Final Optimization Plan for U.S. Army Soldier Systems Center (Sep 2018).pdf

Final Optimization Plan

For U.S. Army Soldier Systems Center

Natick, Massachusetts

Prepared for

United States Army Environmental Command

Northeast Environmental Services and Support Division 2450 Connell Road, Bldg. 2264

JBSA Ft Sam Houston, TX 78234-7664

Prepared by:

Plexus Scientific Corporation 5510 Cherokee Avenue, Suite 350

Alexandria, VA 22312

Contract W91ZLK-13-D-0010

Delivery Order 0004

September 2018

U. S. Army Natick Soldier System Center, Natick, Massachusetts i

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 PURPOSE

2.0 SITE DESCRIPTION AND CONCEPTUAL SITE MODEL

2.1 GEOLOGY

2.2 HYDROGEOLOGY

2.3 CONTAMINANTS OF CONCERN

2.4 MONITORED NATURAL ATTENUATION (MNA) POTENTIAL

3.0 CURRENT GROUNDWATER REMEDIATION APPROACH

4.0 ARIEM BUILDING AREA ALTERNATIVE REMEDY

4.1 PERIODIC SLUG VOLUME REMOVAL ACTIONS

5.0 OPTIMIZATION OF THE GWETS

5.1 EXTRACTION WELL REHABILITATION

5.2 EXTRACTION WELL ATTAINMENT EVALUATIONS

5.2.1 Extraction Well EW-5

5.2.2 Extraction Well MW-40BR

5.3 PUMPING STRATEGY

5.3.1 T-25 Area

5.3.2 Buildings 22 and 36 Area

5.3.3 Buildings 63, 2, and 45 Area

5.3.4 ARIEM Building Area

5.4 INDIVIDUAL COMPONENTS

6.0 OPTIMIZATION OF THE 1,4-DIOXANE PRE-TREATMENT SYSTEM (PTS)

6.1 SYSTEM CONDITION

6.2 EXTRACTION WELL EW-4 FLOW RE-ROUTING

7.0 IMPLEMENTATION

8.0 REFERENCES

ii

TABLES

Table 1 Groundwater MNA Parameter Analytical Results Table 2 Soil MNA Parameter Analytical Results Table 3 Optimized Extraction Well Design Pumping Rates Table 4 1,4-Dioxane Groundwater Analytical Results

FIGURES

Figure 1 Site Layout, Natick Soldier Systems Center Figure 2 Interpreted Deep Overburden Piezometric Surface – Event 73 Figure 3 Distribution of PCE in Groundwater Figure 4 Distribution of TCE in Groundwater Figure 5 Distribution of 1,4-Dioxane in Groundwater Figure 6 Distribution of Primary COCs in Groundwater Figure 7 GWETS Instrumentation Diagram Figure 8 1,4-Dioxane PTS Instrumentation Diagram Figure 9 Proposed New Extraction Wells and Pipe Routing Figure 10 Optimized Particle Traces for T-25 Area Figure 11 Optimized Particle Traces for Buildings 22 and 36 Area Figure 12 Optimized Particle Traces for Buildings 63, 2, and 45 Area Figure 13 Modeled Distribution of TCE with Optimization, Bldgs 63, 2, 45 Area, 10 Years Figure 14 Modeled Distribution of TCE without Optimization, Bldgs 63, 2, 45 Area, 10 Years Figure 15 Optimized Particle Traces for ARIEM Building Area Figure 16 Modeled Distribution of TCE with Optimization, ARIEM Bldg Area, Six Years

APPENDICES

Appendix A Calibration Forms Appendix B Low Flow Groundwater Purging and Sampling Forms Appendix C Groundwater Sample Analysis Laboratory Reports iii

LIST OF ACRONYMS AND ABBREVIATIONS

µg/L micrograms per liter ADL Arthur D. Little AOP Advanced Oxidation Process ARIEM Army Research Institute of Environmental Medicine bgs below ground surface COCs Contaminants of Concern ECC Environmental Chemical Corporation ESD Explanation of Significant Differences FPGS Former Proposed Gymnasium Site ft feet or foot gpm gallons per minutes GW Groundwater GWETS Groundwater Extraction and Treatment System ICF ICF International, Inc.

LGAC Liquid-Phase Granular Activated Carbon LTM Long-Term Monitoring MCL Maximum Contaminant Level MCP Massachusetts Contingency Plan MNA Monitored Natural Attenuation NSSC Natick Soldier Systems Center O&M Operations and Maintenance PCE Tetrachloroethene PLC Programmable Logic Controller Plexus Plexus Scientific Corporation PTS Pre-Treatment System PVC polyvinyl chloride RAOs Remedial Action Objectives ROD Record of Decision SCADA Supervisory Control and Data Acquisition TCE Trichloroethene TCZ Target Capture Zone TOC Total Organic Carbon UCL Upper Confidence Limit UFP-QAPP Uniform Federal Policy - Quality Assurance Project Plan USEPA United States Environmental Protection Agency UV Ultraviolet VGAC Vapor-phase Granular Activated Carbon WSW Water Supply Well

1.0 INTRODUCTION

Plexus Scientific Corporation (Plexus) has been awarded Delivery Order 0004 under contract number W91ZLK-13-D-0010, with the Department of the Army, U.S. Army Mission and Installation Contracting Command to provide environmental remediation services for groundwater remediation at U. S. Army Natick Soldier Systems Center (NSSC) in Natick, Massachusetts.

This Optimization Plan builds on the optimization investigation results and recommendations as presented in the Technical Memorandum: Evaluation of Data from the 2016-2017 Optimization Investigation (“Optimization Investigation Tech Memo”; Plexus, 2017a) to recommend specific alternative technologies, remedy upgrades, and additions at the following four groundwater treatment areas:

T-25 Area, which requires extraction well rehabilitation;

Buildings 22 and 36 Area, which requires extraction well rehabilitation, and at which two extraction wells can be taken offline;

Buildings 63, 2, and 45 Area, which requires extraction well rehabilitation, upgrade or replacement of a pre-treatment system (PTS), re-routing of flow through a PTS, the installation of additional extraction wells, and adjustment of design pumping rates; and

U.S. Army Research Institute of Environmental Medicine (ARIEM) Building Area, which requires implementation of an alternative remedial technology, which will include installing additional extraction wells and setting design pumping rates.

Additionally, the Groundwater Extraction and Treatment System (GWETS), which services each of the above treatment areas, requires upgrades to and replacements of various individual components.

The Optimization Plan field activities (specifically, the collection of 1,4-dioxane samples in the Buildings 63, 2, and 45 Area) were performed in accordance with the Uniform Federal Policy – Quality Assurance Project Plan (UFP-QAPP; Plexus, 2017b). Otherwise, this Optimization Plan utilizes analytical results from the optimization investigation (Plexus, 2017a) and the Fall 2016 semi-annual groundwater monitoring event (Event 73; Plexus, 2017c).

1.1 Purpose

As documented in the Optimization Investigation Tech Memo (Plexus, 2017a), the GWETS is starting to provide diminishing returns. The reduction of the GWETS effectiveness is due to multiple factors that are related to the decrease of contaminant concentrations in groundwater, the reliability of the system, and the ability of the GWETS to sustain yields in extraction wells. The Optimization Investigation Tech Memo (Plexus, 2017a) identified those factors and areas of the current remedy that require an updated strategy to optimize the remedial approach and minimize the time to achieve site closure, along with recommendations towards meeting those optimization goals. This Optimization Plan presents specific technologies and approaches that, once implemented, will meet the recommendations presented in the Optimization Investigation Tech Memo (Plexus, 2017a).

2.0 SITE DESCRIPTION AND CONCEPTUAL SITE MODEL

NSSC is located approximately 17 miles west-southwest of Boston in the Town of Natick, Massachusetts. NSSC is a research facility that occupies approximately 74 acres on the eastern shore of the South Pond of Lake Cochituate (Figure 1).

NSSC, formerly called the Quartermaster Research and Engineering Command and subsequently the U.S. Army Natick Research and Development Command, has been a permanent U.S. Army installation since October 1954. NSSC’s mission includes research and development activities in food engineering, food service, clothing, equipment, materials engineering, and aero-mechanical engineering.

Previous investigations at NSSC have focused on characterizing physical conditions and contaminant distribution at several locations or sites within NSSC. These sites consist of: the T- 25 Area, the Water Supply Well (WSW) Site, the Former Proposed Gymnasium Site (FPGS); the Boiler Plant Area; the Buildings 22 and 36 Area; the Buildings 63, 2, and 45 Area; and the ARIEM Building Area (Figure 1). The primary Contaminants of Concern (COCs) are tetrachloroethene (PCE), trichloroethene (TCE), and 1,4-dioxane. A summary of previous monitoring events is presented in the Groundwater Monitoring Event 73 and 2016 GWETS Annual Report (Plexus, 2017c).

The Record of Decision (ROD) for the T-25 Area (Arthur D. Little [ADL], 2001) specified the following Remedial Action Objectives (RAOs):

Prevent contamination in the groundwater, above federal and state drinking water standards, from migrating outside of the T-25 Area toward off-facility receptors;

Prevent any potential exposure to groundwater beneath the T-25 area and off-facility with contaminant concentrations in excess of federal and state drinking water standards;

Restore aquifer to drinking water standards within a reasonable time frame; and, Monitor potential future migration of groundwater contamination to verify that elevated concentrations decrease over time.

An Explanation of Significant Differences (ESD; Environmental Chemical Corporation, LLC.

[ECC], 2013) was later developed to expand application of the T-25 Area RAOs to additional areas at NSSC, including the Buildings 22 and 36 Area; the Buildings 63, 2 and 45 Area; and the ARIEM Building Area.

NSSC is located in a Zone 2 aquifer and is located approximately 2,500 feet (ft) southeast of the Town of Natick’s Springvale Municipal Water Supply Well Field.

2.1 Geology

The geology at the facility consists predominantly of fill and reworked native soils underlain by glaciolacustrine, lacustrine, and glacial till deposits. Surficial soils are comprised of primarily well-graded sands. The surficial soils are underlain by poorly graded, very-fine to fine grained sands which are embedded with thin layers of silty sand and sandy silt. A layer of grey clayey silt and silt underlies the sands (MACTEC Engineering and Consulting, Inc., 2008).

Soil boring observations have noted a transition to poorly graded sands and gravels below the grey clayey silt in the southern portion of the Buildings 22 and 36 Area that continues south into the Building 63, 2, and 45 Area. Along the eastern shoreline, adjacent to Pegan Cove, a subsurface layer of peat has been observed in soil borings and excavations. Logs of borings advanced during the 2017 optimization investigation were consistent with the known descriptions of, and the heterogeneity of, the previously described site soil formations (Plexus, 2017a).

Bedrock is not exposed at NSSC, but does outcrop on the eastern shore of South Pond of Lake Cochituate near Pegan Brook. Historically, w ell borings from the three study areas have noted the bedrock is composed of granodiorite/hornblende gabbro, which is consistent with the regional bedrock geology.

2.2 Hydrogeology

NSSC is located within the Lake Cochituate drainage basin, which encompasses approximately

17.7 square miles. The main hydrogeologic feature at NSSC and the surrounding area is the South Pond of Lake Cochituate. The South Pond of Lake Cochituate occupies 0.9 square miles, flows northward to the Middle Pond, and through to North Pond of Lake Cochituate. The North Pond drains via the Cochituate Brook into the Sudbury River.

Groundwater in the unconsolidated soils at the Installation is divided into two aquifer intervals:

the unconfined water table aquifer, or “A” interval, and the locally semi-confined, deeper overburden aquifer, or “B” interval. The water table ranges in depth from 0 to 28 ft below ground surface (bgs).

Figure 2 illustrates the interpreted groundwater flow conditions for the deep overburden aquifer (“B” interval) across the NSSC while the GWETS is in operation. Deeper overburden groundwater appears to move from east to west beneath NSSC, discharging to the South Pond of Lake Cochituate with local variations beneath the eastern bay and the central and southern portion of the installation. The influence of groundwater pumping is apparent in Figure 2 as cone-of-depression distortions of the piezometric contours in the vicinity of extraction wells.

Based on the current data, all impacted groundwater is found entirely within the locally semi-confined, deeper overburden aquifer, or “B” interval, and no contamination is present in the unconfined water table aquifer, or “A” interval. The average hydraulic conductivity rates in the “B” interval estimated during the 2017 optimization investigation (Plexus, 2017a) ranged from

0.45 to 1.87 ft/day across the installation, which is consistent with previous capture zone model input values and the known descriptions of, and heterogeneity of, the screened soil formations.

2.3 Contaminants of Concern

PCE, TCE, and, 1,4-dioxane are the primary COCs in groundwater at NSSC. Concentrations of COCs are compared to U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) and the Massachusetts Contingency Plan (MCP) Groundwater (GW)-1 criteria.

The applicable screening criteria for the primary COCs are as follows:

PCE: MCL of 5 micrograms per liter (µg/L)

TCE: MCL of 5 µg/L

1,4-Dioxane: MCP GW-1 of 0.3 µg/L

The current extents of the PCE, TCE, and 1,4-dioxane plumes, based on the results of both Event 73 (Plexus, 2017c) and the Optimization Investigation, are illustrated in Figure 3, Figure 4, and Figure 5, respectively. Figure 6 presents the areas in which COCs exceed clean-up levels; these are considered the Target Capture Zones (TCZs) in the capture model analysis.

T-25 Area: PCE and TCE are the primary COCs, where the highest concentrations are 7.7 µg/L for PCE (MW-96B-4) and 21 µg/L for TCE (MW-88B-HP2).

Buildings 22 and 36 Area: PCE is the primary COC, where the highest concentration is 22.3 µg/L

(EW-8).

Buildings 63, 2, and 45 Area: TCE and 1,4-dioxane are the primary COCs, where the highest concentrations are 155 µg/L for TCE (TMW-6; 136 µg/L in duplicate sample) and 3.4 µg/L for 1,4-dioxane (MW-160A-2).

ARIEM Building Area: TCE is the primary COC, where the highest concentration is 28.2 µg/L

(MW125-2).

The Boiler Plant Area, FPGS, and NSSC WSW Site do not have exceedances of primary COCs and are therefore not discussed further in this Optimization Plan.

2.4 Monitored Natural Attenuation (MNA) Potential

A secondary objective of the optimization investigation was to better understand the Monitored Natural Attenuation (MNA) potential within the impacted areas. Towards that goal, groundwater samples were collected from monitoring wells TMW-3, TMW-6, TMW-7, MW-182B-4, MW- 37B-HP2, MW96B-4, and EW-7 and analyzed for MNA parameters iron, manganese, sulfate, nitrite, nitrate, and chloride; and soil samples were collected from borings TMW-3, TMW-6, TMW-7, and MW-182B-4 and analyzed for total organic carbon (TOC). The analytical results from this sampling event were presented in the Optimization Investigation Tech Memo (Plexus, 2017a); the groundwater and soil results are re-presented in Table 1 and Table 2, respectively, for ease of reference.

As presented in Table 1, and supported by stabilized purge parameters from Event 73 (Plexus, 2017c), groundwater at NSSC is well oxygenated, providing for an aerobic and oxidizing environment that is not favorable to reductive dechlorination, the preferred natural biodegradation pathway for PCE and TCE. The elevated concentrations of anions and the high ratio of nitrate to nitrite, given the acidic nature of the groundwater, as well as the absence of PCE degradation daughter products, support this interpretation of the geochemical environment of site groundwater and its role in potential natural biodegradation of PCE and TCE. The soil at NSSC is rich in organic carbon, which both preferably retards contaminant transport via sorption and could serve as a favorable electron donor for biodegradation in a reducing environment. These findings are consistent with those of the ICF International, Inc. (ICF) bioremediation investigation at the T-25 Area (ICF, 2011). Therefore, it is concluded that, while MNA may be effective following a driven shift in redox conditions, the current groundwater geochemical environment is not conducive to efficient biodegradation of PCE or TCE. However, when other remedies are found to no longer be efficient, as is expected to be the scenario when concentrations of primary COCs reach asymptotic levels near the clean-up goals (after a period of successful active remediation), MNA is anticipated to be the selected final remedial alternative implemented prior to achieving site closure.

3.0 CURRENT GROUNDWATER REMEDIATION APPROACH

The current groundwater remedial approach at NSSC is extraction and ex situ treatment of impacted groundwater via a GWETS and localized slug volume removal activities at selected impacted wells beyond the treatment system radii of influence.

The GWETS within Building 94 has been in operation since 1997 and currently consists of the following components, as illustrated on Figure 7:

Fourteen (14) groundwater extraction wells (two offline);

Coliform PTS (offline)

Equalization tank;

Particulate Filters;

Air stripper (offline);

Granulated activated carbon to treat vapor discharge from the stripper (vapor phase granular activated carbon [VGAC]; offline); and, Granulated activated carbon for primary treatment of groundwater (Liquid-Phase Granular Activated Carbon [LGAC]).

Water is extracted from the following 12 extractions wells screened in the “B” interval (Figure 1):

T-25 Area: MW-90B-4, MW-94B-4, MW-95B-4, MW-96B-4, and MW-39B-HP4

Buildings 22 and 36 Area: EW-5, EW-6, EW-7 and EW-8

Buildings 63, 2, and 45 Area: EW-3 and EW-4

Boiler Plant Area: MW-40BR.

These extraction wells are screened just above the top of a low-hydraulic-conductivity silt layer that prevents deeper migration of the contaminant plumes.

An ex situ wellhead PTS was installed in 2008 to treat 1,4-dioxane in groundwater from extraction wells EW-3 and EW-4 in the Buildings 63, 2, and 45 Area. This 1,4-Dioxane PTS consists of a Fenton’s Reagent Advanced Oxidation Process (AOP), as illustrated on Figure 8. After treatment for 1,4-dioxane, this groundwater is pumped to the GWETS.

In 2013, another PTS was installed, this one for MW-96B-4, following discovery of suspended solids and coliform in MW-96B-4, apparently caused by a sanitary sewer line leak discovered and repaired in the Spring of 2012. In August 2016, the PTS was taken off-line after multiple quarters with no detections of coliform in the influent samples. Groundwater extracted from MW-96B-4 is currently pumped directly to the GWETS. Quarterly sampling of MW-96B-4 for coliform continues, and the PTS remains in “stand-by” mode, ready to be placed back in service with minimal effort if necessary.

Groundwater capture zone assessments have been used to evaluate the effectiveness of the GWETS in capturing the interpreted plume extents above screening criteria based on extraction well locations and operating pumping rates. The most recent capture zone assessment, based on early 2017 pumping rates, was presented in the Optimization Investigation Tech Memo (Plexus, 2017a). In general, the models have suggested that contaminant plumes in groundwater have been completely captured at the T-25 Area and the Buildings 22 and 36 Area, and were largely captured at the Buildings 63, 2, and 45 Area.

Areas of impacted groundwater outside of the GWETS capture zone, specifically in the ARIEM Building Area and at MW-114B-2 near the eastern shoreline in the parking lot east of Building 1, have been treated by periodic slug volume removal actions. Historically, the slug removal activities have been successful at monitoring wells MW114B-2 and MW165B-2, but not at MW-181B-2 (which was supplemented by nearby MW-182B-4 as part of the optimization investigation). Low well yields due to hydrogeological constraints minimize the effectiveness of periodic slug volume removal actions near these wells; therefore, it was recommended that remedial alternatives be considered for this area (Plexus, 2017a).

A Long-Term Monitoring (LTM) program (ECC, 2011) is in place to characterize the nature and extent of groundwater contamination at NSSC and the surrounding area, to evaluate trends in contaminant concentrations over time, to characterize the local and regional groundwater flow conditions, to assess the effectiveness of the GWETS, and to collect data for use in designing possible future remedial actions. The most recent annual sampling and analysis event for which data are available was conducted in November 2016—Monitoring Event 73 (Plexus, 2017c).

Results from the optimization investigation groundwater sampling effort supplemented the Monitoring Event 73 data (Plexus, 2017a). In general, concentrations of primary COCs are declining and the lateral extents of the COC plumes are decreasing.

The GWETS is monitored weekly and sampled monthly (with an expanded analyte list on a quarterly basis) to continuously evaluate the system’s efficiency and effectiveness, to continuously implement micro-optimizations, to assure compliance with discharge limits, and again to collect data for use in designing possible future remedial actions. The treatment of groundwater at the GWETS from the Buildings 22 and 36 Area and the Buildings 63, 2, and 45 Area has been successful and continues to remove the bulk of contaminant mass from groundwater. However, as noted in the Introduction above, the GWETS is starting to provide diminishing returns, especially in the Buildings 63, 2, and 45 Area.

4.0 ARIEM BUILDING AREA ALTERNATIVE REMEDY

Following review of the results of the optimization investigation, it was concluded that low well yields due to hydrogeological constraints minimize the effectiveness of periodic slug volume removal actions in the ARIEM Building Area; therefore, it was recommended that remedial alternatives be considered for this area (Plexus, 2017a). Regular slug volume removal activities will be continued until a remedial alternative is implemented.

Due to regulatory requirements, the selected remedial alternative is required to capture both impacted groundwater and any materials potentially injected for in situ treatment of contaminants.

Given that, the preliminary evaluation of alternative remedial technologies to be potentially implemented in the ARIEM Building Area found that extraction of groundwater must be either the selected remedial alternative or a component thereof. Evaluated alternative remedial technologies included in situ chemical oxidation (ISCO), in situ chemical reduction (ISCR), and enhanced reductive bioremediation. Given the relatively low contaminant concentrations, unfavorable existing groundwater geochemical environment, and low “B” interval aquifer permeability, the evaluated in situ remedial alternatives were found to not be efficient options. Ultimately, due to the requirement to achieve capture, following review of the particle trace model for this area under the optimal extraction scenario, as presented and discussed in Section 5.3.4, and given the presence of the existing GWETS infrastructure, it was found that constant groundwater extraction alone will be most efficient to achieve site cleanup goals in a reasonable timeframe. Therefore, constant groundwater extraction and treatment is the recommended remedy for the ARIEM Building Area.

Specifically, it is recommended that two new extraction wells be installed, one near MW125B-2 (identified as EW-11) and one between MW-182B-4 and MW165B-2 (identified as EW-12), and that existing monitoring wells MW-182B-4 and MW165B-2 be converted to extraction wells.

Refer to Figure 9 for the locations of proposed new and converted extraction wells, as well as the proposed routing of piping from these extraction wells to the GWETS. The existing GWETS infrastructure has an influent flow capacity of 160 gallons per minute (gpm), well above its current and anticipated future rate (approximately 87 gpm), and able to accept the anticipated 4 gpm of extracted groundwater from the ARIEM Building Area.

As discussed in Section 2.4, and as is the scenario at the T-25 Area, Buildings 22 and 36 Area, and Buildings 63, 2, and 45 Area, following a period of successful active remediation, it is anticipated that the recommended groundwater extraction and treatment remedy at the ARIEM Building Area will reach asymptotic conditions as concentrations of TCE near the MCL, at which time a shift to MNA, as a final remedy, is expected to be recommended. Prior to this change in remedy, it is anticipated that a detailed MNA evaluation will be conducted to determine which, if any, supplemental nutrient, culture, or geochemical adjusting augmentations would increase MNA effectiveness to achieve site closure more efficiently.

Specific details of the selected alternative remedy are presented in Section 5.3.4 below.

4.1 Periodic Slug Volume Removal Actions

Regular slug volume removal activities will be continued until MW-182B-4, MW165B-2, and EW-11 are operating as GWETS extraction wells.

Periodic extraction of contaminated groundwater from the newly installed extraction well MW- 182B-4 and existing well MW165B-2 (Figure 1), both in the ARIEM Building Area and outside the capture zones for the GWETS, will occur on a quarterly basis. If groundwater results indicate a rebound of contamination at MW-114B-2, then this well will be added to the periodic slug volume removal scope of work.

The periodic slug volumes will be removed by “pulse pumping” via vacuum extraction. The vacuum-enhanced extraction will maximize groundwater recovery. By increasing the pressure gradient at the extraction well, groundwater flow rates, radius of influence, and overall effectiveness of the remedy will be maximized. Extracted groundwater will be transported to Building 94 where the water will be processed in the GWETS.

Subsequent removals will target the same volumes and frequency that have been previously established (ECC, 2015). Target slug volumes of contaminated groundwater to be removed from MW-182B-4 and MW165B-2 combined will be approximately 960 gallons every quarterly event (480 gallons from each well). It is planned to extract groundwater from these two wells at an approximate rate of four gallons per minute, simultaneously from both wells, for four hours.

However, historically, MW-181B-2 and MW-182B-4 have provided low yields, so actual extracted volumes may be closer to 500 gallons total over those four hours.

Performance monitoring of the remedy will consist of sampling groundwater at MW182B-4 and MW165B-2 prior to and one week after each slug removal event. Groundwater samples will be collected in accordance with USEPA Region I Low Stress (low-flow) Purging and Sampling Procedure (USEPA, 2010) and analyzed for PCE and TCE by Method 8260B.

5.0 OPTIMIZATION OF THE GWETS

Following review of the results and conclusions of the optimization investigation, in which the factors affecting GWETS effectiveness and areas of the current remedy that require and updated strategy were identified, the Optimization Investigation Tech Memo (Plexus, 2017a) presented recommendations toward optimizing the remedial approach and minimizing the time to achieve site closure. The following subsections detail the approaches to implement those recommendations.

The Operations and Maintenance (O&M) Manual, including all drawings (layout, piping and instrumentation, and electrical) will be updated to capture the system upgrades, equipment changes, and recent changes in site conditions. Of note, this update will include new traffic rating requirements for future and repaired extraction well vaults.

5.1 Extraction Well Rehabilitation

Precipitation of metals, primarily iron, has fouled extraction well screens and sand packs, reducing sustainable extraction rates. In order to re-establish and maintain complete capture at Buildings 22 and 36 Area, to increase efficiency at the T-25 Area, and to increase capture at the Buildings 63, 2, and 45 Area, the Optimization Investigation Tech Memo (Plexus, 2017a) found that existing extraction wells MW-90B-4, MW-96B-4, EW-3, EW-4, EW-6, EW-7, and EW-8 specifically need be rehabilitated to attain improved pumping rates. However, it is recommended that all extraction wells be rehabilitated regularly, at least once every two years. Therefore, all currently operating extraction wells will initially be rehabilitated to restore all recovery capacities to a baseline that can be used for future evaluations of well-specific rehabilitation schedules.

Pantonite acid will be introduced to each extraction well and the water will be actively surged, catalyzing reactions with the metal oxides fouling the well. The surge water, containing the acid, will then be extracted from the well by the GWETS, and the condition of the recovered surge water will be observed and documented prior to GWETS treatment. Excessively turbid and discolored water is indicative of a highly fouled well. For extraction wells at which these conditions are observed, the acidization process will be repeated until recovered water is indicative of a well screen and sand pack free of significant fouling. It is anticipated that the initial acidization effort will take one day per extraction well.

Additional acidization events will be planned based on the observed initial condition of each well.

It is expected that extraction wells most afflicted by fouling will be rehabilitated twice per year, and the other extraction wells will be rehabilitated on an annual or biennial basis. The rehabilitation schedule will be reevaluated annually.

Other rehabilitation technologies, such as rehabilitation using carbon dioxide, were evaluated.

Pantonite acid was selected based on cost and product availability. Although carbon dioxide rehabilitation has been shown effective in several situations, it is less commonly utilized due to the above reasons—availability and cost efficiency (usually evaluated on a cost per foot of screen basis).

5.2 Extraction Well Attainment Evaluations

Based on modeling simulations presented in the Optimization Investigation Tech Memo (Plexus, 2017a), it was recommended that extraction wells EW-5 and MW-40BR be evaluated for shutdown, as they no longer contribute to capture of TCZs and have not had exceedances of COCs in the past five years.

5.2.1 Extraction Well EW-5

Extraction well EW-5 was installed and connected to the GWETS in August 2007 to capture PCE -5 since November 2010.

Therefore, it is recommended that extraction well EW-5 be taken offline.

To monitoring for rebound of PCE in the EW-5 TCZ, following shutdown of extraction well EW- 5, monitoring wells MW-156A-2 and MW-157A-2 will be temporarily added to the LTM program, to be sampled semi-annually for VOCs, and the sampling frequency for monitoring well MW105A-2 will temporarily be increased to semi-annual.

Following four rounds of sampling MW-156A-2, MW-157A-2, EW-5, and MW105A-2 as part of the LTM program, the groundwater remedial action in the EW-5 TCZ will be evaluated in accordance with the USEPA’s Groundwater Completion Strategy (USEPA, 2014a).

5.2.2 Extraction Well MW-40BR

Extraction Well MW-40BR was installed and connected to the GWETS in August 2010 to address dieldrin persisting in groundwater. Dieldrin has not exceeded the MCP GW-1 at MW- 40BR since May 2011. Therefore, it is recommended that extraction well MW-40BR be taken offline.

To monitoring for rebound of dieldrin in the MW-40BR TCZ, following shutdown of extraction well MW-40BR, monitoring wells MW-40BR and MW-168B-2 will continue to be sampled for pesticides semi-annually as part of the LTM program.

Following four rounds of sampling MW-40BR and MW-168B-2, the groundwater remedial action in the MW-40BR TCZ will be evaluated in accordance with the USEPA’s Groundwater Completion Strategy (USEPA, 2014a).

5.3 Pumping Strategy

Particle trace and fate and transport modeling simulations were run to optimize the pumping strategy at each area, including adjusting design pumping rates of existing extraction wells and adding extraction wells to the system where optimal. During simulation runs, the maximum allowable extraction flow rate for each well was set based on historic (i.e., sustainable through rehabilitation) flow rates, to ensure that adjusted design pumping rates are attainable. Table 3 presents optimized design pumping rates by extraction well; total optimized flow rate for the GWETS will be 86.65 gpm, well below the system’s 160 gpm design capacity influent flow rate.

5.3.1 T-25 Area

Modeling efforts have shown that, after implementation of well rehabilitation activities as discussed in Section 5.1, the following pumping rates for existing extraction wells at the T-25 Area are sustainable and will be sufficient to maintain efficient capture of the TCZ, including impact near monitoring well MW-208B-HP2, while permitting a reasonable cleanup timeframe:

MW-39B-HP4 15 gpm

MW-90B-4 20 gpm

MW-94B-4 10 gpm

MW-95B-4 24 gpm

MW-96B-4 5 gpm

Under this approach, the total extraction rate from the T-25 Area will be 74 gpm. Figure 10 presents the contaminant particle traces under this pumping scenario; all of the 422 particles seeded are captured.

5.3.2 Buildings 22 and 36 Area

Modeling efforts have shown that, after implementation of well rehabilitation activities, as discussed in Section 5.1, and after taking extraction wells EW-5 and MW-40BR offline, as discussed in Section 5.2 above, the following pumping rates for existing extraction wells at the Buildings 22 and 36 Area are sustainable and will be sufficient to maintain efficient capture of the TCZ while permitting a reasonable cleanup timeframe:

EW-6 1 gpm

EW-7 1.75 gpm

EW-8 1.9 gpm

Under this approach, the total extraction rate from the Buildings 22 and 36 Area will be 4.65 gpm.

Figure 11 presents the contaminant particle traces under this pumping scenario; of the 107 particles seeded, only one escapes capture.

5.3.3 Buildings 63, 2, and 45 Area

The particle trace modeling presented for the Buildings 63, 2, and 45 Area in the Optimization Investigation Tech Memo (Plexus, 2017a) found that, due to declining pumping capacities and the bulk of the remaining contaminant mass being downgradient of existing extraction wells, most particles seeded were not captured and therefore that additional extraction wells are required to re-attain capture of the TCZ. Figure 9 presents the locations of two proposed new extraction wells (identified as EW-9 and EW-10), as well as the conceptual proposed routing of piping from these extraction wells to the GWETS; actual proposed routing will be refined during the design phase.

It is anticipated that all piping from extraction wells in the Buildings 63, 2, and 45 Area will be routed through the 1,4-Dioxane PTS shed to allow for the flow from each individual well to be pre-treated or not by the PTS, as needed.

Based on the results of the optimization investigation (Plexus, 2017a), groundwater extracted from both new extraction wells EW-9 and EW-10 is not expected to, but may, have concentrations of 1,4-dioxane above the MCP GW-1. Therefore, all new piping for the Buildings 63, 2, and 45 Area will be routed through the 1,4-Dioxane PTS shed, so that groundwater extracted from the new wells can be pre-treated for 1,4-dioxane as needed prior to treatment by the GWETS.

Both proposed new extraction wells EW-9 and EW-10 will be constructed of four-inch-diameter, schedule 40 polyvinyl chloride (PVC) casing and screened within the “B” aquifer interval.

Extraction well EW-9 will be installed to approximately 30 ft bgs, with a 15-foot screened interval;

EW-10 will be installed to approximately 29 ft bgs, with a 20-foot screened interval.

Modeling efforts have shown that, using the two online, existing extraction wells (EW-3 and EW-

4) and these two new extraction wells, the network will be sufficient to maintain efficient capture of the TCZ while permitting a reasonable cleanup timeframe. Optimization simulations of the pumping strategy indicated that the design pumping rates for wells should be as follows, by extraction well:

EW-3 1 gpm

EW-4 1 gpm

EW-9 1 gpm

EW-10 1 gpm

Under this approach, the total extraction rate from the Buildings 63, 2, and 45 Area will be 4 gpm.

Figure 12 presents the contaminant particle traces under this pumping scenario; of the 96 particles seeded, only three escape capture. The expected cleanup timeframe under this optimized extraction design, based on fate and transport modeling, is approximately 20 years from now (circa 2037).

However, given the results of the fate and transport modeling, it is expected that, following an initial period effective and efficient treatment, the extraction remedy will reach asymptotic conditions in 10 years, after which it is anticipated that MNA is will be implemented until cleanup levels are achieved, as discussed in Section 2.4. Figure 13 and Figure 14 present the anticipated aerial extent of the TCE plume at the Buildings 63, 2, and 45 Area after 10 years, based on fate and transport modeling, with and without the optimization measures proposed in this Optimization Plan, respectively, for comparison. For point of reference, without implementing the optimization measure, the fate and transport model forecasts that concentrations of TCE will continue to exceed the MCL at the Buildings 63, 2, and 45 Area for greater than 50 years.

5.3.4 ARIEM Building Area

As discussed in Section 4.0, the recommended alternative remedy for the ARIEM Building Area is continuous groundwater extraction utilizing two new extraction wells, one near MW125B-2 (identified as EW-11) and one between MW-182B-4 and MW165B-2 (identified as EW-12), as well as existing wells MW-182B-4 and MW165B-2 converted to extraction wells, each tied into the existing GWETS. Figure 9 presents the locations of proposed new and converted extraction wells, as well as the conceptual proposed routing of piping from these extraction wells to the GWETS; actual proposed routing will be refined during the design phase.

Extraction wells EW-11 and EW-12 will be constructed of four-inch-diameter, schedule 40 PVC casing, installed to approximately 40 ft bgs and 37 ft bgs, respectively, both in the “B” aquifer interval with a 15-foot screen.

Modeling efforts have shown that, using these four extraction wells, the network will be sufficient to maintain efficient capture of the TCZ while permitting a reasonable cleanup timeframe.

Optimization simulations of the pumping strategy indicated that the design pumping rates for wells should be as follows, by extraction well:

MW-182B-4 1 gpm

MW165B-2 1 gpm

EW-11 1 gpm

EW-12 1 gpm

Under this approach, the total extraction rate from the ARIEM Building Area will be 4 gpm.

Figure 15 presents the contaminant particle traces under this pumping scenario; all particles seeded are captured. The expected cleanup timeframe under this optimized extraction design, based on fate and transport modeling, is approximately 6.25 years from now (circa 2024).

However, given the results of the fate and transport modeling, it is expected that, following an initial period effective and efficient treatment, the extraction remedy will reach asymptotic conditions in six years, after which it is anticipated that MNA will be implemented until cleanup levels are achieved, as discussed in Section 2.4. Figure 16 presents the anticipated aerial extent of the TCE plume at the ARIEM Building Area after six years, based on fate and transport modeling, given implementation of the optimization measures proposed in this Optimization Plan.

5.4 Individual Components

Upgrades to individual components of the existing GWETS will be completed to allow for increased flow from additional extraction wells and to replace obsolete control software, computer, and hardware. These upgrades will include:

Replacement of the existing Programmable Logic Controller (PLC) with a new one that has readily available replacement parts;

Upgrade of the existing Wonderware Supervisory Control and Data Acquisition (SCADA) program to the most recent version;

Replacement of the existing control computer with one that is able to efficiently run the most recent version of the Wonderware SCADA program;

Installation of two multi-bag filter housings to permit increased flow through the system;

Installation of a higher-pressure transfer pump to allow for full-capacity use of the bag filters and allow for the increased flow through the system;

Relocation of the MW-96B-4 electrical pull box out of the roadway to avoid future issues related to snow plowing;

Repair the damaged electrical pull box near extraction well EW-3;

Add controls to allow for automatic switching between bag filter units, increasing uptime;

and

Replace all flowmeters, and add one at MW-39B-HP2, so that all extraction wells have dedicated meters for measurement of precise flow rates at each location.

6.0 OPTIMIZATION OF THE 1,4-DIOXANE PRE-TREATMENT

SYSTEM (PTS)

Following review of the results and conclusions of the optimization investigation, in which the factors affecting the 1,4-Dioxane PTS effectiveness were identified, the Optimization Investigation Tech Memo (Plexus, 2017a) presented recommendations toward optimizing the 1,4-dioxane remedial approach. The following subsections present the results of 1,4-dioxane groundwater sampling at select monitoring wells around extraction well EW-4 and detail the approaches to implement the related Optimization Investigation Tech Memo recommendations.

6.1 System Condition

The existing 1,4-Dioxane PTS utilizes Fenton’s chemistry to reduce levels of 1,4-dioxane to below the permitted limits. This technology is dependent on the level of iron in the water, introduction of acid to lower the pH to the ideal reaction pH, and addition of hydrogen peroxide. If the iron levels in groundwater change with the introduction of additional wells, as discussed in Section

5.3.3 above, it may be necessary to introduce iron into the groundwater stream to achieve effective treatment.

Other methods of treating 1,4-dioxane include ozone or ultraviolet (UV) light AOPs. Both technologies also create free hydroxyl radicals that destroy 1,4-dioxane. Based on knowledge of the groundwater at the Buildings 63, 2, and 45 Area, utilizing of the ozone AOP is recommended.

High levels of iron from extraction well EW-3 would rapidly foul the UV bulbs, requiring greater energy requirements and maintenance. Although the oxidation reactions within an ozone PTS may also precipitate metals, simple bag filtration and routine cleaning of the reactor will ensure no significant impact to treatment. The ozone process will still require hydrogen peroxide, as the existing PTS does, but will not require pH adjustment. Controlled introduce of ozone allows for a more controlled reaction, providing greater reliability for treatment of 1,4-dioxane to below discharge limits.

Prior to final design of the ozone PTS, a bench scale test will be conducted to determine specific ozone dosing, and therefore hydrogen peroxide dosing, air compressor size, oxygen sieve size, and other O&M requirements.

Installation of the ozone PTS will require demolition and disposal of the existing equipment, installation of the PTS, system piping, electrical connections, and piping of new extraction wells through the remote building. The ozone PTS is anticipated to fit within the existing treatment shed, although electrical capacity supplied to the shed may need to be increased. The system and utility infrastructure requirements will be determined during the “sizing” of the PTS, which will be based on the results of the bench scale test.

6.2 Extraction Well EW-4 Flow Re-routing

The Optimization Investigation Tech Memo (Plexus, 2017a) recommended that an evaluation be made regarding potentially re-routing flow from extraction well EW-4 directly to the GWETS (without first passing through the 1,4-Dioxane PTS) based on 1,4-dioxane concentrations in the area surrounding EW-4. Groundwater at monitoring wells EW-4, PZ144-2, MW159A-2, and MW103A*4 (refer to Figure 1 for well locations) was low-flow sampled on October 26, 2017, and submitted for analysis of 1,4-dioxane by Method 8270 SIM by ALS Environmental of Middletown, Pennsylvania. Refer to Appendix A for equipment calibration forms, and to Appendix B for groundwater purging and sampling sheets.

Refer to Table 4 for the analytical results by monitoring well, and to Appendix C for the laboratory analytical report for these groundwater samples. All four groundwater samples (EW-4, PZ144-2, MW159A-2, and MW103A*4) were non-detect for 1,4-dioxane, each with limits of detection of 0.039 less. The MCP GW-1 standard for 1,4-

Therefore, it is recommended that flow from extraction well EW-4 be re-routed directly to the GWETS. This re-routing will minimize the dilution of 1,4-dioxane concentrations in groundwater extracted from extraction well EW-3 prior to 1,4-dioxane pre-treatment. The effect will be reduction of flow through the 1,4-Dioxane PTS, increasing mass-removal efficiencies and minimizing the impact of maintenance issues that may occur at the PTS.

7.0 IMPLEMENTATION

Following approval of the Optimization Plan recommendations, the U.S. Army will prepare and submit an ESD to incorporate the optimized remedy and facilitate implementation of the alternative remedy at the ARIEM Building Area. Concurrently, an LTM Plan update will be prepared and submitted.

Following acceptance of the ESD, an Optimization Work Plan will be prepared and submitted.

The Optimization Work Plan will be implemented and subsequent performance monitoring will show that the remedy operating at designed. The O&M Manual will be updated to reflect implementation of the Optimization Plan and Optimization Work Plan. Completion of the Optimization Work Plan will be documented in an Optimization Completion Report. Once the remedy is operating as designed, the program will return to just periodic system O&M and LTM.

It is anticipated that the ESD and Optimization Work Plan will both be completed and approved in calendar year 2018, the remedy will achieve designed operation in calendar year 2019, and system O&M and LTM will be conducted until further optimization efforts (specifically, the shift to MNA at an Area) is recommended.

8.0 REFERENCES

Arthur D. Little (ADL), 2001. Record of Decision, T-25 Area Ground Water (Operable Unit 1), U.S. Army Soldier Systems Center, Natick, Massachusetts. April.

Environmental Chemical Corporation, LLC. (ECC), 2011. “October 2010 Draft Final Long Term Monitoring Plan Amendment.” U.S. Army Natick Soldier Systems Center. Natick, Massachusetts. February 28.

ECC, 2013. Explanation of Significant Differences T-25 Area Groundwater (Operable Unit 1), U.S. Army Soldier Systems Center, Natick, Massachusetts. March.

ECC, 2015. Draft Operations and Maintenance Manual. OU-1 T-25 Area; Buildings 22 and 36 Area; and the Buildings 63, 2, and 45 Area Groundwater Treatment System and 1,4-Dioxane Treatment System. U.S. Army Natick Soldier Systems Center, Natick, Massachusetts. June.

ICF International, Inc. (ICF), 2011. Ground Water Remedial Optimization Study at the T-25 Area, Final Summary of Event 09 HRC-A Injection Ground Water Monitoring. Memorandum.

August 16.

MACTEC Engineering and Consulting, Inc., 2008. Final Buildings 22 and 36 Feasibility Study Report. Soldier Systems Center, Natick, Massachusetts. March 18.

Plexus Scientific Corporation (Plexus), 2017a. Final Technical Memorandum: Evaluation of Data from 2016-2017 Optimization Investigation. U.S. Army Soldier Systems Center, Natick, Massachusetts. August.

Plexus, 2017b. Final Uniform Federal Policy – Quality Assurance Project Plan (UFP-QAPP) for Environmental Remediation Services. U.S. Army Soldier Systems Center, Natick, Massachusetts. May.

Plexus, 2017c. Final Groundwater Monitoring Event 73 and 2016 Groundwater Extraction and Treatment System Annual Report. U.S. Army Soldier Systems Center, Natick, Massachusetts.

June.

U.S. Environmental Protection Agency (USEPA), 2010. Region I Low Stress (low flow) Purging and Sampling Procedure for the Collection of Ground Water Samples from Monitoring Wells; Revision 3 – January 2010.

USEPA, 2014a. Groundwater Remedy Completion Strategy, “Moving Forward with the End in Mind.” Office of Solid Waste and Emergency Response. OSWER Directive 9200.2-144.

May.

USEPA, 2014b. Groundwater Statistics Tool. Office of Solid Waste and Emergency Response.

August.

TABLES

FIGURES

APPENDIX A

Calibration Forms

APPENDIX B

Low Flow Groundwater Purging and Sampling Forms

APPENDIX C

Groundwater Sample Analysis Laboratory Reports

Report ID: 2272333 - 11/14/2017 Page 1 of 9

Mr. Nathan Farrar Plexus Scientific 5510 Cherokee Avenue Suite 350 Alexandria, VA 22312

November 14, 2017

Dear Mr. Farrar:

Certificate of Analysis

Project Name:

Purchase Order:

Workorder:

Workorder ID:

2272333Natick Sampling

PFD054|Natick Sampling

CC: Liz Heness , Mr. Richard Souza , Mr. Mike Brewin

This page is included as part of the Analytical Report and must be retained as a permanent record thereof. Project Coordinator

Ms. Susan J Scherer

Enclosed are the analytical results for samples received by the laboratory on Saturday, October 28, 2017.

The ALS Environmental laboratory in Middletown, Pennsylvania is a National Environmental Laboratory Accreditation Program (NELAP) accredited laboratory and as such, certifies that all applicable test results meet the requirements of NELAP.

If you have any questions regarding this certificate of analysis, please contact Ms. Susan J Scherer (Project Coordinator) at (717) 944-5541.

Analyses were performed according to our laboratory’s NELAP-approved quality assurance program and any applicable state requirements. The test results meet requirements of the current NELAP standards or state requirements, where applicable. For a specific list of accredited analytes, refer to the certifications section of the ALS website at www.alsglobal.com/en/Our-Services/Life-Sciences/Environmental/Downloads.

This laboratory report may not be reproduced, except in full, without the written approval of ALS Environmental.

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DL ID - 57306, QC…