Remedial evaluations conducted in 2015 reviewed historical groundwater data and the 2014

MiPHT Study results and determined that areas of deeper contamination were not being effectively treated in Area 1. The evaluation indicated that injections into existing injection wells were preferentially treating the shallow impacts due to soil conditions. The 2015 injection program was modified to address deeper areas of residual contamination present in the Source Area. The work included directly injecting substrate at depth using DPT, which resulted in more effective placement and deeper distribution of the ERD product. In addition, a new substrate product was utilized in Area 1 to increase residence time.

The 2015 ERD injections included the use of ABC®-Ole' and ABC®-Ole'+, and ABC®. Injections were performed at 15 Area 1 DPT injection locations, 12 Area 1 fixed-screen injection wells, five

Area 2 injection wells, five Area 3 injection wells, seven Area 4 injection wells, and six Area 5 injection wells. Evaluation of 2016 monitoring data after the 2105 injections indicates anaerobic biodegradation is occurring in the groundwater downgradient of many of the injection areas even though injections were not conducted in 2016 (KGS, 2017).

The ERD injection program is evaluated after each event and adapted as needed to improve the effectiveness of the injection program. A summary of the ERD injections will be presented in the

Annual Report. Maintenance of injection wells will be conducted as issues (e.g., reduced injection rate of the injection media) are identified. Injections wells where reduced injection rates of the injection media are observed will be redeveloped prior to the next injection event.

2.3.1 Substrate Injection Quantities

Injection volumes at each zone are dependent upon current groundwater concentrations and chemistry. The volume and percent weight of the specific substrate to be injected at specific locations will be designed prior to each injection event based on results of the ongoing long-term groundwater monitoring program.

Use of persistent ABC®-Ole' and ABC®-Ole'+, was intended to extend the active treatment period for the cVOCs. Given the longevity of the ABC®-Ole' substrate and decrease of cVOC mass, ERD injections will be conducted on a less frequent basis than previous injections and the cVOC concentrations will be monitored until cleanup levels are achieved.

2.3.2 Substrate Injection System

The ERD substrate is mixed on-site using a mixing tank and water obtained from an on-site potable water source. The substrate is mixed with the potable water immediately prior to injection. The substrate is pumped directly from the mixing tank/tanker truck to a distribution system, which allows the substrate solution to be delivered in measured quantities. The substrate is introduced to the bottom of each direct injection point or well. A specific volume of substrate is pumped into at 5-ft section at low pressure (less than five pounds per square inch[psi] at the wellhead). The process is repeated every five feet of the injection interval until the appropriate volume for the injection point is completed.

The injections are paced to minimize sudden and sustained mounding effect generated during single day events. Substrate injections are staggered within each transect and boring to avoid an injection pressure wave that could potentially displace contaminated groundwater beyond its existing defined perimeter. The single injection point scheme ensures adequate and thorough distribution of the ERD substrate within its intended target zone. A staggered arrangement minimizes groundwater mounding within any particular injection area. No two adjacent wells in any transect are injected sequentially. Injections proceed from the outer wells to the interior transect wells. If substantial mounding (greater than approximately six inches) is observed in adjacent monitoring wells, then the injection rate will be reduced to decrease the amount of mounding.

2.3.3 Substrate Injection Documentation

The ERD injection activities, observations, and results are documented in a bound field notebook.

Each injection log records the observed flow rate and pressure utilized at the pump and recorded at the well head, total quantities of injected substrate, water used per well, and any physical observations noted during the process. In addition, monitoring of groundwater elevations and total methane at the injection well prior to injection activities is recorded. Surrounding observation wells are monitored periodically during injection activities to observe potential groundwater mounding.

3.0 LONG-TERM MONITORING AND MAINTENANCE PROGRAM

The objectives of the long-term groundwater monitoring program at AOC 50 are to monitor groundwater conditions, to evaluate the effectiveness of the remedial system, and to document that

COC concentrations decrease over time to a level that achieves the cleanup goals established in the ROD. A review of historical groundwater data concluded that the use of ERD was effective at reducing the COC concentrations. This review is illustrated in Figures 3, 4, 5, 6, 7, 8, 9, and 10.

Historical 2004, 2010, 2014, 2015, and 2016 PCE plume maps indicate a significant reduction in the plume area attributed to the ERD process. Historical monitoring results are presented in Table

2. Continued monitoring in concert with ERD remediation will effectively achieve the objectives outlined in the ROD.

To achieve the stated objectives in the Source Area and Southwest Plume, the monitoring program needs to document the establishment of reducing conditions (i.e., low DO and ORP), increased total organic carbon (TOC) concentrations, and degradation of PCE and its anaerobic biological degradation compounds (TCE, cis-1,2-dichloroethene [cis-1,2-DCE], trans-1,2-dichloroethene, [trans-1,2-DCE], 1,1-dichloroethene [1,1-DCE], and VC) as achieved through implementation of the ERD remedy. The program also monitors the mobilization of metals (iron, manganese, and arsenic) and dissolved methane to determine if adjustments in the ERD strategy are warranted.

In addition, once the remedy has reduced the COC VOCs to site cleanup goals, groundwater monitoring will be performed to monitor the geochemistry of the aquifer (including mobilized metals) to verify the aquifer returns to an acceptable condition for the protection of human health and the environment. The cleanup goals for the primary target COCs at AOC 50 are as follows:

PCE [5 microgram per liter (μg/L)], TCE (5 μg/L), cis-1,2-DCE (70 μg/L), VC (2 μg/L), and a secondary target analyte arsenic (10 μg/L).

Due to ongoing ERD substrate injections and changes in the plume extent and composition, a re-evaluation of the LTM program is required in regard to monitoring wells incorporated into the monitoring network, frequency of monitoring, and required analytes. The ERD injections have reduced the extent of the PCE plume, but have also generated changes in the plume composition and groundwater geochemistry. The monitoring well network was evaluated relative to groundwater flow at the site, the PCE plume extent, and the groundwater geochemistry.

The LTM program includes the measurement of water levels (Table 3) and collection of groundwater samples for off-site laboratory analysis at selected wells on a semiannual, annual, or biennial (every other year) basis (Table 4). Wells within the Source Area and portions of the plume where ERD is performed are monitored on a semiannual basis to track COC concentration trends and geochemistry conditions. Wells where ERD has successfully reduced COC concentrations to the cleanup levels, where arsenic concentrations are elevated due to previous

ERD injections, and wells close to the current plume perimeter are sampled annually to monitor the plume extent and aquifer conditions related to the ERD injections. Wells outside of the historic plume extent where data have shown little change over time, but data would help confirm plume delineation or metals concentrations are monitored biennially.

Maintenance needs, including well development, of the monitoring wells identified during sampling activities will be addressed as they arise. Monitoring wells that are sampled as part of the LTMMP, with greater than 0.5 foot of sediment accumulated in the well, will be redeveloped.

A discussion of the groundwater at AOC 50, followed by a description of the wells selected for sampling and the monitoring methodology is presented below.

3.1 Hydrogeologic Conditions

Numerous groundwater monitoring wells, MicroWells®, and boreholes have been installed at the former MAAF and AOC 50 to characterize the site’s hydrogeology. The following section describes the hydrogeologic environment based on a review of the data presented within the

Remedial Investigation Report Area of Contamination (AOC) 50 (Harding Lawson Associates

[HLA], 2000), Final Feasibility Study, AOC 50, Devens Reserve Forces Training Area

(ARCADIS 2002a), Supplemental Investigation Report (ARCADIS 2002b), Final Long-Term

Monitoring Plan, AOC 50, Devens, Massachusetts (HGL, 2012), Enhanced Reductive

Dechlorination Operations and Maintenance Manual Addendum I (HGL, 2009), subsequent investigations and LTM events up to and including the fall 2016 event.

A single water table aquifer occurs within the overburden deposits below the former MAAF and

AOC 50. Restrictions to vertical groundwater flow, such as narrow silty clay layers, are present, but are not obvious in boring logs within the ‘kame’ glacial deposit or along the Nashua River.

These thin, silty-clay layers were encountered during the MiHPT investigation (Sovereign, 2015) conducted in 2014, within the AOC 50 Source Area. These thin layers reduce the vertical permeability, contribute to a slight increase in the water table elevation, and increase the difference between shallow and deep water levels. These thin, silty-clay layers are also less permeable than the surrounding sands and this results in less ERD material being accepted in the thin layers.

Measurements of the depth to groundwater have been collected from a network of monitoring wells and sampling points on a regular basis since 1997. Groundwater is encountered at approximately 10 ft bgs in the AOC 50 Source Area and approximately 64 ft bgs at the southwestern end of the former MAAF. Groundwater elevations within deeper wells at and to the north of AOC 50 typically have lower heads 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, 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 demonstrate that groundwater is recharged near the AOC 50 Source Area, travels below the former MAAF, and discharges to the Nashua River.

The historical and ongoing groundwater monitoring at the site shows a consistent groundwater flow direction from the northeast to the southwest. The flow direction has not varied over the course of the monitoring. Hydraulic conductivities at the Site range from 1 feet/day (ft/day) to more than 50 ft/day, with seepage velocities ranging from 0.024 to 1.19 ft/day. The groundwater average velocity for the Site is approximately 0.60 ft/day.

3.2 Groundwater Monitoring Program

Groundwater monitoring well locations were selected to provide representative samples from impacted groundwater areas and ERD treatment areas. The selected wells evaluate the site progress toward achieving the cleanup goals and changes in the site’s groundwater chemistry downgradient of the in situ reactive zones (IRZ). Table 3 lists the selected monitoring wells for water level measurement. Table 4 lists the selected monitoring wells for groundwater sampling and presents the sampling rationale, analytical parameters, and sampling frequency. Figure 11 presents the locations of the wells in the LTM program. Table 5 lists the well screen information and descriptions for wells at AOC 50.

The LTM program includes seven wells sampled semiannually to evaluate cVOC degradation, inorganic solubilization, and geochemistry. The 34 wells sampled annually to provide a more comprehensive network to evaluate cVOC extent and inorganic solubilization (i.e., the mobilization of iron, manganese and arsenic). The six wells sampled biennially provide confirmation of plume delineation or metals concentrations. A discussion of the current monitoring network is presented below.

3.2.1 North Plume

Wells G6M-96-22A and G6M-96-22B, located north of Route 2A, are monitored for water level elevations to verify groundwater flow direction. These locations have been removed from the

LTM program because COC concentrations in this area have been below the PCE cleanup criterion since 2001 and all COCs have been below cleanup criteria since 2009. Future sampling of these wells may be considered when Source Area wells (Area 1) achieve cleanup criteria and long-term monitoring of the aquifer water quality to pre-remedial conditions is required.

3.2.2 Area 1 (Source Area)

A total of 14 monitoring wells from Area 1 are incorporated into the LTM program (Table 4). At the Former Drum Storage area, G6M-07-02X is monitored semiannually for VOCs, metals, and geochemistry where residual contamination is present above cleanup levels. G6M-04-10A is also monitored semiannually for VOCs, metals, and geochemistry to monitor the edge of the residual contamination. G6M-04-10X and G6M-04-13X are monitored annually for VOCs to monitor plume extent in an area where VOC concentrations have decreased due to treatment. Arsenic concentrations at G6M-04-10X and G6M-04-13X have been below 2 µg/L for the past five years and; therefore, regular sampling for metals is not needed.

Well G6M-13-05X is monitored semiannually for VOCs, metals, and geochemistry data for groundwater conditions in an area of elevated PCE concentrations.

Well G6M-02-08X is monitored annually for VOCs, metals, and geochemistry data for plume extent and groundwater conditions in the IRZ created near the former drywell. Well G6M-13-06X is monitored annually for VOCs, metals, and geochemistry for plume extent and groundwater conditions in the IRZ downgradient of the former drywell.

Wells G6M-95-19X and G6M-95-20X monitor groundwater conditions upgradient of the former drywell area and the Former Drum Storage Area and are sampled annually. Both wells are sampled for VOCs and G6M-95-20X is sampled for metals due to historically elevated arsenic concentrations.

Well G6M-04-09X is located approximately 100 ft downgradient of the Source Area and along with G6M-04-15X is monitored for VOCs and metals for plume extent and to monitor historically elevated arsenic concentrations.

Further downgradient, well G6M-04-22X monitors groundwater conditions downgradient of the former drywell. Well G6M-04-31X monitors groundwater conditions south of the Former Drum

Storage Area. These wells, along with G6M-04-11X, are sampled biennially rather than annually based on a consistent trend of diminished VOC concentrations. The samples will be analyzed for

VOCs and metals.

3.2.3 Area 2 (Southwest Plume)

Three monitoring wells comprise the LTM well network in Area 2. Well G6M-02-01X is located approximately 60 ft downgradient of the ERD injection transect and well G6M-04-03X is located approximately 200 ft downgradient of the ERD injection transect. Well G6M-04-01X is located approximately 50 ft upgradient of the ERD injection transect. All three of the wells are sampled annually to monitor the VOC concentrations and IRZ that was created by previous injections.

These wells are screened in the deep portion of the aquifer where the COC impact was present and where the ERD treatment was previously applied. The VOC cleanup goals were achieved at the three monitoring wells by 2016 but arsenic concentrations are currently elevated in the IRZ.

3.2.4 Area 3 (Southwest Plume)

Four monitoring wells (G6M-03-07X, G6M-04-02X, G6M-04-04X, and G6M-13-03X) are incorporated into the well network in Area 3. Well G6M-04-02X is located approximately 50 ft upgradient and indicates there is residual contamination upgradient of the injection well transect.

G6M-04-02X will be monitored semiannually to monitor the degradation of the residual contamination and geochemistry at the well. Well G6M-03-07X is located approximately 60 ft downgradient of the ERD transect and will be sampled annually to provide the VOC and geochemical data to monitor the IRZ. Well G6M-13-03X is located approximately 50 ft crossgradient of the injection well transect, and will be sampled biennially to monitor potential contamination north of the historic plume location. Well G6M-04-04X is located approximately

200 ft downgradient of the ERD transect and is sampled annually to monitor VOC concentrations in an area were VOC concentrations decreased due to treatment and arsenic concentrations are currently elevated in the IRZ.

3.2.5 Area 4 (Southwest Plume)

Four monitoring wells are incorporated into the monitoring well network in Area 4. This includes semiannual sampling of well G6M-13-02X, located 150 feet downgradient of the injection well transect, for VOCs, metals, and geochemistry, where VOC concentrations remain above the cleanup levels. Well G6M-02-13X, located approximately 60 feet downgradient of the ERD transect, and well G6M-02-04X, located approximately 150 ft upgradient of the ERD transect, are sampled on an annual basis to monitor VOC concentrations in an area were VOC concentrations decreased due to treatment and arsenic concentrations are currently elevated in the IRZ. In addition, well G6M-97-28X is included for annual sampling to monitor elevated arsenic concentrations.

3.2.6 Area 5 (Southwest Plume)

A total of 22 monitoring wells are incorporated into the well network in Area 5. This network includes annual sampling of wells in the IRZ created by injections in the Area 5 injection well transect that has resulted in the reduction of PCE to the cleanup goal and elevated arsenic concentrations at a number of locations (i.e., MW-3, MW-7, and G6M-02-11X). These wells will be sampled for VOCs and metals.

There is residual plume contamination at G6M-97-05B and G6M-13-01X, which will be sampled semiannually for VOCs, metals, and geochemistry.

To monitor the eastern extent of the plume, wells G6M-13-04X and G6M-03-10X will be monitored annually for VOCs and metals, to monitor plume extent and elevated arsenic concentrations.

In the downgradient portion of the plume, wells G6M-04-06X, G6M-02-07X, XSA-12-95X, XSA-

12-97X, and XSA-12-98X will be sampled annually to monitor VOC trends and metals concentrations. Wells G6M-04-7X and XSA-12-96X will be sampled semiannually to monitor

VOC trends and metals concentrations.

Well G6M-04-05X will be sampled biennially for VOCs. At G6M-04-05X there have been a few detections of VOCs and arsenic since 2010, all of which were below the cleanup goals. Wells

G6M-02-12X and G6M-03-08X will be sampled biennially for VOCs and metals. At G6M-02-

12X there have been no detections of VOCs since 2014 and decreasing arsenic concentrations. At

G6M03-08X there have been no detections of PCE since 2011 and low arsenic concentrations.

Monitoring well G6M-02-06X, located on the east side of the Nashua River and monitoring well

G6M-04-14X, located on the west side of the Nashua River, are sampled annually to monitor groundwater quality downgradient of the plume.

To monitor the western extent of the plume, two new monitoring wells will be installed on the west side of the plume. The wells will be sampled initially for VOCs, metals, and geochemistry parameters. The wells will be monitored annually for VOCs and metals for three years, after which the sampling frequency will be reviewed. During well installation, groundwater profiling for

VOCs will be conducted every ten feet from 30 feet below the water table to bedrock. A 10-foot well screen will be installed at the highest concentration of plume contaminants. If no VOCs are detected, the screen will be set at the estimated plume elevation based on adjacent locations.

4.0 SAMPLING AND ANALYSIS PLAN FOR GROUNDWATER

This section constitutes the sampling and analysis plan for AOC 50. It was prepared in accordance with the guidelines set forth in the Department of Defense (DoD) Quality Systems Manual (QSM) for Environmental Laboratories (Version 5.1, 2017) and U.S. Environmental Protection Agency

(USEPA), Region 1, Low Stress (low flow) Purging and Sampling Procedure for the Collection of

Ground Water Samples from Monitoring Wells (USEPA, Region 1, 2010).

Two groundwater monitoring events will be performed (semiannual in the spring and annual in the fall). The monitoring wells included in the long-term monitoring and maintenance program are listed in Table 4. Construction details for wells at AOC 50 are summarized in Table 5.

Groundwater monitoring will be conducted semiannually for wells used to evaluate residual plume contamination and to monitor COC and geochemistry fluctuations influenced from the ERD injections. The semiannual monitoring will also be used to plan the injection strategy for each ERD event. Other wells will be monitored annually to assess the overall remedy effectiveness and the long-term effects of the ERD treatment. Annual monitoring of wells downgradient of the plume will be conducted to monitor dissolved inorganics that may have been mobilized from the cVOC plume area, and to be protective of the river. Biennial monitoring of select wells will be performed during the fall event to augment the long-term evaluation of site COCs.

Recommendations/modifications will be made as appropriate, regarding sampling frequency, monitoring locations, and analyses for subsequent year(s) in the Annual Reports and subsequent revisions of this LTMMP. These documents will be submitted to the regulatory agencies for review.

4.1 Analytical Methods and Analytes

Analytical methods and analytes utilized for the AOC 50 LTM sample events will be in accordance with this document and the Quality Assurance Project Plan – Annual Long Term Monitoring and

Maintenance Program (KGS, June 2016). Table 6 lists the analytical parameters, methods, sample containers, and preservation requirements for groundwater monitoring. Specific analytical parameters and methods to be used during AOC 50 LTM sample events are summarized below.

• VOCs - SW846/8260B or 8260C;

• Dissolved Metals (arsenic, iron and manganese) – SW846/6010B/6020A;

• Dissolved Gases (methane, ethane, ethane) – RSK-175;

• Alkalinity – SM2320B;

• Nitrate/Nitrite-N –E353.2;

• Sulfate – SW9056A or E300;

• Sulfide – SW9034; and

• Total Organic Carbon (TOC) – SW9060;

Field measurements will be collected during groundwater monitoring low-flow well purging activities to compliment laboratory analytical methods. Specific parameters will include pH, temperature, specific conductance, DO, ORP, and turbidity. The collection of field measurements is discussed in Section 4.3.2.

4.2 Pre-sampling activities

Prior to conducting the sampling event, the appropriate equipment and supplies shall be obtained, and the laboratory shall be contacted (approximately two weeks prior to commencement of the sampling event) to communicate and coordinate the sampling event. The following sections provide a more detailed discussion of the pre-sampling activities that will be conducted prior to the collection of groundwater samples at AOC 50.

4.2.1 Equipment and Supplies

The following equipment and supplies will be utilized in the collection of low-flow groundwater samples:

• Variable speed submersible bladder pumps and peristaltic pumps,

• Water level indicator,

• DO, pH specific conductance, ORP, and temperature probes (within a single unit) and appropriate calibration solutions, turbidity meter (separate meter from the above unit), flow-through cell,

• Pre-preserved sample containers, equipped with Teflon®-lined lids or septa,

• Decontamination supplies including powdered lab grade detergent,

• VOC-free deionized water,

• 500-milliliter graduated cylinder,

• Graduated 5-gallon buckets for purge water and decontamination,

• Plastic sealable bags,

• 0.45 micron (µm) in-line filters,

• Well keys,

• Field logbook and field sampling forms,

• Chain of custody forms and seals,

• Cooler with packing material and ice to cool all samples to 4 degrees Celsius (ºC), +/- 2 ºC,

• Trip blanks (for VOC analyses), and

• Paper towels.

4.2.2 Site Location, Security and Access

Arrangements will be made to coordinate LTM activities at AOC 50 with appropriate site personnel. Some AOC 50 wells may not be accessible due to training activities at the Moore Army

Airfield. Every effort will be made to ensure that LTM activities are conducted in a timeframe that is acceptable to all stakeholders.

4.2.3 Initial Well Opening and Inspection

Olfactory and visual observations will be made upon opening the well casing protective cap. Such observations, including any detected odors, will be documented in the logbook. The general condition of the protective cover, its associated concrete apron, well casing protective cap, and the well casing will be inspected and noted in the logbook. Any damage, evidence of tampering, or immediately necessary repairs will be communicated to the USACE-NAE Project Manager.

4.2.4 Water Level Measurements

Prior to well purging or sampling, groundwater measurements will be made using an electronic water level indicator. Water levels will be recorded from the top of the well plastic casing and will be recorded to the nearest 0.01 foot. The probe will be cleaned following the appropriate decontamination procedures between sample points. The depth to water will be measured in each well using the decontaminated water level indicator, taking care not to lower the probe below the water surface any further than necessary. Depth to water will be determined with as little physical disturbance of the water in the wells as possible. Note that dedicated tubing may be suspended in the well during water-level measurements. A round of water level measurements shall be taken on the day prior to sample collection for use in contouring a synoptic water level event

(Table 3). Water level measurements shall also be collected during sampling and recorded on the Monitoring Well Sampling Log located in Appendix A.

4.3 Sampling Procedures

4.3.1 Equipment Calibration

Some equipment to be used during the LTM event will require periodic calibration to ensure optimum performance, including the photoionization detector (PID), YSI 600XL (or suitable alternative) water quality meter, and turbidimeter. This equipment will be calibrated in accordance with manufacturer’s instructions before its initial use at the site and at the beginning of each work day thereafter. The equipment calibration also will be checked at the conclusion of each work day.

Calibrations will be documented in log books or on log sheets.

4.3.2 Low-Flow Well Purging

Each groundwater monitoring well will be purged in accordance with the USEPA Region 1

Guidance Document titled Low Stress (low-flow) Purging and Sampling Procedure for the

Collection of Ground Water Samples from Monitoring Wells (USEPA, Region 1, 2010), included as Appendix B. The goal of low-flow purging and sampling is to remove stagnant water from the well and collect representative samples at near ambient conditions. Dedicated and non-dedicated variable speed submersible bladder pumps along with peristaltic pumps will be used to purge the wells. Tubing for the dedicated wells will be Teflon-lined.

A properly calibrated water quality parameter probe will be fitted into the flow-through cell provided with the…