November 13, 2007 Mr. Michael McCluskey, PE 29 Hazen Drive LIberty... · GEI Consultants, Inc. i Table of Contents Executive Summary iii 1. Introduction 1 1.1 Purpose 1 1.2 Site Information

November 13, 2007 Mr. Michael McCluskey, PE Hazardous Waste Remediation Bureau New Hampshire Department of Environmental Services (NHDES) 29 Hazen Drive Concord, New Hampshire 03302-0095 RE: Remedial Action Plan Addendum

Gilford—Lower Liberty Hill Road Site DES Site #200411113 Dear Mr. McCluskey: Attached please find the Remedial Action Plan Addendum prepared as directed in your letter dated September 21, 2007. As the Department requested, KeySpan has reevaluated four remedial alternatives, and now recommends the hybrid approach suggested in your letter: removing all of the tar-saturated soils coupled with secondary containment. I look forward to your comments on this plan. Meanwhile, I can be reached at 781-466-5414 or at [email protected], if you need additional information. Sincerely,

Patricia A. Haederle, CPG, LSP New England MGP Program Manager Attachment cc: John Regan, NHDES Ralph Wickson, NHDES Evans Juris, Town of Gilford Gilford Board of Selectmen Katherine Dormody, Gilford Public Library (document repository—2 copies) File: RAPaddendumtransmittal.doc

Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007

GEI Consultants, Inc. i

Table of Contents

Executive Summary iii

1. Introduction 1 1.1 Purpose 1 1.2 Site Information and Description 1

1.2.1 Contact Person 2

2. Remedial Action Plan Addendum 4 2.1 Regulatory Requirements 4 2.2 Objectives 4 2.3 Identification and Initial Screening of Remedial Technologies 5

3. Detailed Evaluation of Remedial Action Alternatives 7 3.1 Remedial Action Alternatives Retained from RAP 7 3.2 Remedial Action Alternatives Descriptions 7

3.2.1 RAA1 – Excavate Tar-impacted Soil and Treat Soil Off-site with Thermal Desorption 8

3.2.2 RAA4 – Excavate Tar-impacted Soil to 3 Feet Deep, Contain Tar-impacted Soil Below 3 Feet Deep, and Treat Soil Off-site with Thermal Desorption 9

3.2.3 RAA5 – Excavate Tar-impacted Soil to 3 Feet, Excavate Tar-saturated Soil Below 3 feet, Contain Remaining Tar-impacted Soil Below 3 Feet Using a Slurry Wall, and Treat Soil Off-site with Thermal Desorption 9

3.2.4 RAA6 – In-Situ Thermal Desorption of All Tar-impacted and Tar-saturated Soil. 10

3.3 Detailed Evaluation Criteria 11 3.4 Qualitative Scoring of RAAs 12 3.5 Selected Remedial Action Alternative 12

4. Conclusions and Recommendations 14

5. Limitations 16

6. References 17

7. Acronyms and Abbreviations 19

Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 Tables 1. Detailed Evaluation Summary Figures 1. Site Location Map 2. Site Plan 3. Remedial Action Alternative No. 1 4. Remedial Action Alternative No. 4 5. Selected Remedial Action Alternative (No. 5) 6. Remedial Action Alternative No. 6 Appendices A. DES Response Letter to RAP, September 21, 2007 B. RAA Cost Estimate Information C. Additional Information on In-Situ Thermal Desorption SEO/JRA:rr M:\PROJECT\2005\05069\Reports\07\RAP Addendum Nov07.doc

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Executive Summary GEI Consultants, Inc. prepared this Remedial Action Plan (RAP) Addendum on behalf of KeySpan Energy Delivery New England (KeySpan) to document our evaluation of additional remedial alternatives for the Lower Liberty Hill Road Site (NHDES Site Identification No. 200411113) in Gilford, New Hampshire (the Site). The RAP Addendum addresses contamination in environmental media resulting from a reported discharge of coal tar, a manufactured gas plant (MGP) byproduct, on a Liberty Hill Road property during the dismantling of the Laconia MGP in the early 1950s. A RAP was prepared by GEI on behalf of KeySpan and submitted to NHDES in February 2007. In its comment letter to KeySpan dated September 21, 2007, NHDES requested that a RAP Addendum be prepared that provided greater emphasis on removal and/or treatment of contaminants at the Site, instead of containment. This RAP Addendum includes a detailed evaluation of four remedial action alternatives (RAAs) for the Site. RAA2 from the RAP was not included in this RAP Addendum because it scored last among the alternatives evaluated in the February 2007 RAP. RAA3 was eliminated because it is very similar to RAA4 in terms of effectiveness and reliability, but scored lower due to other factors. RAA1 and RAA4 were retained from the February 2007 RAP, and RAA5 and RAA6 were added to the evaluation based on the comments from NHDES. The four alternatives evaluated are:

RAA1 - Excavate all tar-impacted soil;

RAA4 - Excavate tar-impacted soil to 3 feet deep and contain tar-impacted soil below 15 feet deep with a slurry wall and impermeable cap;

RAA5 – Excavate tar-impacted soil to 3 feet and tar-saturated soil below 3 feet, treat soil off-site by thermal desorption, contain remaining tar-impacted soil below 3 feet using a slurry wall and impermeable cap; and

RAA6 – In-situ thermal desorption of all tar-impacted and tar-saturated soil.

These four RAAs were compared to each other and ranked based on nine criteria, including effectiveness, ease of implementation, reliability, timeliness, public impacts, short-term risks, long-term risks, long-term benefits, and cost effectiveness. The selected alternative is RAA5. This alternative would remove 80 percent of the contaminant mass and contain the remaining 20 percent of the mass with the slurry wall and impermeable cap. Implementation of the selected alternative would result in a deed

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Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 restriction on certain residential uses of the 83, 77, and 69 Liberty Hill Road properties, which would be converted to landscaped open space following the work. This alternative complies with the requirements of the New Hampshire Code of Administrative Rules for remedial actions [Env-Or 606.10], and achieves the most favorable balance of benefits and costs when compared to other alternatives. In accordance with Env-Or 606.16, design plans and construction specifications will be prepared that present the engineering design for the selected remedy. The plans and specifications will be included in a Remedial Design Report. KeySpan will submit this report to NHDES for review and approval within six months of NHDES approval of the selected alternative. The six months is required to conduct detailed groundwater modeling and refinement of the design of the proposed remedial alternative. The remedial design plans will used by the selected contractor to implement the proposed remedial alternative. A public meeting will be held following submittal to update the community on the remedial plans. Once approved by NHDES, construction of the remedy is planned to start in fall 2008 and is expected to take about one year.

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1. Introduction 1.1 Purpose GEI prepared a RAP for the Site, dated February 28, 2007, which evaluated four remedial alternatives to remove, treat, or contain the contamination in environmental media resulting from a reported discharge of coal tar, a manufactured gas plant (MGP) byproduct, on a Liberty Hill Road property during the dismantling of the Laconia MGP in the early 1950s. GEI recommended Remedial Action Alternative RAA4, which consisted primarily of construction of a slurry wall around the contaminated soil and an impermeable cap, for implementation at the Site. The NHDES responded in a September 21, 2007, letter to KeySpan and requested that a RAP Addendum be prepared that provides greater emphasis on removal and treatment as the primary remedial actions. A copy of the NHDES letter is included in Appendix A. The purpose of this Addendum is to respond to the September 21, 2007, letter from NHDES by providing an evaluation of two additional remedial alternatives that address NHDES comments, and a revised recommendation of a remedial action to be implemented at the Site. Detailed information regarding the Site history, geology, hydrogeology, and the nature and extent of tar-related contamination at the Site were provided in the February 28, 2007, RAP and are not repeated in this report. 1.2 Site Information and Description The Site is listed as “Lower Liberty Hill Disposal Site, Liberty Hill Road, Gilford, New Hampshire,” by the New Hampshire Department of Environmental Services (NHDES), and has NHDES Site identification number 200411113. The Site location is shown on Fig. 1. Subsurface investigations to date have been conducted on the properties at 63, 69, 77, 78, 83, and 87 Liberty Hill Road, and on a small portion of the Lakes Region Golf Course, on the western bank of Jewett Brook. A Site Investigation Report was prepared for the Site, dated June 30, 2006, and a Remedial Action Plan was prepared for the Site, dated February 28, 2007. The “Site” is defined as the four properties on which tar-impacted soil have been found (69, 77, 83, and 87 Liberty Hill Road), the western (undeveloped) portion of 63 Liberty Hill Road, and a small portion of the adjacent golf course property. Tar-impacted soil was not

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Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 found at 63 Liberty Hill Road; however, the western portion of this property will be included in the Groundwater Management Zone (GMZ) because dissolved phase contaminants have been detected in several monitoring wells in the western portion of the property. Similarly, the portion of the Lakes Region Golf Course in the vicinity of the newly-installed monitoring well cluster MW118 will also be included in the GMZ due to the detection of low concentrations of Site-related contaminants in groundwater and to serve as the downgradient monitoring point. (Soil and groundwater data collected during installation of the MW118 well cluster has been provided separately to NHDES.) The eastern half of the Site, along Liberty Hill Road, is relatively flat (Fig. 2). Beginning in the middle of the Site, the topography slopes steeply towards Jewett Brook, with an elevation change of about 30 feet. A cleared area at this lower level, near Jewett Brook, exists on the 87 and 83 Liberty Hill Road properties. The remainder of the Site is densely wooded with mature trees. As indicated in the SIR, there was no complete current exposure pathway for residents at the Site, visitors, trespassers, or residents of abutting properties. Since submittal of the SIR, KeySpan purchased the four properties where tar impacts are present to eliminate potential future pathways such as those that may result from excavation of subsurface soil. A Stage I Ecological Screening included in the RAP preliminarily concluded that a condition that is protective of the environment exists or has been achieved and a Stage II Environmental Risk Characterization is not required. The Stage I recommended a round of surface water samples be collected at a time of low flow to confirm that COPC concentrations would not exceed the ambient water quality criteria (AWQC) in Jewett Brook during seasonal variations in flow. A round of surface water samples were collected in July 2007. The results of these samples indicate that although benzene was detected at three locations in the brook, concentrations are well below the AWQC. Complete results of the surface water sampling were provided separately to NHDES. Energy North Natural Gas d/b/a KeySpan Energy Delivery New England (KeySpan) has purchased the properties at 69, 77, 83, and 87 Liberty Hill Road. In December 2006, the structures at 77 and 83 Liberty Hill Road were demolished. The 63 Liberty Hill Road property remains privately owned and is in residential use. 1.2.1 Contact Person The contact person for this Site is: Ms. Patricia Haederle CPG New England MGP Program Manager, Environmental Asset Management


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 KeySpan Corporation 52 Second Avenue Waltham, MA 02451 Phone: 781.466.5414; Fax: 781.890.4587; email: [email protected]



2. Remedial Action Plan Addendum 2.1 Regulatory Requirements The RAP Addendum was designed to comply with the requirements cited in New Hampshire Code of Administrative Rules Chapter Env-Or 600 – Contaminated Site Management. 2.2 Objectives Specific objectives of the RAP Addendum were to address comments from the NHDES in its letter dated September 21, 2007. NHDES stated that the RAP could not be approved because the recommended alternative (RAA4) may not meet the criteria for RAP approval (Env-Or 606-13), particularly the criteria of “(l)ong-term management including …… site monitoring requirements, will be minimized.” The NHDES letter also indicated that the emphasis of the selected remedy should be on removal or treatment of the source and secondarily on containment. However, NHDES concurred with KeySpan regarding excavation of all tar impacted soils: “RAA1 may not be cost effective and has a significantly greater impact on the community in terms of construction activity, truck traffic, duration of construction and noise.” NHDES suggested consideration of a hybrid alternative that removes tar saturated soil below 15 feet, combined with containment of the tar-impacted soil that would remain at the Site. Therefore, in this RAP Addendum we have evaluated a new alternative, RAA5, which is essentially the hybrid remedy that NHDES had suggested. RAA5 is similar to RAA2 in the original RAP (removal of tar saturated material below 15 feet), but also includes a slurry wall and impermeable cap similar to what was proposed in RAA4. We also included evaluation of a second additional alternative, RAA6, which consists of insitu thermal desorption of all tar-affected soil. This technology was not included in our original RAP because it was our opinion that Site conditions would preclude its effectiveness. However, after consultation with a vendor of the technology, we have learned that it would likely be effective and feasible to implement at the Site and therefore deserved detailed evaluation. Similar to the original RAP, the objectives of this RAP Addendum are to provide for protection of human health and the environment, provide a detailed evaluation of remedial alternatives, and to recommend action to (1) remove, treat, or contain the source to prevent the additional release of contaminants to soil, groundwater and surface water; (2) contain contaminated groundwater within the limits of a proposed groundwater management zone;


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 (3) restore groundwater quality to meet the criteria identified in Env-Or 603.03; and (4) restore soil quality to meet the soil cleanup standards identified in Env-Or 606-19. 2.3 Identification and Initial Screening of Remedial Technologies In the February 2007 RAP, we presented the results of an initial screening evaluation (ISE) to identify remedial technologies that would likely meet the remedial objectives for the Site. The screening included the following elements:

Identify Site-specific considerations that may influence the timeliness and cost effectiveness of remedial alternatives.

Summarize the primary Constituents of Potential Concern (COPCs) to be addressed by remedial technologies.

Identify potentially feasible remedial technologies (including innovative technologies) based on professional experience and literature searches. Determine the feasibility of the identified technologies to meet the remedial objectives based on:

o Effectiveness: The technologies to be employed by the alternative are reasonably likely to achieve a permanent solution.

o Implementability: Individuals with the expertise needed to effectively implement available solutions would be available.

Recommend Remedial Action Alternatives (RAAs) to be considered for a detailed evaluation.

Following initial screening, the retained in-situ technologies were: institutional controls, solidification/stabilization, and containment. Retained ex-situ technologies were excavation and thermal desorption (on-site or off-site). Descriptions of the technologies retained following the screening evaluation were presented in the February 2007 RAP and are not repeated in the report. The technologies that comprise RAA5, a combination of excavation and containment, both passed the initial screening evaluation. No in-situ treatment options (bioremediation, bioventing, chemical reduction/oxidation, monitored natural attenuation, soil flushing, and soil vapor extraction) were retained for detailed evaluation primarily due to the limited reliability of these technologies, the recalcitrance of high molecular weight PAHs, and subsurface conditions at the Site that would limit their effectiveness, such as the dense till layers. However, as part of this RAP Addendum, KeySpan and GEI evaluated in-situ thermal desorption (ISTD) as an additional potential remedial technology. This technology was not considered in the RAP, but discussions with a vendor indicated that the technology could accomplish removal of mobile


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 NAPL, and removal of the lighter phase constituents (primarily benzene, toluene, ethylbenzene, xylenes, and naphthalenes) which are the primary contaminants in the downgradient groundwater plume. The remainder of the contaminants (the heavier phase – i.e., 3, 4, and 5-ring PAHs and other constituents of tar) would be solidified in place into an asphalt-like material. In addition, the technology may be comparable in cost to the complete excavation alternative (RAA1) and the potential neighborhood impacts would be less because ISTD is much less invasive than excavation. Therefore, insitu thermal desorption was included in this RAP Addendum as RAA6. Additional detail regarding this technology is provided in Appendix C.



3. Detailed Evaluation of Remedial Action Alternatives 3.1 Remedial Action Alternatives Retained from RAP Four Remedial Action Alternatives (RAAs) were presented in the February 2007 RAP. Two of the RAAs, RAA1 and RAA4, were retained for the RAP Addendum. RAA4 was retained because it was the selected alternative of the February 2007 RAP. RAA1 was retained because it represents complete removal of tar-affected soil and addresses NHDES’s request to consider alternatives that emphasized contaminated mass removal, rather than containment. RAA2 from the RAP was not included in this RAP Addendum because it scored last among the alternatives evaluated in the February 2007 RAP. RAA3 was eliminated because it is very similar to RAA4 in terms of effectiveness and reliability, but scored lower due to other factors. In this section, we distinguish between ‘tar-impacted soil’ and ‘tar-saturated soil’ when we describe the effectiveness of each alternative. ‘Tar-impacted soil’ consists of all soil identified during the field investigation that contained visual evidence of tar impacts, such as staining, blebs of tar, and saturated tar lenses. ‘Tar-saturated soil’ is a subset of tar-impacted soil and consists only of soil where most or all of the void space in the soil is occupied by tar. Soil with odors only was not considered to be tar impacted, because the odors are likely the result of presence of dissolved phase contaminants in groundwater, rather than presence of tar in soil. The tar-saturated soil is estimated to contain the majority of the mass of residual contamination at the Site and is likely to be the primary source of contaminants in groundwater downgradient from the source area. 3.2 Remedial Action Alternatives Descriptions In this section, we provide a description of each remedial alternative that we considered in this RAP Addendum. The descriptions of RAA1 and RAA4 are identical to the descriptions of these alternatives provided in the February 2007 RAP. RAA5 and RAA6 are the two new alternatives that were evaluated in response to NHDES comments. .


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 3.2.1 RAA1 – Excavate Tar-impacted Soil and Treat Soil Off-site with Thermal

Desorption Soil with tar-impacts will be excavated using standard construction excavation equipment (e.g., track-mounted excavators, bulldozers, dump trucks, etc.). The estimated limits of the excavation are shown in Figure 3. To a depth of 25 feet, the excavation will generally be open and unsupported, with the excavation sidewalls sloped 1:1. Adjacent to Liberty Hill Road, adjacent to the residence at 87 Liberty Hill Road, and for deep excavation areas below 25 feet deep, the excavation sidewalls will be supported by driven steel H-piles and wood lagging spanning the H-piles. We estimate that the total volume of excavated soil will be approximately 114,000 cubic yards. Approximately 33,000 cy of this soil is not tar-impacted, but must be removed to construct stable excavation side-slopes or to access the tar-impacted soil at depth. This alternative would remove 100 percent of the source material (tar-impacted soil) present at the Site, and would cost approximately $15,900,000. Dewatering wells or sumps will be required to excavate soil below the groundwater table. We have assumed that dewatering effluent will require on-site treatment for particulates and VOCs before being discharged to Jewett Brook in compliance with the New Hampshire Remediation General Permit. The excavated soil will be loaded into triaxial dump trucks (20-ton capacity) and transported off-site to Environmental Soil Management Incorporated in Loudon, New Hampshire (ESMI) for treatment using a thermal desorption process. The remedial excavation will be backfilled with either excavated Site soil suitable for reuse (contaminant concentrations less than S1 standards) or clean imported fill. We estimate that approximately 6,000 tri-axle dump trucks will be required to transport the 121,000 tons of tar-impacted soil off-site to ESMI for treatment and the same number of tri-axle dump trucks will be required to import clean backfill. After backfilling is complete, the Site will be restored for residential reuse and will not require an Activity and Use Restriction (AUR). The estimated duration for the construction phase of this alternative is approximately two construction years (e.g., April 2008 through December 2009). Of the RAP objectives, restoring the quality of groundwater downgradient from the tar-impacted soil will take the longest period of time. We estimate that New Hampshire Groundwater Quality Criteria would be achieved in groundwater near Jewett Brook in approximately 35 years following soil removal. A solute transport model developed by the USEPA, Bioscreen, was used to model effects of remedial alternatives on downgradient groundwater quality. Details of this model are included in the RAP.


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 3.2.2 RAA4 – Excavate Tar-impacted Soil to 3 Feet Deep, Contain Tar-

impacted Soil Below 3 Feet Deep, and Treat Soil Off-site with Thermal Desorption

This alternative consists of excavation of the tar-impacted soil at the Site to a depth of 3 feet. A 3-foot-wide, soil-clay slurry wall will then be installed around the remaining tar-impacted soil to a depth of 50 feet. The estimated limits of the proposed excavation and location of the proposed containment wall are shown in Fig. 4. This alternative would remove 0.5 percent of the source material and contain the remaining 99.5 percent of the source material with the slurry wall and cap. The estimated cost of this alternative is $5,500,000 (approximately 35 percent of the cost of RAA1). The 47-foot effective depth of the containment wall in this alternative may require a clamshell excavator in addition to the long-reach bucket excavator to advance the trench to the full design depth in the dense glacial till at the Site. The area within the completed containment wall would be capped with an impermeable geomembrane and clean, imported fill to control the infiltration of stormwater and precipitation into the contained area. Excavated soil that is suitable for reuse or imported fill will be used to backfill the 3-foot-deep excavation to the ground surface. The soil excavated from the slurry wall trench that is not used for backfill will be shipped off-site for thermal desorption treatment. We estimate that approximately 560 tri-axle dump trucks will be required to transport the estimated 11,000 tons of tar-impacted soil off-site for treatment. The same number of trucks would be required to import clean backfill. The estimated duration for the construction phase of this alternative is approximately seven months. After backfilling is complete, the Site will be re-landscaped. An AUR will be required to restrict residential use and prohibit activities that may disturb the cap or slurry wall. We estimate that New Hampshire Groundwater Quality Criteria would be achieved in groundwater near Jewett Brook in approximately 35 years following remedy implementation, similar to RAA1. 3.2.3 RAA5 – Excavate Tar-impacted Soil to 3 Feet, Excavate Tar-saturated

Soil Below 3 feet, Contain Remaining Tar-impacted Soil Below 3 Feet Using a Slurry Wall, and Treat Soil Off-site with Thermal Desorption

This alternative is similar to a combination of RAA2 and RAA4 from the February 2007 RAP. It consists of excavation of tar saturated soil and construction of a slurry wall and impermeable cap to contain residual tar-impacted soil outside the tar-saturated area. The methods of soil excavation are similar to those in RAA1. The estimated excavation limits are shown in Figure 5. The reduced extent of the excavation, compared to RAA1, would significantly reduce the volume of soil to be excavated and transported off-site for treatment, as well as the extent of deep excavation support and duration of dewatering required.


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 For this alternative, we propose that the containment wall be installed prior to the excavation of tar-saturated soil so that the wall can be used as excavation support where necessary and to reduce the dewatering requirements during excavation. The portion of the containment wall adjacent to the proposed excavation would be constructed with reinforced concrete rather than clay slurry to allow it to serve as excavation support. Under this alternative, approximately 1,370 tri-axle dump trucks will be required to transport the estimated 27,500 tons of tar-impacted soil off-site for treatment. The same number of trucks would be required to import clean backfill. We estimate that this alternative would remove approximately 80 percent of the source material and would cost approximately $8,700,000 (55 percent of the cost of RAA1). The duration of the construction phase is estimated to be one construction year (e.g., April through December). The area within the completed containment wall would be capped with an impermeable geomembrane and to control the infiltration of stormwater and precipitation into the contained area. A geocomposite drainage mat or layer of crushed stone will be installed above the geomembrane to facilitate drainage from the cap and overlain by a clean soil layer, graded and landscaped. An Activity and Use Restriction (AUR) will be required to restrict residential use and prohibit activities that may disturb the cap or slurry wall. We estimate that New Hampshire Groundwater Quality Criteria would be achieved in groundwater near Jewett Brook in approximately 35 years following remedy implementation, similar to RAA1. 3.2.4 RAA6 – In-Situ Thermal Desorption of All Tar-impacted and Tar-

saturated Soil. This alternative consists of in-situ thermal desorption (ISTD) to treat in-place the entire mass of tar-impacted soil at the Site. The technology uses electricity to heat the soil and groundwater to mobilize DNAPL and volatile fractions of non-mobile DNAPL. These contaminants would be captured by a combination of dual-phase extraction (DPE) and vapor phase extraction systems. The captured DNAPL would be taken offsite for disposal, and the captured gases would be treated by an on-site thermal oxidation system. The approximate network of heating points and extraction wells is shown on Figure 6. Associated treatment equipment would likely be placed on the 87 and 69 Liberty Hill Road properties. The dual-phase and horizontal vapor extraction systems would pipe the recovered fluids and vapors to fractionation tanks (water and NAPL mixture) and thermal oxidizer (vapors) for treatment and disposal. A vapor barrier/ infiltration cover consisting of light-weight concrete would be installed over the treatment zone to ensure capture of generated vapors by the DPE and vapor extraction systems and to minimize infiltration of precipitation. The ISTD system would be operated for approximately 150 – 250 days to heat the soil to the goal temperature


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 (100 degrees Celcius) and maintain the temperature for the desired time for treatment. During this time, vapors, water and NAPL would be recovered and treated or disposed off-site. The dual phase extraction system would also function to maintain hydraulic control because it includes groundwater extraction on the downgradient side of the treatment area. Following completion of the treatment process, confirmatory soil samples would be collected to confirm that the treatment goals have been achieved. Truck traffic would be limited to equipment needed to install, maintain, and demobilize the treatment system, and to transport remediation wastes (DNAPL, waste carbon, etc.) offsite. Other neighborhood impacts would be limited to noise associated with the equipment. We estimate that this alternative would remove approximately 84 percent of the source material, while the remaining 16 percent would be solidified into an asphalt-like material. This alternative would cost approximately $12,900,000 (81 percent of the cost of RAA1). The duration of the construction phase is estimated to be 6 months (e.g., April through September) and operations/treatment would last 5 to 9 months. After demobilizing the treatment equipment, the Site will be re-landscaped. An AUR may be required to restrict residential use and prohibit activities that may disturb subsurface soil. We estimate that New Hampshire Groundwater Quality Criteria would be achieved in groundwater near Jewett Brook in approximately 35 years following remedy implementation, similar to RAA1. 3.3 Detailed Evaluation Criteria A comparative evaluation of the four RAAs was performed using the following detailed evaluation criteria:

Effectiveness in achieving the RAP objectives Ease of implementation Reliability Timeliness Neighborhood impacts Short-term risks Long-term risks Benefits Cost effectiveness



3.4 Qualitative Scoring of RAAs We ranked each of the RAAs for each criterion using a numeric scoring system, with a score of one being the best for that criterion, and a score of four being the least preferred. We then added the scores for each RAA to get a cumulative ranking based on all criteria. A summary of our scoring of the RAAs for each of the nine criteria, along with the overall qualitative scores for the RAAs, are presented in Table 1 (lower score preferred). In the scoring, we considered NHDES preference for removal and treatment over containment. 3.5 Selected Remedial Action Alternative Based on the scoring relative to the detailed evaluation criteria, RAA5 was selected as the most appropriate remedial action alternative with the most favorable balance of benefits and cost. This alternative consists of excavation of tar-impacted soil to 3 feet and tar-saturated soil below 3 feet, treatment soil off-site with thermal desorption, and containment of remaining tar-impacted soil below 3 feet using a slurry wall and impermeable cap. RAA5 would result in removal of 80 percent of the source material and containment of the remainder, and it achieves the RAP objectives at about half the cost and half the construction time of RAA1. This alternative would rely on a slurry wall and cap to contain the remaining 20 percent of source material that is located in thin lenses within unimpacted soil. The slurry wall will be designed to minimize the migration of contaminated groundwater by creating a low permeability containment around the remaining tar-impacted soil. A review of documentation prepared by the United States Environmental Protection Agency (EPA) indicates that slurry walls are the most commonly used type of vertical engineered barriers to contain or divert groundwater (EPA, 2007). Of the 67 vertical engineered barriers designed for Superfund sites between 1982 and 2005, 54 were slurry walls. Prior to implementing the selected remedy, we propose to prepare a groundwater model of the Site to help evaluate and predict specific flow characteristics, and to confirm the appropriate design for the slurry wall and cap. In addition, bench scale testing will be performed to select the appropriate the slurry mix for the Site conditions. We also propose to provide site-specific information to one or more construction contractors and request a constructability review and an independent assessment of construction risks and predicted effectiveness. The proposed modeling and constructability review may result in modifications to the proposed design to improve its effectiveness and reliability. Examples of potential modifications include a deeper, or shallower, slurry wall, or addition of groundwater flow controls, such as drains installed on the upgradient side of the slurry wall, or a passive


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 groundwater treatment cell, or ‘gate’, installed into the slurry wall. Selection of these modifications would be reported in the design report but would not be considered justification for a re-evaluation of remedial alternatives unless the modifications had a significant effect on estimated cost, construction duration, or implementability.



4. Conclusions and Recommendations

1. Four remedial alternatives were evaluated and ranked for this RAP Addendum. Two alternatives, RAA1 (complete excavation) and RAA4 (slurry wall and cap), were retained from GEI’s February 2007 RAP. Two additional alternatives, RAA5 (combination of excavation and containment) and RAA6 (insitu thermal desorption) were included in response to NHDES September 2007 letter which requested an emphasis on contaminant mass removal or treatment rather than simply containment. These new alternatives were evaluated and ranked along with two retained alternatives from the February 2007 RAP.

2. The selected alternative (RAA5) consists of excavation of tar-impacted soil to 3 feet,

excavation tar-saturated soil below 3 feet, construction of a soil-clay slurry wall around the remaining tar-impacted soil, and construction of an impermeable cap. This alternative would remove 80 percent of the contaminant mass and contain the remaining 20 percent of the mass with the slurry wall and cap. This alternative complies with the requirements of the New Hampshire Code of Administrative Rules, and achieves the most favorable balance of benefits and costs when compared to other alternatives.

3. Implementation of the selected alternative would result in reuse of the properties at

83, 77, and 69 Liberty Hill Road as open space and would restrict residential use. Groundwater quality downgradient from the contained area would improve over time as a result of natural attenuation processes and is expected to achieve the New Hampshire Groundwater Quality Criteria in groundwater near Jewett Brook approximately 35 years following remedy implementation.

4. In accordance with Env-Or 606.16, design plans and construction specifications will

be prepared that present the engineering design for the selected remedy. The plans and specifications will be included in a Remedial Design Report. KeySpan will submit this report to NHDES for review and approval within six months of NHDES approval of the selected alternative. The six months is required to conduct detailed groundwater modeling and refinement of the design of the proposed remedial alternative. The remedial design plans will used by the selected contractor to implement the proposed remedial alternative. A public meeting will be held following submittal to update the community on the remedial plans.



5. Prior to soil excavation, KeySpan will conduct a soil sampling program to collect sufficient analytical data to characterize the material to be shipped offsite for disposal and to provide additional subsurface information that can be used for the detailed design of the proposed containment system. Bench scale testing will be performed to select the appropriate the slurry mix for Site conditions.

6. The Site hydrology is complex as a result of large changes in topography, strong

downward hydraulic gradients in the area with tar-impacted soil, and strong upward hydraulic gradients in the vicinity of Jewett Brook. As a result, a three-dimensional groundwater flow model (MODFLOW or equivalent) of the Site will be prepared to confirm the proposed configuration and effectiveness of the containment system and to finalize the design of the slurry wall. The model will help in final design of the remedy, including final location and depth of the wall, evaluating the effects on local hydrology, and evaluation of the need for hydraulic relief within the containment wall.



5. Limitations This report was prepared for the use of KeySpan, exclusively. The conclusions provided by GEI in this report are based on the information reported in this document. Additional information not available to GEI at the time this report was prepared may result in a modification of the findings of this report. This report has been prepared in accordance with generally accepted engineering and geohydrological practices. No warranty, expressed or implied, is made.



6. References

Federal Remediation Technologies Roundtable, 2002. Remediation Technologies Screening Matrix and Reference Guide, 4th Edition, January. SFIM-AEC-ET-CR-97053. http://www.frtr.gov/matrix2/top_page.html

GEI Consultants, Inc., 2005. Interim Data Report and Scope of Work for Additional Site Investigation, 69, 77, 83, and 87 Liberty Hill Road, Gilford, NH. October 12.

GEI Consultants, Inc., 2006. Site Investigation Report, Liberty Hill Road, Gilford, NH. June 28.

GEI Consultants, Inc., 2006. Supplemental Scope of Work, Liberty Hill Road, Gilford, NH. September 19.

GEI Consultants, Inc., 2006. Interim Data Report No. 2, 69, 77, 78, 83, and 87 Liberty Hill Road, Gilford, NH. December 20.

GEI Consultants, Inc., 2007. Remedial Action Plan, Liberty Hill Road, Gilford, NH. February 28, 2007.

Hvorslev, M.J., 1951. Time Lag and Soil Permeability in Ground-Water Observations, Bulletin No. 36, U.S. Army Corps of Engineers. April.

KeySpan Energy Delivery, 2004. Letter to John Regan, NHDES, re: Laconia MGP, NHDES No. 199312038, October 19.

KeySpan Energy Delivery, 2004. Letter to Robert Minicucci, NHDES, re: Liberty Hill Road Disposal Site, Gilford, NH, NHDES Site No. 200411113, December 3.

New Hampshire Department of Environmental Services (NHDES), 2005. Draft Vapor Intrusion Guidance, April.

United States Environmental Protection Agency, 2007. Treatment Technologies for Site Cleanup: Annual Status Report (Twelfth Edition), September. EPA 542-R-07-012. http://www.epa.gov/tio/download/remed/asr/12/asr12_full_document.pdf

United States Environmental Protection Agency, 1998. Evaluation of Subsurface Engineered Barriers at Waste Sites, August. EPA 542-R-98-005. http://www.epa.gov/tio/download/remed/subsurf.pdf

United States Geological Survey (USGS), 1970. Laconia Quadrangle, New Hampshire, 7.5-Minute Topographic Map Series, 1:25,0000 scale U.S. Geological Survey, 1970.


http://www.epa.gov/tio/download/remed/asr/12/asr12_full_document.pdf

http://www.epa.gov/tio/download/remed/subsurf.pdf

Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 Van Diver, Bradford B., "Roadside Geology of Vermont and New Hampshire," 1987.

Mountain Press Publishing Company, Missoula, MT.

Websites

Belknap County Registry of Deeds website,

http://www.nhdeeds.com/belk/web/start.htm

New Hampshire Geographic Information System (NHGIS) website,

http://www2.des.state.nh.us/gis/onestop/

New York State Department of Health, 2005. Summary of Indoor and Outdoor Levels of Volatile Organic Compounds from Fuel Oil heated homes in New York State, 1997-2003, November 14,

http://www.health.state.ny.us/nysdoh/indoor/docs/fuel_oil.pdf

Federal Remediation Technologies Roundtable (FRTR) website,

http://www.frtr.gov

Remedial Technologies Screening Matrix and Reference Guide,

http://www.frtr.gov/matrix2/section3/table3_2.html

Risk Reduction Engineering Laboratory (RREL) treatability database,

http://www.frtr.gov/matrix2/appd_c/appd_c21.html

Vendor Information System for Innovative Treatment Technologies (VISITT) database,

http://www.clu-in.org/pub1.cfm



7. Acronyms and Abbreviations Accutest Accutest Laboratories Alpha Alpha Woods Hole Labs AUR Activity and Use Restriction Bartlett Richard D. Bartlett and Associates, LLC bgs below ground surface Boart Boart Longyear BTEX benzene, toluene, ethylbenzene, xylene cm/sec centimeters per second COPCs contaminants of potential concern DNAPL dense non-aqueous phase liquid DO dissolved oxygen EPA U.S. Environmental Protection Agency ESMI Environmental Soil Management, Inc. FRTR Federal Remediation Technologies Roundtable GEI GEI Consultants, Inc. GMZ Groundwater Management Zone ISE Initial Screening Evaluation KeySpan Energy North Natural Gas d/b/a KeySpan Energy Delivery New England LNAPL light non-aqueous phase liquid MGP manufactured gas plant ml/min milliliters per minute MTBE methyl tert butyl ether NGVD National Geodetic Vertical Datum NHDES New Hampshire Department of Environmental Services NHGIS New Hampshire Geographic Information System NYSDOH New York State Department of Health ORP oxygen reduction potential PAHs polycyclic aromatic hydrocarbons PID photoionization detector PVC polyvinyl chloride RAA Remedial Action Alternative RAP Remedial Action Plan RCMP Risk Characterization and Management Policy


Remedial Action Plan Addendum Lower Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services November 9, 2007 RCRA Resource Conservation and Recovery Act RREL Risk Reduction Engineering Laboratory SIR Site Investigation Report SVOCs semivolatile organic compounds UCL Upper Concentration Limit µg/m3 micrograms per cubic meter USCS Soil Conservation Service Unified Soil Classification System USGS United States Geological Survey VISITT Vendor Information System for Innovative Treatment Technologies VOCs volatile organic compounds YSI YSI Instruments


Table 1Detailed Evaluation SummaryRemedial Action Plan AddendumLower Liberty Hill RoadGilford, NH

Remedial Action AlternativeRAA1

Excavate All Tar-impactedSoil and Treat Soil Off-sitewith Thermal Desorption

RAA4Excavate Tar-impacted Soil to3 Feet Deep and Contain All

Tar-impacted Soil below 3 Feet Deep

RAA5Excavate Tar-impacted Soil to

3 Feet Deep; Excavate Tar-saturated Soil Below 3 feet; Off-Site Thermal Desorption; and

Contain Residual Tar-impacted Soil below

3 Feet Deep

RAA6In-Situ Thermal Treatment of All Tar-Impacted

Soil

Effectiveness Ability to achieve the RAP goals: remove, treat, or contain the contaminant source and eliminate health hazards associated with direct exposure to the contaminant source; restore groundwater quality.

Rank = 1: RAA1 is expected to be the most effective alternative because it consists of complete removal and treatment of tar-impacted soil.

Rank = 4: RAA4 ranked last in effectiveness because although this alternative contains all contaminated soil, it removes only 0.5 percent of the source material.

Rank = 3: RAA5 was ranked third because it removes 80 percent of the source material and contains the remainder.

Rank = 2: RAA6 was ranked second because it treats all the contaminated soil and removes an estimated 84 percent of the source material.

Ease of Implementation Degree of design and construction complexity; availability of experienced contractors or specialized equipment.

Rank = 4: RAA1 was considered most difficult to implement because of the requirements for designing and installing deep excavation support systems, the considerable dewatering effort to enable deep excavations below the water table, and the effort required to coordinate controls for a multi-year construction project. RAA1 also requires more than double the truck traffic, soil treatment, and backfill volumes than any other alternative.

Rank = 1: RAA4 was considered the most easily implemented alternative because it relies on readily available excavation equipment and contractors, does not require deep excavation support or dewatering, and required the least excavation and offsite transportation of soil.

Rank = 2: RAA5 was ranked second because it also relies on readily available equipment and contractors. A reinforced concrete wall will be used instead of a slurry wall in the area where deep excavation is required. The reinforced concrete wall will provide both structural support and containment. The slurry wall will be installed prior to excavation, which will reduce the amount of dewatering.

Rank = 3: RAA6 was ranked third because there are limited contractors available for this specialized treatment technology. Although no excavation is required, this technology will require extensive drilling, specialized equipment, and implementation of a confirmation sampling program.

Reliability Predicted certainty of success, difficulty to maintain success long-term.

Rank = 1: RAA1 ranked as the most reliable alternative because all tar-impacted soil would be removed from the Site. It had the greatest certainty for success and no future obligations would be required to address contamination remaining at the Site.

Rank = 4: RAA4 was considered last in reliability because of the limited amount of source removal. However, it would contain all tar-impacted soil at the Site.

Rank = 2: RAA5 was ranked second because all the tar-saturated soil would be removed and the remainder of the tar-impacted soil would be contained.

Rank = 3: RAA6 was ranked third because treatment was considered less reliable than removal of the tar-saturated material and this alternative does not include provisions for containment of the residual treated material.

Timeliness Time period required to achieve the RAP goals (stated under "Effectiveness").

The ranking of timeliness was a function primarily of construction duration – the time to achieve the remedial goals for contaminated soil - because all four alternatives either remove, treat, or contain the source material and achieve groundwater standards at the same time.

Rank = 4: RAA1 would restore groundwater quality downgradient from the tar-affected soil in approximately the same time period as the other alternatives, and therefore ranked similarly for long-term timeliness. However, it would take the longest to implement and therefore scored lowest.

Rank = 1: RAA4 would restore groundwater quality downgradient from the tar-affected soil in approximately the same time period as the other alternatives; however, RAA4 required the least construction time, and was therefore ranked first.

Rank = 2: RAA5 would require more construction time than RAA4, but less than RAA1 and RAA6.

Rank = 3: RAA6 was ranked third because construction and treatment together would take longer than RAA5 construction.

Public Impacts Adverse effects to the neighborhood (e.g. noise, dust, odors, construction activity, and increased traffic on local roads) are primarily a function of the project duration and intensity of the remedial construction. Therefore, the alternatives were ranked from shortest to longest in duration based on construction time, amount of construction activity, and off-site truck traffic required.

Rank = 4: RAA1 ranked last due to the longest construction period (2 years) and the most increase in local traffic (6000 truckloads)

Rank = 1: RAA4 ranked first due to the least amount of truckloads (560) necessary to meet the objectives. Construction timeframe of one year equaled that of RAA5.

Rank = 2: RAA5 was ranked second because it requires more truckloads (1250) than RAA4, though construction time frame is one year, equal to RAA4.

Rank = 3: RAA6 was ranked third because of the significant time and construction activity required for system installation and operation. The overall duration of this alternative is third longest.

Criteria Criteria Description

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Table 1Detailed Evaluation SummaryRemedial Action Plan AddendumLower Liberty Hill RoadGilford, NH

Remedial Action AlternativeRAA1

Excavate All Tar-impactedSoil and Treat Soil Off-sitewith Thermal Desorption

RAA4Excavate Tar-impacted Soil to3 Feet Deep and Contain All

Tar-impacted Soil below 3 Feet Deep

RAA5Excavate Tar-impacted Soil to

3 Feet Deep; Excavate Tar-saturated Soil Below 3 feet; Off-Site Thermal Desorption; and

Contain Residual Tar-impacted Soil below

3 Feet Deep

RAA6In-Situ Thermal Treatment of All Tar-Impacted

Soil

Criteria Criteria Description

Risks, short-term On-site or off-site risks: potential for construction or traffic accidents; spills or releases to the environment.

These potential short-term risks are proportional to the duration and complexity of soil excavation, the number of trucks arriving and departing the Site, and the volume of dewatering effluent that needs to be treated and discharged. The alternatives requiring excavation were ranked in order of increasing total excavation volume, truck traffic, and duration of dewatering.

Rank = 4: RAA1 ranked last because it required the highest amount of contaminated soil handling, and had the greatest excavation volume, excavation depth, dewatering duration, and off-site truck traffic.

Rank = 1: RAA4 had the least potential for short-term risks primarily due to its limited, shallow soil excavation and installation of a slurry wall which requires the least handling and management of contaminated soil.

Rank=2: RAA5 ranked second because it requires more soil handling than RAA4, and it will require excavation dewatering for a limited period of time.

Rank = 3: RAA6 ranked third because it requires treatment of large quantities of fluids and vapors over an extended period of time.

Risks, long-term Potential risks posed by contamination remaining at the site.

Rank = 1: RAA1 ranked first because no contamination above soil remediation standards will remain on-site after excavation is complete.

Rank = 4: RAA4 ranked last because it would result in the removal of 0.5% and containment of 99.5% of the tar-impacted material. An AUR would be implemented that further limited potential contact with contaminated soil by restricting single-family residential use of the properties.

Rank = 2: RAA5 was ranked second because it removes 80 percent of the source material and contains the remainder. An AUR would be implemented that further limited potential contact with contaminated soil by restricting single-family residential use of the properties.

Rank = 2: RAA6 was also ranked second because an AUR may still be required to restrict future single-family residential use. It would treat all the source material and remove 84% of the contaminants. The contaminants remaining will be in an inert asphalt-like material.

Benefits, long-term Avoid restrictions for site reuse Rank = 1: RAA1 ranked first because no restrictions on future use would be required and residential reuse would be consistent with local land-use.

Rank = 4: RAA4 ranked last because residential reuse would be prohibited by the AUR and it provides the least potential long term benefit associated with contaminant mass removal or treatment.

Rank = 2: RAA5 was ranked below RAA1 because an AUR would be required. It was ranked the same as RAA6 because similar restrictions would be required.

Rank = 2: RAA6 was ranked below RAA1 because an AUR would be required. It was ranked the same as RAA5 because similar restrictions would be required.

Cost Effectiveness Costs to design, construct, maintain, and monitor the remedy.

The RAAs were ranked in order of increasing cost.

Rank = 4: RAA1 was ranked last due to a total cost of $15,900,000.

Rank = 1: RAA4 was ranked first with the lowest cost of $5,500,000.

Rank = 2: RAA5 was ranked second with a cost of $8,700,000.

Rank = 3: RAA6 was ranked third with a cost of $12,900,000.

Total Rank (Lowest Rank is preferred) 24 21 19 24

Note: The ranking system was based on assigning a relative rating of 1 to 4 for each RAA for each criteria, with the lower rank preferred. Some or all of the RAAs may be assigned the same rating. The ratings were then summed to produce a total rank for each

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Appendix A

NHDES Comment Letter regarding RAP, September 21, 2007

GEI Consultants, Inc.

September 21, 2007 Patricia A. Haederle, CPG KeySpan Energy Delivery 52 Second Avenue Waltham, MA 02451 SUBJECT: Gilford – Lower Liberty Hill Road Site, Liberty Hill Road DES Site # 200411113, Project RSN # 14262 Remedial Action Plan (RAP), prepared by GEI Consultants, Inc., dated

February 28, 2007 Dear Ms. Haederle: The New Hampshire Department of Environmental Services (Department) has received the Remedial Action Plan (RAP) prepared by GEI Consultants, Inc. (GEI) on behalf of KeySpan Energy Delivery New England (KeySpan). The RAP presents the results of an evaluation of potential remedial alternatives to address manufactured gas plant (MGP) impacts to soil and groundwater at the subject site and the rationale for the selection of the recommended remedy. On August 28, 2007 the Department and Keyspan participated in a working meeting to discuss the Department’s initial comments on the RAP. The RAP follows a focused site investigation to determine the lateral and vertical extent of MGP impacts to soil, to further assess groundwater impacts, and define potential exposure pathways. The findings of the investigation are presented in the Site Investigation Report (SIR) prepared by GEI dated June 28, 2006. The conceptual model presented in the SIR provided the basis for the evaluation of remedial alternatives. Pursuant to Env-Or 606.12, the evaluation included an assessment of: 1) effectiveness and reliability; 2) feasibility and ease of implementation; 3) risk reduction and associated benefits; 4) cost effectiveness; and 5) estimated time to reach the no further action criteria pursuant to the requirements of Env-Or 609.02. An initial screening evaluation was preformed to identify technologies potentially appropriate for addressing coal tar-impacted soil and groundwater. As a result of the screening process and a detailed evaluation of specific remedial technologies, the following four remedial action alternatives (identified as RAA-1 through RAA-4) were retained by GEI for further consideration:

• RAA1 - Excavate all tar-saturated and tar-impacted soil and treat off-site with thermal desorption;

• RAA2 - Excavate tar-impacted soil to 15 feet and tar-saturated soil below 15 feet and treat soil off-site with thermal desorption;

• RAA3 - Excavate tar-impacted soil to 15 feet deep, contain tar-impacted soil below 15 feet deep and treat soil off-site with thermal desorption; and

• RAA4 - Excavate tar-impacted soil to 3 feet deep, contain tar-impacted soil below 3 feet deep and treat soil off-site with thermal desorption.

The State of New Hampshire DEPARTMENT OF ENVIRONMENTAL SERVICES

____________

Thomas S. Burack, Commissioner

DES Web Site: www.des.nh.gov P.O. Box 95, 29 Hazen Drive, Concord, New Hampshire 03302-0095

Telephone: (603) 271-2908 Fax: (603) 271-2181 TDD Access: Relay NH 1-800-735-2964

Patricia A. Haederle, CPG DES Site # 200411113 September 21, 2007 Page 2 of 5

Based on this assessment, KeySpan/GEI selected RAA4 as the recommended alternative.

The Department reviewed the four alternatives identified in the RAP in accordance with the requirements of New Hampshire Administrative Rule Env-Or 600, Contaminated Site Management, specifically Env-Or 606.13. Our review focused on the following performance standards:

• Protection of human health and the environment;

• Achieving groundwater quality criteria specified in Env-Or 603.01;

• Controlling the source of contamination to reduce further discharges to the environment;

• Removal, treatment, or containment of the contaminant source to reduce the health risk associated with direct exposure via dermal contact, ingestion, and inhalation;

• Reduction of the risk to human health and the environment to the greatest extent practicable, balancing costs and benefits;

• Long-term management of the remedy; and

• The reliability of long-term institutional and engineering controls. Community input with respect to the remedy is not one of the selection criteria but is a significant consideration as the Department and KeySpan have stated at several public informational meetings. Of note is the degree that the various remedial alternatives will impact the local population from both a temporary and long-term standpoint. Based on our review, the Department has the following comments: RAA1 – Excavate All Tar-Saturated and Tar-Impacted Soil and Treat Soils Off-site with

Thermal Desorption This alternative consists of excavating all of the tar-saturated and tar-impacted soil identified at the site and treating it off-site with thermal desorption technology. RAA1 meets all of the criteria for RAP approval. However, the cost for implementation of RAA1, which results in 100 percent removal of the source material, is more than twice the cost of RAA2 where 83 percent of the source material would be removed. To remove the additional 17 percent of source material, RAA1 would potentially have a much greater impact to the community with respect to noise, construction activity, duration of construction and traffic. RAA1 entails the excavation of 2.7 times the amount of contaminated soil than required for RAA2 (113,830 cubic yards for RAA1 versus 41,913 cubic yards for RAA2). It also results in a similar increase in truck traffic for shipping and disposal (6035 truck loads for RAA 1 versus 2,480 truck loads for RAA2). The weeks required for trucking the contaminated soil increases from 60 weeks over the course of two years for RAA1 compared to 25 weeks over one year for RAA2. It is important to note that no potential exposure pathways (e.g., drinking water, direct contact, ingestion and inhalation) have been identified at the site. For both alternatives RAA1 and


RAA2, precluding future exposure pathways would be a condition of a groundwater management permit. When comparing the cost effectiveness of alternative RAA1 to RAA2, the Department believes that the limited reduction in risk to human health and the environment may not warrant the substantial incremental increase in cost. RAA2 – Excavate Tar-impacted Soil to 15 feet and Tar-saturated Soil Below 15 feet and

Treat Off-site with Thermal Desorption The remedial actions proposed for RAA2 are similar to RAA1 with the exception that tar-impacted soil below 15 feet would be left in place. RAA2 does include, however, the removal of “tar-saturated” source material near the well cluster MW 113 A, B and C. This remedy involves the removal and disposal of 5,236 tons more than RAA3 (49,601 tons for RAA2 versus 44,365 tons for RAA3) With this incremental increase in soil volume, an additional 77% of the source material is removed (83% source removal for RAA2 versus 6 % for RAA3). The remaining 17% of the source material is expected to naturally attenuate. Contaminant concentrations in groundwater would be expected to improve over time and eventually meet groundwater quality standards. RAA2 also meets all of the criteria for RAP approval. It is worth noting that one of the performance measures assessed for each of the alternatives was the estimated time required to reach no further action criteria. For alternative RAA2, the time required for groundwater in the overburden adjacent to Jewett Brook to meet ambient groundwater quality standards is greater than three times that of the other alternatives (i.e., 120 years versus 35 years). That said, one criterion for RAP approval is that the resource value of groundwater impacted by the contamination will be protected to the greatest extent practicable taking into account current and anticipated future land use (ref. Env-Or 606.13(h)). Groundwater impacted by site contaminants has been limited to groundwater in the overburden. On-site drinking water wells and most of the individual drinking water wells adjacent to the site are bedrock wells. Site investigation work performed to date indicates that bedrock water quality at and adjacent to the site has not been impacted by coal tar related contaminants. Regardless of the alternative ultimately approved by the Department, routine monitoring of drinking water wells adjacent to the site and management of the groundwater plume will be required as part of a groundwater management permit. This remedy is less costly than RAA3, has greater reliability and requires less long-term management responsibilities than RAA3 and RAA4. RAA3 – Excavate Tar-impacted Soil to 15 Feet Deep, Contain Tar-Impacted Soil Below 15

Feet Deep, and Treat Soil Off-site with Thermal Desorption; and RAA4 - Excavate Tar-impacted Soil to 3 Feet Deep, Contain Tar-Impacted Soil Below 3

Feet Deep, and Treat Soil Off-site with Thermal Desorption

Alternatives RAA3 and RAA4 include the excavation of impacted soil to 15 and 3 feet respectively and containment of the impacted soils that remain by means of a slurry wall and cap system. The following comments apply to both alternatives:

• Alternatives RAA3 and RAA4 result in leaving approximately 94 and 99.5 percent of the source material respectively in place. Accordingly, long-term monitoring of the


performance of the slurry wall we be a necessity. As a result, the Department believes that these alternatives do not meet the criteria that “[l]ong-term management, including…site monitoring requirements, will be minimized”.

• The Department contacted several of the regulatory contacts provided in Appendix J of the RAP. While these contacts indicated that the slurry walls performed well with respect to the containment of mobile non-aqueous phase liquids (NAPLs), containment of dissolved phase contaminants was not a primary objective. Furthermore, none of the aforementioned regulatory contacts had contemplated the performance of the slurry walls utilized for their projects for essentially permanent containment. KeySpan/GEI must be able to demonstrate that the “[l]ong-term…engineering controls [i.e., the slurry wall] will be reliable” pursuant to Env-Or 606.13(j). It is not readily apparent how this can be accomplished to the Department’s satisfaction. The current conceptual approach is passive containment of groundwater from the source area with the combination of the slurry wall and impermeable cap and would not require any active measures (e.g., pumping). As we discussed at the August 28, 2007 meeting, the Department is willing to consider additional information to address the performance of the slurry wall and its long-term reliability. As part of the additional information, an estimate should be provided on how long groundwater within the slurry wall will be contaminated above groundwater quality standards as that will provide information on how long the wall will have to successfully perform.

• Pursuant to Env-Or 606.10 (d), the remedial action plan shall recommend action to: a) remove or treat the source of contamination; and b) contain the contamination source to limit the impact to groundwater, surface water and soil to the extent feasible. While not explicit this requirement infers emphasis primarily on removal and treatment of the source of contamination and secondarily on containment, which is consistent with our approach at other sites. Alternatives RAA3 and RAA4 rely primarily on containment.

Based on our comments above, the Department concurs with KeySpan/GEI that alternative RAA1 may not be cost effective and has a significantly greater impact on the community in terms of construction activity, truck traffic, duration of construction and noise. In addition, the Department has determined that given the available information the recommended alternative RAA4 (and by extension RAA3) may not meet the criteria for RAP approval pursuant Env-Or 606.13. Therefore, the Department cannot approve the RAP as proposed. As a result, the Department hereby requests that KeySpan prepare a revised RAP that provides greater emphasis on removal and treatment as the primary remedial actions. Containment can be a component of the remedy. However, the remedy shall not rely primarily on containment if removal and/or treatment are feasible. At the August 28, 2007 meeting, the Department suggested consideration of an alternative that is a hybrid of RAA2 and RAA3; i.e., removal of the tar-saturated soil below 15 feet, which would represent 77 percent of the source material, combined with containment of the tar-impacted soil that remains. The Department understands that as a result of our discussions at the aforementioned meeting, KeySpan may also evaluate some other remedial alternatives not previously considered to address the Department’s concerns.


Should you have any questions, please contact me at the Department’s Waste Management Division. Sincerely,

Michael McCluskey, P.E. Hazardous Waste Remediation Bureau Tel: (603) 271-2183 Fax: (603) 271-2181 E-mail: [email protected] cc: Evans Juris, Town of Gilford Town of Gilford Health Officer Katherine Dormody, Gilford Public Library (repository) James Ash, P.E., GEI Consultants, Inc. John Regan, P.G., Supervisor, HWRB Ralph Wickson, P.G., HWRB


Appendix B

RAA Cost Estimate Information


Appendix B - Preliminary Remediation Cost Estimate for Lower Liberty Hill Road, Gilford, NH (2007)Unit

Quantity Cost Quantity Cost Quantity CostPreconstruction

Engineering Design, Plans, Specs, Bid, Regulatory Submittals % 6.0 1 $318,875 1 $173,162 1 $266,251 1 $253,508Permitting Lump Sum $20,000 1 $20,000 1 $20,000 1 $20,000 1 $20,000Pre-characterization Borings and Soil Testing for Reuse/Disposal 500 tons $1,125 341 $384,177 29 $32,871 98 $110,268 $0

Construction ManagementResident Engineering/Project Management Week $5,525 76 $419,900 30 $165,750 38 $209,950 65 $359,125Air Monitoring Technician and Equipment Week $7,750 55 $426,250 12 $93,000 38 $294,500 39 $302,250Site Survey (Layout, Excavation Bottoms, As-builts) Each $4,725 6 $28,350 3 $14,175 6 $28,350 1 $4,725

General ConditionsGeneral Mobilization/Demobilization % 2.0 1 $79,136 1 $50,000 1 $50,000 1 $355,366Misc. Surface Site Preparation Lump Sum $50,000 1 $50,000 0.5 $25,000 1 $50,000 1 $50,000Site Access Roads Construction/Liberty Hill Rd. improvement Lump Sum $25,000 2 $50,000 1 $25,000 1.5 $37,500 1.0 $25,000Temporary Perimeter Fencing (6' ) Linear Foot $5 2,100 $11,130 2,100 $11,130 2,100 $11,130 2,100 $11,130Temporary office trailers (2) Month $820 21 $17,163 7 $5,740 9 $7,380 9 $7,380Temporary Utilities/Office Expenses (2) Month $1,244 21 $26,037 7 $8,708 9 $11,196 9 $11,196Demo Water Supply Well Each $1,775 3 $5,325 3 $5,325 3 $5,325 3 $5,325Install Dewatering Wells/Pumps to 75' Each $6,274 4 $25,094 0 $0 4 $25,094 $0

ExcavationRemedial Excavation 0 to 10 feet CY $6 39,262 $251,943 9,739 $62,498 18,621 $119,489 $0Remedial Excavation 10 to 15 feet CY $8 17,839 $143,093 0 $0 5,175 $41,510 $0Remedial Excavation 15 to 25 feet CY $10 32,095 $308,932 0 $0 6,493 $62,502 $0Remedial Excavation 25 to 50 feet CY $13 24,634 $316,153 0 $0 2,383 $30,583 $0Hauling/stockpiling for reuse CY $5 33,374 $175,212 2,266 $11,894 14,393 $75,565 $0Dewatering and Treatment Week $7,500 60 $450,000 0 $0 20 $150,000 $0Drilled H-Pile Excavation support SF $65 5,000 $325,000 0 $0 1,800 $117,000 $0

Demolition $0Demo - Concrete Foundation Walls SF $14 3,800 $54,530 1,900 $27,265 2,940 $42,189 $0Demo - Concrete Footings LF $15 475 $7,315 0 $0 260 $4,004 $0Demo - Concrete Slabs SF $6 4,265 $25,377 0 $0 2,278 $13,554 $0Demo - Septic tank EA $1,175 2 $2,350 2 $2,350 2 $2,350 $0

Backfill/RestorationBorrow/spread for 25 to 50 feet (No reuse) CY $17 24,634 $418,778 0 $0 2383 $40,510 $0Borrow/spread for 15 to 25 feet CY $17 25,366 $431,214 0 $0 6,493 $110,387 $0Borrow/spread for 10 to 15 feet CY $17 10,824 $184,012 0 $0 5,175 $87,975 $0Borrow/spread for 10 to 1 feet CY $17 15,589 $265,021 4,227 $71,865 981 $16,675 4,227 $71,865Borrow/spread, 12" topsoil CY $26 4,043 $105,124 3,246 $84,409 3,246 $84,409 3,246 $84,409Haul reuse/spread CY $7 33,374 $232,949 2,266 $15,814 14,393 $100,466 2,266 $15,814Compaction CY $0.2 113,830 $23,904 9,739 $2,045 32,672 $6,861 9,739 $2,045Finish grading SY $1 12,130 $8,369 9,739 $6,720 9,739 $6,720 9,739 $6,720Hydroseeding MSF $71 109 $7,751 88 $6,224 88 $6,224 88 $6,224Replace #69/#87 water supply wells Each $5,000 2 $10,000 2 $10,000 2 $10,000 2 $10,000Liberty Hill Road Repairs Lump Sum $25,000 1 $25,000 1 $25,000 1 $25,000 1 $25,000

Off-site Treatment/DisposalSoil Transportation/Disposal Ton $50 120,685 $6,034,236 11,211 $560,538 27,418 $1,370,899 $0Demolition Debris Transportation and Disposal CY $50 208 $10,400 47 $2,346 134 $6,702 $0Slurry Wall Spoil Disposal (15% of wall volume) CY $75 0 $0 869 $65,154 736 $55,166 $0Waste and GAC $29,361NAPL Disposal $100,000

Slurry Wall/CapBackfill design/permeability testing LS $25,000 1 $25,000 1 $25,000 $0Mobilization/Demobilization Lump Sum $150,000 1 $150,000 1 $150,000 $0Three foot thick soil/clay slurry wall (to effective 35-foot depth) SF $20 38,815 $776,300 32,865 $657,300 $0Three foot thick soil/clay slurry wall (below effective 35-foot depth) SF $50 13,308 $665,400 11,268 $563,400 $0Reinforced concrete wall with tiebacks (to effective 35-ft depth) SF $60 5,950 $357,000 $0Reinforced concrete wall with tiebacks (below effective 35-ft depth) SF $90 2,040 $183,600 $0Membrane Cap Installed at top of wall SF $2.4 76,247 $179,424 76,247 $179,424 76,247 $179,424Additional cap system components for shallow cap SF $4.0 76,247 $307,123 76,247 $307,123 76,247 $307,123

In-Situ Thermal DesorptionDrill and Install wells $2,034,859Vapor Cover Installation $488,243Electrical and Mechanical Construction $570,131Vapor and Water Treatment System and Commissioning $509,873Operation hardware, labor, travel, per diem, rental and fees $695,282Power and Propane $2,699,000Sampling and Analysis, Reporting $141,529

Long-term Groundwater Monitoring (30 years)Net Present Value (year 2007) Year $35,000 $538,036 $538,036 $538,036 $538,036Contingency % 30% $3,664,841 $1,267,580 $2,002,370 $2,975,983

$15,880,979 $5,492,845 $8,676,938 $12,895,926Notes/Assumptions:A Assumed GEI 2006 standard rates for engineering fees. RAA1: RAA4: RAA5: RAA6:B Prices in 2007 dollars Number of triaxial trucks for disposal shipping 6034 561 1371 0C Most costs from RSMeans, 2007 Heavy Construction Cost Data, 21st Edition. Assumed RSMeans location factor = 1 (actual for Manchester = 0.94) Work days for disposal (20 trucks/d) 302 28 69 0D No costs for home reconstruction included Work weeks for disposal trucking 60 6 14 0E Construction season = April 1 thru December 21 (38 weeks) Percent Removal 100% 0.5% 80% 84%F Scenario RAA1 - Excavation braced below 25' in some perimeter areas, 1:1 bench above 25' and within interior areas. For reuse: 15-25': assumed 50% of excess excavate suitable; 0-15' = 75% excess excavate reused.G Scenario RAA4: Future Residential Use Prohibited. For reuse 0-3': assumed 75% excess excavate reused.K Scenario RAA5: Future Residential Use Prohibited. Reinforced concrete wall instead of slurry wall along 180 ft of alignment for use as structural support and containment. For reuse 0-3': assumed 75% excess excavate reused.L Scenario RAA6: Future Residential Use Prohibited.M Long-term groundwater monitoring = $35,000/year, discount rate of 5.0% for 30 years. Sampling = 20 monitoring wells, semiannually for VOCs/SVOCs; 10 drinking water wells, annually for VOCs. Semiannual reports to DES.

RAA6In-Situ Thermal Desorption of all tar-impacted and

tar-saturated soil.

RAA5Excavate All Tar-impacted Soil to 3 ft; Excavate All

Tar-saturated Soil Below 3 feet; Offsite Thermal Desorption; Slurry Wall to Contain Contaminated

Soil 3-50 feet

PROJECT TOTAL

RAA1Excavate All Tar-Impacted Soil; Offsite Thermal

Desorption

RAA4Excavate All Tar-impacted soil to 3 feet; Slurry Wall

to Contain Contaminated Soil 3-50 feet; Offsite Thermal Desorption

UnitCost

GEI Consultants, Inc. Project 05069November 2007

M:\PROJECT\2005\05069\Tables\2007\RAP Addendum Cost Estimate


Appendix C

Additional Information on In-Situ Thermal Desorption


Documents

November 13, 2007 Mr. Michael McCluskey, PE 29 Hazen Drive LIberty... · GEI Consultants, Inc. i Table of Contents Executive Summary iii 1. Introduction 1 1.1 Purpose 1 1.2 Site Information