SHL_-_Barrier_Wall_-_RACR_-_Final_-_Vol_1_2013.pdf

Prepared for:

US Army Corp of Engineers

New England District Concord, Massachusetts

Prepared by:

Sovereign Consulting Inc.

Contract No.: W912WJ-10-D-0003 Delivery Order: 0002

REMOVAL ACTION

COMPLETION REPORT

FOR SHEPLEY’S HILL LANDFILL BARRIER WALL

SHEPLEY’S HILL LANDFILL

FORMER FORT DEVENS ARMY INSTALLATION, DEVENS, MA

FINAL

JULY 2013

Removal Action Completion Report – Shepley’s Hill Landfill Barrier Wall Sovereign Consulting Inc.

Final Version

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-10-D- 0003 and Delivery Order 0002. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Removal Action Completion Report Shepley’s Hill Landfill

Barrier Wall

Final

Devens, Massachusetts

July 2013

CERTIFICATION:

I hereby certify that the enclosed Report, shown and marked in this submittal, is that proposed to be incorporated with Contract Number W912WJ-10-D-0003 DO#0002. This Document has been prepared in accordance with USACE Scope of Work and is hereby submitted for Government Approval.

Reviewed By:

7/24/2013

Sovereign Project Manager Date

7/24/2013

Sovereign Quality Control Manager Date

Received By:

USACE Project Manager Date

IORIO.MARYELLEN.1228893800 Digitally signed by IORIO.MARYELLEN.1228893800 DN: c=US, o=U.S. Government, ou=DoD, ou=PKI, ou=USA, cn=IORIO.MARYELLEN.1228893800 Date: 2013.07.24 12:39:30 -04'00' ii

TABLE OF CONTENTS

1.0 PROJECT DESCRIPTION

1.1 SITE BACKGROUND AND CONTAMINANTS

2.0 NATURE AND EXTENT OF CONTAMINATION AND CONCEPTUAL SITE

MODEL

3.0 OBJECTIVES AND SCOPE

3.1 REMOVAL ACTION OBJECTIVES

3.2 REMOVAL ACTION SCOPE

3.3 REMOVAL ACTION DESIGN

3.4 BARRIER WALL BACKFILL MIX DESIGN

3.4.1 Phase I Laboratory Testing

3.4.2 Phase II Laboratory Testing

4.0 SOIL BENTONITE BARRIER WALL CONSTRUCTION ACTIVITIES

4.1 SUBMITTALS

4.2 PRE-MOBILIZATION

4.3 MOBILIZATION

4.4 SITE PREPARATION

4.4.1 Pre-construction Survey

4.4.2 Access Road Upgrade and Haul Road Construction

4.4.3 Staging Area Construction

4.4.4 Erosion and Sedimentation Control

4.4.5 Working Platform Construction

4.5 BARRIER WALL INSTALLATION ACTIVITIES

4.5.1 Slurry Wall Installation

4.5.2 Slurry Wall Capping

4.5.3 Landfill Liner Repair

4.6 SITE RESTORATION AND DEMOBILIZATION

4.6.1 Site Restoration

4.6.2 Demobilization

4.6.3 Piezometer Installation

4.6.4 Post Construction Survey

4.7 MODIFICATIONS DURING CONSTRUCTION

iii

4.7.1 BACKFILL MIX MODIFICATIONS

4.7.2 SITE RESTORATION MODIFICATIONS

4.7.3 PIEZOMETER INSTALLATION CHANGES

5.0 WASTE DISPOSAL

5.1 SOLID WASTES

5.1.1 On-site Stockpiling of Landfill Waste-laden Soils

5.1.2 Screening and Disposal of Waste

5.2 LIQUID WASTES

6.0 PERFORMANCE STANDARDS & QUALITY CONTROL (QC)

6.1 BARRIER WALL INSTALLATION QUALITY CONTROL

6.2 LANDFILL LINER QUALITY CONTROL

6.3 PIEZOMETER INSTALLATION QUALITY CONTROL

6.4 HEALTH AND SAFETY

7.0 DEMONSTRATION OF COMPLETION

7.1 REMOVAL ACTION COMPLETION

8.0 PERFORMANCE MONITORING

9.0 PROJECT COST SUMMARY

10.0 COMMUNITY RELATIONS

11.0 CERTIFICATION STATEMENT

12.0 REFERENCES

iv

List of Figures

Figure 1 - Site Location Map Figure 2 - Site Plan Figure 3 - Barrier Wall As-Built Profile Figure 4 – Slurry Wall Cap As-Built Detail Figure 5 – As-Built Survey Figure 6 – Enlarged As-Built Survey

List of Tables

Table 1: Groundwater Quality Parameters Monitored During Piezometer Development Table 2: Barrier Wall Performance Monitoring Piezometer Construction Details

Appendices

Appendix A – Submittal Packages Appendix B - Results of Off-site Laboratory Backfill 25%/75% Mix Testing Appendix C - Piezometer Boring Logs Appendix D - Waste Disposal Documentation Appendix E - Results of On-site Quality Control Measures Appendix F - Results of Off-site Laboratory Backfill Quality Control Testing Appendix G - Construction Trench Profiles Appendix H - Results of Laboratory Backfill Cap Quality Control Testing Appendix I - Results of Laboratory Landfill Liner Repair Destructive Testing Appendix J - Contractors Quality Control Reports Appendix K - Construction Completion Inspection Documentation Appendix L – Response to Comments v

ABBREVIATIONS, ACRONYMS, AND SYMBOLS

Accutest Accutest Laboratories AHA Activity Hazard Analysis AOC Area of Contamination AM Action Memorandum AMEC AMEC Earth and Environmental, Inc.

API American Petroleum Institute ASTM American Society for Testing and Materials ATP Arsenic Treat Plant BCT Base Closure Team bgs Below Ground Surface BMI Benthic Macro Invertebrates CERCLA Comprehensive Environmental Response, Compensation, and Liability Act COC Contaminant of Concern COPC Contaminants of Potential Concern CQC Contractor Quality Control CQCP Contractor Quality Control Plan CQCR Contractor’s Quality Control Report cys Cubic Yards DERP Defense Environmental Restoration Program Devens Former Fort Devens DFW Definable Feature of Work DOD Department of Defense DOT Department of Transportation DTW Depth to Water eBMI Epibenthic Macro Invertebrates EE/CA Engineering Evaluation/Cost Analysis ERA Ecological Risk Assessment E&S Erosion and Sedimentation EQNE The Environmental Quality Company - Northeast FS Feasibility Study g/day Grams per Day Goulet Goulet Trucking HSO Health and Safety Officer HDPE High Density Polyethylene MA Massachusetts MassDEP Massachusetts Department of Environmental Protection MassDOT Massachusetts Department of Transportation MCP Massachusetts Contingency Plan Moretrench Moretrench American Corporation MSR Material Shipping Record NCP National Oil and Hazardous Substances Pollution Contingency Plan NHSEP Natural Heritage and Endangered Species Program NTCRA Non-Time-Critical Removal Action PACE People of Ayer Concerned about the Environment vi

PCBs Polychlorinated Biphenyls pcf Per Cubic Foot PVC Polyvinyl Chloride QC Quality Control QCM Quality Control Manager RAB Restoration Advisory Board RACR Removal Action Completion Report RAWP Removal Action Work Plan RCRA Resource Conservation and Recovery Act RAO Removal Action Objective RI Remedial Investigation ROD Record of Decision SHL Shepley’s Hill Landfill SOP Standard Operating Procedure Sovereign Sovereign Consulting Inc.

SOW Statement of Work SSHP Site Safety and Health Plan SVOCs Semivolatile Organic Compounds SWQS Surface Water Quality Standards TEC Threshold Effects Concentration Terrafix Terrafix Environmental U.S.A. Inc.

TDS Technical Drilling Services TPH Total Petroleum Hydrocarbons USCS Unified Soil Classification System USACE United States Army Corp of Engineers USEPA United States Environmental Protection Agency VOCs Volatile Organic Compounds WSP SELLS WSP SELLS Transportation and Infrastructure

1.0 PROJECT DESCRIPTION

This Removal Action Completion Report (RACR) was prepared by Sovereign Consulting Inc.

(Sovereign) to document Non-Time-Critical Removal Action (NTCRA) activities for the installation of a vertical hydraulic barrier (barrier wall) along the eastern portion of Shepley’s Hill Landfill (SHL) at the former Fort Devens Army Installation (Fort Devens) located in Devens, Massachusetts (MA). A Site Location Map is provided as Figure 1. The actions described in this document were performed by Sovereign under United States Army Corps of Engineers (USACE) Contract W912WJ-10-D-0003 DO#0002 and in accordance with the Final Removal Action Work Plan (RAWP) for Shepley’s Hill Landfill Barrier Wall (Sovereign, 2012b).

The NTCRA was performed pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) and the Defense Environmental Restoration Program (DERP). The Army is the lead agency for environmental cleanup at the former Fort Devens under Executive Order 12580 and the NCP. The Army has responsibility for implementing appropriate investigations, removal and/or remedial actions at sites where the release of hazardous substances may have or has occurred and where such releases may constitute a threat to human health and the environment. An Engineering Evaluation/Cost Analysis (EE/CA) (Sovereign, 2012c), a Final Action Memorandum (AM) (Sovereign, 2012b), and a RAWP (Sovereign, 2012a) were prepared in support of this NTCRA and describe the decision to proceed with the project and removal action specifics.

The primary project goals were to:

Mitigate the arsenic-in-groundwater flux from SHL to Red Cove/Plow Shop Pond to reduce potential risk to environmental receptors consistent with local conditions in Plow Shop Pond, and;

Comply with and/or achieve ARARs as applicable to Red Cove as summarized in the Appendix A of the RAWP (Sovereign, 2012a).

1.1 Site Background and Contaminants

Devens, MA 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 Committee closure in 1996.

SHL encompasses approximately 84 acres in the northeast corner of the main post of the former Fort Devens. The landfill is bordered to the northeast by Plow Shop Pond, to the west by Shepley’s Hill, to the south by recent commercial development, and to the east by land formerly containing a railroad roundhouse. Nonacoicus Brook, which drains Plow Shop Pond, is located north of the landfill (Figure 1).

SHL was reportedly operating by the early 1940s, and 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 incinerator ash, demolition debris, asbestos, sanitary wastes, glass, and other wastes. The maximum depth of the refuse occurs in the central portion of the landfill and is estimated to be about 40 feet below ground surface (bgs). The volume of waste in the landfill has been estimated at over 1.5 million cubic yards (cys), of which approximately 160,000 cys (11%) is below the water table. The saturated wastes appear to be emplaced in a wetland reducing environment; at least two areas previously mapped as wetlands were filled (Harding ESE, 2002) and have been found to be underlain by peat deposits (Sovereign, 2011).

The landfill was closed in five phases between 1987 and 1992-93 in accordance with Massachusetts Regulations at 310 CMR 19.000. The Massachusetts Department of Environmental Protection (MassDEP) approved the closure plan in 1985. Closure consisted of installing a 30 to 40-mil polyvinyl chloride (PVC) membrane cap, covered with soil and vegetation and incorporating 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.

Subsequent to closure of the landfill, remedial investigations (RIs) completed under CERCLA 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, particularly certain inorganics and volatile organic compounds (VOCs), in groundwater, sediment, and surface water at or adjacent to SHL. A Feasibility Study (FS) and Record of Decision (ROD) resulted in a remedy that required long term monitoring and maintenance of the existing landfill cap and groundwater monitoring. The ROD (USAEC, 1995) required the Army to perform groundwater monitoring and five-year reviews to evaluate the effectiveness of the selected remedial action, which relied heavily on the previously installed landfill cap to attain groundwater cleanup goals by 2008 and to reduce potential exposure risks. If groundwater contaminant concentrations, primarily arsenic, met risk-based performance standards (cleanup goals) over time, the ROD did not require further action; however, if cleanup goals were not met, the ROD required implementation of a groundwater extraction contingency remedy. Due to continued elevated contaminant concentrations, the Army installed and operated a groundwater extraction and treatment system in March 2006 as a contingency remedy to address groundwater contamination emanating from the northern portion of the landfill (Sovereign, 2011a).

All available data indicate that the current remedies – landfill capping and groundwater extraction – have reduced but not eliminated groundwater flow and arsenic migration from SHL into Red Cove / Plow Shop Pond, identified as Area of Contamination (AOC) 72. The AOC 72 RI (AMEC, 2011) results suggest that groundwater discharge contributes arsenic to sediment that may accumulate to levels that result in conditions that pose unacceptable risks, and therefore remedies that minimize such arsenic-in-groundwater flux to Red Cove would be most protective.

2.0 NATURE AND EXTENT OF CONTAMINATION AND CONCEPTUAL SITE

MODEL

The predominant source of the dissolved arsenic emanating from the landfill appears to be naturally occurring arsenic within aquifer sands and bedrock materials. Arsenic is being mobilized by both naturally-occurring and landfill-induced conditions through the geochemical process of reductive dissolution which releases dissolved arsenic to the aquifer.

Elevated arsenic concentrations in groundwater at SHL have subsequently impacted Red Cove/Plow Shop Pond which is located down-gradient and in close proximity to the northern portion of the landfill. Red Cove is a shallow cove with a water depth of less than one meter.

Current arsenic flux to Red Cove, which is a shallow cove with a water depth of less than one meter, is estimated at ~14.6 grams per day (g/day) and was estimated to be 20 g/day with the landfill cap in place before the groundwater extraction and arsenic treatment plant (ATP) were installed (Sovereign, 2011a).

The Army evaluated whether a significant risk to human health or the environment exists at the SHL with the current remedy in place (AMEC, 2011). The human health risk assessment indicated that potential exposures to Contaminants of Potential Concern (COPCs) (principally arsenic) in surface water and sediment in Plow Shop Pond, including Red Cove, by recreational receptors, are within the USEPA’s acceptable cancer risk range and do not exceed a Hazard Index (HI) limit of 1. Furthermore, the results of a qualitative evaluation of the potential for fish ingestion indicate that the estimated risks and hazards associated with arsenic do not exceed the risk management limits, even with conservative exposure assumptions. As a result, no contaminant of concern (COC) is identified in either surface water or sediment in Plow Shop Pond, specifically Red Cove, exceeding risk thresholds based on the quantitative human health risk characterization. Although concentrations of arsenic in surface water exceed the Massachusetts Surface Water Quality Standards (SWQS) protective of fish ingestion, arsenic is not identified as a COC related to SHL’s influence to Red Cove in surface water considering the results of the quantitative risk characterization. The arsenic surface water criterion protective of fish ingestion by humans is currently under review by USEPA. The arsenic cancer slope factor may increase pending toxicological review within the next few years, and such an increase may increase the human health risk estimated in the RI beyond USEPA’s acceptable cancer risk range.

The ecological risk assessment indicated a risk of adverse effects for several receptors. Risk of adverse effects to benthic macro invertebrates/epibenthic macro invertebrates (BMI/eBMI) from exposure to COPCs is indicated not only in Red Cove, but throughout both Plow Shop Pond and Grove Pond. The BMI/eBMI results suggest that a weight of evidence finding on the potential for ecological impacts associated with Red Cove is not possible. This is because all locations associated with this study show significant indications of impact related to either exceedance of threshold effects concentrations (TECs) or diminishment of benthic and/or epibenthic markers. Hence, the BMI/eBMI risks are not distinguishable between the various sampling locations based on the currently available data. These findings are consistent with earlier ecological risk assessments (ERAs) which identified apparent adverse effects on BMI/eBMI, but were not able to identify specific causes. Those ERAs concluded that sediment quality guidelines were exceeded most often for mercury, chromium, and arsenic, which is similar to the current finding (Gannett Fleming 2006). A localized risk of adverse effects to fish from exposure to ammonia at a Red Cove location is suggested by an aquatic bioassay.

3.0 OBJECTIVES AND SCOPE

3.1 Removal Action Objectives

The basis for action under the NCP is determined by the potential threats to public health, welfare, and the environment posed by conditions at Plow Shop Pond. In accordance with the RAWP (Sovereign, 2012a), the general removal action objective (RAO) was the following:

Mitigate the arsenic-in-groundwater flux from SHL to Red Cove/Plow Shop Pond to reduce risk to environmental receptors consistent with local conditions in Plow Shop Pond.

3.2 Removal Action Scope

To mitigate the arsenic-in-groundwater flux from SHL to Red Cove/Plow Shop Pond and reduce risk to environmental receptors consistent with local conditions in Plow Shop Pond, groundwater flowing to Red Cove from the SHL should be diverted, treated, or captured.

Particle track analysis conducted under present-day ambient pumping conditions has demonstrated that a barrier located along the eastern edge of the landfill would effectively mitigate the arsenic-in-groundwater flux by intercepting and diverting water flowing east into Red Cove/Plow Shop Pond from the landfill footprint to the north along the eastern landfill boundary under non-pumping conditions from the Arsenic Treatment Plant.

The barrier wall was installed along the eastern limit of the landfill and to the west of Red Cove.

The barrier wall extended from the ground surface, through the landfill cap and a thin mantling of waste (encountered in some northern areas), through native sandy glacial deposits and glacial till, and to the bedrock surface. The boundaries and length of the barrier wall were based on the identified areas of impacted sediment in Red Cove, groundwater concentrations along the eastern edge of the SHL, and particle track analysis. Specific details of the remedial action design are presented in the following subsections. Details of the barrier wall construction activities are discussed below in Section 4.0.

3.3 Removal Action Design

To achieve the RAOs, a barrier wall was designed to intercept and divert groundwater flowing in the overburden soils away from Red Cove. Groundwater modeling was performed to aid in designing the location, length, and depth of the barrier wall. The barrier wall consisted of an 850-foot long minimum barrier that extends through the overburden soils to the top of competent rock, with an effective hydraulic conductivity of 1 x 10-7 cm/sec. The location of the barrier wall is shown in Figure 2. The design of the barrier consisted of the development of project work plans and development of design drawings and specifications. The barrier wall drawings and specifications were presented in the RAWP (Sovereign, 2012a).

The design included the preparation of site plans, preparation of the site, soil/bentonite barrier wall construction, capping of the barrier wall and repair of the landfill liner/cap, management of excess soil material and landfill waste debris, and site restoration.

The results of a third party Green and Sustainable Remediation (GSR) study on the proposed Barrier Wall remedy as well as other alternatives evaluated during the FFS, performed by the US Army Engineering and Support Center, Huntsville (USAESCH), Environmental and Munitions Center of Expertise (EM CX), pursuant to the Department of Defense (DoD) Memorandum “Consideration of Green and Sustainable Remediation Practices in the Defense Environmental Restoration Program” (DoD, 2009) was incorporated into the design. During construction of the barrier the idling of the heavy diesel powered equipment was reduced the greatest extent possible. Additionally, all borrow material was provided via a local quarry. It should be noted that as reductions in green house gases were only associated with emissions and/or resource use, a qualitative analysis on resultant reductions was not appropriate for this scenario and therefore not included.

3.4 Barrier Wall Backfill Mix Design

The design of the barrier wall required development and testing of the slurry characteristics and a backfill mix design test to serve as the basis for determining the optimal backfill mix to be used during construction. The testing was performed in two phases. Phase I consisted of developing a mix design for the barrier wall, and Phase II consisted of testing the selected backfill mix to confirm that the mix was compatible with the site groundwater. Each phase of testing is briefly described in the following subsections.

3.4.1 Phase I Laboratory Testing

Bentonite Testing: Initial testing included selection of API Section 9 bentonite. The testing consisted of preparation of bentonite-water slurries (about 0.05 to 0.06 by weight). Slurry was mixed using site source water (hydrant on Cook Street), and tested for density, filtrate loss, viscosity, and pH.

Backfill Mixing: Backfill mixes (Mix 1 and Mix 2 with additional 0.5% dry bentonite added) were prepared and tested using the bentonite slurry previously tested, site soil (native overburden), plastic fines/clay borrow (Graves sample), and dry bentonite. The Graves sample source had a USCS characterization of ML-CL. Testing of the prepared backfill included density, slump, gradation, and hydraulic conductivity testing. The laboratory results of the backfill mixing tests are summarized as follows:

1) Testing was performed on three mix designs with the following proportions: Mix 1 – 50% sample No. 6 with 50% Graves sample with 0.5% dry Hydrogel bentonite; Mix 2

- 50% sample No. 5 with 50% Graves sample with 0.5% dry Hydrogel bentonite; and Mix 2 (with additional 0.5% dry bentonite added) - 50% sample No. 5 with 50% Graves sample with 1% dry Hydrogel bentonite.

2) Backfill Mix 1 consisted of 52.9% sand and 47.1% silt and clay. Backfill Mix 2 consisted of 59.9% sand, 0.9% gravel, and 39.2% silt and clay.

3) The initial bulk density values of Mix 1, Mix 2, and Mix 2 (with additional 0.5% dry bentonite added) were 98.3 lb/ft3, 106 lb/ft3, and 118 lb/ft3, respectively.

4) The final bulk density values of Mix 1, Mix 2, and Mix 2 (with additional 0.5% dry bentonite added) were 125 lb/ft3, 124 lb/ft3, and 134 lb/ft3, respectively.

5) For Mix 1, hydraulic conductivity values ranged from 2.1x10-7 to 2.4x10-7 cm/sec at 20° C. The average hydraulic conductivity was 2.2x10-7 cm/sec.

6) For Mix 2, hydraulic conductivity values ranged from 1.1x10-7 to 1.2x10-7 cm/sec at 20° C. The average hydraulic conductivity was 1.1x10-7 cm/sec.

7) For Mix 2 (with additional 0.5% dry bentonite added – i.e., total of 1% dry bentonite), hydraulic conductivity values were less than the 1x10-7 required value and ranged from 3.7x10-8 to 4.0x10-8 cm/sec at 20° C. The average hydraulic conductivity was 3.9x10-8 cm/sec. The fines content of the tested samples was 39.2% by weight.

Based on these results, Backfill Mix 2 (with a total of 1% dry bentonite) was selected for the mix design. In addition, this sample was also designated for long-term permeability / compatibility testing as detailed below.

3.4.2 Phase II Laboratory Testing

Long-term compatibility testing was performed on Backfill Mix 2 (with a total of 1% dry bentonite) sample as established in the Phase I testing and using site contaminated groundwater as the permeant. The testing simulated the performance of the backfill over the intended design life of the barrier. A minimum of two permeability tests were performed and consisted of one backfill sample permeated with site groundwater and one control sample using DI water as the permeant. Each sample was tested at a gradient sufficient to push a minimum of one pore volume through the sample over approximately one and a half months of permeation. At the completion of testing, the daily measured permeability and plots of flow versus time for each sample were reported. The laboratory results of the long-term compatibility testing are summarized as follows:

For the long-term testing of Mix 2 (with additional 0.5% dry bentonite added), hydraulic conductivity values were less than the 1x10-7 required value and ranged from 8.2x10-8 to 8.7x10-8 cm/sec at 20° C. The average hydraulic conductivity was 8.5x10-8 cm/sec.

4.0 SOIL BENTONITE BARRIER WALL CONSTRUCTION ACTIVITIES

The following is a description of the major elements associated with the construction of the barrier wall. These activities were completed by Sovereign between July 23, 2012 and November 20, 2012. For the implementation of this effort Sovereign subcontracted the following firms:

Construction Contractor: Moretrench American Corporation (Moretrench), of Rockaway, NJ responsible for the excavation and installation of the soil/bentonite wall construction

Engineering Consultant: AMEC of Portland, ME, who were engineer-of-record and responsible for the geotechnical engineering oversight of the soil bentonite slurry wall.

4.1 Submittals

During implementation of the SHL barrier wall NTCRA activities, construction-related required submittals were made to the USACE for review and approval under a USACE Engineering Form 4025. The submittal packages contained information pertaining to materials utilized during construction of the barrier wall. Copies of submittal packages are included as Appendix A.

4.2 Pre-mobilization

On July 19, 2012 a pre-construction meeting with USACE representatives and the Sovereign project team was conducted to discuss the barrier wall construction approach, define project requirements and expectations, and ensure that all team members understood applicable roles and responsibilities. Prior to mobilization, Sovereign’s subcontractor coordinated utility clearances. No further Federal or State permits were required.

4.3 Mobilization

After pre-mobilization requirements were completed, equipment and personnel were mobilized to the site to prepare and organize for construction activities. Mobilization activities were conducted from July 23 to August 13, 2012. All on-site personnel were trained and had the necessary certifications in accordance with the Site Safety and Health Plan (SSHP) (Sovereign, 2011a). The tasks for mobilization included, but were not limited to, the following:

Review of the Activity Hazard Analysis (AHA) for the activities that were conducted for that day with site personnel in accordance with the SSHP;

Inspection and transport of heavy construction equipment, slurry plant equipment, frac-tanks, tool containers, and generator to the site;

Installation of temporary facilities including an office trailers and sanitary facilities.

Temporary power was provided to the office trailers by a diesel powered generator; and

Established traffic control procedures.

4.4 Site Preparation

Site preparation activities were conducted in conjunction with mobilization activities from July 23 to August 13, 2012. The tasks for site preparation included the following:

4.4.1 Pre-construction Survey

On July 23, 2012 a detailed pre-construction survey of the removal action work area was completed by WSP SELLS Transportation and Infrastructure of Nashua, New Hampshire (WSP SELLS). The pre-construction survey included location and elevations of structures within the work area including existing long term monitoring wells as well as landfill surface drainage features along with the characterization existing conditions including ground surface topography in the vicinity of the work area. As part of the pre-construction survey the barrier wall alignment was staked out by the surveyor every fifty (50) feet from station 0+00 on the southern end of the wall to station 8+50 on the northern end. Additionally 10 foot offsets to the east of the barrier wall alignment and 60 foot offsets to the west of the barrier wall alignment were staked by the surveyor to establish the horizontal limits of the working platform. Station locations were staked every twenty (20) feet along the east side of the barrier wall alignment from station 0+00 to station 8+50.

4.4.2 Access Road Upgrade and Haul Road Construction

The existing landfill access road was upgraded in areas, as necessary to accommodate heavy vehicle traffic, from the Cook Street entrance extending to the northern portion of the barrier wall. Upgrades included the grading and filling of any uneven portions of the access along with the application of additional 1 ½ inch processed gravel to the road surface. Processed gravel was received from Powell Stone and Gravel in Lunenburg, MA. A new haul road was constructed by the barrier wall construction contractor, Moretrench, between the barrier wall and the staging area for equipment transportation and material hauling. The new haul road consisted of a sand and gravel surface underlain by a geomembrane.

4.4.3 Staging Area Construction

An approximate 10,000 square foot area consisting of sand and patches of grass located approximately 300 feet southeast of the barrier wall was grubbed and graded by Sovereign’s subcontractor – Moretrench, to function as the staging area for the removal action. The staging area housed office trailers, slurry plant equipment, frac-tanks, tool containers, and a diesel generator. The staging area was also used for the storage of bentonite supplies. Bentonite was stored on site within sealed pallets containing 50 pound bags along with sealed 2,800 pound bulk bags. A combination of approximately 2,100 feet of four and six inch high-density polyethylene (HDPE) piping was fused and installed from the fire hydrant on Cook Street to slurry plant located in the staging area, to provide the required volume of water for slurry wall mixing operations. A backflow preventer was obtained from and installed by the Devens Water Department prior to the connection of the HDPE piping to the fire hydrant.

4.4.4 Erosion and Sedimentation Control

To mitigate the spread of excavated soils and bentonite-water slurry to water drainage courses and Plow Shop pond during project construction activities, erosion and sedimentation (E&S) control measures were installed prior to the commencement of any earthwork activities. An augmented siltation fence (combination of hay bale and silt fence) was installed east and down-slope of the barrier wall between the barrier wall and Plow Shop Pond from Stations 2+50 to 7+00. The installation of siltation fence was not required east of the remaining portions of the barrier wall as elevation of the ground surface was greater than the barrier wall in these areas.

At the top and east side of the barrier wall working platform, a slurry control berm, constructed of common borrow, was installed to mitigate overflow and splashing of slurry from leaving the working platform.

4.4.5 Working Platform Construction

Construction of the barrier wall required that a constant elevation be maintained at the ground surface. As part of site preparation activities, a level surface (or working platform) capable of supporting heavy construction loads (e.g. large tracked excavator, dozers and loaders) was constructed by the Moretrench. The working platform was constructed to an area approximately 40 feet wide which included a 10-foot wide portion to the east of the barrier wall alignment and a 30-foot wide section to the west of the barrier wall alignment and extended approximately 50 feet south and north of Stations 0+00 and 8+50. The working platform was constructed with borrow from an existing soil stockpile located near the staging area as instructed by the USACE. Borrow was mined from the existing soil stockpile with the use of an excavator and all large boulders were removed from the mined material prior to use in the construction of the working platform. Prior to the placement of the borrow material the working platform area was grubbed and stripped of topsoil.

4.5 Barrier Wall Installation Activities

Barrier wall installation activities consisted of the construction of a soil-bentonite barrier and capping of the barrier. The soil-bentonite barrier was constructed using a slurry trench method of construction. Capping of the soil-bentonite barrier to complete the barrier wall consisted of two types:

Capping of the barrier outside the landfill limits using a woven geotextile and low-permeability backfill; and

Capping of the barrier within the landfill using a woven geotextile and low-permeability backfill followed by repair of the landfill cap system over the barrier.

Soil-bentonite barrier construction methods and details as well as capping details are described in the following subsections.

4.5.1 Slurry Wall Installation

The soil-bentonite barrier wall was constructed using a slurry trench method of construction, in which a narrow and deep linear trench was excavated through the overburden soils until bedrock was encountered. During excavation, the trench is filled with a bentonite-water slurry, which maintains a positive outward pressure on the trench sidewalls and maintains stability of the trench. The soil-bentonite barrier is then completed by placing low permeability soil (native and imported soil blend) to achieve a soil-bentonite mixture with hydraulic conductivity lower than the design value (1.0 X 10-7 cm/sec). Slurry wall installation activities were conducted from August 15 through September 13, 2012.

Excavation and installation of slurry trench was completed by Moretrench with the use of a Caterpillar 375 excavator equipped with a long-stick and boom attachment and a 2.5 feet wide “V” shaped rock bucket with multiple ripping teeth. Prior to the commencement of excavation activities station locations were established along the barrier wall alignment every ten (10) feet from station 0+00 to station 8+50. These “stations” were established along the barrier wall alignment to designate specific points at which soundings of the excavation would be taken throughout slurry wall installation activities as required by the specifications. In order to ensure clean contact with competent bedrock throughout the entire excavation of the trench, Sovereign requested that Moretrench supersede the specifications by establishing stations every 10 feet instead of specified 20 feet at which soundings would be taken and refusal determined during construction of the slurry wall. In order to reach the desired depth at station 0+00 and to allow for a gradual transition of backfill, a lead in trench with the bottom sloped between 1H:1V and 2H:1V (horizontal to vertical) was excavated from station 0+25 to station 0+00. Starting at station 0+00 the trench was excavated through the overburden and completed to the top of competent bedrock at each ten foot station. Refusal was defined as the depth at which a minimum of three (3) passes of the excavator bucket resulted in less than 0.1 feet or less of advancement of the excavation using full downward pressure of the excavation equipment.

The following procedure was used at each 10foot station from station 0+00 to station 8+50 in order to determine that a competent bedrock surface had been encountered:

Once it was apparent that the bedrock surface had been encountered from observations of the trench cuttings and “reaction of the excavator,” a preliminary manual sounding was taken at the station using a weighted tape to confirm that the depth was similar to the estimated depth that was developed based on the results of the pre-design investigations (i.e., borings and seismic refraction survey results).

Following the initial sounding, three to five more passes with the excavator bucket were completed followed by a second sounding.

Results of the second sounding were compared to the results of the first sounding. If the results were not within 0.1 feet, an additional three to five passes were made with the excavator bucket followed by an additional sounding.

Sets of three to five additional passes were made until back-to-back soundings were within 0.1 feet of each other and it was the determination of the AMEC engineer, based on sounding results, observation of cuttings, along with the reaction of the excavator, that refusal at competent bedrock had been reached for that particular station.

The depth at which refusal was determined by AMEC engineer was then recorded by Sovereign on-site QC manager as “Final Trench Depths” in the Contractor’s Quality Control Reports (QCR) and used to construct an as-built profile of the refusal (bedrock) surface elevation.

USACE representatives were on-site periodically throughout excavation and installation of the slurry trench to conduct construction progress inspections during which refusal criteria procedures were witnessed. During inspections USACE representatives were in concurrence with refusal criteria procedures being utilized.

As mentioned above, during construction of the barrier wall an as-built vertical profile of the refusal (bedrock) surface elevation was constructed utilizing the refusal determinations at each ten foot station as described above. The on-going as-built vertical profile was compared to the Interpretive Subsurface Profile Along Vertical Hydraulic Barrier (Sheet 6, 100% Design Submission) of the RAWP throughout construction activities. The Interpretive Subsurface Profile Along Vertical Hydraulic Barrier (Sheet 6, 100% Design Submission) was a profile that was extrapolated from a series of borings spaced approximately 100 feet apart in the vicinity of the barrier wall alignment. These borings also had lateral off-sets in the east-west direction from the final barrier wall alignment ranging from 0 to 56 feet. The anticipated bedrock topography depicted on the Interpretive Subsurface Profile Along Vertical Hydraulic Barrier of the RAWP was therefore extrapolated from these borings. Considering both the spacing of the borings and the off-sets, the subsurface conditions encountered during the construction of the barrier wall are generally consistent with anticipated subsurface conditions. Certain variation is expected as bedrock topography can be affected locally by former tectonic shear zones, artifacts from glaciation and erosion, among other factors. A final As-built Barrier Wall Profile is included as Figure 3.

Throughout the excavation of the trench a bentonite-water slurry, exhibiting an initial unit weight of approximately 64 pounds per cubic foot (pcf), was pumped from the mixing tanks and into the trench to provide trench stability. During excavation activities the slurry level in the trench was maintained by Moretrench with the combination of introducing additional slurry from the mixing tanks to the trench or the addition of backfill material in completed trench areas. The slurry level was kept as close to the working platform surface as was practical and was not allowed to drop below a level of more than three feet below the working platform surface.

Slurry unit weight generally increases with increased suspension of excavated material (up to 90 pcf or greater). A maximum unit weight of 90 pcf is typical for this application, and deposition of material would not be expected to occur at slurry unit weights below this value.

As detailed in Section 6.1.2 on-site field testing of the slurry was conducted twice per a work shift prior to placement in the trench and three (3) times per a work shift on slurry from within the trench excavation to monitor unit weight of the slurry. The 90 pcf unit weight was considered an action level, where adjustments were made to the slurry if the 90 pcf unit weight value was exceeded during on-site field testing. Potential deposition of material was also monitored by daily measurement of the trench depth and compared to previously measured values as detailed in Section 6.1.2.

During trenching operations batches of low-permeability backfill consisting of excavated overburden native soils from the trench supplemented with approximately 50 percent imported plastic silt/clay fines and approximately 1.5 percent bentonite were mixed alongside the southern portion of the trench. Backfill mixing was conducted in an area of the site outside the limits of the existing landfill cap limit, to reduce the amount of heavy machinery atop of the existing landfill cap. Each backfill batch was approximately 100 cubic yards (cys) and was mixed by blending of component materials using an excavator with smooth-edged cutting buckets (no teeth) and a loader. During blending operations the backfill batches were hydrated with slurry from the mixing tanks and mixed to ensure homogeneity consistent with the backfill mix design. Following mixing/blending of each backfill batch, as detailed in Section 6.1.2, samples were collected from each backfill batch for on-site and submitted for off-site QC testing prior to placing the backfill batch in the trench excavation to ensure backfill would exhibit a hydraulic permeability of at least 1 x 10-7 cm/sec.

Low-permeability backfill was placed into the trench excavation with the use of a loader.

Backfill was placed continuously from the beginning of the trench in the direction of the excavation starting initially by lowering the backfill into beginning of the lead-in trench.

Additional backfill was then placed in the trench in a manner such that the backfill entered the trench by sliding down the face of the previously placed backfill. Backfill was mounded approximately two feet above the working platform grade to accommodate consolidation.

4.5.2 Slurry Wall Capping

Barrier wall capping activities were completed from September 20 through September 26, 2012 and consisted of the placement of a low-permeability backfill above the soil-bentonite backfill (barrier wall).

The barrier wall was capped after removal of the working platform by excavation of the soil-bentonite backfill down to depth of approximately two feet below preconstruction grade. The soil-bentonite backfill and sides of the excavation were lined with a woven geotextile (TenCate Mirafi 600X) as a separator. Pins were installed into the sidewalls of the barrier wall trench every 20 feet or more as needed to secure the geotextile to the trench sidewalls. An overlap with a minimum width of 24 inches was used at the joint of the geotextile. Following the installation of the geotextile the trench was backfilled with two feet of a low-permeability backfill placed in loose lifts not exceeding 12 inches and compacted with an excavator bucket to achieve a stable lift of material without disturbing the soil-bentonite backfill sub-grade. The low-permeability backfill was then covered with at least six inches of sandy soils. Slurry wall capping details are presented on Figure 4.

During barrier wall capping activities quality control (QC) samples of the low-permeability backfill were collected for off-site laboratory analysis. Details of QC sampling and results are detailed in Section 6.1.2.

4.5.3 Landfill Liner Repair

A geomembrane patch was installed atop the barrier wall cap as a portion of the existing landfill liner was removed during removal action activities to allow for the construction of the slurry wall. Prior to the installation of a new geomembrane patch, the existing liner was exposed approximately five (5) to eight (8) feet on each side the barrier to check for any additional damage to the existing liner that may have occurred during construction of the slurry wall. In addition the surface to be covered by the geomembrane was cleared of sharp objects, angular stones, sticks, or any materials that may contribute to punctures or tearing of the geomembrane material.

Landfill liner repairs were conducted by Terrafix Environmental U.S.A. Inc. of Lewiston, Maine (Terrafix) on October 5 and 9, 2012. The geomembrane patch was constructed of Solmax International Solmax-240 40 mil PVC. All geomembrane repair seams were at a minimum two

(2) inches wide and constructed using a chemical fusion weld. Prior to the application of the chemical fusion agent both the existing landfill liner and the new PVC were cleaned of all dust, dirt, debris and excess moisture. The two PVC materials were compressed together with a roller until a thin excess of the chemical fusion agent was forced out of the seam and a bond was formed. Following the completion of landfill liner repairs, the repaired areas were backfilled with one (1) foot of drainage sand prior to top-dressing the area with sandy soils. During landfill liner repair activities, destructive QC samples of chemically welded seams were collected and submitted to an off-site testing facility. Details of QC sampling and results are detailed in Section 6.2.

4.6 Site Restoration and Demobilization

4.6.1 Site Restoration

Upon completion of the barrier wall installation and landfill liner repairs site restoration activities were conducted in areas of the SHL that were disturbed during barrier wall construction activities, which totaled approximately 2.2 acres. At the request of the USACE, excavated soils containing no landfill waste and the working platform were re-graded into the existing disturbed area, while ensuring that grades were achieved to allow for proper drainage off the landfill. Additionally the drainage swale located between barrier wall station 2+50 and station 3+00 disturbed during barrier wall construction activities was re-constructed to match pre-construction conditions. During the construction of the barrier wall approximately 500 cys of landfill waste-laden soils containing plastic, wood, metal and concrete were encountered. As part of site restoration activities all waste was segregated from the soils and properly disposed of off-site at appropriate receiving facilities. Solid waste disposal activities are detailed in Section 5.1.

At the request of the USACE, no top soil was applied to the disturbed areas. The disturbed areas were top-dressed with sandy subsoil material and power-raked to remove all rocks greater than six inches. A warm season grass mix as requested by the USACE, following coordination with the Natural Heritage and Endangered Species Program (NHSEP) of the MA Division of Fisheries and Wildlife, and consisting of the following was applied to all disturbed areas via hydroseeding on October 25 and November 5, 2012. USACE will monitor the seeded area and submit a monitoring report to NHESP in the Fall of 2013.

Species/Variety Pounds/Acre

Pure Live Seed

Niagara or Kaw Big bluestem 4

Aldous, Camper, or Blaze Little bluestem 6

Rumsey, Osage, or NE-54 Indiangrass 2

Blue false indigo 0.01

Lance leaved coreopsis 0.05

Perennial lupine 0.05

Blackeyed susan 0.1

4.6.2 Demobilization

Demobilization activities for the removal action were initiated on September 13, 2012 with the breakdown of the slurry plant. Breakdown of the slurry plant included the cleaning of the three frac-tanks, disassembly and cleaning of hoses and pumps, disassembly of the slurry plant electrical system, along with the disassembly of the HDPE piping. All slurry plant components including frac-tanks, pumps, and diesel generator were removed from the site by September 18, 2012. All heavy equipment including excavators, loaders and dozers were removed from site during restoration activities on an as needed basis. All remaining materials and equipment used during the removal action were removed from the site by November 20, 2012.

4.6.3 Piezometer Installation

In accordance with the RAWP (Sovereign, 2012a), a series of overburden groundwater piezometers were installed along the barrier wall alignment to provide hydraulic performance monitoring of the barrier wall. Well screens for each of the piezometers were set at similar depths across the length of the wall to the extent possible considering the saturated overburden thickness, versus the original plans to set atop the bedrock surface. In addition and given the layout of the barrier wall, ten (10) piezometers rather than eight (8) piezometers were installed to measure the piezometric heads across the barrier wall. The piezometers consisted of five (5) sets of wells (two wells per set), with one point per set located up-gradient of the barrier wall (westerly side) and the other down-gradient (easterly side) of the barrier wall. Figure 2 displays the locations of the piezometers. The spatial orientation of the piezometers was determined based on both a review of the depth to rock observations documented during the barrier wall construction and based on lateral spacing considerations to allow for a pair at the barrier wall hinge point closest to Red Cove. The piezometers were off-set approximately eight to ten feet from each side (or the edge) of the barrier wall.

The ten (10) piezometers were installed via hollow-stem auger drilling methods at the site by Technical Drilling Services of Sterling Massachusetts (TDS) from October 9 through October 11, 2012. Soils were visually characterized in two-foot sampling lengths until desired depths were achieved. Each piezometer was constructed with ten (10) feet of two-inch diameter PVC well screen, with two-inch PVC riser extending to approximately three feet above final grade. Filter sand was placed around the screen and extended two to three feet above the well point screen.

Next, a two-foot thick bentonite seal was installed, followed by grouting the remainder of the void to within two feet of grade, where then a Portland cement grout mixture was emplaced.