Final 2017 Third Five Year Review Report U.S. Army Soldier Systems Center, Natick MA (APR 2017).pdf

FINAL 2017 THIRD FIVE-YEAR REVIEW REPORT

For

U.S. Army Natick Soldier Systems Center

Natick, Massachusetts

Prepared for:

U.S. Army Natick Soldier Systems Center

Natick, Massachusetts and

U.S. Army Environmental Command, Fort Sam Houston, Texas

Prepared by:

U.S. Army Corps of Engineers

New England District

Concord, Massachusetts

April 2017

FINAL 2017 THIRD FIVE= YEAR REVIEW REPORT

For

U.Se Army Natick Soldier Systems Center

Na tick, Massachusetts

Prepared for:

U.S. Army Natick Soldier Systems Center

Natick, Massachusetts

Ryan L. Raymond Lieutenant Colonel, U.S. Army Garrison Commander and

U.S. Army Environmental Command, Fort Sam Houston, Texas

Prepared by:

U.S. Army Corps of Engineers

New England District

Concord, Massachusetts

April2017

APR 0 4 2017

Date

TABLE OF CONTENTS

SECTION PAGE

EXECUTIVE SUMMARY……………………………………………………………………… E-i

1.0 INTRODUCTION……………………………………………………………………….. 1

2.0 SITE CHRONOLOGY…………………………………………………………………… 3

3.0 SITE BACKGROUND…………………………………………………………………… 4

3.1 Physical Characteristics and Land Use…………………………………………... 4

3.2 History of Contamination…………………………………………………………. 5

3.3 Initial Response Action…………………………………………………………… 6

3.4 Basis for Taking Action…………………………………………………………... 6

4.0 REMEDIAL ACTIONS…………………………………………………………………. 7

4.1 Remedial Action Objectives……………………………………………………... 7

4.2 Remedy Selection………………………………………………………………... 8

4.3 Remedy Implementation………………………………………………………… 9

4.3.1 Groundwater Extraction and Treatment System

4.3.2 Operation and Maintenance of Treatment Plant…………………………. 10

4.3.3 Long-Term Groundwater Monitoring …………………………………… 11

4.3.4 Monitored Natural Attenuation………………………………………….. 12

4.3.5 Institutional Controls ………………………

4.3.6 Operation and Maintenance of the Springvale Plant…………………….. 12

5.0 PROGRESS SINCE THE LAST FIVE-YEAR REVIEW………………………………. 12

6.0 FIVE-YEAR REVIEW PROCESS……………………………………………………… 12

6.1 Administrative Components of the Five-Year Review Process………………

6.2 Community Notification and Involvement……………………………………… 13

6.3 Document Review……………………………………………………………….. 13

6.3.1 Review of ARARs………………………………………………………. 13

6.3.2 Review of Toxicity Values and Exposure Assumptions………………… 14

6.4 Data Review……………………………………………………………………... 15

6.4.1 Overview of Groundwater Plume……………………………………….. 15

6.4.2 Groundwater Analysis and Trends………………………………………. 15

6.4.3 Groundwater Extraction, Capture and Mass Removal………………….. 19

6.4.4 Groundwater Treatment System………………………………………

6.4.5 Vapor Intrusion………………………………………………………….. 22

6.4.6 Institutional Controls……………………………………………………. 22

6.4.7 Interviews………………………………………………………………... 22

6.4.8 Site Inspection …………………………………………………………… 23

7.0 TECHNICAL ASSESSMENT…………………………………………………………… 23

7.1 Question A……………………………………………………………………….. 23

7.2 Question B……………………………………………………………………….. 25

7.3 Question C……………………………………………………………………….. 26

7.4 Technical Assessment Summary………………………………..……………….. 26

8.0 ISSUES…………………………………………………………………………………... 26

9.0 RECOMMENDATIONS AND FOLLOW-UP ACTIONS……………………………

9.1 Other Findings……………………………………………………………………. 27

10.0 PROTECTIVENESS STATEMENT…………………………………………………….. 28

11.0 NEXT REVIEW……………………………………………………..…………………

12.0 REFERENCES…………………………………………………………………………

TABLES

1 Five-Year Review Summary Form

2 Summary of Operable Units

3 Chronology of Events, Operable Unit 1 (Groundwater)

4 T-25 Area Groundwater Cleanup Levels Established in Record of Decision

5 Changes Affecting Chemical-Specific ARARs for Groundwater

6 Summary of Data Trend Results for the Five-Year Review Period

7 Issues, Operable Unit 1 (Groundwater)

8 Recommendations and Follow-Up Actions, Operable Unit 1 (Groundwater)

FIGURES

1 Natick Soilder Systems Center Site Location Map

2 Natick Soldier Systems Center Site Layout

3 PCE and TCE Areas of Groundwater Contamination

(2013 Explanation of Signficant Differences)

4 Geologic Cross Section A-A’

5 Interpreted Water Table Piezometric Surface

6 Interpreted Deep Overburden Piezometric Suface

7 GWET System Components

8 1,4-Dioxane Pre-treatment System Components

9 Distribution of TCE and PCE from Groundwater Fall 2011 (Event 63)

10 Distriubtion of PCE and TCE in Groundwater Fall 2015 (Event 71)

11 Capture Zone Analysis for T-25

12 Capture Zone Analysis for Buildings 22 and 36

13 Capture Zone Analys for Buildings 63, 2 and 45

14 Cummulative Mass of PCE and TCE Removed

15 Monthly Mass Removal Rates PCE, TCE, and Dioxane

16 Cumulative Mass of 1,4-Dioxane Removed

APPENDICES

A Institutional Control Certifications

B Community Involvement

C Operable Unit 1 ARARs

D Changes in Toxicity Values and Exposure Factors

E Groundwater Analtyical Data

F Time Series Plots for Chemicals of Concern

G Mann-Kendall/Thiel Sen Slope Trend Plots for PCE, TCE, and 1,4-Dioxane

H Extraction Well Flow Rates and Mass Removal Rates

I Site Interviews

J Site Inspection

K Responses to Regulatory Agency Comments

ABBREVIATIONS AND ACRONYMS

ARARs Applicable or Relevant and Appropriate Requirements

ARIEM U.S. Army Research Institute for Environmental Medicine

Army U.S. Army bgs below ground surface

CERCLA Comprehensive Environmental Response, Compensation and Liability Act

CFR Code of Federal Regulations

COC contaminants of concern

CVOC chlorinated volatile organic compound

DDT dichlorodiphenyltrichloroethane

DoD Department of Defense

ECC Environmental Chemical Corporation

ERA ecological risk assessment

ESD Explanation of Significant Differences

ETA Engineering Technology Associates, Inc.

FFA Federal Facility Agreement

FFS focused feasibility study

FPGS Former Proposed Gymnasium Site (FPGS)

FR Federal Register

FS feasibility study ft feet ft/day feet per day

FYR Five-Year Review gpm gallons per minute

GWETS groundwater extraction and treatment system

HHRA human health risk assessment

HI hazard index

IC institutional controls

LGAC liquid phase granular activated carbon

LTM long-term monitoring

LTMP Long-Term Monitoring Plan µg/L micrograms per liter

MassDEP Massachusetts Department of Environmental Protection

MCL maximum contaminant level

MCP Massachusetts Contingency Plan mg/L milligrams per liter msl mean sea level

NAE North Atlantic Division, New England District

NCP National Oil and Hazardous Substances Contingency Plan

NERI New England Research Institute

NFA No Further Action

NPL National Priorities List

NSSC Natick Soldier Systems Center

O&M operations and maintenance

OU operable unit

PCB polychlorinated bipheynls

PCE tetrachloroethene

PP Proposed Plan ppb parts per billion ppm parts per million ppmv parts per million by volume

RAB Restoration Advisory Board

RAGS Risk Assessment Guidance for Superfund

RAO remedial action objectives

RCRA Resource Conservation and Recovery Act

RI remedial investigation

ROD Record of Decision

SARA Superfund Amendment and Reauthorization Act

SSI Supplemental Site Investigation

SVOC semi-volatile organic compound

TBC To Be Considered

TCE trichloroethene/trichloroethylene

TS treatability study

USACE U.S. Army Corps of Engineers

USAEC U.S. Army Environmental Command

U.S. EPA U.S. Environmental Protection Agency

USTHAMA U.S. Army Toxic and Hazardous Materials Agency

UU/UE unlimited use/unrestricted exposure

VI vapor intrusion

VGAC vapor phase granular activated carbon

VOC volatile organic compound

2017 Third Five-Year Review Report

Natick Soldier Systems Center i

EXECUTIVE SUMMARY

This is the third five-year review (FYR) report for the U.S. Army Natick Soldier Systems Center (NSSC) and was prepared in accordance with the Comprehensive Environmental Response, Compensation, and

Liability Act (CERCLA) § 121, and the National Oil and Hazardous Substances Pollution Contingency

Plan (NCP) 40 Code of Federal Regulations (CFR) § 300.430(f)(4)(ii).

The purpose of the five-year review is to determine whether the remedy is protective of human health and the environment, and whether the remedy is functioning as intended. A FYR is required by statute when hazardous substances, pollutants or contaminants remain at the site above levels that allow for unlimited use and unrestricted exposure (UU/UE). NSSC was listed on the National Priorities List (NPL) as a result of groundwater contamination found in the T-25 Area and its location relative to the Natick

Springvale Municipal Water Supply Well Field.

NSSC is an active research and testing facility owned and operated by the federal government through the Department of the Army. NSSC is located approximately 17 miles west-southwest of Boston in

Natick, MA (Figure 1). NSSC has been a permanent Army installation since October 1954. The facility is on a peninsula and is bounded by Lake Cochituate to the south, east and west and by a residential area to the north and northwest. A security fence currently surrounds NSSC. The groundwater beneath the

Site is designated as a Zone II wellhead protection area for the Town of Natick’s Springvale municipal water supply well field.

Operations at the NSSC include or have included research and development activities in food engineering, food service, clothing, equipment, materials, engineering and aero-mechanical engineering.

Some of these operations used solvents including tetrachloroethene (PCE) and trichloroethene (TCE), which resulted in releases to the environment in the past.

NSSC is divided into four operable units (OUs) for environmental cleanup.

OU1 - Groundwater (Facility-wide and T-25 Area)

OU2 - Sediment

OU3 - Soil Removal Actions (Former Proposed Gym Site and Building T62 and T68 Area)

OU4 – Soil Removal Actions (Former Buildings 13 and 14 Area, Boiler Plant Area, and T-25 Area)

A preliminary close out report prepared by the United States Environmental Protection Agency (U.S.

EPA) in December 2014 (U.S. EPA, 2014b) concluded that response actions have been completed for the

OUs. The response actions at OU2 included the removal of 4,395 cubic yards of PCB-contaminated sediment from three hotspots in Lake Cochituate (Pegan Cove) to unrestricted reuse levels (ICF

International, 2010b). OU3 and OU4 included several areas where soil removal actions were performed to unrestricted exposure levels (MATEC, 2007a and ICF International, 2008).

For OU1, the subject of this FYR, the Army continues to operate a groundwater treatment plant to meet remedial action objectives and performance metrics specified in the 2001 Record of Decision (ROD)

(U.S. Army, 2001) and 2013 Explanation of Significant Differences (ESD) (U.S. Army, 2013) for the

T-25 Area Ground Water (OU1).

OU1 includes all of the contaminated groundwater at NSSC. Site locations (current and historical) are ii shown on Figure 2. The areas of remaining PCE and TCE contamination are shown on Figure 3.

The remedy for OU1 as specified in the 2001 ROD included the following components to address the primary chemical of concerns (PCE and TCE). Secondary contaminants of concern were also identified as they resulted in increased site risk.

Groundwater extraction with air stripping and carbon absorption

Long-term monitoring

Institutional controls

Monitored natural attenuation

The remedial action objectives specified in the 2001 ROD are:

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.

OU1 was later expanded as specified in the 2013 ESD to include:

Increased flow to the T-25 Area Treatment Facility from the Buildings 22 and 36 Area, the

Buildings 63, 2 and 45 Area, the MW114B-2 Area, and the Building 42, U.S. Army Research

Institute for Environmental Medicine (ARIEM) Area

Removal of the air stripper from the treatment train and the vapor phase carbon;

Lowering the ROD cleanup level for manganese to correspond to the U.S. EPA health advisory for manganese

Adding a clean-up level for 1,4-dioxane in accordance with Massachusetts Department of

Environmental (MassDEP) Drinking Water Guidelines

Currently, groundwater remedial activities include: operation of extraction wells; groundwater treatment through the T-25 Area Treatment System located at Building 94; well-head pre-treatment for 1,4-dioxane in the Buildings 63, 2 and 45 area; periodic slug volume removal from wells outside the capture zones in two areas (the MW114B-2 and the ARIEM Building Areas); long-term monitoring for COCs (spring and fall sampling events) and land-use control verification to ensure no potable water supply wells are installed on or off-facility in a prescribed area.

The FYR team as part of this evaluation: (1) reviewed documents prepared during the five-year review period including the annual reports describing the operation of the treatment system; (2) evaluated data from the long-term monitoring program and treatment operations; (3) conducted a site inspection to assess the treatment systems and remedy components; and (4) completed interviews with individuals involved in the cleanup. The results of this review are summarized in the report and overall conclusions are discussed below.

The remedy at OU1 currently protects human health and the environment. PCE and TCE concentrations in groundwater continue to decline, and the extraction wells prevent migration of these contaminants.

iii

Isolated locations of PCE and TCE in groundwater outside the plume capture zone are pumped at the well locations and trucked to the T-25 Treatment System at Building 94. Institutional controls as documented by the annual institutional control certifications prepared by the U.S. Army and Town of

Natick during the FYR continue to prohibit the use or installation of private drinking water wells within or near the plume, where the restriction is applied. However, in order for the remedy to be protective in the long-term, the following action needs to be taken:

1. Optimize the slug volume removal process or evaluate and implement alternative methods to address the localized area of trichloroethene contamination in the ARIEM Building Area; TCE remains above the cleanup level in this area following two years of periodic slug volume removal.

This FYR also includes recommendations that do not affect overall protectiveness of the remedy but may enhance the evaluation and performance of the groundwater extraction system. These recommendations are included in Section 9.1.

The Five-Year Review Summary Form is included as Table 1.

iv

Table 1

Five -Year Review Summary Form

SITE IDENTIFICATION

Site Name: U.S. Army Natick Soldier Systems Center

EPA ID: MA1210020631

Region: 1 State: MA City/County: Natick/Middlesex

SITE STATUS

NPL Status: NPL

Multiple OUs?

Yes

Has the site achieved construction completion?

Yes

REVIEW STATUS

Lead agency: Other Federal Agency

If “Other Federal Agency” was selected above, enter Agency name: U.S. Army

Author name (Federal or State Project Manager): U.S. Army Corps of Engineers

Author affiliation: Department of Defense

Review period: September 1, 2016 – November 4, 2016

Date of site inspection: U.S. Army Corps of Engineers Inspection (September 7, 2016) and U.S.

EPA Inspection (October 6, 2016)

Type of review: Policy

Review number: 3

Triggering action date April 12, 2012

Due date (five years after triggering action date): April 12, 2017 v

Table 1 (Continued)

Issues and Recommendations Identified in the Five-Year Review:

Operable Unit 1 –

Groundwater

Issue Category: Remedy Performance

Periodic slug volume removal in ARIEM Building Area has not reduced

TCE concentrations to below MCLs.

Recommendations:

Optimize the slug volume removal process or evaluate and implement alternative methods to address the localized area of trichloroethene (TCE) contamination in the ARIEM Building Area.

Affect Current

Protectiveness

Affect Future

Protectiveness

Implementing

Party

Oversight Party Milestone Date

No Yes Army EPA and

MassDEP

August 2017

Protectiveness Statement

Groundwater

Operable Unit 1

Protectiveness Determination:

Short-term Protective

Addendum Due Date

(if applicable): N/A

Protectiveness Statement:

The remedy at OU1 currently protects human health and the environment. PCE and TCE concentrations in groundwater continue to decline and the groundwater extraction wells prevent migration of these contaminants. Isolated locations of PCE and TCE in groundwater outside the plume capture zone are pumped at the well locations and trucked to the T-25 Treatment System at Building 94. Institutional controls as documented by the annual institutional control certifications prepared by the U.S. Army and

Town of Natick during the FYR continue to prohibit the use or installation of private drinking water wells within or near the plume, where the restriction is applied. However, in order for the remedy to be protective in the long-term, the following action needs to be taken:

1. Optimize the slug volume removal process or evaluate and implement alternative methods to address the localized area of trichloroethene contamination in the ARIEM Building Area; TCE remains above the cleanup level in this area following two years of periodic slug volume removal.

Other Comments:

None.

vi

Sitewide Protectiveness Statement

Protectiveness Determination:

Protective

Addendum Due Date

If applicable: N/A

Protectiveness Statement:

The remedy at the Site currently protects human health and the environment because the groundwater exposure is mitigated through institutional controls and the extraction wells contain the plume from moving to the Town of Natick’s Water Supply Wells. However, in order for the remedy to be protective in the long-term, the Army needs to optimize the slug volume removal process or evaluate and implement alternative methods to address the localized areas of TCE contamination in the ARIEM Building Area.

1.0 INTRODUCTION

This five-year review (FYR) evaluates the performance of the groundwater remedy (Operable Unit [OU]

1) implemented at the Natick Soldier Systems Center (NSSC) in Natick, Massachusetts. This is the third five-year review for NSSC.

The purpose of this FYR is to determine whether the groundwater remedy is protective of human health and the environment, and whether the remedy is functioning as intended. A FYR is required by statute

(at least once every five years) when hazardous substances, pollutants or contaminants remain at the site above levels that allow for unlimited use and unrestricted exposure (UU/UE).

The FYR was conducted by the United States Army Corps of Engineers New England District on behalf of the U.S. Army in accordance with the Comprehensive Environmental Response, Compensation, and

Liability Act (CERCLA) §121(c) and the National Oil and Hazardous Substances Pollution

Contingency Plan (National Contingency Plan, NCP) as described below.

CERCLA § 121c, as amended, states:

“If the President selects a remedial action that results in any hazardous substances, pollutants, or contaminants remaining at the site, the President shall review such remedial action no less often than each five years after the initiation of such remedial action to assure that human health and the environment are being protected by the remedial action being implemented. In addition, if upon such review it is the judgment of the President that action is appropriate at such site in accordance with section

[104] or [106], the President shall take or require such action. The President shall report to the Congress a list of facilities for which such review is required, the results of all such reviews, and any actions taken as a result of such reviews.”

The U.S. Environmental Protection Agency (U.S. EPA) interpreted this requirement further in the NCP;

40 CFR § 300.430(f)(4)(ii) states:

“If a remedial action is selected that results in hazardous substances, pollutants, or contaminants remaining at the site above levels that allow for unlimited use and unrestricted exposure, the lead agency shall review such action no less often than every five years after the initiation of the selected remedial action.”

Management of the contamination at the facility was divided into four operable units. These OUs are listed in Table 2. A preliminary close out report prepared by U.S. EPA in December 2014 (U.S. EPA, 2014b) concluded that response actions have been completed for the operable units. The response actions at OU2 included the removal of 4,395 cubic yards of PCB-contaminated sediment from three hotspots in Lake Cochituate (Pegan Cove) to unrestricted reuse levels (ICF International, 2010b). OU3 and OU4 included several areas where soil removal actions were performed to unrestricted exposure levels (MATEC, 2007 and ICF International, 2008).

At OU1, remaining long-term actions include operation and maintenance of the groundwater treatment system and annual reporting until performance metrics specified in the 2001 ROD are met.

Table 2

Summary of Operable Units, Natick Soldier Systems Center

Operable Unit (OU) Name Army Designation Decision Document/Status

OU1 – Groundwater

(Facility Wide including T-25 Area, Buildings 22 and 36 Area, Buildings 63, 2 and 45 Area, Monitoring Well 11B-2 Area and

ARIEM Building Area)

NRDEC-05 (T-25

Groundwater Area)

NRDEC-11 (Post Drinking

Water Wells)

NRDEC-16 (Buildings 22 and 36)

Record of Decision (U.S. Army, 2001)

Explanation of Significant Differences

(U.S. Army, 2013)

Continued operation of treatment system and long-term monitoring;

FYR policy review required until unlimited use/unrestricted exposure

(UU/UE) achieved.

OU2 – Sediment

Sediment at transitory shelter at T-

25 and Buildings 2 and 45 Parking

Lot Outfall. Soil and sediment at

Building 5, PCB Contamination

Site.

NRDEC-07 (Transitory

Shelter Area of T-25)

NRDEC-10 (Building 5

PCB Contamination Site and Pad)

NRDEC-17 (Building 2 and 45 Parking Lot Outfall)

Record of Decision (ICF International, 2009)

Response action complete; conditions allow for UU/UE; no FYR required.

OU3 – Soil

(Soil Removal Action Former

Proposed Gym Site and Building

T62 and T68 Area)

NRDEC-06 (Former

Proposed Gym Site)

NRDEC-03 (Buildings 62 and 68)

Record of Decision (MATEC, 2007a)

Response action complete; conditions allow for UU/UE; no FYR required.

OU4 – Soil

(Soil Removal Actions Former

Buildings 13 and 14 Areas, Boiler

Plant Area, and T-25 Area)

NRDEC-12 (Building 13)

NRDEC-09 (Building 14)

NRDEC-14 (Boiler Plant

Area)

NRDEC-16 (Storage

Area/Chlordane

Contamination)

Record of Decision (ICF International, 2008)

Response action complete; conditions allow for UU/UE; no FYR required.

2.0 SITE CHRONLOGY

The site chronology presented in Table 3 includes the dates of major events associated with actions related to the investigation and cleanup of groundwater OU1 at NSSC.

Table 3

Chronology of Events for Operable Unit 1 (Groundwater), Natick Soldier Systems Center

Date Event

1980 Installation Assessment – U.S. Army Toxic and Hazardous Materials Agency

(USATHMA, 1980).

1989-1990 New England Research Institute (NERI) performed soil gas surveys in the T-25

Area (NERI, 1989 and 1990).

1991-1992 Expanded Site Investigations by Dames and Moore in the T-25 Area resulting in the installation of monitoring wells (Dames and Moore, 1991).

1993/1994 Phase I RI performed in the T-25 Area (Arthur D. Little, Inc., 1995) to evaluate nature, extent and source of contamination.

1994 NSSC (formerly Natick Army Laboratory Research and Development Center) listed on NPL as a result of groundwater contamination found in the T-25 Area and its location relative to the Natick Springvale Municipal Water Supply Well

Field.

1995/1996 Phase II RI performed in the T-25 Area by Arthur D. Little (Arthur D. Little, Inc., 1998). Source of PCE and TCE not determined.

1995-1997 Engineering Technical Associates, Inc. (ETA), developed a groundwater flow and transport model to support evaluation of contaminant transport at NSSC. The model was used to estimate potential T-25 Area groundwater cleanup times (ETA, 1997).

1997 First extraction wells on-line in T-25 Area to contain contaminants.

1999 Final Focused Feasibility Study/ Treatability Study (FFS/TS) for T-25 Area

Groundwater (Arthur D. Little, Inc., 1999).

1999 Proposed Plan and Public meeting detailing the Army's preferred remedial alternative (a pump-and-treat system) for the T-25 Area (U.S. Army, 1999).

2001 Final ROD selecting T-25 Groundwater Area remedy (U.S. Army 2001).

2002 MassDEP approved the Town of Natick Zone II delineation for Springvale and

Evergreen supply wells. The groundwater beneath the entire NSSC facility was included within the delineated Zone II.

2002-2003 Updated groundwater flow and transport model for the T-25 Area

(HydroGeologic, Inc., 2002).

2004 T-25 Groundwater Treatment System Operations and Maintenance Manual (ICF

Consulting, 2004b); subsequent updates in 2011 and 2015.

2005 Sampling begins for 1,4-dioxane; 1,4-dioxane detected in the Building 63, 2 and

45 Area.

2006-2010 Ground Water Remedial Optimization Study to evaluate the potential of in-situ biological enhancement to decrease tetrachloroethene (PCE) and trichloroethene

(TCE) concentrations in groundwater (ICF Consulting Services, 2010).

2007 First Five-Year Review (ICF International, 2007a)

2007 T-25 System in Building 94 begins receiving and treating groundwater from the

Buildings 2 and 36 Area and Buildings 63, 2, and 45 Area under Pilot Study for groundwater containment at Buildings 22 and 36 and Buildings 63, 2 and 45

(MACTEC, 2008a).

2008 An ex-situ wellhead treatment unit was installed to treat the groundwater from the new extraction wells in the Buildings 63, 2, and 45 Area to remove 1,4-dioxane.

Date Event

2009 Long Term Monitoring Plan for T-25 Area, Buildings 22 and 36 Area and

Buildings 63, 2 and 45 Area (Environmental Chemical Corporation (ECC), 2009).

2012 Second Five-Year Review (ECC and AMEC, 2012)

2012 ARIEM Building Investigation Report evaluating vapor intrusion pathway (ICF

International, 2012).

2013 Explanation of significant differences prepared by Army to document increasing flow to the Building 94 Area Treatment Facility from four other areas (Buildings

22 and 36 Area, the Buildings 63, 2 and 45 Area, the MW114B-2 Area, and the

ARIEM Building Area); removal of the air stripper from the treatment train;

lowered the cleanup level for manganese; and expanded clean-up level for 1,4-dioxane (U.S. Army, 2013).

2014 Preliminary Close Out Report prepared by U.S. EPA documenting that all construction activities at NSSC have been completed and no further response actions are anticipated for the site (U.S. EPA, 2014b).

2014 Draft Final Technical Memorandum on Remedial Actions for Small Plumes

Outside Capture Zone (ECC, 2014b).

2015 Slug Volume Removal Technical Memorandum documenting removal of CVOCs from the MW114B-2 Area, and the ARIEM Building Area (ECC, 2015c).

1996 -2016 Quarterly groundwater sampling reports and annual reports documenting groundwater sampling and operation and maintenance of the treatment system.

3.0 SITE BACKGROUND

NSSC is an active U.S. Army research and testing facility located approximately 17 miles west-southwest of Boston (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.

Environmental investigations began at NSSC in the 1980s. NSSC was added to the United States

Environmental Protection Agency’s National Priorities List (NPL) in May 1994 as a result of groundwater contamination found in the T-25 area and its location relative to the Town of Natick’s Springvale Municipal

Water Supply Well Field, which is located 2,500 feet to the northwest (Figure 1).

In August 2006, the U.S. Department of the Army and U.S. EPA entered into a Federal Facility

Agreement under CERCLA relating to the remedial investigation and cleanup of hazardous substances, pollutants, or contaminants at NSSC. The lead agency for sites at NSSC is the U.S. Department of the

Army, and the support agency is the U.S. EPA.

3.1 Physical Characteristics and Land Use

NSSC occupies 78-acres on a small peninsula extending from the eastern shoreline of Lake Cochituate

(Figure 1). NSSC is mostly covered with asphalt and buildings. Open, uncovered areas include a baseball field for employee use near the T-25 Groundwater Area and the unpaved perimeter road and embankment.

The facility is surrounded by a chain-link fence. The land use surrounding NSSC is residential.

The groundwater beneath the NSSC is designated as a Zone II wellhead protection area for the Town of

Natick’s Springvale municipal water supply well field (Figure 1).

Groundwater flow at NSSC occurs mainly in the glacially derived overburden soils and fractured portions of the bedrock. The overburden across the installation is comprised mainly of glacial outwash sediments and includes sand and gravel, fine to coarse sand, silty sand, and clayey silt as shown on the 2004 geologic cross section prepared by ICF International Consulting (Figure 4). Peat has also been found in soil borings advanced in the eastern portion of the site. The lithologic units are variable and appear to be laterally discontinuous. Bedrock is comprised of metamorphic and igneous rock, primarily granodiorite, and follows a regional trend of dipping to the west. Bedrock outcrops are visible along the eastern shore of the South

Pond of Lake Cochituate.

NSSC is located within the Lake Cochituate drainage basin, which encompasses approximately 17.7 square miles. The main hydrogeologic features at NSSC and the surrounding area include the South Pond of Lake

Cochituate and Fisk Pond. The South Pond of Lake Cochituate, which occupies approximately 0.9 square miles, flows northward to the Middle Pond and then North Pond of Lake Cochituate; the North Pond drains via the Cochituate Brook into the Sudbury River.

Unconsolidated materials at the site form two separate and distinct aquifers. The unconfined water table aquifer, or “A” interval, is monitored by wells screened in a zone between 5 and 35 feet below ground surface. The locally semi-confined, deeper overburden aquifer, or “B” interval, is monitored by wells screened in a zone between approximately 35 and 80 feet below ground surface.

In the shallow or A interval, there is a groundwater divide across the center of the installation. Flow from the groundwater divide radiates outward toward the South Pond of Lake Cochituate (Figure 5). To the east of the divide, groundwater appears to discharge to Pegan Cove, the shallow eastern bay of the South Pond of Lake Cochituate. To the north and west of the divide, water table groundwater flow is generally to the west-northwest.

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 central and southern portion of the installation (Figure 6).

3.2 History of Contamination

Historic uses of PCE and TCE, the primary COCs, have included; indoor and outdoor storage of chemicals;

laboratory research; clothing and textile research; drop-testing, and garage operations including spray painting, vehicle maintenance, metals and brush cleaning. However, in most cases the specific source of the PCE and TCE was not identified.

Investigations initially began in a drum storage area in the T-25 Area, where solvents had reportedly leaked but the source was not confirmed. In 1997, the T-25 groundwater treatment system began operation to both contain and treat groundwater in the T-25 Area (Arthur D. Little, Inc., 1995).

In addition to the T-25 Area, previous investigations at NSSC have focused on characterizing the contaminant distribution of PCE and TCE at other locations within NSSC (Figures 2 and 3). The current areas of groundwater contamination and suspected source of contamination are discussed below.

In the Buildings 22 and 36 Area, the primary site related contaminant is PCE in groundwater (Figures 2 and 3). The source of the PCE was inferred to be historic cleaning of kitchen drain grease trap within

Building 36. Additional information pertaining to history and contamination in this area can be found in the Final Buildings 22 and 36 Remedial Investigation Report (Harding ESE, 2005) and the Buildings 22 and 36 Feasibility Study Report (Harding ESE, 2008).

In the Buildings 63, 2, and 45 Area, formerly referred to as the Post Drinking Water Well Site, the primary site-related contaminant is TCE in groundwater. The suspected source of the release was historic leakage of heat transfer brine from the Building 2 climate control system into the unlined crawl space beneath

Building 2. In the 1980s, TCE use was discontinued, TCE storage tanks were removed, and the crawl space was lined with an impervious membrane. Additional information pertaining to the history and contamination in this area can be found in the Buildings 63, 2, and 45 Site Investigation Report (Harding

ESE, 2008).

The ARIEM Building Area is located approximately 100 feet east of Building 2 on the eastern side of the peninsula (Figures 2 and 3). TCE has been found exceeding the maximum contaminant level in a small triangular area north of the building. The source has not been determined. Further information regarding this contamination can be found in the ARIEM Building Investigation Report (ICF International, 2012).

The MW114B-2 Area is located directly east of Building 1 in the parking lot area adjacent to Pegan Cove

(Figure 3). This small area of groundwater contamination is defined by PCE contamination in only one well (MW114B-2). The source of PCE has not been determined. Further information regarding this contamination can be found in the Investigation Report MW-114B-2 Area (ICF International, 2010a).

At the Former Proposed Gymnasium Site, which was historically use as a helicopter landing pad; a petroleum, oil, and lubricant bladder test site; and a parking lot, the primary contaminant initially monitored was petroleum hydrocarbons (U.S. EPA, 2014b). In 2002, the Army conducted a time critical removal action in this area to address soil contaminants in particular benzene that were leaching to groundwater.

Approximately 1,233 tons of contaminated soil was excavated from a 40-by 40-by 10-foot deep area to meet unrestricted residential use standards. No further action was recommended at the site for soil per the

2007 ROD (MATEC, 2007a). While benzene was not detected at levels of concern in groundwater collected from a well installed in the soil excavation area, chlorinated compounds were observed (ICF

International, 2007a), and consequently groundwater wells in this area continue to be monitored as part of the OU1 Remedy. Additional soil removal actions were completed at the Former Proposed Gymnasium

Site in 2012 and 2014 to remove laboratory debris and soil found in the vicinity of the time critical removal action area. Following these soil removals, confirmation samples were collected to confirm that soil levels remaining were below the unrestricted residential use standards (U.S. EPA, 2014b).

The Boiler Plant Site (Building 19) was identified as a potential concern based on the former use of the basement in the building as a pesticide storage and mixing area. In 2001, Army completed a removal action the leach field adjacent to the building to the south. Approximately, 768 cubic yards of soil containing PAHs, PCBs and lead at concentrations exceeding MCP S1/GW-1 standards were removed and confirmation samples were collected to determine that the standards were met. In 2008, a no further action ROD was signed for the Site (ICF International, 2008). While SVOCs were found to be below drinking water criteria from wells sampled as part of the Phase II SI at the site, dieldrin, a pesticide, was detected sporadically above the MCP GW-1 criteria in Well MW-40B-2. While dieldrin was not identified as a COC in the ROD, it is monitored under the long-term monitoring program at this location.

3.3 Initial Response Action

Pre-ROD response actions included the installation and operation of the groundwater extraction at Building

94 at the T-25 Area in November 1997 to contain contaminant migration.

3.4 Basis for Taking Action

The basis for taking action at NSSC was the results of the human health risk assessment (HHRA) prepared during the Phase II RI (Arthur D. Little, Inc., 1998) in the T-25 Area. The HHRA evaluated the probability and magnitude of potential adverse human health risks from contaminants associated with the T-25 Area groundwater (Arthur D. Little, Inc., 1998) for the following scenarios:

Media Exposure Scenario Timeframe

Soil Facility employees using the ball field Current and future

Trespassers on the ball filed Current and future

Residents near the site potentially exposed to windblown dust from the ball field

Current and future

Construction workers in the T-25 Area Future

Groundwater Workers using site groundwater for industrial uses Future

Potential residential users of groundwater from the beneath the T-25 Area

Future

The HHRA determined that groundwater beneath the T-25 Area, resulted in estimated risks that exceeded the PCE and TCE drinking water standards and U.S. EPA's cancer target risk range of 10-4 to 10-6 and noncancer hazard index of 1 for future residential groundwater use and for dermal contact during future industrial use. PCE and TCE contributed the majority of the site-related risk from exposure to groundwater and were designated as primary COCs. In addition, six metals (chromium, lead, manganese, nickel, thallium, and vanadium), bis(2-ethylhexyl)phthalate, and dichlorodiphenyltrichloroethane (DDT), exceeded their respective drinking water standards and/or caused some increases in site-related risks. As described in the ROD, these chemicals were designated as secondary COCs, since it was unclear whether their presence was site related or attributable to either background conditions or turbidity resulting from the sampling technique (non-low flow procedures were used in the mid- to late-1990's when the RI was completed).

A Tier I ecological risk assessment (ERA) was conducted to assess the ecological impact and risks associated with the surface soil of the Phase II RI (Arthur D. Little, Inc., 1998). The Tier I ERA found no significant ecological risks for the surface soils in the T-25 Area. Ecological risks were not evaluated for the T-25 Area groundwater

The ROD concluded that a response action was necessary to protect public health or welfare from actual or threatened releases of pollutants or contaminants in groundwater.

4.0 REMEDIAL ACTIONS

The ROD for OU1 was signed in September 2001 documenting the cleanup decision for T-25 Groundwater

Area. In 2013, an ESD for OU1 was prepared to document changes from the original remedy.

4.1 Remedial Action Objectives (RAOs)

RAOs were developed for the T-25 Groundwater Area to aid in the development and screening of alternatives in the feasibility study.

The RAOs as specified in 2001 ROD are:

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.

Table 4 lists the groundwater COCs, cleanup levels and the basis for the cleanup levels as specified in the

ROD.

Table 4

T-25 Area Groundwater Cleanup Levels Established in 2001 Record of Decision

Chemical of Concern (COC) Cleanup Level (μg/L) Basis for Cleanup Level1

Primary COC

Tetrachloroethene 5 MCL

Trichloroethene 5 MCL

Secondary COC

Chromium 100 MCL

Lead 15 U.S. EPA Action Level

Manganese 1,700 U.S. EPA Region 9 Preliminary

Remediation Goal for Drinking Water

Nickel 100 MCL

Thallium 2 MCL

Vanadium 50 MCP

DDT 0.3 MCP

Bis(2-ethylhexyl) phthalate 6 MCL

Notes:

1MCL – Federal Safe Drinking Water Act, Maximum Contaminant Level 1MCP- Massachusetts Contingency Plan, Method GW-1 Standard ug/l = microgram per liter

4.2 Remedy Selection

The selected remedy for the T-25 Area in the feasibility study was Alternative 3: Groundwater Extraction with Air Stripping/Carbon Adsorption and Long-Term Monitoring, Institutional Controls, and Monitored

Natural Attenuation.

The original groundwater extraction and treatment system was constructed to contain T-25 Area groundwater within NSSC, while MNA was selected to address on-and off-site contamination not captured by the extraction and treatment system. Institutional controls were emplaced to prohibit the use of water for drinking water at the facility as well as an ordinance prohibiting installation of potable drinking wells near NSSC. An ESD was prepared in 2013 to include additional extraction of groundwater from the

Buildings 22 and 36 Area and the area near Buildings 63, 2 and 45 to reduce migration of contaminated groundwater to Lake Cochituate. Groundwater from these areas is piped through a buried force main and combined with extracted groundwater from the T-25 Area.

The 2013 ESD also included slug volume removal of contaminated groundwater from two localized areas outside of the capture zone of the extraction system to reduce migration to Pegan Cove. The two areas include the ARIEM Building Area (Building 42) and the parking lot area east of Building 1, referred to as the MW114B-2 Area.

The slug volume removal specified in the ESD for the MW114B-2 Area was 2,400 gallons every 3 months.

The slug volume removal specified in the ESD for the ARIEM Building Area at Wells MW165B-2 and

MW-181B-2 was 960 gallons every three months equally divided between the two wells. The ESD also specified that extraction well MW96B-4 be restarted for two years beginning in 2013 to reduce concentrations to below the PCE MCL. If contaminant volume is not reduced within two years, slug volume removal was to be initiated at that well.

Other changes specified in the ESD included:

Removal of the air stripper from the treatment train at the T-25 Treatment System

Establishing MassDEP’s revised drinking water guideline for 1,4-dioxane of 0.3 μg/L as a To Be

Considered criteria for treatment

Lowering the manganese cleanup goal specified in the ROD from 1,200 μg/L to 300 μg/L based on the current U.S. EPA health advisory

4.3 Remedy Implementation

The following subsections discuss the implementation of the remedy.

4.3.1 Groundwater Extraction and Treatment System

The Army completed construction of a groundwater extraction and treatment system (GWETS) in 1997 and began operation of the system as a pilot study in November of that year. The ROD was signed in 2001 to document the system, which was installed at Building 94. The system described in the ROD is installed in Building 94 and is referred to as T-25 Area Treatment System. The T-25 Area Treatment System continues to operate.

The GWETS currently includes the following major components (Figure 7):

Five extraction wells in the T-25 Area (MW-90B-4, MW-94B-4, MW-95B-4, MW-96B-4 and MW

39B HP4); four extraction wells in the Buildings 22 and 36 Area (EW-5, EW-6, EW-7 and EW 8);

two extraction wells in the Buildings 63, 2 and 45 Area (EW-3 and EW-4); and one extraction well in the Boiler Plant Area (MW-40BR)

Equalization tank

Particulate Filters

Air stripper (off-line since 2012)

Vapor-phase granulated activated carbon (VGAC) to treat vapor discharge from the stripper (off-line since 2012)

Liquid-phase granulated activated carbon (LGAC) to remove VOCs from the groundwater

A programmable logic controller controls the function of these treatment components. A detailed description of each of the treatment system's major components is presented in the Operation and

Maintenance (O&M) Manual (ECC, 2015a).

Since August 2007, the T-25 Area Treatment System, has also received and treated PCE and TCE contaminated groundwater extracted from the Buildings 22 and 36 Area and the Buildings 63, 2, and 45

Area. In August 2008, a small treatment unit was installed at the Buildings 63, 2, and 45 Area to remove

1,4-dioxane that was found to occur in a portion of the TCE plume in this area. Since neither the carbon filtration nor the air stripping module in the T-25 Area treatment facility efficiently removes 1,4-dioxane, a pre-treatment system was installed to treat the dioxane. The extracted groundwater from the Buildings

63, 2, and 45 Area is pumped to a “remote” equipment shed that houses a chemical oxidation treatment system (see schematic in Figure 8). The remote 1,4-dioxane treatment system is located adjacent to extraction well EW-4. This pre-treatment system acidifies the water, and then uses hydrogen peroxide and iron (Fenton's reagent) in an advanced oxidation treatment process to destroy the 1,4-dioxane before the water is pumped to T-25 Area system.

Treated water from the GWETS is pumped to a storage tank behind Building 10 that supplies the installation’s non-potable water distribution system used for lawn sprinklers, cooling tower make up and restroom flushing water. Overflow from the system is discharged to the storm sewer, which discharges to

Lake Cochituate. Effluent samples are collected monthly following flow through the carbon treatment units.

During this FYR period, there were changes to the treatment system. Per the 2013 ESD, the air stripper and vapor phase carbon were removed from the treatment train as water could be treated effectively with liquid phase carbon (the air stripper and VGAC remain in the building and can be re-connected if necessary). In addition, slug volume removal began at two areas: the ARIEM Building Area from wells

MW165B-2 and MW-181B-2, and east of Building 1 at well MW114B-2. The volumes removed are discussed in Section 6.4.2 and were reported in the Slug Volume Removal Technical Memorandum (ECC, 2015c).

In 2013, a pre-treatment system was installed for Well MW-96B-4, as part of a GWETS upgrade. This pre-treatment system was comprised of an ultraviolet light (UV) disinfection system and filter installed within

Building 94. The pre-treatment system was installed due to the 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. The system was taken off-line in summer 2016 as it was no longer needed.

4.3.2 Operation and Maintenance of Treatment System

The GWETS is operated in accordance with the Groundwater Treatment System O&M Manual (ECC, 2015a). An operator is on-site 2 to 3 days per week to perform routine treatment facility operation and maintenance activities. Due to turbidity in the extracted groundwater and oxidation/precipitation of dissolved iron in the extracted groundwater, the wells and pumps in the Buildings 22 and 36 and Buildings

63, 2, and 45 Areas become clogged and require cleaning on a regular basis. This requires the removal of the clogged pump for cleaning, and replacement of the removed pump with a spare pump while the cleaning is performed. One to two pumps require removal and cleaning every month. Other routine maintenance activities include:

Filter bag replacement approximately once per week;

LGAC vessel backwashing approximately once every 3 weeks;

Processing of backwash solution as needed;

Weekly cleaning and calibration of the 1,4-dioxane pH sensor, level transducer and flow meter;

Regular cleaning of process flow meters;

Chemical drum replacement at the 1,4-dioxane pre-treatment system once per month; and

Periodic replacement of spent LGAC with new carbon.

The following major O&M events have occurred during the FYR period:

2012. The T-25 Treatment System at Building 94 was modified to eliminate the use of the air stripper and associated equipment. A review of historical influent characteristics and the treatment process indicated that effective treatment of the influent groundwater can be achieved by using only the liquid phase granular activated carbon. Eliminating the air stripper and associated equipment

(effluent pump, two air blowers, the air heater, and vapor phase activated carbon) resulted in considerable reduction of energy consumption and reduction of hazardous waste (spent activated carbon). The system modifications were installed in a manner that allows a return to original design operations if necessary. All original equipment remains in “stand-by” mode, ready to be placed back in service with minimal effort (1-2 days) if necessary.

2013. Extraction well MW-96B-4 was shut down for most of the year. Installation in December of a new pre-treatment system to address coliform bacteria in water pumped from MW-96B-4 was brought back on-line and pre-treatment system tested and started up.

2014. Extraction well MW-96B-4 operated intermittently during the beginning of the year. Due to the discovery of an underground pipeline leak outside the MW-96B-4 vault in February, this well was shut down for 6 months until the pipeline could be repaired. Extraction well MW-90B-4 was redeveloped in summer 2014.

2015. From January through April, MW-96B-4 remained offline due to well repairs and rehabilitation. In

2015, extraction well MW-96B-4 operated continuously from May through the end of the year.

Extraction wells EW-3 and EW-4 were taken offline in November and December due to system repairs associated with acid corrosion of the above-ground 1,4-dioxane oxidation system components.

2016. Acid corrosion of various components within the 1,4-dioxane pre-treatment system shed resulted in replacement of much of the system (pumps, control panel components, level switches, etc).

Gaseous hydrochloric acid (the acid used to reduce pH to promote the Fenton’s oxidation reaction) was determined to be the cause of the corrosion. Therefore, in addition to component replacement, the acid used in the process was switched from hydrochloric to sulfuric.