PHASE III REMEDIAL ACTION PLAN (PHASE III RAP) 350 IRVING STREET FRAMINGHAM, MASSACHUSETTS. PREPARED FOR: NSTAR Gas Company Boston, Massachusetts

Transcription

1 PHASE III REMEDIAL ACTION PLAN (PHASE III RAP) 350 IRVING STREET FRAMINGHAM, MASSACHUSETTS PREPARED FOR: NSTAR Gas Company Boston, Massachusetts PREPARED BY: GZA GeoEnvironmental, Inc. Norwood, Massachusetts January 2009 File No Copyright 2009 GZA GeoEnvironmental, Inc.

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3 TABLE OF CONTENTS Page 1.00 INTRODUCTION OBJECTIVES AND SCOPE OF THE PHASE III RAP ORGANIZATION OF DOCUMENT BACKGROUND SITE DESCRIPTION SITE HISTORY MCP COMPLIANCE HISTORY Immediate Response Action, October Phase II Comprehensive Site Assessment, October REMEDIAL OBJECTIVES RESPONSE ACTION OUTCOMES Permanent Solution Temporary Solution DEVELOPMENT OF REMEDIAL ALTERNATIVES NO FURTHER ACTION INSTITUTIONAL CONTROLS INITIAL SCREENING OF SOIL AND NAPL REMEDIAL TECHNOLOGIES Natural Attenuation Containment Technologies In-Situ Technologies In-Situ Physical/Chemical Technologies In-Situ Biological Treatment In-Situ Thermal Treatment Excavation and Off-Site Disposal 19

4 TABLE OF CONTENTS (continued) Page Ex-Situ Treatment Technologies and Off-Site Disposal Options INITIAL SCREENING OF GROUNDWATER REMEDIAL TECHNOLOGIES Natural Attenuation In-Situ Biological Treatment In-Situ Physical/Chemical Treatment Ex-Situ Physical and Chemical Treatment Containment INITIAL SCREENING OF WETLAND REMEDIAL TECHNOLOGIES Natural Attenuation Excavation and Off-Site Disposal Containment In-Situ Treatment Ex-Situ Treatment EVALUATION OF PERMANENT AND TEMPORARY SOLUTIONS DETAILED EVALUATION OF REMEDIAL ALTERNATIVES FOR SOIL/NAPL Permanent Solution Excavation of Off-Site Disposal Solidification/Stabilization Temporary Solution Excavation and Off-Site Disposal of Soil Containment of Soil DETAILED EVALUATION OF REMEDIAL ALTERNATIVES FOR GROUNDWATER Passive Reactive Barriers Groundwater Extraction and Treatment DETAILED EVALUATION OF REMEDIAL ALTERNATIVES FOR WETLANDS 36

5 TABLE OF CONTENTS (continued) Page Permanent Solution Excavation and Off-Site Disposal Containment of Sediment Temporary Solution Excavation and Off-Site Disposal Containment of Sediment SELECTION OF REMEDIAL ALTERNATIVE SELECTION OF THE PREFERRED REMEDIAL ACTION FOR A A PERMANENT SOLUTION SELECTION OF THE PREFERRED REMEDIAL ACTION ALTERNATIVE FOR A TEMPORARY SOLUTION ENTERTAINING STEPS TO OBTAIN A PERMANENT SOLUTION SCHEDULE FOR IMPLEMENTATION PUBLIC INVOLVEMENT SUMMARY AND CONCLUSIONS PHASE III COMPLETION STATEMENT 45 TABLES TABLE 1 TABLE 2 INITIAL SCREENING OF REMEDIAL TECHNOLOGIES TECHNOLOGY SCREENING MATRIX PERMANENT SOLUTION TABLE 3 TECHNOLOGY SCREENING MATRIX TEMPORARY SOLUTION APPENDICES APPENDIX A APPENDIX B TRANSMITTAL FORM BWSC108 LIMITATIONS J:\17,000-18,999\18640\ DDM\Phase III\TABLE OF CONTENTS.doc

6 1.00 INTRODUCTION GZA GeoEnvironmental, Inc. (GZA) has prepared this Phase III Remedial Action Plan (Phase III RAP) on behalf of NSTAR Gas Company (NSTAR Gas) for the property located at 350 Irving Street, in Framingham, Massachusetts (the Site ). The Site was formerly occupied by a manufactured gas plant (MGP) from approximately 1889 to Tar processing and storage also occurred on two portions of the property. The Site is identified by the Massachusetts Department of Environmental Protection (MassDEP) using Release Tracking Number (RTN) This document has been prepared in accordance with Section of the Massachusetts Contingency Plan (MCP), and supports the endorsed Comprehensive Response Action Transmittal Form (BWSC108) contained in Appendix A. This document and the work described herein are subject to the limitations contained in Appendix B. Our analysis employed the procedures and criteria contained in the current version of the MCP (310 CMR In addition, to foster green remediation strategies and environmental stewardship, we considered the relative fossil fuel consumption and greenhouse gas (GHG) emissions from each viable remedial alternative OBJECTIVES AND SCOPE OF THE PHASE III - RAP As defined in the MCP, the objectives of Phase III are: 1. to identify and evaluate Remedial Action Alternatives (RAA) which, when implemented, are reasonably likely to achieve a level of No Significant Risk to surrounding human and environmental receptors; and, 2. to recommend a RAA that is a Permanent Solution or Temporary Solution, where a Permanent Solution includes measures that reduce, to the extent feasible, the concentrations of oil and/or hazardous material (OHM) in the environment to levels that achieve or approach background. The scope of the Phase III consists of the following tasks: 1. identification of the extent of OHM in Site media which require remediation; 2. screening of appropriate remedial technologies; 3. development of applicable RAA based on the screening results; 4. performance of a comparative evaluation of the RAA; and, 5. selection of a preferred RAA. 1

7 The evaluations and recommendations contained in the Phase III are based on fieldwork, environmental explorations, and sampling and analyses performed by GZA on behalf of NSTAR Gas during implementation of an Immediate Response Action (IRA) and Phase II Comprehensive Site Assessment (CSA). The IRA Completion Report was submitted to MassDEP in October 2006, and the Phase II CSA was submitted in October A summary of these assessments are provided below in Section ORGANIZATION OF DOCUMENT This document is organized into eight sections as outlined below: 1. Section 1.00 contains the introduction to and the purpose of the Phase III; 2. Section 2.00 provides relevant project background, including a description of the Site and the immediate vicinity, the historical uses of the Site, MCP compliance history, and the results of previous environmental assessments; 3. Section 3.00 gives a summary of the remedial objectives for the Site; 4. Section 4.00 contains a discussion of general classes of remedial technologies that are typically applicable at similar sites, and presents the results of the initial screening of technologies in these classes; this section includes the first step in the feasibility assessment, where technologies that would be ineffective or not implementable at the Site are eliminated from further consideration; 5. Section 5.00 presents a detailed evaluation of three selected RAA, including a discussion of the screening criteria used for selection; 6. Section 6.00 provides a description of the preferred RAA and the justification for the selection; 7. Section 7.00 provides a summary of the Phase III evaluation; and, 8. Section 8.00 contains the Phase III Completion Statement BACKGROUND The following sections present a brief description of the Site and the immediate vicinity, and summaries of historical Site use, MCP compliance history, and previous environmental assessments. Detailed summaries are provided in Section 2.00 of the Phase II CSA. 2

8 2.10 SITE DESCRIPTION A Site Locus Map showing the location of the Site with respect to topographic and cultural features in the town of Framingham and the physical layout of the Disposal Site is shown on Figures 1 and 2 respectively in the Phase II CSA. These figures also include the delineation of the eight Areas of Concern (AOC) identified during the Phase II. The Site consists of 22 acres of land bounded to the south and southwest by Irving Street, to the west by commercial property, to the north by wetlands and Beaver Dam Brook (which flows from the west, then to the north as it exits the Site), and to the east by wetlands and an unnamed tributary stream that flows north and discharges to Beaver Dam Brook. NSTAR Gas owns the majority of the Site, with the exception of a parcel of land to the southeast owned by the operators of Wellesley Trucking Services, Inc. In addition, a portion of the Beaver Dam Brook area is included with the Site Disposal Boundary, however the Beaver Dam Brook area has not been fully delineated and the Site Disposal Boundary may change in the area of Beaver Dam Brook upon further investigation. The Sudbury Aqueduct, an inactive water supply tunnel owned by the Commonwealth of Massachusetts and operated by the Massachusetts Water Resources Authority (MWRA), bisects the Site from roughly west to east, and divides the Site into north and south parcels. The aqueduct was built in 1878, and is a brick-lined, gravity flow conveyance, with an average diameter of 8.5 feet and a design flow of approximately 90 million gallons per day. The aqueduct connects the Framingham Reservoir system to the Chestnut Hill Reservoir. The MWRA currently considers the aqueduct a water resource for emergencies only, and rehabilitation would be required prior to restoration to active service. MWRA has no immediate plan to rehabilitate the aqueduct. The open areas of the property to the north of the aqueduct are currently used by a landscape materials supplier for staging large piles of loam and mulch, and pallets of dimension and decorative stone and brick. This portion of the property is surrounded by a soil berm containing variable quantities of debris (asphalt, shingles, and concrete) that was imported and placed by the former property owner, Mr. John Glynn. The unused northern and eastern portions of this property are bounded by wetlands associated with Beaver Dam Brook (to the north) and an unnamed tributary (to the east). Areas of mowed vegetation and wetland are on either side of the Sudbury Aqueduct. The western portion of the property to the south of the aqueduct is used by the landscape materials supplier for storing smaller piles of sand and gravel, and pallets of dimension stone and brick. The central portion is used by a variety of tenants for parking cars and storing landscape vehicles and equipment, and for cutting and storing piles of firewood. The southeastern portion of the Site is owned by Wellesley Trucking Services, Inc., and used for parking garbage trucks, storing roll-off containers and trash dumpsters, and for performing maintenance on trucks and equipment. The unused eastern portions of the property south of the aqueduct, and the area along the immediate-southern boundary of the aqueduct, consist of upland forest and wetlands. 3

9 2.20 SITE HISTORY In order to locate potential source-areas of contamination associated with MGP and tar handling operations, GZA reviewed available scaled plans of the Site ranging in date from 1886 to The plans were obtained from various Framingham municipal offices and from NSTAR Gas archives. Based on historical topographic maps, in 1886, the majority of the Site, with the exception of portions along Irving Street, existed as wetlands prior to construction of the Sudbury Aqueduct. Portions of the property were subsequently filled and first developed by the Framingham Gas, Fuel, and Power Company in The Site was used for MGP operations up to Processing and storage of by-product tar was also conducted on portions of the property north and south of the aqueduct from 1926 to at least Areas of the property were sequentially filled as MGP and tar processing operations changed. By 1968, all MGP and tar processing operations ceased and the majority of the infrastructure removed MCP COMPLIANCE HISTORY According to historical records filed with Town of Framingham municipal offices, ComGas, a corporate predecessor of NSTAR, took possession of the property in In 1982, ComGas sold the property to John Glynn of Environmental Restoration, Inc., with the strict requirement that the buyer properly remediate the property. In 1983, ownership of the property was transferred to 350 Irving Street Trust with Mr. John Glynn as trustee. The southeast portion of the Site was subsequently sold to 3D Realty Trust, the operators of Wellesley Trucking Services, Inc. Mr. Glynn failed to remediate the property and achieve regulatory closure under Chapter 21E and the MCP, and in September, 2008 NSTAR Gas acquired the property for the purposes of addressing the historical environmental conditions. With the exception of the Sudbury Aqueduct, NSTAR Gas owns the remainder of the Site. The Site has been the subject of numerous environmental assessments. In 1983, a hydrogeologic assessment was conducted by IEP Geoscience (IEP) on behalf of then owner Mr. John Glynn (350 Irving Street Trust). This study identified levels of organic volatile and semi-volatile contaminants concentrated within the shallow and intermediate portions of the groundwater system. In 1990, under the provisions of the 1988 MCP, the Site was listed by MassDEP as a Priority Disposal Site and RTN was assigned. In 1995, under the revised 1993 version of the MCP, the Site was designated a Tier 1B Disposal Site, and a Public Involvement Site. In 1998, as part of a Release Abatement Measure (RAM) undertaken by the 350 Irving Street Trust, 6 acres of the property were paved with asphalt. In 1998, the Trust submitted MCP Phase II and Phase III reports to MassDEP in response to a Notice of Non- Compliance (NON) issued in In 1999, the Trust submitted a Phase IV report to MassDEP that included plans for paving additional areas of the Site with asphalt, construction of a groundwater treatment system, and drainage improvements. However, those tasks specified in the Phase IV report were not implemented. 4

10 In 1999, Comprehensive Environmental, Inc. (CE) performed an inspection of the interior of the inactive Sudbury Aqueduct on behalf of the MWRA. At that time, oil/tar residue was observed seeping into the aqueduct near Aqueduct Manhole Sta Orange mineral precipitate indicative of oxidized iron was also observed in the seepage. To address this condition, the Trust submitted an IRA Plan to MassDEP in September The IRA Plan included subsurface explorations in the vicinity of the aqueduct and soil and groundwater sampling and analyses. In April 2004 an Addendum to the 1999 IRA Plan was prepared for the Trust by Corporate Environmental Advisors, Inc. (CEA). The Addendum included a proposal to (1) mitigate the seepage of NAPL into the aqueduct using a 700-foot interceptor trench, and (2) removal of coal-tar impacted sediments in the on-site wetlands, followed, and augmented by, bioremediation. In 2004, MassDEP issued RTN following the discovery of NAPL in a monitoring well installed during an assessment performed in support of a real estate transaction. In response, an IRA Plan was prepared by CEA, on behalf of the Trust, and submitted to MassDEP on October 21, In February 2005, MassDEP issued a NON to the Trust for failing to perform certain additional assessment activities and remedial actions. In response to the NON, the Trust submitted a notice of Financial Inability indicating that it was no longer financially able to implement the required MCP Response Actions. In April 2005, MassDEP issued an NOR to NSTAR Gas, the successor to ComGas, as a new Responsible Party (RP) under MGL Chapter 21E. In response to the NOR, NSTAR completed an assessment-only IRA in October 2006 and a Phase II Comprehensive Site Assessment in October Summaries of each investigation are provided in the sections that follow Immediate Response Action, October 2006 The IRA included field explorations and sampling to evaluate: the intrusion of light non-aqueous phase liquid (LNAPL) into the Sudbury Aqueduct; the presence of LNAPL in the wetlands and surface water bodies that border the Site to the north and east; and, the presence of dense non-aqueous phase liquid (DNAPL) in monitoring wells located near the southwest margin of the Site. Stains and incrustations of what appeared to be historic seeps of coal tar were identified during the interior inspection of the Sudbury Aqueduct. The seeps originated from the mortar joints between the bricks of the aqueduct s walls at approximately the elevation of the groundwater table. NAPL was not detected in any of the six new piezometers installed along the alignment of the aqueduct. This data, along with the historical data from the previously installed wells, most of which were subsequently destroyed, did not indicate that a mobile NAPL pool existed outside that section of the 5

11 aqueduct where historic coal tar intrusion was observed. Thus, it was concluded that the available groundwater data, combined with the results of the interior aqueduct inspection, did not indicate that an ongoing condition of Substantial Release Migration, as defined in the MCP, existed at the Site in the vicinity of the aqueduct. Visual observations of the extent of sheens on surface water and within the wetlands indicated that a condition of Readily Apparent Harm (RAH), as defined in the MCP, existed in the wetlands and certain upland areas both north and south of the Sudbury Aqueduct. It was estimated that the limits of visible contamination, as evidenced by the occurrence of sheens, stains, and NAPL, totaled approximately 7 acres. The area of impacted sediments was estimated to be greater than 1,000 square feet. The delineation of the area of RAH, as defined during IRA and Phase II exploration and sampling, is shown on Figures 3 and 4 in the Phase II CSA and further discussed in this report in Sections 4.00 and It was concluded in the IRA that the presence of OHM in the wetland areas did not present an Imminent Hazard to the environment. GZA did not observe readily apparent signs of stress to vegetation in the wetlands, nor gross adverse impacts to the on-site benthic community. The Site wetlands or tributary stream that discharges to Beaver Dam Brook does not function as fish habitat.. An area of cyanide waste and soil, most likely derived from the disposal of spent oxides from the MGP purifier-boxes, was identified in shallow samples (0 to 3 feet below grade) of upland soil collected in the vicinity of the wetlands that fringe the southeastern margin of the Site. The levels of physiologically available cyanide (PAC) in samples were below the level that would represent an Imminent Hazard to human health. The evaluation also indicated that Imminent Hazards to safety and public welfare did not exist at the Site. Further assessment of CN in soil in this area was conducted during the Phase II and is discussed below in Section Borings drilled in the vicinity of MW-6 and MW-17 encountered up to 10 feet of granular fill overlying glacio-lacustrine deposits, overlying glacial till. Refusal, interpreted to be the top of bedrock was encountered at approximately 70 feet below grade. Thin stringers of NAPL characteristic of coal tar were identified within the granular fill deposit and at the contact between the fill and lacustrine deposits; within fine sand seams present in the lacustrine deposits; at the contact between the lacustrine and glacial till units; and within fine sand laminations and fractures within the till. Following the installation of monitoring wells, DNAPL was identified in wells GZ-1M, GZ-2M and GZ-2D, and GZ-6D. The source area (s) for the observed DNAPL was not identified during the IRA. However, based on a review of historic plans of the MGP, it was hypothesized that DNAPL in GZ-1 and GZ-2 originated from the open tar well/tar storage tank formerly located near the southwest corner of the Site, and DNAPL in GZ-6D was attributed to the use of the surrounding vicinity for tar processing and storage. Delineation of historic source areas, as evaluated during the Phase II, is further discussed in Section

12 Phase II Comprehensive Site Assessment, October 2008 In October 2008, NSTAR submitted a Phase II CSA Report to MassDEP. A summary of findings is given below. Historical use of the Site as a MGP and tar processing facility has resulted in the presence of the following OHM in Site soil, groundwater, surface water and sediment: coal tar, light oils, and tar-water emulsions, found as LNAPL and DNAPL in monitoring wells, on the surface of the peat in a number of test pits, and in samples of wetland sediment; hardened tar, found as thin layers above the water table and as components of the granular fill primarily in test pits excavated to the north of the Sudbury Aqueduct; poly-nuclear aromatic hydrocarbons (PAH) and volatile aromatic hydrocarbons detected in soil and sediment samples and dissolved in groundwater and surface water; metals (primarily arsenic, chromium, copper, lead, nickel, and zinc) found sporadically across the Site in soil and sediment samples; and, inorganic compounds such as cyanide found in surface soil in the southwestern portion of the property, dissolved in groundwater throughout the Site, and detected in samples of wetland sediment and surface water. The geology beneath the Site consists of granular fill material which overlies a discontinuous layer of organic silt and peat (and at other locations, fine sand). The organic unit represents the historical wetlands that once covered most of the Site. Beneath the organic layer lies a deposit of glacio-lacustrine silt, and fine sand and silt. Layers of fine and medium sand were identified in several borings advanced through the lacustrine deposit. The lacustrine sediments overlie a unit of grey glacial till. Numerous laminations of fine sand were present in the till layer, and at certain borings, layers of sand up to 1 foot in thickness occurred in the till. Bedrock beneath the Site ranges from approximately 66 to 77 feet below grade. To facilitate the evaluation of historic source areas and contaminant distributions across the Site, the property was divided into eight (8) AOC which were defined based on the locations of historic MGP facilities and tar processing infrastructure, and the potential for each area to function as a contaminant source. The eight AOC were initially defined following a review of historical plans of the Site made available to GZA. Each area was further delineated during Phase II field explorations. 7

13 The eight AOC are defined below: 1. Northern Area of Concern (AOC-1): encompassing the majority of the northern portion of the Site, including filled land and two suspected Infiltration Lagoons north of the Sudbury Aqueduct; 2. OCTC-North (AOC-2): former Old Colony Tar Company (OCTC) tar processing and storage area north of the aqueduct; 3. Open Tar Well (AOC-3): former tar well located near the southwest boundary of the Site; 4. Former MGP Area (AOC-4): including the majority of the former MGP infrastructure south of the aqueduct (gas holders, purifiers, gas generator house, and processing equipment); 5. OCTC-South (AOC-5): former OCTC tar processing and storage area south of the aqueduct, including three large aboveground tar and/or gas-oil storage tanks, and one large aboveground oil storage tank; 6. Spent Oxide Waste (AOC-6): area of suspected spent oxide waste adjacent to the wetlands that occur at the southeast margin of the Site (this AOC overlaps with AOC-5 OCTC-South); 7. Coal Gas Generation Plant (AOC-7): relict structures associated with the former coal gasification plant located adjacent to and north of the Sudbury Aqueduct; and, 8. Wetlands and Beaver Dam Brook (AOC-8): wetlands and surface water that occur along the eastern and northern margins of the Site, and within Beaver Dam Brook north of the Site, where sheens and/or NAPL saturated sediment have been observed. During the Phase II fieldwork and following evaluation of results, GZA identified three primary NAPL source areas based on historical use within the MGP facilities and tar processing infrastructure, field observations, and analytical data: 1. OCTC-North (AOC-2): an area to the north of the Sudbury Aqueduct that consisted of several aboveground tanks used by the OCTC from before 1962 for the processing and storage of tar by-products generated during the gas manufacturing process; 2. A former Open Tar Well/Tar Storage Tank (AOC-3) located at the southwest corner of the Site; and, 8

14 3. OCTC-South (AOC-5): an area to the south of the aqueduct used by OCTC from before 1946 to no later than 1962 and consisting of numerous aboveground tanks for the processing and storage of by-product tar. Once released from these sources, the denser fractions of NAPL migrated horizontally and vertically through discontinuities in the till, through contacts between the fill and lacustrine deposits and lacustrine and till deposits, and within sand layers in the lacustrine and till deposit. DNAPL has migrated vertically and reached the bedrock at multiple well locations. LNAPL from the source areas has historically migrated on the surface of the groundwater table; however, since no widespread areas of measurable LNAPL have been observed, LNAPL appears to have reached a level of residual saturation held by capillary forces between soil particles. Sheens and sporadic, thin discontinuous layers of NAPL continue to be present on the surface of the groundwater. Based on borings drilled to the top of bedrock beyond the limits of the property, NAPL has not migrated off of the property. The viscosity of the denser NAPL fractions precludes significant migration from source areas. While NAPL in the subsurface continues to function as a source of dissolved MGPconstituents in groundwater, levels above applicable MCP Reportable Concentrations (RCs) have not been detected beyond the limits of the property boundaries. Groundwater flowing to the northeast through areas of NAPL continues to produce dissolved MGPrelated compounds from the NAPL at rates based on compound-specific solubilities. Hydrocarbon fractions dissolved in groundwater will continue to attenuate through dilution, mechanical dispersion through and adsorption to the soil matrix (especially soil high in organic content, such as the peat), and biodegradation. Lighter aromatic fractions will also attenuate through volatilization to the vadose zone and the atmosphere. Shallow groundwater in the granular fill (and most likely the lacustrine deposits) flows primarily to the northeast and discharges to the wetlands that bound the property to the east, southeast, and south; deep groundwater in the till also flows to the northeast. Dissolved constituents in groundwater discharge to the wetlands. However, contaminants of concern (COC) discharging to surface water will continue to attenuate through surface water dilution. In addition, the organic deposits in the wetlands function as a substrate for adsorption of COC. Visual observations of the extent of sheens on surface water and within the wetlands indicated that a condition of Readily Apparent Harm (RAH) existed in the wetlands and certain upland areas both north and south of the Sudbury Aqueduct. As defined in the MCP at (3), the following condition constitutes RAH: Visible presence of oil, tar, or other non-aqueous phase hazardous material in soil within three feet of the ground surface over an area equal to or greater than two acres, or over an area equal to or greater than 1,000 square feet in sediment within one foot of the sediment surface. If a condition of RAH harm exists in any environmental medium, then a condition of no significant risk of harm does not exist. It was estimated that the limits of visible 9

15 contamination, as indicated by observations of sheens, stains, and NAPL, totaled approximately 7 acres. The area of impacted sediments was estimated to be greater than 1,000 square feet. NAPL observed in sediments in the wetlands most likely resulted from direct surface discharges that occurred decades ago at multiple locations (as opposed to subsurface migration) during operation of the MGP and tar processing facility. Layers of viscous NAPL (coal tar) observed in test pits excavated near the wetlands occur within and upon the peat layer, indicating direct discharge to historical wetlands. Viscous NAPL in the subsurface has limited potential for migration at this Site. However, NAPL appears to have migrated to impact sediments in the intermittent stream and Beaver Dam Brook downstream from the property boundary. No ongoing discharge of NAPL or sheens to surface water have been observed, except if sediments are physically disturbed or extended precipitation events occur. One source of cyanide was identified in soil adjacent to the wetlands at the eastern margin of the Site; this area functions as a source of dissolved cyanide in groundwater, which most likely discharges to the wetlands; total cyanide was detected in samples of surface water from the wetland to the northeast and east. Cyanide in groundwater throughout the remainder of the Site most likely originates from limited areas of purifier waste included in the materials used to historically fill the wetlands. Localized areas of purifier waste were not observed in test pits excavated outside of AOC-6. With the exception of intermittent sheens and concentrations of MGP-related OHM in surface water and sediments associated with the wetlands and Beaver Dam Brook, and CN-containing surface soil in AOC-7 (adjacent to wetlands), exposure to OHM by human and environmental receptors is limited. Groundwater at the Site and the surrounding area is not used as a source of drinking water, and, with the exception of AOC-6, the majority of the property is surfaced with asphalt or densely compacted gravel. Groundwater containing elevated levels of volatile constituents is not located within 30 feet of occupied structures. Trespassers and facility workers may come into direct contact with surface water and sediment within the wetlands, and surface soil in AOC-6. However, calculated risks for facility workers, emergency utility workers, and trespassers do not exceed MCP risk limits. Cumulative risk estimates for future construction workers exceed MCP risk limits. In addition, the average surface water concentration exceeded applicable public health Ambient Water Quality Criteria (AWQC) protective of fish consumption, for benzene; however there is no evidence of fish or fishing at the Site. Accordingly, a condition of No Significant Risk of harm to human health exists for current uses of the Site; however, a condition of No Significant Risk of harm to human health does not exist for future uses of the Site. 10

16 3.00 REMEDIAL OBJECTIVES 3.10 RESPONSE ACTION OUTCOMES This section identifies potential site remediation outcomes relative to Response Action Outcomes (RAOs) as defined in the MCP (310 CMR ). The remedial alternatives presented in Section 4.00 of this report were evaluated based on their likelihood of achieving a Permanent Solution (Class A or B RAO) or Temporary Solution (Class C RAO). The MCP requires that a Phase III evaluation result in the selection of a RAA that is likely to result in a Permanent Solution, except where it is demonstrated to be infeasible and the implementation of a Temporary Solution is more cost effective and timely. Furthermore, the feasibility of achieving or approaching background levels of OHM shall be evaluated. The definitions of Permanent and Temporary Solutions are presented in the following sections Permanent Solution As described previously, the MCP requires that remedial actions be evaluated based on their ability to reach a Permanent Solution, if feasible. The achievement of a Permanent Solution will result in a Class A or B RAO. As defined in 310 CMR , a Class A RAO applies to sites where remedial activities have: 1. achieved a level of No Significant Risk (in accordance with 310 CMR ); 2. eliminated or controlled sources of oil and/or hazardous material (as defined in 310 CMR (5)); and 3. reduced, to the extent possible, the level of OHM in the environment to background concentrations. A Class A RAO can be further categorized as A-1, A-2, A-3, or A-4. These distinctions are defined below: A-1 A Permanent Solution has been achieved through remediation and the level of OHM has been reduced to background. All threats of release have been eliminated and no AULs are necessary to maintain a level of No Significant Risk. A-2 A Permanent Solution has been achieved through remediation, but OHM concentrations exceed background levels. No AULs are necessary to maintain a level of No Significant Risk. A-3 A Permanent Solution has been achieved, and OHM concentrations exceed background levels but do not exceed applicable MCP Upper Concentration Limits (UCLs) 11

17 in soil or groundwater. AULs are a necessary component of the remedial alternative to maintain a level of No Significant Risk. A-4 A Permanent Solution has been achieved, and AULs are a necessary component of the remedial alternative to maintain a level of No Significant Risk. OHM concentrations in soil deeper than 15 feet beneath the ground surface or beneath an engineered barrier exceed background levels and one or more applicable UCLs. In addition, a Phase III evaluation determines that it is not feasible to reduce OHM concentrations in the soil to less than or equal to applicable UCLs. Except as noted above under a Class A-4 RAO, Class A RAOs do not apply to disposal sites where average groundwater and/or soil concentrations exceed UCLs as specified in 310 CMR Additionally, a Class A RAO cannot be achieved if groundwater concentrations exceed an applicable standard where groundwater is categorized as GW-1. A Class B RAO applies to sites at which a condition of No Significant Risk exists without remedial actions being conducted; as such, a Class B RAO would not apply to this Site since interim remedial actions would be required to achieve a condition of No Significant Risk Temporary Solution A Temporary Solution (Class C RAO) may be applicable if achieving a condition of No Significant Risk at a Site is not feasible and/or timely. In accordance with 310 CMR , a Temporary Solution must mitigate the conditions which cause Substantial Hazard (i.e., a hazard which would present a significant risk if it continued to be present for several years), and, to the extent feasible eliminate, control or mitigate any source of OHM, as that term is defined in the MCP. The condition of RAH which exists based on the extent of tar and sheens in the wetlands and upland areas adjacent to the wetlands constitutes a Substantial Hazard to ecological receptors, specifically, the wetlands, and, in order to achieve a condition of No Substantial Hazard to the environment, steps must be taken to eliminate or mitigate the visible presence of oil, tar or other non-aqueous phase hazardous material in soil within 3 feet of the ground surface over an area equal to or greater than two acres, or over an area equal to or greater than 1,000 square feet in sediment within 1 foot of the sediment surface. Contaminant concentrations may exceed UCLs under a Temporary Solution. The MCP requires periodic evaluation and definitive and enterprising steps towards achieving a Permanent Solution if a Temporary Solution is implemented. Temporary Solutions are further divided into Class C-1 and C-2 RAOs: C-1 A condition of No Substantial Hazard exists and it is concluded that response actions to achieve a Permanent Solution are not feasible. 12

18 C-2 A condition of No Substantial Hazard exists and it is concluded that response actions to achieve a Permanent Solution are feasible and are to be conducted DEVELOPMENT OF REMEDIAL ALTERNATIVES To develop a set of remedial alternatives for detailed analysis, GZA performed an initial screening of available remedial technologies capable of addressing the OHM at the Site. These remedial alternatives are based on technologies included in the Federal Remediation Technologies Roundtable s Remediation Technologies Screening Matrix and Reference Guide, Version 4.0 (Screening Matrix) ( The technology categories screened for soil and NAPL remediation included: No Further Action; Institutional Controls; Natural attenuation; Containment; In-situ treatment; Ex-situ treatment; and Excavation and off-site treatment or disposal Technology categories screened for groundwater remediation included: No Further Action; Institutional Controls; Natural attenuation; Containment; In-situ treatment; and Ex-situ treatment Technology categories screened for wetland sediment remediation included: No Further Action; Institutional Controls; Natural attenuation; Containment; In-situ treatment; and Ex-situ treatment Certain technologies listed in the Screening Matrix within each technology category listed above are not applicable based on Site conditions including the types and concentrations of COCs present and media affected. These technologies are identified by a Worse rating in the Screening Matrix, and were not evaluated in this Phase III investigation. Additionally, a remedial approach involving the implementation of a combination of technologies may be necessary to attain remedial goals. 13

19 Within each category, both standard and innovative technologies were evaluated to determine their potential applicability at the Site. A remedial technology was judged to be acceptable for further evaluation if it was likely to achieve a Permanent or Temporary Solution, and if the individuals with the expertise needed to effectively implement the technology would be available. Remedial alternatives were evaluated with respect to the remedial goals outlined in Section The evaluation of remedial alternatives was based on the following criteria: Technical Feasibility: This evaluation criterion considered the applicability and reliability of the remedial alternative to address the COCs, the success of the technology at similar sites, and history of operational and maintenance performance of the alternative. Environmental and Public Health Impact: This evaluation criterion considered the potential effects of the remedial alternative on public health and the environment during and after implementation of the technology. The following sections present an overview of the classes of technology evaluated and a general description of the nature of each technology, followed by a discussion of its specific applicability to the areas of the Site. As discussed above, this Site has impacts in the vadose zone soil, saturated soil and groundwater, and the wetlands area including sediment and surface water. Due to the different impacted media, this report evaluates remedial technologies relating specifically to soil/napl, groundwater and wetlands and is segregated as such. The initial screening matrix of remedial technologies is presented in Table 1. The remedial alternatives of No Further Action and Institutional Controls are screened independent of the type of media impacted at the Site as these alternatives apply to all media. It should be noted that free phase NAPL is present onsite, and there are conditions of Readily Apparent Harm in the soil at AOC-6 and in the wetlands sediment which may not have a Permanent Solution and therefore are also evaluated for a Temporary Solution. Groundwater containing dissolved COCs above GW-3 standards does not appear to have migrated off site at this time and, although groundwater will be evaluated for a Permanent Solution, it will not be evaluated for a Temporary Solution NO FURTHER ACTION The no further action alternative assumes no additional efforts are made to remediate the Site. This alternative does not reduce Site risks associated with contaminants currently present, and provides no additional protection to safety, public welfare or the environment. However, it does provide a basis for assessing the effects of taking remedial actions and a baseline against which other remedial technologies can be compared. The no further action alternative would be ineffective at reducing the current or potential risks in any of the areas of the Site. As such, the alternative will not result in a Permanent or Temporary Solution in a timely manner and will not be retained for further evaluation. 14

20 4.20 INSTITUTIONAL CONTROLS Institutional controls are mechanisms to limit access to contaminated media and include alternatives such as site fencing and Activity and Use Limitations (AULs) in the form of deed restrictions. AULs are a legal tool to limit future site activities and uses in those areas that pose an unacceptable human health risk of exposure. While institutional controls do not eliminate contamination, they can provide an effective, low cost means for reducing human health exposure potential, and thus risk, in certain cases, if properly maintained and enforced. Some degree of institutional controls, such as the use of AULs to restrict future use in upland areas, may be applicable at this Site. Such controls would serve to limit risk to potential human receptors, including construction workers and potentially future on-site workers. However, the use of institutional controls alone would not address all the identified risks to the environment associated with the Site. Specifically, AULs could not be used to address conditions in the wetland areas. Institutional controls are a viable alternative for this Site to reduce potential risks to human health and will be retained for further evaluation, but only in companion with a more active remedial technology INITIAL SCREENING OF SOIL AND NAPL REMEDIAL TECHNOLOGIES Natural Attenuation Natural attenuation relies on naturally occurring processes such as volatilization, adsorption, dilution, oxidation, reduction, and biodegradation to reduce the mass, concentration, and/or toxicity of contaminants. Biodegradation is the transformation of organic compounds via metabolism by microorganisms. The rate of attenuation is determined by several factors related to the availability of required elements (i.e. carbon and oxygen), nutrients (i.e. nitrogen and phosphorous), and organic growth factors necessary for the growth of the microbial population. Natural attenuation is considered a passive remedial technology in that no active remediation is performed. Often, the rate and progress of natural attenuation is assessed via routine soil and/or groundwater monitoring (i.e., monitored natural attenuation [MNA]); such monitoring may include the assessment of surrogate indicators of attenuation processes. Under this approach, periodic monitoring would be conducted to assess the natural reduction in contaminant concentrations and to monitor potential migration. 15

21 Under favorable Site conditions, natural attenuation may be an appropriate selection depending on chemical concentrations and characteristics, hydrogeologic characteristics of the Site and presence of NAPL. However, the Site conditions are not favorable to natural attenuation due to the presence of NAPL, the proximity to a wetland, and other chemical characteristics and, therefore, natural attenuation is not retained for further evaluation Containment Technologies The primary purpose of containment technologies is to isolate contaminated media, and thus control potential exposure risks. Passive containment involves placement of physical barriers to limit the potential for exposure to contaminated soil. Engineered barriers are the most commonly used passive containment technologies. Passive remediation systems use little or no external energy and typically have a low carbon footprint. Horizontal engineered barrier designs include impermeable caps, which typically consist of a layer of asphalt pavement, concrete, or natural low permeability material such as clay. Impermeable caps limit surface water infiltration into the contaminated media, thereby limiting the potential for contaminant migration. An engineered barrier, as defined in 310 CMR is a cap that meets the following specifications: prevents direct contact with contaminated media; controls any vapors or dust emanating from contaminated media; prevents erosion and any infiltration of precipitation or run-off that could jeopardize the integrity of the barrier or result in the potential mobilization and migration of contaminants; is comprised of materials that are resistant to degradation; is consistent with the technical standards of RCRA Subpart N, 40 CFR , 310 CMR or equivalent standards; and includes a defining layer that visually identifies the beginning of the barrier. This technology would also require implementation of an AUL and monitoring. However, containment does not remediate the soil and must be indefinitely maintained in place. The Phase II Report identified surface soil in the Suspected Spent Oxides Area (AOC-6) which contained physiologically available cyanide at concentrations which exceed the significant risk level. An engineered barrier as well as implementation of an AUL in this area may be feasible as a Temporary Solution. At other portions of this site, the risks associated with direct contact and vapor intrusion can be adequately maintained via the implementation of an AUL in the upland areas, but an engineered barrier could not be adequately designed to address other areas of the Site with active businesses and buildings. Therefore, a horizontal barrier is not considered applicable at this site for either a Permanent Solution or a Temporary Solution, except as noted above. 16

22 Passive containment technologies can also include the removal of NAPL from the subsurface as it collects in trenches and/or wells. In this respect, passive removal systems are differentiated from active containment technologies by the fact that no artificial gradient is induced to draw the NAPL and/or contaminated liquid toward the removal location. Passive removal technologies include the use of adsorbent materials within recovery wells, simple systems that use the natural density difference between oil and water to passively collect SPH in storage containers, manual bailing of wells for NAPL and vertical low permeability barriers which prevent NAPL from migrating but must be designed to prevent groundwater from mounding. Passive containment does not actively address the NAPL exceeding UCL standards and is not effective for use in attaining a Permanent Solution, but can be effective in limiting migration of NAPL off site and may be utilized as part of a Temporary Solution. Due to the size of the site and the fact that a large portion of the NAPL is not LNAPL, only passive removal technologies will be evaluated for a Temporary Solution. Active containment systems are designed to control the migration of NAPL by imposing a gradient toward one or more product and/or groundwater collection locations. This process results in the capture of NAPL through NAPL and/or groundwater depression within a certain distance from the removal location, and limits natural migration. An advantage of active removal technologies, as opposed to strict containment technologies, is that the mass of contaminants in the subsurface is also reduced via the removal, collection, and/or treatment of contaminated groundwater and NAPL. However, although fuel oil LNAPL product recovery technologies have been used extensively and their successes are well documented, they are generally considered infeasible at MGP sites as part of a Permanent Solution. This is because, as demonstrated consistently at other sites, MGP contaminants are not amenable to pumping due to their thick, tar-like consistency as well as their DNAPL components. Active containment does not actively address the NAPL exceeding UCL standards and is not effective for use in attaining a Permanent Solution. Active Containment can be effective in limiting migration of NAPL off site only in conjunction with groundwater extraction and due to the heterogeneous presence of NAPL and limited recovery while extracting groundwater, Active Containment will only be selected for a Temporary Solution as a part of groundwater extraction, if selected, and is not selected as stand alone for a Temporary Solution In-Situ Technologies In-situ treatment destroys, neutralizes, or reduces the toxicity of contaminants while leaving soil in place. In-situ technologies result in limited site disturbance with limited need for excavation, treatment and/or handling of contaminated media. This limits risks to remedial construction workers, on-site employees, and Site abutters that can occur during more intrusive removal activities. In-situ treatment technologies include the following: In-Situ Physical/Chemical Technologies 17

23 Soil flushing is a method of in-situ chemical treatment. According to the Federal Remediation Technologies Roundtable web site, soil flushing may be potentially used for desorbing VOCs, SVOCs and metals from soils; however, the heterogeneity of the vadose zone, varied chemical properties of the COCs, limited technological information regarding the application, and presence of NAPL, treatment and reinjection area make this an unsuitable technology for this particular application. Based on this information, soil flushing was not considered appropriate for use at the Site for a Temporary or Permanent Solution. Soil vapor extraction (SVE) is an in-situ physical treatment technology that is fully developed and widely utilized. An SVE system would apply a vacuum to the vadose soil to induce a controlled flow of air to remove VOCs and some SVOCS from soil. The extracted soil gas may be treated using activated carbon or catalytic oxidation to remove organic contaminants from the system exhaust. The SVOCs, NAPL and metals present in the vadose zone will not volatilize sufficiently to consider this an effective technology and this technology is not considered appropriate for use at the Site for a Temporary or Permanent Solution. Chemical Oxidation is an in-situ chemical treatment technology that has limited full scale development for the COCs, is not effective for metals, and is difficult to implement in vadose soil conditions. Based on this information, chemical oxidation was not considered appropriate for use at the Site for a Temporary or Permanent Solution. Solidification/Stabilization is an in-situ technology which utilizes Portland cement, jet grouting, or other binding agent to encapsulate inorganic compounds to prevent leaching of the inorganic chemical. This technology has been used successfully in fullscale applications for cyanide complexes in soil, but has not been shown to be effective for the organic COCs or NAPL. This technology is retained for detailed evaluation as a Permanent Solution for the treatment of cyanide and metals COCs only at the Site In-Situ Biological Treatment Bioremediation is a managed or spontaneous process in which microbiological activity transforms contaminants to less toxic or non-toxic forms thereby mitigating or eliminating environmental contamination. Microorganisms require carbon sources and nutrients to provide energy for growth and survival. Degradation of natural substances in soil and sediment and carbon from the contaminants of concern provides food for the development of microbial populations in these media. Technical information regarding biodegradation of the COCs indicate that the SVOCs will biodegrade most quickly under aerobic conditions, while the cyanide and NAPL in the soil are resistive to biological treatment. Since cyanide and NAPL are much more widespread and of significant importance in the soil at the Site, in-situ bioremediation by any application method was not considered appropriate for use at the Site for a Temporary or Permanent Solution. 18