KGS_2018g_Draft_Final_2017_Annual_Long-Term_Monitoring_and_Maintenance_Report_SHL_Devens.pdf

DRAFT FINAL

2017 ANNUAL OPERATIONS, MAINTENANCE,

AND MONITORING REPORT

SHEPLEY’S HILL LANDFILL

FORMER FORT DEVENS ARMY INSTALLATION

SEPTEMBER 2018

Prepared for:

Department of the Army

Base Realignment and Closure Division Fort Devens, Massachusetts

Prepared by:

KOMAN Government Solutions, LLC 293 Boston Post Road West, Suite 100

Marlborough, MA 01752 Contract No.: W912WJ-15-C-0002

| NOTICE |

The United States Department of Defense, Department of Army, funded wholly or in part the preparation of this document and work described herein under Contract No. W912WJ-15-C-

0002. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

2017 ANNUAL OPERATIONS, MAINTENANCE, AND MONITORING REPORT

SHEPLEY’S HILL LANDFILL

FORMER FORT DEVENS ARMY INSTALLATION

DEVENS, MASSACHUSETTS

SEPTEMBER 2018

CERTIFICATION:

I hereby certify that the enclosed Report, shown and marked in this submittal, is that proposed to be incorporated with Contract Number W912WJ-15-C-0002. This Document has been prepared in accordance with USACE Scope of Work and is hereby submitted for Government Approval.

Reviewed By:

9/28/18

KGS Project Manager Date

Received By:

USACE Project Manager Date i

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 BACKGROUND

1.2 OBJECTIVES

1.3 REPORT ORGANIZATION

2.0 LANDFILL MAINTENANCE AND MONITORING

2.1 GENERAL LANDFILL MAINTENANCE

2.2 LANDFILL INSPECTION

2.2.1 Cover Surface

2.2.2 Vegetative Growth

2.2.3 Landfill Gas Vents and Gas Points

2.2.4 Monitoring Wells and Piezometers

2.2.5 Drainage Swales

2.2.6 Settlement

2.2.7 Erosion

2.2.8 Access Roads

2.2.9 Culverts and Catch Basins

2.2.10 Security/Fencing

2.2.11 Wetland Encroachment

2.2.12 Other Observations

2.2.13 Recommendations

2.3 LANDFILL GAS MONITORING

2.3.1 Perimeter Gas Monitoring and Results

2.3.2 Landfill Gas Monitoring and Results

3.0 ARSENIC TREATMENT PLANT OPERATIONS, MAINTENANCE, AND

MONITORING

3.1 OPERATIONS

3.1.1 System Description

3.1.2 System Efficiency and Routine Maintenance

3.2 NON-ROUTINE SYSTEM MAINTENANCE, REPAIRS, AND UPGRADES

3.2.1 Polymer Dosing Pump Replacement

3.2.2 T-1 Filter Feed Tank Replacement

3.2.3 Effluent Pump Maintenance

ii

3.2.4 Microfilter Module Replacement

3.2.5 Chlorine Gas Check Valve Replacement

3.2.6 Microfilter Skid PLC and PanelViewer Replacement

3.3 ATP MONITORING

3.3.1 ATP Influent Monitoring

3.3.2 ATP Landfill Discharge Permit and Effluent Monitoring

3.4 ATP OPTIMIZATION

3.5 RECOMMENDATIONS

4.0 LAND USE CONTROLS

5.0 GROUNDWATER AND HYDRAULIC MONITORING

5.1 LONG TERM MONITORING AND MAINTENANCE PLAN MODIFICATIONS .. 17

5.2 GROUNDWATER ELEVATION MONITORING

5.2.1 Site-Wide Monitoring Events

5.2.2 Barrier Wall Hydraulic Monitoring

5.3 GROUNDWATER SAMPLING

5.4 GROUNDWATER SAMPLING RESULTS

5.4.1 Arsenic Concentration Results

5.4.2 Arsenic Concentration Trends

5.4.3 Other Contaminants of Concern Results

5.4.4 Groundwater Monitoring Field Parameters

5.4.5 Data Validation

5.5 MONITORING PROGRAM OPTIMIZATION

6.0 CONCLUSIONS AND RECOMMENDATIONS

6.1 CONCLUSIONS

6.1.1 Landfill Monitoring and Maintenance

6.1.2 SHL Remedy Operations

6.1.3 Groundwater Monitoring

6.2 RECOMMENDATIONS

6.2.1 Landfill Monitoring and Maintenance

6.2.2 SHL Remedy Operations and Performance

6.2.3 Groundwater Monitoring

7.0 REFERENCES

iii

LIST OF FIGURES

Figure 1-1 Former Fort Devens Vicinity and Shepley’s Hill Landfill Figure 1-2 North Impact Area and Shepley’s Hill Landfill Site Plan Figure 1-3 North Impact Area Site Plan Figure 1-4 Area of Land Use Controls Figure 2-1 Shepley’s Hill Landfill Gas Points and Vents Figure 3-1 Influent Metals Concentrations –ATP Figure 5-1 Long-Term Monitoring Well Network Figure 5-2 Groundwater Elevations, Northern Impact Area and Shepley’s Hill Landfill, May 22, Figure 5-3 Groundwater Elevations, Northern Impact Area and Shepley’s Hill Landfill, November 2, 2017 Figure 5-4 2017 Barrier Wall Area Hydraulic Vectors Figure 5-5 Dissolved Arsenic in Groundwater, May/June 2017, Northern Impact Area and

Shepley’s Hill Landfill Figure 5-6 Dissolved Arsenic in Groundwater, November 2017, Northern Impact Area and

Shepley’s Hill Landfill

LIST OF TABLES

Table 1-1 Contaminants of Concern (COC) Cleanup Levels Table 2-1 Annual Landfill Gas Monitoring Results Table 2-2 Landfill Gas Probe Construction Details Table 3-1 Operations Summary – Groundwater Treatment Plant Table 3-2 2017 Monthly Discharge Totals – Groundwater Treatment Plant Table 3-3 2017 Filter Bed Roll-off Disposal Totals – Groundwater Treatment Plant Table 3-4 2017 Routine and Non-Routine System Maintenance, Repairs, and Upgrades –

Groundwater Treatment Plant Table 3-5 2017 As/Fe/Mn Influent Concentrations – Groundwater Treatment Plant Table 3-6 Influent VOC & Dissolved Gasses Concentrations – Groundwater Treatment

Plant Table 3-7 Monthly Effluent Arsenic Sampling Results – Groundwater Treatment Plant Table 3-8 Quarterly Effluent Sampling Results – Groundwater Treatment Plant Table 3-9 Annual Effluent Sampling Results – Groundwater Treatment Plant Table 5-1 LTMMP Sampling Program Table 5-2 LTMMP Hydraulic Monitoring Program Table 5-3 Hydraulic Monitoring Data for Spring and Fall 2017 Table 5-4 Site-Wide Hydraulic Monitoring Results from 2012 to 2017 Table 5-5 2017 Barrier Wall Area Hydraulic Gradients Table 5-6 Spring 2017 LTM Analytical Results and Field Parameters iv

Table 5-7 Fall 2017 LTM Analytical Results and Field Parameters Table 5-8 Summary of Historical Arsenic Results in Groundwater

LIST OF APPENDICES

Appendix A Landfill Inspection Report Appendix B Landfill Gas Monitoring Field Forms Appendix C Laboratory Analytical Reports (on CD) Appendix D LUCIP Pamphlet and Checklist Appendix E Groundwater Monitoring Field Forms (on CD) Appendix F Analytical Data Validation Reports (on CD) Appendix G 2017 SHL Monitoring Well Survey Report Appendix H 3PE Analysis for Barrier Wall (on CD) Appendix I Arsenic Concentration Trend Graphs Appendix J Historical Groundwater Monitoring Well and Gas Vent Analytical Results Appendix K ProUCL Outputs Appendix L 2017 Piezometer Construction Diagrams Appendix M Responses to Comments

LIST OF ACRONYMS AND ABBREVIATIONS

AOC Area of Contamination ATP/GWTP Arsenic Treatment Plant/ Groundwater Treatment Plant bgs Below Ground Surface BOH Board of Health BRAC Base Realignment and Closure CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CIP Clean-in-Place CMR Code of Massachusetts Regulations COC Contaminant of Concern cy Cubic Yard DO dissolved oxygen ESD Explanation of Significant Differences EW Extraction Well FBRO Filter bottom roll-off FS Feasibility Study Global Global Remediation Services Inc.

gpm gallons per minute HDPE high-density polyethylene IC Institutional Control v

IPC Inclined Plate Clarifier KGS KOMAN Government Solutions, LLC LEL Lower Explosive Limit LGP Landfill Gas Points LTM Long-Term Monitoring LTMMP Long Term Monitoring and Maintenance Plan LUC Land Use Control LUCIP Land Use Control Implementation Plan MassDEP Massachusetts Department of Environmental Protection MCL Maximum Contaminant Level MF Microfiltration mg/L milligrams per liter MS Matrix Spike MSD Matrix Spike Duplicate NAVD North American Vertical Datum NIA North Impact Area O&M Operations and Maintenance ORP Oxidation reduction potential POTW Publicly-Owned Treatment Works ppm parts per million PLC programmable logic controller PVC Polyvinyl chloride QA Quality Assurance QC Quality Control RAO Remedial Action Objective RI Remedial Investigation ROD Record of Decision SHL Shepley's Hill Landfill TestAmerica TestAmerica Laboratories, Inc.

USEPA United States Environmental Protection Agency USACE-NAE U. S. Army Corps of Engineers, New England District µg/L micrograms per liter µm micrometer (micron) VOC Volatile Organic Compound

1.0 INTRODUCTION

This Annual Report presents a summary of the groundwater monitoring program and the operation and maintenance (O&M) activities conducted during 2017 at the Shepley’s Hill Landfill (SHL) site, located at the former Fort Devens Army Installation, Massachusetts. The summary includes data from the Army’s operation of the groundwater extraction, treatment, and discharge system, the landfill monitoring and maintenance program, and the groundwater monitoring results for 2017. These activities were conducted in accordance with the Final Long- Term Monitoring and Maintenance Plan (LTMMP) Update (Sovereign, 2015).

1.1 BACKGROUND

The former Fort Devens, Massachusetts is located approximately 35 miles northwest of the city of Boston, within the towns of Ayer, Shirley (Middlesex County), Harvard and Lancaster (Worcester County). The former Fort Devens was established in 1917 for military training and logistical support during World War I. Fort Devens became a permanent base in 1931 and continued service until its Base Realignment and Closure (BRAC) Committee closure in 1996.

Figure 1-1 depicts the area and topography of the former base and surrounding area.

SHL encompasses approximately 84 acres in the northeast corner of the Main Post of the former Fort Devens (Figure 1-2). The landfill is bordered to the east by Plow Shop Pond and land formerly containing a railroad roundhouse, to the west by Shepley’s Hill, to the south by recent commercial development, and to the north by wooded and residential areas. Nonacoicus Brook, which drains Plow Shop Pond, is located north of the landfill in the North Impact Area (NIA) (Figure 1-3).

The Army reportedly operated SHL by the early 1940s; however, evidence from test pits within the landfill suggests earlier usage, possibly as early as the mid-nineteenth century. The landfill contains a variety of waste materials including, but not limited to, demolition debris, asbestos, sanitary wastes, glass, and incinerator ash. The maximum depth of the refuse occurs in the central portion of the landfill and is estimated to extend about 40 feet below ground surface (bgs). The volume of waste in the landfill has been estimated at over 1.5 million cubic yards (cy), of which approximately 160,000 cy (11%) is below the water table. The saturated wastes appear to be emplaced in a wetland; at least two areas previously mapped as wetlands were filled (Harding ESE, 2003), and the waste has been found to be underlain by peat deposits (Sovereign, 2011a).

The Massachusetts Department of Environmental Protection (MassDEP) approved the landfill closure plan in 1985. The landfill was closed in five phases between 1987 and 1993 in accordance with 310 Code of Massachusetts Regulations (CMR) 19.000. Closure consisted of capping the landfill with a 30 to 40-mil polyvinyl chloride (PVC) membrane, covering the cap with soil and vegetation, and installing gas vents. Closure also included installation of wells to monitor groundwater quality around the landfill, and construction of drainage swales to control surface water runoff. MassDEP issued a Landfill Capping Compliance Letter approving the closure in February 1996.

After closure of the landfill, the Army completed Remedial Investigations (RIs) under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) that evaluated soil, sediment, surface water, and groundwater conditions at and in the immediate vicinity of the landfill. The results confirmed the presence of various contaminants at the site, particularly certain inorganics (e.g., arsenic) and volatile organic compounds (VOCs) in groundwater, sediment, and surface water at and adjacent to SHL. The Army’s Feasibility Study (FS) and Record of Decision (ROD) resulted in a Remedial Action that specified long-term monitoring and maintenance of the landfill cap, and long-term groundwater monitoring, and a contingent remedial component requiring design and construction of a groundwater extraction and treatment system if the landfill cap did not result in a reduction of groundwater contaminant concentrations, primarily arsenic, by 2008. Table 1-1 lists the relevant contaminants of concern (COCs) identified in the ROD, and their target cleanup levels.

As described in the ROD (U. S. Army Corps of Engineers [USACE], 1995), the Remedial Action Objectives (RAO) for the SHL Remedial Action are to:

• Protect potential residential receptors from exposure to impacted groundwater migrating from the landfill having chemicals in excess of maximum contaminant levels (MCLs)

• Prevent impacted groundwater from contributing to the contamination of Plow Shop Pond sediments in excess of human health and ecological risk-based concentrations

In addition to requiring Five-Year Reviews, the ROD stipulated that arsenic concentrations in groundwater must be monitored to assess the landfill cap’s effectiveness in attaining risk-based, cleanup goals by 2008 and if the required reductions in risk were not achieved within this timeframe, Army would design and implement a groundwater extraction and treatment system to address continued migration of contamination emanating from the landfill. In March 2006, when it was realized that the risk-reduction goals would not be attained, the Army constructed and began operating a two-well (EW-01 and EW-04) groundwater extraction and treatment system at an initial pumping rate of 25 gpm, which was gradually increased to a combined extraction rate of 50 gpm. In 2017, an average extraction rate of 55 gpm was achieved.

Adjacent to SHL, the Army conducted an investigation of Red Cove/Plow Shop Pond as Area of Contamination 72 (AOC 72). In 2011, the AOC 72 RI (AMEC, 2011) concluded that components of the current SHL remedy (landfill capping and groundwater extraction) did not eliminate groundwater flow and arsenic migration from SHL into Red Cove/Plow Shop Pond.

The AOC 72 RI results suggested that groundwater discharge contributed arsenic to sediment that could accumulate to levels resulting in conditions that posed unacceptable risks, and therefore a remedy component that minimized arsenic-in-groundwater flux to Red Cove was most protective (AMEC, 2011). Consequently, during August-September 2012, the Army installed a slurry barrier wall between the SHL and AOC 72 as part of a Non-Time Critical Removal Action in order to mitigate the arsenic flux to Red Cove/Plow Shop Pond by groundwater flow from the SHL. Documentation of the barrier wall installation was provided in the July 2013, Final Removal Action Completion Report for Shepley’s Hill Landfill Barrier Wall (Sovereign, 2013a).

As stated earlier, one of the RAOs for SHL is to protect potential residents from exposure to impacted groundwater migrating from the landfill at levels that pose a risk to human health and the environment. Because the extent of the impact was not defined at the time, the SHL ROD did not specifically address implementation of Land Use Controls (LUCs) for any non-Army property located north of the landfill. Consequently, LUCs were established for the NIA in 2013 and were documented in the December 2013 Explanation of Significant Differences (ESD) for Land Use Controls to Restrict Groundwater Use (Sovereign, 2013b). The Army subsequently issued a Land Use Control Implementation Plan (LUCIP) in August 2014 to describe the procedures for implementing the LUCs in the NIA (Sovereign, 2014). The specific LUCs are discussed in Section 4.0. The area of LUCs is shown on Figure 1-4.

1.2 OBJECTIVES

The objectives of this Annual Report are as follows:

• Summarize landfill maintenance activities

• Document the landfill cap inspection which was performed to identify areas that may require future maintenance

• Present landfill gas measurements from 18 gas vents and 25 permanent landfill perimeter gas monitoring wells to evaluate long-term trends with regard to gas production and venting

• Summarize O&M, sampling, and reporting associated with the Arsenic Treatment Plant (ATP) and provide recommendations for any modifications

• Present the results of the long-term monitoring (LTM) program for groundwater, including groundwater hydraulics, COC analytical monitoring, and field parameters

1.3 REPORT ORGANIZATION

• Section 2.0 documents the routine landfill maintenance and inspection activities and includes the results of landfill gas monitoring in both gas vents and perimeter soil gas wells

• Section 3.0 summarizes the ATP operations, maintenance, and monitoring

• Section 4.0 summarizes the LUCs monitoring conducted in accordance with the LUCIP

• Section 5.0 summarizes the LTMMP groundwater monitoring results, including synoptic water level measurements, barrier wall hydraulic performance monitoring, arsenic concentrations, and other water quality data

• Section 6.0 presents conclusions and recommendations for future system operations, monitoring, and assessments

• Section 7.0 presents references used to prepare this report

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2.0 LANDFILL MAINTENANCE AND MONITORING

In accordance with the LTMMP Update (Sovereign, 2015), SHL was inspected and routine maintenance was performed during 2017. The annual inspection identifies and corrects any problems pertaining to the effectiveness of the cap system, erosion, and the conditions of gas vents and sampling points. A summary of the landfill cap maintenance, the findings of the inspection, and the results of landfill gas monitoring are presented in the following sections. The landfill inspection report with supporting photographs are presented in Appendix A.

2.1 GENERAL LANDFILL MAINTENANCE

The landfill grass cover and the vegetation atop the utility berm were mowed on 25 and 26 September 2017 by Gatsby Grounds Co., Inc. of Lancaster, Massachusetts. Small shrub growth on the margins of the landfill was removed to maintain an effective cap system. The berm was intact and no adverse effects to the berm were noted. Normal vegetative growth was removed from the landfill cap during the mowing activities. Large vegetative growth was removed from the southern and northern drainage swales and grass mowing was conducted to the edge of the swales.

2.2 LANDFILL INSPECTION

An annual inspection of SHL was conducted on 18 October 2017. Features of the landfill that were inspected included the cover system, drainage system, gas vent system, access road, monitoring wells, and piezometers. Observations were made regarding the vegetative cover, vegetative types, erosion, settlement and general conditions. The overall condition of the landfill was found to be satisfactory. A summary of findings and observations are presented below and within the landfill inspection report included in Appendix A along with supporting photographs.

2.2.1 Cover Surface

There was no evidence of poor conditions affecting the cover surface. No new depressions were observed on the cover surface. No new tree or shrub growth was observed on the landfill surface and observed vegetative growth in the drainage areas was removed during the September 2017 mowing event. The utility berm was intact and no adverse effects to the berm were noted.

2.2.2 Vegetative Growth

The vegetative growth was normal and appeared to have no major stressed areas. The landfill had been properly mowed during the September 2017 mowing event.

2.2.3 Landfill Gas Vents and Gas Points

The landfill gas vents were observed to be in good condition. The vent pipes were functioning, and screens were present to prevent wildlife or debris from entering the vents. The landfill gas points were observed to be in good condition. Gas vents and gas points are located on Figure 2-1.

2.2.4 Monitoring Wells and Piezometers

Monitoring wells and piezometers located on the landfill cap or perimeter that are currently part of the LTMMP network were inspected in accordance with the revised 2015 LTMMP Appendix D checklist and were found to be in good condition (Figure 2-1). A well inventory was performed, and photo documentation of each well was completed during the 2017 Fall gauging event. Refer to Section 5.5 for additional well information.

2.2.5 Drainage Swales

Most of the southern drainage swale exhibited some vegetative growth. Large growth was removed during September 2017 as part of the landfill mowing activities. Small vegetative growth and wetland plant life were not disturbed, as they help prevent erosion of the landfill cover. The northern drainage swales near the ATP also exhibited some vegetative growth.

Growth was removed from the drainage swales during the September 2017 mowing event.

Drainage swales are shown on Figure2-1.

2.2.6 Settlement

No new topographic depressions were observed within the landfill cover.

2.2.7 Erosion

No significant erosion was observed across the landfill.

2.2.8 Access Roads

The landfill access road is shown on Figure 1-2. Tire ruts were observed between the barrier wall and the ATP in some sections (Appendix A, Landfill Inspection Report). The road was observed to be in good condition and with no erosion between the barrier wall and the southern landfill gate.

2.2.9 Culverts and Catch Basins

Three adjacent culverts located at the northern portion of the landfill beneath the access driveway to the ATP were observed to be in good condition. Large vegetative growth was removed during the September 2017 mowing event along the entrance road to the ATP building and the area around the culverts. No catch basins are present at the landfill or along landfill boundary. The culverts are shown on Figure 1-2.

2.2.10 Security/Fencing

There is no perimeter fencing along much of the wooded western boundary of the landfill (along Shepley’s Hill) and along the southeastern landfill boundary near the railroad tracks; however, no public roads have open access to the landfill. Fence repairs were performed at two locations in December 2017. Repairs were made to the section of fence near SB-2017-05 near the ATP and near the fence and gate at the Plow Shop Pond outlet near SHL-13. Fence gates across roads that access the landfill are secured with chains and padlocks, and the security fence surrounding the ATP remains in good condition.

2.2.11 Wetland Encroachment

Wetland encroachment was observed in the swales located in the southern portion of the landfill.

Overall, the individual areas of encroachment are infrequent, small, and confined to the swales.

Extensive encroachment by wetland plants is controlled by mowing of the landfill surface. This will prevent the development and expansion of a wetland beyond the swale areas already invaded by wetland species.

2.2.12 Other Observations

The recreational field located south of the access road in the middle of the southern half of the landfill appeared to be in good condition. The field is being used through a lease to MassDevelopment for recreational use of drones (launching/landing). The area was routinely mowed (Figure2-1) and no tire rutting was observed from recreational activity between the field and the landfill access road. A second mowed area near the southern entrance to the landfill was observed with minor tire ruts in the summer. No damage to the landfill cap was observed at either mowed location.

2.2.13 Recommendations

During the October 2017 inspection, the landfill was observed to be in good condition overall.

The inspection was limited to the landfill area and did not include an inspection of off-landfill wells.

The following recommendations are suggested for 2018:

• Continue annual landfill inspections

• Swales should be monitored for expanded growth of wetland species and vegetative growth during each annual inspection

• Mowing should be continued on an annual basis to maintain the effectiveness of the cover system

• Ensure that the post closure uses of the landfill during MassDevelopment’s leased project period do not compromise the integrity of the landfill cover or the network of landfill gas vents and groundwater monitoring wells

• Conduct routine, drive-by monitoring checks of the condition of the landfill cap in the leased recreational area

• Repair the northern landfill access road from the barrier wall area to the ATP due to vehicle tire rutting observations (planned to be completed during Spring 2018)

2.3 LANDFILL GAS MONITORING

Annual sampling of landfill gas vents and landfill gas points (LGPs) was completed on October 18, 2017. Sampling activities were conducted in accordance with procedures described in the MassDEP Landfill Technical Guidance Manual, as revised May 1997. Landfill gas sampling included the following parameters:

• VOCs concentration in parts per million (ppm)

• Percent oxygen (O2)

• Hydrogen sulfide (H2S) concentration in ppm

• Percent lower explosive limit (LEL)

• Carbon monoxide (CO) concentration in ppm

• Percent carbon dioxide (CO2)

• Percent methane (CH4)

Landfill gas sampling was conducted using properly calibrated equipment. A LandTech Gem 2000 meter was used to measure CO2, O2, LEL, and CH4. A multiRAE chemical gas detector was used to measure total VOC, CO, and H2S. Each gas sampling device was connected directly to the sampling port at the top of the probe/vent to measure initial levels of gas concentrations.

After the initial measurements were recorded, two probe/vent volumes were purged from each probe/vent. Following purging, the gas sampling equipment was connected directly to the sampling port and post purge gas concentrations were measured and recorded. Figure 2-1 depicts the locations of landfill gas vents and LGPs. Results of the annual landfill gas monitoring are presented in Table 2-1 and are discussed in the following sections. Refer to Table 2-2 for landfill gas probe construction details. Landfill gas monitoring field forms are provided in Appendix B.

2.3.1 Perimeter Gas Monitoring and Results

Annual LGP monitoring was performed on October 18, 2017 during which barometric pressure ranged from 29.90 to 30.02 inches of mercury. Barometric pressure data are provided in Table 2-1. Background barometric pressure was recorded as 30.0” Hg at the ATP at the start of the day. Pressure readings were then collected at each well and were relatively stable throughout the day. Pressure readings ranged from 29.90” Hg at 1:19 PM at GV-16 to 30.03” Hg at 10:00 AM at LGP-05-13X.

Nine LGPs located at the northern edge of the landfill were screened during the 2017 monitoring event. Methane was measured below the instrument detection level at each of the northern LGPs during initial or post purge screening. Additionally, hydrogen sulfide, and carbon monoxide were not measured above the instrument detection limit in any of the northern LGPs during initial or post purge readings. Initial total VOCs was detected in one LGP at 1 ppm and no VOCs detected in post readings. Oxygen and CO2 concentrations ranged from 19.8% to 20.5% and 0.6% to 1.5%, respectively in initial landfill gas perimeter measurements and 19.8% to 20.4% and 0.9% to 1.6%, respectively in post purge monitoring.

Sixteen LGPs located along the southern edge of the landfill were screened during the October 2017 monitoring event. Methane was detected in landfill gas at 5 of 16 LGPs in initial landfill gas monitoring with concentrations ranging from 0.1% (2% of LEL) to 4.6% (>100% of LEL).

In post purge monitoring, methane was detected in 0 of 16 LGPs.

Oxygen and CO2 were measured at concentrations ranging from 7.3% to 18.6% and 0.1% to 15.2% respectively in initial landfill gas monitoring and 6.5% to 18.4% and 3.5% to 15.8% respectively in post-purge monitoring.

Hydrogen sulfide and carbon monoxide were below instrument detection levels at all perimeter LGPs during initial and post-purge screening. The 2017 perimeter gas monitoring results (Table 2-1) are consistent with previous year’s results with the exception that no post methane was detected in 2017 compared to five post-methane detects in 2016.

2.3.2 Landfill Gas Monitoring and Results

Annual landfill gas vent monitoring was performed on October 18, 2017 in conjunction with the annual LGP monitoring. Landfill gas vents in the southwest section of the landfill typically exhibited some of the highest levels of methane/LEL and CO2. The 2017 gas monitoring results (Table 2-1) are consistent with the results during the previous year’s measurements. A summary of historical gas vent measurements is presented in Appendix J.

Methane was detected in landfill gas at 10 of 18 gas vents in initial monitoring with concentrations ranging from 0.1% (5% of LEL) to 2.1% (61 % of LEL). In post purge monitoring, methane was detected in landfill gas at 9 of 18 gas vents ranging from 0.1% (0% of LEL) to 10.3% (>100% LEL). Methane was measured at greater than 100% of LEL in post purge monitoring at 1 of 18 gas vents (GV-9); a substantial reduction from 11 of 18 vents in 2016. The highest methane concentrations were measured at GV-4 in initial monitoring and GV 9 in post-purge monitoring.

Oxygen and CO2 concentrations ranged from 13.3% to 20.9% and 0.1% to 4.8%, respectively, during initial landfill gas monitoring and 10.1 % to 20.9% and 0.1% to 43.0%, respectively, during post-purge monitoring.

No VOCs were detected in landfill gas in 2017. Hydrogen sulfide and carbon monoxide were measured below instrument detection levels at all landfill gas vents during initial and post purge monitoring.

3.0 ARSENIC TREATMENT PLANT OPERATIONS, MAINTENANCE,

AND MONITORING

The SHL ATP treated and discharged 26,650,300 gallons of groundwater between January 1 and December 31, 2017, bringing the cumulative treated volume total to approximately 247.3 million gallons since system startup in 2006.

3.1 OPERATIONS

The ATP operations, maintenance, and monitoring history for the period of January 1 through December 31, 2017 was conducted by Sovereign Consulting, Inc. The 2017 data are presented in the following sections.

3.1.1 System Description

The treatment system is designed to remove dissolved arsenic from extracted groundwater through co-precipitation with iron followed by microfiltration. The treatment system is housed in a 40-foot by 40-foot steel building and consists of the following components:

• Extraction system (two extraction wells)

• Chlorine dioxide (ClO2) generation and addition in order to oxidize iron

• Coagulation via a contact tank with a direct drive batch tank mixer

• Microfiltration (MF) of the water to concentrate precipitated solids

• Solids removal via an inclined plate clarifier (IPC)

• Bag filtration and discharge of the IPC decant water

• Polymer aided flocculation of sludge using a filter bed roll-off (FBRO)

• Treated water discharge to the Devens Publicly Owned Treatment Works (POTW)

The extraction system consists of two extraction wells (EW) located at the northwestern portion of the landfill cap. These extraction wells, EW-01 and EW-04 (Figure 1-2), can achieve the required combined extraction rate of 50 gpm by operating simultaneously. Extracted groundwater enters the ATP and is dosed with chlorine dioxide which oxidizes and precipitates dissolved metals, including arsenic, iron, and manganese. These precipitates are then filtered by the MF system and the effluent or treated water is discharged to the Devens POTW collection system. Every 15 minutes, the MF control unit conducts Flux Maintenance, which backwashes the filtered precipitates from the membranes. These solids are fed to the IPC and allowed to settle out of suspension and form a residual sludge. The backwash effluent supernatant is fed through two bag filters configured in parallel and discharged to the plant effluent sump. The sludge is then pumped out of the IPC, dosed with polymer to increase flocculation, and pumped to the FBRO. The accumulated sludge in the FBRO is removed from the plant at least twice a month for disposal.

An operational summary of the monthly on-line hours, flow totals, and operating status during 2017 is presented in Table 3-1. Historical monthly discharge totals are shown in Table 3-2.

3.1.2 System Efficiency and Routine Maintenance

During 2017, the treatment plant was operational approximately 92% of the total available hours during the calendar year (i.e., “up-time”), which is an increase from the 2015 average up-time of 85% and slightly less than the 2016 average up-time of 95%. A significant part the non-operational time is due to routine plant maintenance and system repairs and performing clean-in-place (CIP) maintenance on the MF skid. Additional downtime is associated with non-routine systems maintenance, repairs, and upgrades as noted below in Section 3.2. When online, the average flow through the plant during the year was 55.2 gpm. The plant achieved an effective average extraction rate (i.e., the extraction rate calculated by dividing the volume pumped by the elapsed time during the year, not the actual on-line time) of 50.7 gpm over the year. This is consistent with the previous year.

The ATP system continues to generate a significant amount of sludge. The FBRO was emptied every 1 to 2 weeks in 2017, depending on the flow and after treatment of approximately 650,000 to 1,250,000 gallons of groundwater. The cause of the high sludge generation is the high concentration of inorganics (primarily iron) in the influent. Influent arsenic concentrations have continued to decrease when compared to influent arsenic concentrations at the time of startup of the ATP in 2006; however, the average annual inorganic concentrations (iron, arsenic, and manganese) remain high at approximately 65.94 mg/L. Influent inorganic loading is discussed in more detail in Section 3.3.1.

A subcontracted vendor, Global Remediation Services Inc. (Global), uses a vacuum truck to remove the dewatered sludge from the FBRO. The sludge is transported by Global under a Non- Hazardous Waste Manifest for disposal at Turnkey Landfill, which is operated by Waste Management in Rochester, New Hampshire. By coordinating FBRO pump-outs with Global before the container was full, the sludge removal process was optimized which resulted in zero downtime due to the FBRO operations for the ATP in 2017. A total of 251.86 tons of sludge was removed in 2017. The FBRO disposal totals for 2017 is shown in Table 3-3.

The ATP microfiltration system continues to require periodic CIP procedures to prevent long-term fouling of the filter membranes. The CIP procedure is a multistep process that begins by flushing potable water though the MF skid after it is taken offline. Next, a 98% sulfuric acid (H2SO4) solution is cycled through the MF skid followed by a flush of potable water, a cycle of a 25% sodium hydroxide (NaOH) solution and then another flush of potable water. Prior to restart, the MF skid is filled with potable water one last time. The acid and caustic solutions are cycled through the MF skid at approximately 90°F and allow for the dissolution of the iron and manganese precipitate that accumulate on the filter membranes during forward flow.

Modifications have been made to the CIP procedure since March 2009. Prior to March 2009, the CIP events were conducted for approximately 30 hours every two weeks. The Army has continued to optimize system operations, and currently CIP events are conducted approximately every 28 to 43 days. The optimization was accomplished by further modifying the CIP procedure to include air scouring during acid and caustic circulation to facilitate the removal of precipitate.

This modification appears to have increased the effectiveness of the CIP events, thereby increasing the time between CIP cycles and resulting in a greater average extraction rate.

Optimizations to the CIP process have reduced the likelihood that an extended CIP (prolonged acid and caustic circulation times) or double CIP (acid solution recirculation/soak repeated after caustic solution recirculation) is conducted. Currently, extended CIPs are only conducted in situations when the level of filter fouling is greater than normal, most likely because of non-optimal dosage concentration of chlorine dioxide. The CIP process continues to be evaluated and refined to improve the process and minimize system non-pumping time. The system non-operational time associated with CIP procedures are detailed in Table 3-1 for each month.

3.2 NON-ROUTINE SYSTEM MAINTENANCE, REPAIRS, AND UPGRADES

This section details major system non-routine maintenance activities encountered or implemented, along with system upgrades completed during 2017. Shutdown and maintenance events, along with associated system downtimes, are presented in Table 3-1 for each month. A summary of routine and non-routine maintenance activities is presented in Table 3-4.

3.2.1 Polymer Dosing Pump Replacement

On 3 March 2017, the polymer dosing pump used in the sludge thickening failed due to normal operational wear. The pump was subsequently replaced with a new unit on 9 March 2017.

3.2.2 T-1 Filter Feed Tank Replacement

On 10 July 2017, the T-1 filter feed high-density polyethylene (HDPE) tank was observed to be leaking process water from a section of the welded seam. Consequently, the tank was replaced on 14 August 2017 during a scheduled routine CIP to minimize plant downtime with a filter feed tank constructed of polypropylene for stronger welded seams.

3.2.3 Effluent Pump Maintenance

On 4 August 2017, effluent pump #2 experienced an overload protection failure. On 15 August 2017, the overload protection relays and motor starters for effluent pumps #1 and #2 were replaced and it was determined that no damage to the pumps or motors occurred relating to this failure.

On 31 August 2017, cavitation was observed in effluent pump #1. Upon inspection it was determined that the internal check valve had failed causing the pump to lose prime and as a result the pump impeller suffered damage. The pump was taken out of service, and on 5 September 2017 during a scheduled plant power outage during which the local power utility was working on nearby power lines, the pump manufacturer inspected the pumping equipment, and the failed components were replaced. The pump was subsequently put back into service that day.

3.2.4 Microfilter Module Replacement

On 6 September 2017, eight of ten existing microfilter modules were replaced in kind during a scheduled plant shutdown. The two modules left in place were installed with system upgrades performed in January 2015. Prior to replacement, system trends were displaying inefficiencies with the filtration process and effluent water quality was decreasing. The attempts to repair leaking tubules or to isolate individual modules for heavy cleansing were met with no gain in performance. The eight modules replaced were original to the system and in operation since initial system start-up in 2005, and system filtration efficiency and effluent water quality data has improved following replacement.

3.2.5 Chlorine Gas Check Valve Replacement

On 28 November 2017, a check valve located on the ClO2generator skid failed resulting in plant shutdown. Because a replacement check valve is a specialty item that needed to be ordered, the plant had to remain offline until it was replaced on 30 November 2017. No damage to other equipment was observed.

3.2.6 Microfilter Skid PLC and PanelViewer Replacement

On 30 November 2017, upon restarting the plant following the chlorine gas check valve repair, the SCADA system went into alarm due to lost communication with the microfilter skid’s programmable logic controller (PLC), and the system shut down once more. Upon investigation of the issue, it was determined that the PanelViewer touch screen, which was original to the plant, had failed and was inoperable. The manufacturer of the skid components, Pall Corporation, was contacted, and a PALL engineer was dispatched to the plant to replace the failed PanelViewer and program the new microfilter skid PLC to correct the problem. Upon completion of this work, the system was restarted on 7 December 2017, and a copy of the software and programming has been loaded to an external device for storage in the microfilter PLC cabinet to minimize future downtime in the event of PLC failure.

3.3 ATP MONITORING

The following sections detail ATP influent and effluent sampling for arsenic and other COCs conducted during 2017. The associated laboratory analytical reports for the ATP monitoring conducted by Sovereign are included as Appendix C.1.

3.3.1 ATP Influent Monitoring

3.3.1.1 Influent Inorganic Monitoring

Influent inorganic loading characteristics are assessed quarterly. Influent inorganic sampling is not required either by the ATP’s MassDevelopment Landfill Discharge Permit 020 or by the LTMMP Update (Sovereign, 2015), but is monitored to gauge system loading and to ensure that a sufficient iron concentration is maintained to promote iron and arsenic co-precipitation and coagulation. The original system design recommended a minimum iron concentration of 40 milligrams per liter (mg/L). Current influent iron concentrations remain well above this level.

The ATP was designed with a ferric chloride addition system with ability to add ferric chloride to the influent if deemed necessary based on results of influent organic sampling; however, due to dissolved iron concentrations in the groundwater, this component of the system was never used. It has subsequently been decommissioned.

Loading of iron, arsenic, and manganese has declined since system start-up in 2006, but remains high enough for effective treatment, averaging 65.94 mg/L during 2006-2017. Individual average concentrations for iron, arsenic, and manganese are 60.85, 2.94 and 2.16 mg/L, respectively for that time period. During 2017, the average iron, arsenic, and manganese concentrations were 52.9, 2.59, and 2.44 mg/L, respectively (57.9 mg/L total). Influent loading concentrations of iron, arsenic, and manganese are presented in Table 3-5 and are graphically illustrated on Figure 3-1.

3.3.1.2 Influent Dissolved Gases and VOC Monitoring

In accordance with the LTMMP, annual ATP influent sampling was conducted for VOCs and dissolved gas (methane and ethane) using off-site analysis on September 13, 2017. Influent samples were collected by an ATP operator and submitted to SGS Accutest Laboratories of Marlborough, Massachusetts (Accutest) for analysis. Annual influent VOC and dissolved gas sampling results for EW-1 and EW-4 are detailed in Table 3-6.

The concentrations of methane were 1,870 micrograms per liter (µg/L) and 777 µg/L in the influent sampled from EW-1 and EW-4, respectively. Current methane concentrations are more than the 2016 sampling results of 999 µg/L at EW-1 and 504 µg/L at EW-04. Ethane was not detected above laboratory detection limits in the influent sample at EW-4. Ethane was detected at

0.39 µg/L at EW-01. Results of influent ethane concentrations sampling are consistent with 2016 sampling results for EW-04.

Results of the influent VOC sampling indicated total VOC concentrations of 43.72 µg/L and

3.72 µg/L in influent sampled from EW-01 and EW-04, respectively. Influent from extraction well EW 1 had detections of p/m-xylenes at 32.6 µg/L, ethyl ether at 5.5 µg/L, benzene at 0.97 µg/L, and ethyl benzene at 1.2 µg/L. Sampling results from EW-1 additionally reported estimated concentrations of cis-1,2-Dichloroethene at 0.66 J µg/L, isopropylbenzene at

0.26 J µg/L, chlorobenzene at 0.62 J µg/L, 1,3,5-Trimethylbenzene at 0.22J µg/L and 1,2,4-trimethylbenzene at 0.57 J µg/L. Sampling results from EW-4 reported only estimated concentrations of ethyl ether at 3.0 µg/L, benzene at 0.32J µg/L and chlorobenzene at

0.40 J µg/L. No other VOCs were detected at EW-4. The detections of low concentrations of VOCs in the ATP influent are consistent with the previous year’s sampling results.

3.3.2 ATP Landfill Discharge Permit and Effluent Monitoring

The USACE is authorized to discharge treated groundwater from the ATP to the Devens Municipal Sewerage System in accordance with Landfill Discharge Permit Number 020. The current permit, which mandates effluent sampling for arsenic and other select parameters on a monthly, quarterly, and/or annual basis and a maximum daily flow of 93,600 gallons per day (gpd), was last amended on June 28, 2016 and is in effect until June 28, 2019.

3.3.2.1 Permit Required Effluent Arsenic Monitoring

In accordance with the ATP’s discharge permit, the collection of effluent samples for the off-site analysis of arsenic concentration is required monthly. The discharge permit contains a Special Condition which applies an effluent limitation of 75 µg/L of arsenic for each monthly sampling event. Effluent samples were collected by an ATP operator each month throughout the year and submitted to SGS Accutest of Marlborough, Massachusetts for analysis.

Overall the plant has been effective at removing arsenic from the influent water stream. The analytical results did not exceed the effluent limitation of 75 µg/L. The monthly effluent arsenic in 2017 results ranged from 0.96 J µg/L (November 2017) to 39.4 µg/L (March 2017) with an average effluent arsenic concentration of 14.0 µg/L. The current and historical monthly effluent arsenic sampling results are presented in Table 3-7.

3.3.2.2 Quarterly Permit Required Effluent Monitoring

The ATP’s discharge permit requires quarterly sampling of plant effluent for metals (barium, manganese, and magnesium) and other select parameters (chloride, nitrate, and sulfate) for laboratory analysis. Quarterly effluent samples were collected on March 2, June 9, September 13, and December 11, 2017. The samples were submitted to SGS Accutest for analysis. Concentrations of all parameters sampled as part of the quarterly effluent monitoring were within permit defined discharge limitations. The current and historical quarterly effluent sampling results are presented in Table 3-8.

3.3.2.3 Annual Permit Required Effluent Monitoring

The ATP’s discharge permit requires annual sampling of plant effluent for laboratory analysis of select metals along with Total Toxic Organics and Total Petroleum Hydrocarbons. Total Toxic Organics are determined by the summation of results of VOCs, semi-volatile organic compounds, pesticides, and polychlorinated biphenyls. Annual effluent samples were collected during the September 13, 2017 quarterly event and submitted to Accutest for analysis.

Concentrations of all parameters sampled as part of the annual effluent monitoring were within permit defined discharge limitations. Annual effluent sampling results are presented in Table 3-9.

3.4 ATP OPTIMIZATION

The deployment of pressure transducers in the extraction wells and the MF module upgrades in January 2015 has allowed for further optimization of the ATP. The pressure transducers deployed in the extraction wells have eliminated the potential exposure of the well screen to air that is known to cause iron fouling. Thus, system downtime has been reduced and the system can now be controlled in a manner to optimize flow rates to best meet hydrogeologic capture goals.

The MF module upgrades have increased the total number of MF modules to a total of ten and has allowed for the increase of the average flow rate and throughput of the ATP.

3.5 RECOMMENDATIONS

No major system modifications were necessary in 2017. The system non-routine maintenance activities, along with system upgrades completed during 2017 are discussed in detail in Section 3.2.

The plant will continue to operate at 50+ gpm each month, with continued maintenance to include the following:

• To prevent unscheduled downtime due to the build-up of precipitate within the system influent piping that could restrict influent flow, the influent piping will be inspected annually and cleaned, if necessary, during a scheduled CIP event.

• To minimize operational downtime associated with equipment failure, system components will be regularly inspected and replaced prior to the end of their operational life.

4.0 LAND USE CONTROLS

In accordance with the LUCIP (Sovereign, 2014), the Army conducts annual monitoring and maintenance activities, which include Institutional Controls (ICs) and Affirmative Measures.

The ICs include monitoring the LUCs in accordance with the LTMMP Update (Sovereign, 2015), as well as the Town of Ayer and MassDEP enforcement related to the moratorium on groundwater extraction in the NIA. Affirmative Measures include reminder mailings sent by the Army to residents and property owners in the NIA, as well as annual communications between the Army and the town Board of Health (BOH) to review the groundwater restrictions.

As outlined in the LUCIP, the monitoring and maintenance activities include annual review to ensure LUC performance objectives are met. These include:

Institutional Controls

• The LUCs Area (Figure 1-4) is actively monitored and any required changes to the LUCs

Area will be made to the LUCIP, in consultation with and concurrence from EPA and MassDEP.

• Monitor and report on the implementation and enforcement of the ICs by the Town of Ayer and MassDEP, including the restriction of groundwater extraction and use within the NIA; record any instances where the groundwater use was identified, and corrective actions taken.

Affirmative Measures

• The informational pamphlet and contact information will be distributed annually to properties within the NIA and is included on the Ayer Board of Health website at https://www.ayer.ma.us/board-health/pages/shepleys-hill-landfill-resources under the title: Land Use Control Implementation Plan: Restriction of Groundwater Use, October 2017.

• A list of all property owners and resident addresses within the LUCs Area will be generated for implementation of the LUCIP actions noted.

• The LUCIP will be distributed to appropriate parties.

• The Army will meet with the BOH annually, or if a change in the groundwater contamination distribution in the aquifer occurs.

A review of the ICs was conducted during 2017. Interviews were conducted with the USACE, the Ayer DPW, the Ayer Building Inspector, the Ayer BOH, and the Nashoba Associated BOH.

These interviews confirmed that no new drinking water or irrigation wells were installed in the LUCs Area to their knowledge. No new construction activities or other changes were observed in the LUCs Area in 2017.

Affirmative measures identified in the LUCIP, including educational pamphlets, were mailed to owners and residents of the NIA in summer 2017 to ensure that owners and residents were informed of the…