Remedial Action Plan - Lower Liberty Hill Site Liberty... · GEI Consultants, Inc. i Table of Contents Executive Summary v 1. Introduction 1 1.1 Site Information and Description 1

Remedial Action Plan Liberty Hill Road, Gilford, NH New Hampshire Department of Environmental Services February 28, 2007

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Table of Contents

Executive Summary v

1. Introduction 1 1.1 Site Information and Description 1

1.1.1 Contact Person 1 1.2 Purpose and Objectives 2 1.3 Previous Investigations 2

2. Site Information 3 2.1 Site History 3 2.2 Surrounding Land Use 3

3. Site Investigation Addendum 4 3.1 Boring and Monitoring Well Installation 4 3.2 Groundwater Level Gauging 6 3.3 Soil Sampling 6 3.4 Groundwater Sampling 7 3.5 Drinking Water Sampling 8 3.6 Soil Gas, Indoor Air and Ambient Air Sampling 9

3.6.1 Soil Gas 9 3.6.2 Indoor Air 9 3.6.3 Ambient Air Sampling 10

3.7 Surface Water Sampling 10

4. Hydrogeologic Characteristics 11 4.1 Topography and Surface Drainage 11 4.2 Regional Geology 11 4.3 Site Geology 11 4.4 Site Hydrogeology 12

4.4.1 Groundwater Elevation Monitoring 12 4.4.2 Gradients and Permeability 12

5. Conceptual Site Model 14 5.1 Nature and Extent of Constituents of Potential Concern 14

5.1.1 Nature and Extent of COPCs in Soil 14 5.1.2 Nature and Extent of COPCs in Groundwater 17 5.1.3 Nature and Extent of COPCs in Soil Gas and Air 18 5.1.4 Nature and Extent of COPCs in Surface Water 20


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5.2 Sources 21 5.3 Migration Pathways 21

6. Risk Characterization 22 6.1 Human Health Risk 22 6.2 Stage I Ecological Screening 22

7. Remedial Action Plan 24 7.1 Regulatory Requirements 24 7.2 Objectives 24 7.3 Site-Specific Considerations 24 7.4 Identification and Initial Screening of Remedial Technologies 24 7.5 Description of Remedial Technologies Retained for Detailed Evaluation 26

7.5.1 Institutional Controls 26 7.5.2 Solidification/Stabilization 26 7.5.3 Containment 27 7.5.4 Excavation 27 7.5.5 Soil Treatment –Thermal Desorption 28

8. Detailed Evaluation of Remedial Action Alternatives 29 8.1 Development of Remedial Action Alternatives 29 8.2 Remedial Action Alternatives Descriptions 30

8.2.1 RAA1 – Excavate Tar-impacted Soil and Treat Soil Off-site with Thermal Desorption 30

8.2.2 RAA2 – Excavate Tar-impacted Soil to 15 feet and Tar-saturated Soil Below 15 Feet Deep and Treat Soil Off-site with Thermal Desorption 31

8.2.3 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 32

8.2.4 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 32

8.3 Detailed Evaluation Criteria 33 8.4 Qualitative Scoring of RAAs 33 8.5 Selected Remedial Action Alternative 34

9. Conclusions and Recommendations 35 9.1 Conclusions 35 9.2 Recommendations 37

9.2.1 Recommended Remedial Action Alternative 37 9.2.2 Delineation of Groundwater Management Zone 37 9.2.3 Design Plans and Construction Specifications 37

10. Limitations 39


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11. References 40

12. Acronyms and Abbreviations 42 Tables 1. Property Ownership Information 2. Summary of Borings and Monitoring Wells 3. Groundwater Elevation Measurements 4. Vertical Groundwater Gradients 5. Subsurface Soil Chemical Testing Results – by Property 6. Surface Soil Chemical Testing Results – by Property 7. Groundwater Chemical Testing Results – Monitoring Wells 8. Groundwater Chemical Testing Results – Private Drinking Water Wells 9. Groundwater Chemical Testing Results – Public Drinking Water Wells 10. Soil Gas Chemical Testing Results – by Property 11. Sub-slab Soil Gas Chemical Testing Results – by Property 12. Indoor Air Chemical Testing Results – by Property 13. Ambient Air Chemical Testing Results – by Property 14. Surface Water Chemical Testing Results 15. In-Situ Technologies 16. Ex-situ Technologies 17. Summary of Initial Screening Evaluation in In-Situ Applications 18. Summary of Initial Screening Evaluation in Ex-Situ Applications 19. Detailed Evaluation Summary Figures 1. Site Location Map 2. Site Plan 3. Surface Water Samples 4. Groundwater Elevation Contour Plan – Shallow Groundwater 5. Groundwater Elevation Contour Plan – Intermediate Groundwater 6. Estimated Lateral Extent of Impacted Soil 7. Geologic Cross Section A-A’ 8. Geologic Cross Section B-B’ 9. Groundwater Concentrations Exceeding GW1 Standards – November 2006 10. Remedial Action Alternative No. 1 11. Remedial Action Alternative No. 2 12. Remedial Action Alternative No. 3 13. Selected Remedial Action Alternative (No. 4)


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Appendices A. Boring Logs and Monitoring Well Installation Reports B. Laboratory Data Reports – Soil C. Laboratory Data Reports – Groundwater from Monitoring Wells D. Laboratory Data Reports – Groundwater from Drinking Water Wells E. Laboratory Data Reports – Soil Gas and Air F. Laboratory Data Reports – Surface Water G. Stage I Ecological Screening H. RAA Cost Estimates I. Bioscreen Modeling J. Slurry Wall Project Descriptions ALA/SEO/JRA:lek M:\PROJECT\2005\05069\Reports\07\RAP 0207\RAP 022807.doc


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Executive Summary GEI Consultants, Inc. prepared this Remedial Action Plan (RAP) on behalf of KeySpan Energy Delivery New England (KeySpan) to document our evaluation of remedial alternatives for the Liberty Hill Road Site (NHDES Site Identification No. 200411113) in Gilford, New Hampshire (the Site). The purpose of the RAP was to recommend action 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 prepared a Site Investigation Report (SIR), dated June 28, 2006, which provided a history of the Site, a description of Site investigation activities and methods, and a summary of the estimated extent of tar-related contaminants in environmental media. The impacts observed during the site investigation warranted the development of a RAP. Since submittal of the SIR, KeySpan acquired the four properties where tar-impacts have been observed in soil (69, 77, 83, and 87 Liberty Hill Road). Additional site investigation activities proposed in the SIR were conducted in September and October 2006. A total of 92 borings were advanced and 47 monitoring wells were installed to date. Based on the results of this additional investigation, the extent of tar impacts in soil have been established and are limited to the properties at 69, 77, 83, and 87 Liberty Hill Road. Tar-impacts in soil at these properties consist of tar-stained soil, tar-coated soil, occasional blebs of tar, and naphthalene odor. Results from these additional investigation activities were consistent with the Conceptual Site Model presented in the June 2006 SI Report. Groundwater impacts consist of benzene, naphthalene, styrene, toluene, and 1,2,4 trimethylbenzene concentrations exceeding the drinking water (GW-1) standards in monitoring wells installed within and downgradient of the tar-impacted soil. The extent of impacts to groundwater have been established to the east, along Liberty Hill Road, to the south on the 87 Liberty Hill Road property, and to the north and northwest on the 63 Liberty Hill Road property. Additional investigation is warranted across Jewett Brook, on the adjacent golf course property, to evaluate the downgradient extent of impacts in groundwater. This work will be conducted in spring 2007. GEI conducted a Stage I Environmental Screening for the Site to evaluate the potential effects of MGP byproducts on Jewett Brook near the northwestern boundary of the 69 Liberty Hill Road property. The impacts to Jewett Brook and surrounding wetland are


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limited to sediment and surface water in small pools adjacent to Jewett Brook. MGP byproducts were not observed in surface water or sediment of Jewett Brook itself. Our Stage I Environmental Screening preliminarily concluded that the impacts to Jewett Brook and the adjacent pools are limited and do not pose a risk to ecological receptors. However, we have proposed a round of surface water samples from Jewett Brook during seasonal low flow conditions, likely in June or July 2007, to confirm these conclusions. This RAP includes a detailed evaluation of four remedial action alternatives (RAAs) for the Site:

RAA1 - Excavate all tar-impacted soil;

RAA2 - Excavate tar-impacted soil to a depth of 15 feet, and tar-saturated soil below 15 feet deep;

RAA3 - Excavate tar-impacted soil to 15 feet deep and contain tar-impacted soil below 15 feet deep; and

RAA4 - Excavate tar-impacted soil to 3 feet deep, and contain tar-impacted soil below 15 feet deep.

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, RAA4, consists of excavation of the tar-impacted soil at the Site to a depth of three feet below ground, construction of a soil-clay slurry wall to a depth of 50 feet around the remaining tar-impacted soil, construction of an impermeable cap 3 feet below ground, and construction of a landscaped vegetated cover. This alternative would contain 99.5 percent of the mass (tar material in soil) within the slurry wall and remove the remaining 0.5 percent of the contaminant mass. Implementation of the selected alternative would result in a restriction on the residential use of the 83 and 77 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. Following NHDES approval of the RAP, KeySpan will submit Design Plans and Construction Specifications by the end of August 2007 detailing the proposed remedy. These documents will detail the engineering design for the proposed remedy and will be used by the selected contractor to construct the remedy. A public meeting will be held in September


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2007 to update the community on the design. Once approved by NHDES, construction of the remedy is planned to start in fall 2007 and is expected to take about one year.


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1. Introduction 1.1 Site Information and Description The Site is listed as “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 (Fig. 1). Subsurface investigations to date have been conducted on the properties at 63, 69, 77, 78, 83, and 87 Liberty Hill Road and drinking water samples were collected at 28, 47, 48, 58, 63, 64, 69, 70, 77/83, 78, 87, and 97 Liberty Hill Road. 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 the adjacent golf course property where dissolved phase compounds were detected in groundwater samples. Tar-impacted soil was not found at 63 Liberty Hill Road; however, the western portion of this property will be included in the Groundwater Management Zone (GMZ). 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. Energy North Natural Gas d/b/a KeySpan Energy Delivery of New England (KeySpan) has purchased the properties at 69, 77, 83, and 87 Liberty Hill Road (Table 1). 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. 1.1.1 Contact Person The contact person for this Site is:

Ms. Patricia Haederle New England MGP Program Manager, Environmental Asset Management KeySpan Corporation 52 Second Avenue Waltham, MA 02451 Phone: 781.466.5414; Fax: 781.890.4587



1.2 Purpose and Objectives The purpose of the Remedial Action Plan (RAP) is to provide an evaluation of remedial alternatives and to recommend action to remove, treat, or contain the contamination in environmental media at the Site. The contamination was caused by a reported discharge of Manufactured Gas Plant (MGP) byproducts on a Liberty Hill Road property during the dismantling of the Laconia MGP in the early 1950s. KeySpan has taken responsibility for the Site because it is the successor to Gas Service, Inc., the owner of the former MGP. In addition to the evaluation of remedial alternatives, this report presents the following:

An updated Site conceptual model based on additional data collected;

A Stage I Ecological Screening; and

A qualitative evaluation of potential risks to human health.

1.3 Previous Investigations GEI Consultants, Inc. conducted a preliminary evaluation of the 69, 77, 83, and 87 Liberty Hill properties in July and August 2005. The results of that preliminary investigation were presented in a data report to NHDES, dated October 12, 2005. GEI conducted more comprehensive investigations of the four properties between August 2005 and May 2006 and presented the results in a Site Investigation Report (SIR) to NHDES, dated June 28, 2006. The findings of the SIR indicated that additional Site characterization was necessary to confirm the lateral extent of contaminants in soil and groundwater, and additional borings and monitoring wells were proposed. GEI prepared a Scope of Work for the additional field investigation and submitted it to NHDES on September 19, 2006. GEI conducted additional field investigations at the 63, 69, 77, 78, 83, and 87 Liberty Hill properties between August and November 2006. The results of the additional investigation were presented in an interim data report to NHDES, dated December 18, 2006, and a summary is included in Section 3 of this report.



2. Site Information 2.1 Site History In 1952, an explosion at the MGP in Laconia left it inoperable and it was decommissioned. At the same time, the natural gas pipeline arrived in New Hampshire, and replaced manufactured gas throughout the State. During the decommissioning of the MGP, the demolition contractor pumped liquids from a former gas holder into tanker trucks, and received permission from the owner of a gravel pit on Liberty Hill Road in Gilford to dispose of those liquids in the gravel pit. More detail on the Site history was provided in the June 2006 SIR. 2.2 Surrounding Land Use The Site and surrounding properties are primarily residential. Most properties have a house located within 100 feet of Liberty Hill Road with wooded land to the west towards Jewett Brook. Other structures located on the properties include garages and sheds. With the exception of 48 and 70 Liberty Hill Road, which are serviced by shallow dug wells, properties adjacent to the Site on Liberty Hill Road are serviced by private drinking water wells screened in bedrock. The Site is located approximately 0.4 miles west of the Saltmarsh Pond State Forest, which is classified as Conservation Land. It is also within 0.3 miles southwest and hydraulically downgradient of Saltmarsh Pond, which is classified as a Local Resource Protection Priority (LRPP) Site [NHGIS].



3. Site Investigation Addendum Additional site investigation activities were conducted from August through November 2006 in accordance with the proposed scope of work that was included in our June 2006 SIR. The field program consisted of:

Advancing 17 soil borings using Rotosonic techniques.

Installing 12 groundwater monitoring wells.

Installing 4 subslab soil gas sampling points (2 each at 77 and 87 Liberty Hill Road).

Collecting and chemically testing soil, groundwater, drinking water, surface water, soil gas, ambient air, and indoor air samples.

Boring and monitoring well locations are shown in Figure 2. Surface water sampling locations are shown in Figure 3. The methods used in our investigation are described in the sections below. The results of the sampling are discussed in Section 5. GEI engaged Richard D. Bartlett and Associates, LLC of Concord, New Hampshire (Bartlett) to conduct a topographic and physical features survey of the 47 and 63 Liberty Hill Road properties and a portion of the 78 Liberty Hill Road property. Bartlett also surveyed new soil boring and monitoring well locations and elevations. 3.1 Boring and Monitoring Well Installation GEI observed Boart Longyear, of North Reading, Massachusetts (Boart) advance 17 borings using Rotosonic drilling techniques on the 63, 77, 78, 83, and 87 Liberty Hill Road properties in September and October 2006 (Fig. 2). Overburden material encountered during GEI’s boring program generally included 5 feet of fill and sand overlying a dense till. The fill material generally consisted of sand and was very similar in composition to the native till. The till consisted of dense silty sand with occasional gravel. The boring logs are presented in Appendix A.



The following table summarizes the boring and monitoring well locations and their purpose: Borings advanced in Fall 2006 Boring ID (Street Number)

Evaluate Total Boring Depth

(feet bgs) MW112A and MW116A (78)

Shallow soil and groundwater conditions crossgradient of the area with visible tar in subsurface soil at MW108B.

35

MW117A/B (87) Shallow and intermediate soil and groundwater conditions crossgradient of the area with dissolved phase groundwater impacts at MW109A/B/C.

13.5/40

MW122A/B (63) Downgradient extent of dissolved-phase impacts in groundwater at MW111C.

15/50

MW123A/B/C (83)

Lateral extent of dissolved-phase impacts in groundwater at MW111C.

20/80/125

B201, B202, B203 (87)

Lateral extent of visible tar impacts in subsurface soil at MW113A/B/C.

50

B204 (83) Deeper soil conditions in area with visible tar in shallow soil [GP1(MW), GP2, and GP3].

50

MW205 (83) Lateral extent of visible tar in subsurface soil and dissolved-phase impacts observed in MW102B.

50

B206 (77) Lateral extent of visible tar in subsurface soil at MW104B. 50 MW207 and MW208 (77)

Deeper soil and groundwater conditions downgradient/ crossgradient of GP24(MW) and GP37(MW).

40/40

The borings were advanced using Rotosonic drilling techniques to depths of up to 125 feet. Samples were collected continuously in the first boring in each location using a 4.25-inch sample barrel with a length of either 5 or 10 feet. A 5.5-inch diameter casing was advanced around the sample barrel, prior to retrieving it from the bore hole. In borings B205 and B207, samples were collected in the same manner; however, a 7⅝-inch diameter casing was advanced over the sample barrel because larger diameter wells were installed in these locations. Soil samples were screened using jar headspace screening for total volatile organic compounds (VOCs) using a photoionization detector (PID). GEI logged soil types according to the Soil Conservation Service Unified Soil Classification System (USCS). During September and October 2006, GEI coordinated the installation of a total of 12 groundwater monitoring wells on the 63, 77, 78, 83, and 87 Liberty Hill Road properties. Eight shallow monitoring wells were screened in the sand and shallow till (MW112A, MW116A, MW117A, MW122A, MW123A, MW205, MW207, and MW208), two intermediate monitoring wells were screened in intermediate till (MW122B and MW123C),



one monitoring well was screened in the deep till (MW123B), and one monitoring well was screened in bedrock (MW117B). With the exception of monitoring wells MW205 and MW207, well construction materials consisted of 2-inch-diameter polyvinyl chloride (PVC) screen and riser, with up to 10-foot-long PVC screen sections, and 0.010-inch slots. Wells MW205 and MW207 were constructed with 4-inch PVC screen and riser, with 10-foot-long PVC screen sections, and 0.010-inch slots. Wells were capped using 4-inch-diameter guard pipes except for MW112A, MW116A, MW205, MW207, and MW208, which were finished with flush-mounted road boxes. Well screen depths for the monitoring wells are summarized in Table 2. Well construction logs are included in Appendix A. Each well was developed at least two weeks prior to groundwater sampling. 3.2 Groundwater Level Gauging Groundwater was encountered in each of the borings advanced by GEI in September and October 2006. Depth to groundwater was consistent with previous investigations and varied depending on location of the borings in relation to the top of slope and Jewett Brook. GEI measured the depth to groundwater in monitoring wells installed at the Site in November 2006 (Table 3). Based on the November 2006 measurements, the vertical head differences within monitoring well clusters were calculated (Table 4). These hydrogeologic data are discussed in Section 4.4.2. Vertical head differences were similar to previous gauging events. The direction of groundwater flow is to the west and southwest (Figs. 4 and 5). The nearest surface water body is Jewett Brook, which runs in a northwesterly direction through the southern portions of the subject properties. The ground surface of the subject properties is relatively flat near Liberty Hill Road. The southern portions of each of the properties along the south side of Liberty Hill Road slope steeply toward Jewett Brook, with an elevation change of 30 to 60 feet. 3.3 Soil Sampling The soil sampling program consisted of collecting soil samples for chemical analysis for VOCs by U.S. Environmental Protection Agency (EPA) Method 8260 and semivolatile organic compounds (SVOCs) by EPA Method 8270. Chemical testing for other analytes (Resource Conservation and Recovery Act [RCRA] 8 metals, polychlorinated biphenyls [PCBs], and total cyanide) were not performed for these samples because testing completed during the SI confirmed that these analytes were not compounds of concern at the Site. Soil samples were collected from a depth of maximum visual impacts, depth of maximum



anticipated impact based on surrounding borings, and/or depths likely to confirm vertical extent of contamination. Soil samples were submitted to Accutest Laboratories of Marlborough, Massachusetts (Accutest) for chemical analyses. Samples were managed under chain-of-custody protocol and preserved on ice. Samples collected for VOC analyses were preserved in methanol in accordance with EPA Method 5035. Subsurface soil chemical testing results for samples collected to date are summarized by property in Table 5, along with the NHDES S-1 Soil Standards and Upper Concentration Limits (UCLs) for comparison. Figure 6 shows the lateral extent of impacted soil. Laboratory data reports for soil samples are included in Appendix B. Surficial soil chemical testing results for samples collected as part of the SI are summarized by property in Table 6. Surficial soil results were described in the SIR and are not re-presented in this report. 3.4 Groundwater Sampling GEI collected groundwater samples from all onsite wells in November 2006 for analysis of VOCs by EPA Method 8260, and SVOCs by EPA Method 8270. Select samples were also submitted for sulfate, total iron, and dissolved iron for use in natural attenuation modeling. Groundwater chemical testing results for the monitoring wells are summarized in Table 7 and laboratory data reports for monitoring well groundwater samples are included in Appendix C. Purging and sampling was performed with low-flow (minimal drawdown) techniques using a peristaltic pump or submersible pump with dedicated tubing. The tubing intake was set at the approximate center of the saturated portion of the well screen. Field parameters (dissolved oxygen [DO], oxidation reduction potential [ORP], conductance, temperature, turbidity, and pH) were monitored continuously during purging using a flow-through cell. Measurements were performed with YSI Instruments, Inc. (YSI), Model 6000 multi-parameter meter calibrated for all parameters. Wells were purged until parameters stabilized except at wells MW120A and GP11(MW), which both went dry during purging and were sampled from the middle of the screened interval the following day. Monitoring well MW106 was purged dry using a bailer and also sampled from the middle of the screened interval using a bailer the following day. Each of the three wells had recovered back to their static condition prior to sampling. Site wells were gauged for the presence of light or dense non-aqueous phase liquid (LNAPL or DNAPL). DNAPL was measured at a thickness of 0.05 feet in MW113C (87 Liberty Hill Road) on November 16, 2006; no groundwater sample was collected from this monitoring



well. Monitoring well MW113A was found to have an insufficient volume of water to collect a sample. Groundwater samples were submitted to Accutest for chemical analysis for VOCs and SVOCs and select samples were also submitted for sulfate, total iron, and dissolved iron. Samples were managed under chain-of-custody protocol and preserved on ice. Samples collected for VOC analysis were preserved with hydrochloric acid. Samples collected for dissolved iron analysis were filtered in the field with a 45-micron filter and preserved with nitric acid. 3.5 Drinking Water Sampling The Site and immediate surrounding properties are serviced by private on-site drinking water wells screened in bedrock. Two properties (48 and 70) along Liberty Hill Road are serviced by shallow, dug drinking water wells. At the request of the NHDES and property owners, GEI collected drinking water samples from the 28, 58, 64, 70, 78, and 97 Liberty Hill Road properties in August 2006. In October 2006, GEI collected a sample from the private water supply well at 48 Liberty Hill Road and in November 2006, GEI collected samples from the private water supply wells located at 77/83 and 87 Liberty Hill Road. The samples were submitted to Accutest for analysis of VOCs by EPA Method 524.2. Chemical testing results for the drinking water wells are summarized in Table 8 and laboratory data reports for the drinking water samples are included in Appendix D. Chemical testing results for public drinking water wells serving a nearby condominium complex on Country Club Lane are summarized in Table 9 and were previously discussed in the SIR. Contaminants of Potential Concern (COPCs) associated with the Site were not detected in samples from the drinking water wells. Methyl-tert-butyl ether (MTBE) was detected in the sample from 58 Liberty Hill Road at a concentration below the NHDES GW-1 standards in August 2006. Acetone was detected in the sample from the shared well located at 77 Liberty Hill Road at a concentration below the NHDES GW-1 standards during the most recent November 2006 event. Neither MTBE nor acetone are attributable to the MGP byproducts and thus are not attributable to the Site. VOCs were not detected above laboratory detection limits in any of the other drinking water samples. According to NHDES Public Water Supply System personnel in correspondence dated February 1, 2007, no VOCs were detected for the Gilford Village West Condominiums sample in October 2006. A copy of the email correspondence is included in Appendix D.



3.6 Soil Gas, Indoor Air and Ambient Air Sampling 3.6.1 Soil Gas

77 Liberty Hill Road: GEI collected four soil gas samples adjacent to the foundation of the former 77 Liberty Hill Road residence on August 30, 2006, one from each side (north, south, east, and west). The soil gas probes adjacent to the former residence were screened at a depth of 4 to 4.5 feet below ground surface (bgs). Two sub-slab soil gas samples were also collected from 77 Liberty Hill Road: beneath the basement foundation on the north and south sides of the slab. The sub-slab probes beneath the basement were installed at a depth of 1.2 feet beneath the bottom of the slab. The soil gas and sub-slab results by property are compared on Tables 10 and 11 to NHDES soil gas standards and background data collected by the New York State Department of Health (NYSDOH). The laboratory results are in Appendix E.

Prior to sampling, one to five sample string volumes were purged from the sample points and tubing using a PID. The soil gas samples were collected into 6-liter Summa® canister over a period of one hour to minimize risk of short-circuiting the seal in the borehole. This collection period corresponds to a flow rate of 100 milliliters per minute (ml/min). The soil gas samples were submitted to Alpha Analytical, Inc. in Westborough, Massachusetts (Alpha) and analyzed for VOCs via EPA Method TO-15.

87 Liberty Hill Road: GEI collected three soil gas samples adjacent to the foundation of the 87 Liberty Hill Road residence on November 6, 2006. The fourth point was found to contain water and could not be sampled. The soil gas probes adjacent to the residence were screened at a depth of 4 to 4.5 feet bgs. Two sub-slab soil gas samples were also collected from 87 Liberty Hill Road beneath the basement slab. The sub-slab probes beneath the basement were installed at a depth of approximately one foot beneath the bottom of the slab.

3.6.2 Indoor Air

77 Liberty Hill Road: Four indoor air samples were collected at the former 77 Liberty Hill Road residence on August 29, 2006. The indoor air samples included two from the basement and two from the first floor. The indoor air samples were collected in 6-liter Summa® canisters over 24 hours and submitted to Alpha for TO-15 analysis. Prior to the sampling round, a GEI representative identified and removed potential sources of VOCs from the former residence to minimize false positive readings caused by storage of these products. The chemical testing results for indoor



air sampling are summarized in Table 12, and the laboratory data reports for indoor air are in Appendix E.

87 Liberty Hill Road: Four indoor air samples were collected at the 87 Liberty Hill

Road property on November 6, 2006. The indoor air samples included two from the basement and two from the first floor (bedroom and living room). The indoor air samples were collected in the same manner as at 77 Liberty Hill Road and submitted to Alpha for TO-15 analysis.

3.6.3 Ambient Air Sampling

77 Liberty Hill Road: GEI collected four ambient air samples (outside the former residence) at the 77 Liberty Hill Road property on August 29, 2006, using Summa® canisters and submitted them to Alpha for TO-15 analysis. The ambient air samples included one at the front door, one at the back door, one in the front yard and one in the backyard. The upwind ambient air sample located in the front yard was collected as a 24-hour composite sample and the remaining outdoor air samples were 8-hour composite samples. The chemical testing results for ambient air sampling are summarized in Table 13, and the laboratory data reports for ambient air are in Appendix E.

87 Liberty Hill Road: GEI collected four ambient air samples (outside the residence) at the 87 Liberty Hill Road property on November 6, 2006, using Summa® canisters. The ambient air samples included one at the front steps, one at the back porch steps, one inside the barn, and one adjacent to the fence west of the barn. The outdoor air samples were collected as 8-hour composite samples and submitted to Alpha for TO-15 analysis.

3.7 Surface Water Sampling On November 29, 2006, GEI personnel collected 11 surface water samples (SW101 through SW111) from Jewett Brook. Samples were collected from the same locations as in April 2006 and were collected from downstream to upstream. The locations are shown in Figure 3. The samples were submitted to Accutest for analysis for VOCs by EPA Method 8260 and SVOCs by EPA Method 8270. The surface water chemical testing results are summarized in Table 14 and the laboratory data report for surface water is in Appendix F.



4. Hydrogeologic Characteristics This section includes much of the same information as the SIR. It was repeated in this report for completeness. Results from additional investigation activities were consistent with the Conceptual Site Model presented in the SIR. 4.1 Topography and Surface Drainage Based on the U.S. Geologic Survey Topographic Map for the Laconia Quadrangle, the Liberty Hill Road properties are at an elevation of approximately 800 feet above the National Geodetic Vertical Datum (NGVD) of 1929 [USGS, 1970]. The nearest surface water body is Jewett Brook, which runs in a northwesterly direction through the southern portions of the subject properties. The ground surface of the properties slopes gently to the northwest near Liberty Hill Road. The southern portions of each of the properties slope steeply toward Jewett Brook, with an elevation change of approximately 30 to 60 feet. Surface runoff from the properties drains toward Jewett Brook. Jewett Brook discharges into Lake Winnipesaukee in Laconia (Fig. 1). 4.2 Regional Geology Surficial geologic deposits in the area consist of glacial deposits (primarily till). Bedrock in the area of the properties consists of sillamanite-bearing gneiss with some migmatic and granitic veining and fine-grained granitic dikes [Van Diver, 1987]. 4.3 Site Geology Geologic cross sections are presented in Figures 7 and 8. Cross section transect locations are shown in Figure 2. Overburden deposits at the properties typically consist of approximately 5 to 8 feet of sand, underlain by approximately 50 to 120 feet of till overlying bedrock. Sand deposits at the Site generally varied from narrowly to widely graded sands with minor amounts of silt and gravel. However, several borings appeared to contain minor amounts of gravel. The fill material resembled the native sand. Till at the properties can be divided into a dense upper layer consisting of sandy silt, or silty sand, with approximately 20-percent gravel, and a looser lower layer typically consisting of narrowly graded sand with gravel. Bedrock was encountered in four of the borings across the Site: B109, B110, B117, and B119. Bedrock slopes downward to the north and west from a high point in the southern



portion of the Site. Bedrock encountered in borings B109B, B110B, and B119B consisted of micaceous schist. Bedrock encountered at approximately 25 feet in boring B117 consisted of gneiss containing biotite, amphibole, sillimanite, muscovite, quartz, and feldspar. 4.4 Site Hydrogeology 4.4.1 Groundwater Elevation Monitoring Groundwater at the Site is divided into three separate zones: shallow groundwater in wells screened in the upper 15 feet, intermediate groundwater in wells screened in the till at a depth of about 25 to 90 feet, and deep groundwater in wells screened in till at depths greater than 90 feet and in shallow bedrock. The shallow groundwater (wells screened in upper 15 feet) appears to be perched on the dense upper till. Depth to groundwater averaged approximately 3 to 8 feet bgs in the shallow wells. Two shallow wells in the rear of the 87 Liberty Hill Road property (MW113A and MW120A) have a greater depth to groundwater of more than 11 feet. The piezometric surface in wells screened at depths of 25 to 90 feet in the till is generally at a depth of 15 to 30 feet. Groundwater elevations measured in November 2006 are presented in Table 3, along with prior measurements. Depth to groundwater in the intermediate and deep monitoring wells in the paddock were 2 to 4 feet in the southern portion of the paddock (119 cluster), 11 to 25 feet in the northern portion of the paddock (109 cluster), and 6 to 19 feet above ground surface (artesian) adjacent to Jewett Brook north of the paddock (MW110B/C, MW117B, MW122B, and MW123B/C). Groundwater elevation contours for shallow and intermediate groundwater measured on November 13, 2006, are shown in Figures 4 and 5, respectively. Groundwater elevations were similar in previous rounds. As shown in Figure 4, shallow groundwater flows to the northwest in the vicinity of Liberty Hill Road and to the west and southwest on the southern portion of the Site, toward Jewett Brook. Intermediate groundwater follows a similar pattern (Fig. 5). 4.4.2 Gradients and Permeability Horizontal gradients are quite steep as a result of the topography of the Site, and range from 0.048 to 0.18 feet per foot based on data collected in November 2006. The gradients calculated based on the April 2006 data were similar. Vertical gradients are downward at most locations at the Site, except near Jewett Brook where upward vertical gradients were observed as a result of artesian conditions in wells installed in deeper till and bedrock. Estimated hydraulic conductivities ranged from 0.05 to 0.3 feet per day in the till, and 0.02 to 0.2 feet per day in bedrock.



The average horizontal hydraulic gradient in shallow groundwater across the upper portion of the Site (in vicinity of Liberty Hill Road) was approximately 0.048 feet per foot, based on the November 2006 groundwater elevation measurements between GP1(MW) and GP37(MW). The hydraulic gradient in shallow groundwater from the upper portion of the Site (GP1[MW]) to monitoring well MW110A near Jewett Brook was approximately 0.18 feet per foot. The horizontal hydraulic gradient in the intermediate groundwater in the upper portion of the Site (from MW101B to MW111C) was approximately 0.065 feet per foot. The hydraulic gradient in intermediate groundwater from the upper portion of the Site (MW101B) to monitoring well MW109C in the paddock is much steeper, 0.12 feet per foot. The hydraulic gradient in intermediate groundwater from the upper portion of the Site (MW101B) to MW110C near Jewett Brook is similar to that of the upper portion of the Site, 0.084 feet per foot, because of the artesian conditions observed near Jewett Brook. Downward hydraulic head differences of at least 1.5 feet were observed in all well couplets and triplets at the Site, except for the monitoring well couplets and triplets adjacent to Jewett Brook (Table 4). Couplets with a shallow well (screened to depths of 25 feet) and an intermediate well (screened to depths of 90 feet) in the vicinity of Liberty Hill Road had downward head differences of 6.77 feet at MW101A/B to 25.46 feet at MW113B/C, as a result of perched water in some of the shallow wells. The couplets/triplets (MW110A/B/C, MW117A/B, MW122A/B, and MW123A/B/C) adjacent to Jewett Brook had a range of upward hydraulic head differences of 12.55 feet at the MW110 triplet to 21.92 feet at the MW122 triplet as a result of the artesian conditions at these locations, indicating groundwater discharges to the brook. Groundwater discharge to the brook was most apparent in the small side channel just downstream of the MW110A/B/C cluster, where there is no stream flow under low or normal stream flow conditions, but standing water was present in the pools during all site visits.



5. Conceptual Site Model The additional Site Investigation activities conducted in August through November 2006 were conducted to evaluate (1) extent of COPCs in soil and groundwater across Liberty Hill Road; (2) extent of groundwater plume downgradient of MW111 cluster; (3) potential impacts to indoor air and ambient air at 77 and 87 Liberty Hill Road; and (4) potential impacts to drinking water along Liberty Hill Road. The additional investigation activities have not resulted in a change of the Conceptual Site Model, but these data helped refine our understanding of the extent of COPCs in soil and groundwater at the Site. Based on the results of the investigation:

COPCs in soil and groundwater are not present across Liberty Hill Road to the east.

Tar-impacted soil is limited to the four properties owned by KeySpan (69, 77, 83, and 87 Liberty Hill Road).

The groundwater plume is limited to the four properties owned by KeySpan and the adjacent 63 Liberty Hill Road property.

No impacts from Site COPCs were found in indoor air or ambient air at 77 and 87 Liberty Hill Road.

No impacts from Site COPCs were found in drinking water collected from properties located along Liberty Hill Road.

5.1 Nature and Extent of Constituents of Potential Concern COPCs at the Site consist of SVOCs (primarily polycyclic aromatic hydrocarbons [PAHs]) and VOCs (primarily benzene, toluene, ethylbenzene, xylene [BTEX]). These analytes are typical constituents of coal tar. Coal tar has a wide range of physical properties, although it has generally high viscosity and high interfacial tension. Coal tar is relatively insoluble in water, is not very volatile, tends to sorb to organic carbon and solids, and does not biodegrade rapidly. 5.1.1 Nature and Extent of COPCs in Soil Based on the results of subsurface investigations, the area impacted by coal tar is primarily located on the central portion of the 77 and 83 Liberty Hill Road properties, but also extends to the western portion of the 87 Liberty Hill Road property (near the barn). The impacts



include tar stained soil, tar-coated soil, occasional blebs of tar, and naphthalene odor. In addition, a separate, smaller area with coal tar impacts is located near the 69 and 77 Liberty Hill Road property boundary. COPCs detected in subsurface soil consist of primarily of BTEX and PAHs. Visual evidence of tar was observed in a number of borings, and the extent of soil contamination that exceeds S1 standards coincides with the area with visible tar. Concentrations of COPCs were generally highest in the area within about 100 feet of the rear of the former residences at 77 and 83 Liberty Hill Road. The area where tar was observed in the upper 10 feet (area where tar may have been originally deposited) is approximately 100 by 320 feet. At a greater depth (20 to 40 feet) tar impacts extend to a larger area of about 200 by 400 feet. Evidence of tar (such as tar staining and odors) and locations where the concentration of one or more constituents exceeded the S1 standard are shown in plan view in Figure 6. This plan also indicates the estimated lateral extent of soil with COPC concentrations exceeding S1 standards. Lateral extent of soil contamination at the Site has been established in all directions by borings. Vertically, visible tar impacts were observed to depths up to 50 feet as shown on cross sections (Figs. 7 and 8). At B113B and B204, the impacts from 30 to 43 feet and 17 to 20 feet, respectively, included tar-saturated sand and gravel. At the other borings, impacts were limited to tar-saturation in coarser grained sand lenses within the till, and the finer grained portions of the till had no apparent visual impacts. Naphthalene odors and high headspace readings were observed at depths up to 60 feet in B102B, B104B, B106, B108, B113B, B201, B202, B203, B204, B206, MW205, MW207, and MW208 and at depths from 45 to 90 feet in B111B. As with the lateral extent, vertical extent of COPCs in soil was defined by visual presence of tar. S1 exceedances in samples collected from depths greater than 40 feet were limited to benzene and are likely the result of benzene in groundwater within the soil matrix. Results for VOCs and SVOCs in samples collected during the addendum investigation are discussed below by property.

63 Liberty Hill Road: GEI collected five samples for chemical analysis from the five borings advanced on the 63 Liberty Hill Road property. Naphthalene odors were observed in one boring (B122B), located approximately 190 feet and downgradient of MW111C on the 69 Liberty Hill Road property. GEI collected two samples from B122B and two samples from B123B, including one from the upper 10 feet in each boring and a deeper sample. An additional sample from B123B was analyzed based on field observations of elevated headspace readings. Benzene and toluene were detected above the laboratory method detection limits in the sample from 5 to 7.5 feet in B122B; only benzene exceeded the S-1 standards. VOCs were not detected above



the laboratory method detection limits in sample B122B-S10B or the three samples collected from boring B123B. SVOCs were not detected above the laboratory method detection limits in any of the samples collected. No visible tar impacts were observed on the 63 Liberty Hill Road property.

77 Liberty Hill Road: GEI collected three samples for chemical analysis from the three borings advanced on the 77 Liberty Hill Road property. Each of the soil samples (B206, B207, and B208) were collected from visually unimpacted soil at depth to establish a lower boundary on the soil contamination found on the 77 and 83 Liberty Hill Road properties. VOCs including benzene, naphthalene, and toluene were detected in each of these samples. The concentration of benzene in the samples collected from borings B207 and B208 exceeded the S-1 standard. SVOCs were not detected above the laboratory method detection limits in any of the samples collected.

Visible tar impacts in the three boring locations included blebs, globs, and lenses of stained soil at 8 to 10 feet bgs in B206, at various intervals between 12 and 50 feet in B207, and at various intervals between 16 and 40 feet in B208. Soil lenses with tar saturation were also observed in B208 at 30 to 35 feet bgs.

78 Liberty Hill Road: GEI collected four samples for chemical analysis from the two borings (B112 and B116) advanced on the 78 Liberty Hill Road property to evaluate whether impacts observed at B108 at the 83 Liberty Hill Road property extended onto the 78 Liberty Hill Road property. VOCs and SVOCs were not detected above the laboratory method detection limits in any of the samples collected. No visible tar impacts were observed in the two borings.

83 Liberty Hill Road: GEI collected two samples for chemical analysis from the two borings advanced on the 83 Liberty Hill Road property. One soil sample (B205) was analyzed to establish an outer boundary for the contamination found on the central portion of the property and one sample (B204) was collected from a tar-impacted location. Several VOCs including BTEX, methylene chloride, naphthalene, styrene, and trimethyl benzene isomers were detected in soil samples B204 and B205. Of these compounds, methylene chloride and naphthalene exceeded the S-1 standards in the soil sample collected from B204 and benzene exceeded the S-1 standards in the soil sample collected from B205. Methylene chloride is not associated with coal tar, it is a common laboratory contaminant and it is not considered a COPC. SVOCs were not detected above the laboratory method detection limits in soil samples B204 or B205.

GEI observed tar staining and a naphthalene-like odor in both borings completed at the 83 Liberty Hill Road property. In addition, a tar-saturated layer was observed between 18 and 20 feet below grade in boring B204.



87 Liberty Hill Road: GEI collected four soil samples for chemical analysis from the five borings advanced on this property to define extent of tar impacts observed at B113B. VOCs were detected in three of the four samples (B201, B202, and B203) above the laboratory method detection limits, but below the Method 1 S-1 standards. SVOCs including naphthalene, acenaphthylene, anthracene, benzo(a)anthracene, chrysene, fluoranthene, fluorene, phenanthrene, and pyrene were detected in the sample collected from B203, but concentrations were below the S-1 standards. SVOCs were not detected above the laboratory method detection limits in soil samples B117, B201, or B202.

GEI observed black staining and a naphthalene-like odor in one boring on the 87 Liberty Hill Road property (B203). A naphthalene-like odor was also observed in borings B201 and B202.

5.1.2 Nature and Extent of COPCs in Groundwater Monitoring Wells COPCs detected in groundwater consist primarily of BTEX and PAHs. In addition, 0.05 feet of DNAPL was measured in monitoring well MW113C, near the barn at 87 Liberty Hill Road. Concentrations of COPCs in groundwater are generally greatest in the area with visible tar impacts in soil in the backyards of the 77 and 83 Liberty Hill Road properties, and extend to areas where soil impacts were limited to odors and elevated headspace readings below and downgradient of areas with visible tar (Fig. 9). Lateral extent of groundwater impacts has been defined along Liberty Hill Road to the north and east of the 77 and 83 Liberty Hill Road properties (MW112A and MW116A), to the north and northwest at 63 Liberty Hill Road (MW122 and MW123 clusters), and to the south and southwest by MW101A/B, MW120A/B, MW119A/B/C, and MW117A/B. The downgradient extent of COPCs in groundwater beyond Jewett Brook has not been established. A monitoring well cluster will be installed on the west side of Jewett Brook in spring 2007. The vertical extent of COPCs in groundwater appears to be limited to groundwater in till based on conditions encountered in deep wells MW110B, MW111B, MW117B, MW122B, and MW123B. A strong upward gradient in the vicinity of Jewett Brook indicates groundwater discharge to the brook, which is also indicated by detections of BTEX and naphthalene in surface water at one location in pools adjacent to Jewett Brook. Total VOC concentrations in groundwater are shown on the cross-sections (Figs. 7 and 8).



GW1 standards were exceeded at 6 shallow wells, 10 intermediate wells, and 1 deep well (Fig. 9). GW1 exceedances were limited to five compounds: benzene, naphthalene, styrene, toluene, and 1,2,4 trimethylbenzene. The GW1 standard for naphthalene was exceeded at 15 of the 17 locations, and the GW1 standard for benzene was exceeded at 14 of the 17 locations. The GW1 standards for styrene, toluene, and 1,2,4 trimethylbenzene were exceeded at 7 locations (GP1(MW), MW106, MW109C, MW111C, MW205, MW207, and MW208). Impacts in bedrock groundwater are unlikely because the vertical extent of COPCs in groundwater has been established upgradient (MW101B, MW119B, and MW120B), crossgradient (MW108B and MW109B), and downgradient (MW111B and MW110B) of the area with visible tar impacts. Groundwater samples from three wells (MW102B, MW104B, and MW113B) screened below the area of visible tar impacts in soil, contained benzene and naphthalene at concentrations greater than GW1 standards. At these locations COPCs in groundwater extend somewhat deeper than those wells (85 feet). However, impacts are unlikely to extend much deeper into the till because no COPCs were detected in groundwater at MW111B in May 2006, and only benzene at 17.7 ppb was detected in this location in November 2006. MW111B is screened from 120 to 130 feet directly downgradient of MW102B and MW104B. Drinking Water Wells VOCs, SVOCs, and total cyanide were not detected above the laboratory detection limit in any of the samples collected from private drinking water wells at and near the Site in 2004 and 2005 by GEI and NHDES (Table 8). MTBE and acetone were detected during the 2006 sampling events in the drinking water samples collected from 58 Liberty Hill Road and 77/83 Liberty Hill Road, respectively. MTBE and acetone are not associated with coal tar. GEI reviewed available reports for public drinking water wells located at Gilford Village West Condominiums at the intersection of Liberty Hill Road and Country Club Lane (Table 9). The complex is served by two wells that are each sampled annually for VOCs. No VOCs were detected in the samples collected between 2000 and 2006. GEI also reviewed available reports for the well at the Pheasant Ridge Country Club. However, this well was only sampled for bacteria and nitrate/nitrite. 5.1.3 Nature and Extent of COPCs in Soil Gas and Air Soil Gas The NHDES vapor intrusion guidance provides screening values for COPCs in soil gas below which migration to indoor air at significant concentrations is not likely and further



evaluation of the vapor intrusion pathway is not necessary. Soil gas samples contained a number of compounds associated with coal tar impacts (BTEX compounds, naphthalene, and trimethylbenzene). However, these concentrations were several orders of magnitude below the SG screening values, indicating that the vapor intrusion pathway is not complete and further evaluation of the soil gas pathway is not necessary (Tables 10 and 11). Indoor Air

83 Liberty Hill Road: Compounds attributable to coal tar were not detected in indoor air samples collected inside the former residence at 83 Liberty Hill Road in August 2005 and February 2006. These results were further described in the SIR.

77 Liberty Hill Road: Compounds attributable to coal tar were not detected in indoor air samples collected inside the former residence at 77 Liberty Hill Road in August 2006 and most compounds detected were below the range of typical indoor air background concentrations typically present within indoor air. The concentration of 1,2,4-trimethylbenzene was detected above the New Hampshire IAIR screening value in the basement south sample. However, the concentration of this compound was below the NYSDOH indoor air concentrations range of typical indoor air background concentrations for homes heated with fuel oil. Compounds detected above the New Hampshire IAIR and the NYSDOH indoor air concentrations at 77 Liberty Hill Road included chloroform in the basement north sample (likely associated with indoor sources of this chemical) and methylene chloride (a common laboratory contaminant).

87 Liberty Hill Road: Compounds attributable to coal tar were generally not detected in indoor air samples collected inside the residence at 87 Liberty Hill Road in November 2006 and most compounds detected were below the range of typical indoor air background concentrations typically present within indoor air. The concentrations of 1,3-dichlorobenzene, tetrahydrofuran, 1,1,2-trichlorotrifluoroethane (Freon 113), and xylenes in the sample collected at the basement divider and 1,2,4-trichlorobenzene in the living room sample were detected above NYSDOH indoor air screening values. Compounds detected above the New Hampshire IAIR and the ATSDR minimum risk values include methylene chloride in each of the samples and naphthalene in the living room sample.

The majority of the constituents detected in the basement are likely associated with indoor sources or can be attributed to the storage of fuel oil. Methylene chloride is a common laboratory contaminant. The detection of naphthalene in the living room sample may be associated with an indoor source because concentrations in basement samples were lower and it was not detected above standards in the perimeter and sub slab soil gas samples.



Ambient Air Sampling

77 Liberty Hill Road: A number of compounds were detected in the outdoor air samples at 77 Liberty Hill Road; however, most compounds are not associated with the coal tar release at the Site and were below the NYSDOH background concentrations for outdoor air. 1,1,2-trichloroethane was detected above the New Hampshire IAIR values in one of the four outdoor air samples collected at the 77 Liberty Hill Road property. The presence of 1,1,2-trichloroethane in an upwind sample at concentrations above the New Hampshire IAIR value indicates a potential off-site source of contaminants in outdoor air, since that compound is not present in coal tar.

87 Liberty Hill Road: A number of compounds were detected in the outdoor air samples at 87 Liberty Hill Road; however, most compounds are not associated with the coal tar release at the Site and were below the NYSDOH background concentrations for outdoor air. The concentrations of naphthalene and 1,2,4-trichlorobenzene in the back porch sample were detected above the New Hampshire IAIR and the NYSDOH outdoor air screening values and 1,2-dichlorobenzene was also detected above the NYSDOH outdoor air screening values in the back porch sample. Naphthalene is a constituent of coal tar but has other potential sources, such as moth balls. The concentration of naphthalene in the sample from the back porch (39.7 micrograms per cubic meter [µg/m3]) was similar to or greater than the concentrations detected in soil gas around and beneath the house (concentration in one sample was 41.8 µg/m3, and remaining samples were 1 µg/m3 or less). These data indicate the soil gas is not the source of the naphthalene in ambient air on the back porch. 1,2,4-trichlorobenzene and 1,2-dichlorobenzene are not associated with coal tar. In addition, methylene chloride was detected above the New Hampshire IAIR and the ATSDR minimum risk values in each of the samples; however, methylene chloride is a common laboratory contaminant and is not associated with coal tar.

5.1.4 Nature and Extent of COPCs in Surface Water COPCs were detected in two of the eleven surface water samples during the April and November 2006 sampling events. The analytical results for the two sampling rounds were similar. COPCs in surface water were limited to BTEX and naphthalene. These compounds were also found in groundwater samples collected near the stream, indicating that the mechanism by which COPCs migrated to surface water in the stream was by groundwater discharge. COPCs were detected in surface water from pools in the side channel (SW107) and at the confluence of the side channel with the main portion of Jewett Brook (SW108). Water from Jewett Brook does not flow through the side channel during normal flow



conditions and during the two sampling rounds water in the side channel was limited to several pools. COPCs were not detected in surface water downstream from SW108, indicating the area with COPCs in surface water is limited. 5.2 Sources The Site was undeveloped land until 1951 when the area was cleared to become a gravel pit. The source of the COPCs at the Site is related to the placement of coal tar in a former gravel pit at the Site in the 1950s. The coal tar was deposited at the Site following an explosion and subsequent demolition of the former MGP in Laconia. Following demolition of the plant, the area was converted to natural gas and further manufacturing of gas was ceased, including generation of by-products such as tar. The Site area was subdivided and developed into residential house lots in the late 1960s and early 1970s. 5.3 Migration Pathways Migration pathways at the Site include tar migration through the soil matrix, dissolved COPCs moving with groundwater flow, and volatilization to indoor air and ambient air. Information gathered during this investigation shows that:

Tar migration in soil has likely reached its maximum extent.

Dissolved COPC migration in groundwater is occurring, but it has not resulted in impacts to bedrock groundwater and therefore bedrock drinking water wells.

Volatilization to indoor and ambient air is not a complete pathway at this Site.

These pathways were explained further in the SIR [GEI, 2006].



6. Risk Characterization 6.1 Human Health Risk

A quantitative human health risk characterization was not conducted because remediation is planned for the Site, and the selection of a remedial solution is not dependent on the outcome of a quantitative evaluation of risk. As indicated in the SIR, there was no complete current 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.

This RAP proposes a remedy to eliminate potential future pathways. The selected remedy is discussed in detail in Section 8. Short term risks during construction of the remedy (fugitive dust, volatization of VOCs, etc.) will be managed under a health and safety plan. 6.2 Stage I Ecological Screening GEI conducted a Stage I Ecological Screening in accordance with the NHDES Contaminated Sites Risk Characterization and Management Policy (RCMP), and the NHDES Draft Evaluation of Sediment Quality Guidance. The characterization of risk of harm to the environment was conducted for current and reasonably foreseeable site activities and uses. It includes an assessment of chemical data, potential contaminant migration pathways, an evaluation of biota and habitats at and in the immediate vicinity of the Site, and a comparison to Upper Concentration Limits. The risk of harm to the site biota and habitats is characterized by evaluating ecological parameters using a two-stage approach. In Stage I, the objective is to identify and document conditions which do not warrant a Stage II Risk Characterization, either because of the absence of a potentially significant exposure pathway or because environmental harm is readily apparent and, therefore, additional assessment would be redundant. The impacts to Jewett Brook and surrounding wetland are limited to sediment and surface water in small pools adjacent to Jewett Brook. MGP byproducts were not observed in surface water or sediment of Jewett Brook itself. Based on the sediment and surface water data collected to date for this investigation, there is no current or potential future significant exposure by ecological receptors to COPCs in the pools. Therefore, it is our preliminary



opinion that a condition that is protective of the environment exists or has been achieved, and a Stage II Environmental Risk Characterization is not required. However, we recommend that a round of surface water samples be collected at a time of low flow conditions during the summer of 2007 to confirm our conclusion that COPCs would not exceed the AWQC in Jewett Brook during seasonal variations in flow.



7. Remedial Action Plan 7.1 Regulatory Requirements The RAP was designed to comply with the requirements cited in New Hampshire Code of Administrative Rules Chapter Env-Or 600 – Contaminated Site Management. 7.2 Objectives Specific objectives of the RAP were 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; (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. 7.3 Site-Specific Considerations Conditions unique to the Liberty Hill Road properties that impact the selection of potential remedial technologies include:

Till at the Site consists of a dense upper layer consisting of sandy silt, or silty sand, with approximately 20-percent gravel, and a looser lower layer typically consisting of narrowly graded sand with gravel. The dense upper layer may make several remedial technologies infeasible.

Site is located in a residential area and would be adversely affected by noise, truck traffic, odors, and dust.

7.4 Identification and Initial Screening of Remedial Technologies The objective of the initial screening evaluation (ISE) was to identify remedial technologies that would likely meet the remedial objectives presented in Section 7.2. The screening included the following elements:



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

Summarize the primary 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 presented in Section 7.2 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.

We performed a review to identify technologies that could potentially achieve the remedial objectives described in Section 7.2 regardless of the Site-specific constraints. Both in-situ technologies (technologies that treat or contain contaminants in place) and ex-situ technologies (technologies that rely on out of ground treatment) were identified. Technologies were obtained from a review of EPA documents and databases including, but not limited to, Remedial Technologies Screening Matrix and Reference Guide, the VISITT database, the RREL treatability database, and the Federal Remediation Technologies Roundtable website. We screened the technologies listed in Tables 15 (in-situ technologies) and 16 (ex-situ technologies) as to their potential effectiveness and implementability in meeting Site remedial objectives. The ISE results for each technology are presented in Tables 17 and 18. Tables 17 and 18 contain summaries of the performance characteristics and relative costs of the alternatives, and the rationale for retention or elimination of identified technologies. 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 are presented in Section 7.6. Several ex-situ treatment options (incineration, biological treatments, soil washing, solvent extraction, and vitrification) were eliminated from further consideration primarily due to the limited effectiveness and reliability of these technologies or to their high comparative costs. 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. 7.5 Description of Remedial Technologies Retained for Detailed

Evaluation 7.5.1 Institutional Controls Institutional controls are restrictions imposed on access to property or on the uses of a property, including natural resources and structures. Legal instruments, such as an Activity and Use Restriction (AUR), impose such restrictions. Institutional controls may be used for environmental or health protection concerns, for example, prohibiting residential use of some properties, maintaining a cap, and specifying health and safety requirements during excavation and soil management. The implementation of institutional controls would allow tar-impacted soil to remain in place. However, the exposure pathways to human or environmental receptors would be restricted. This alternative would create no additional risks to the community, workers, or the environment. Institutional controls are cost-effective, easily implemented, and may be used effectively in conjunction with other technologies. Long-term monitoring may be combined with institutional controls to assess the natural degradation and attenuation of COPCs. 7.5.2 Solidification/Stabilization Solidification/stabilization reduces the mobility of COPCs in the environment by trapping or immobilizing them within their original media (i.e., soil) instead of removing them through chemical or physical treatment. By immobilizing COPCs, solidification/stabilization can potentially meet the remedial objectives for the Liberty Hill Road properties. The process would require a grout injection to be mixed with the Site soils; however, implementation of this technology is highly dependent on the physical properties of soil. The mixing of affected soil would be performed using standard auger/caisson and injector head systems to soils to trap or immobilize contaminants. Emissions of fugitive dust, volatile compounds, and odors would require control measures during mixing activities. Dust and odor control measures were assumed to consist of spraying with water or foam and using dust screens to contain particulates.



7.5.3 Containment Use of a physical barrier can meet the remedial objectives for the Site. Physical barriers such as a cap or slurry wall, can be used to contain impacted groundwater, divert surface water infiltration and groundwater flow, and provide a barrier that limits or eliminates potential direct contact. Slurry walls typically consist of vertically excavated trenches that are filled with a soil, bentonite, and cement mixture. The resulting subsurface wall provides a barrier with low permeability and high chemical resistance. Before construction, a mix design program will be conducted to determine the components of the slurry wall backfill necessary to achieve a very low permeability wall (e.g., less than 1.0 x 10-7 cm/sec). Slurry walls are constructed using long-reach excavators or crane-mounted clamshell bucket. While the trench is excavated, it is held open with a bentonite clay/water slurry. Boulders and cobbles are removed from the soil that is excavated from the trench and dry clay (typically bentonite) and some trench slurry fluid is mixed with the excavated soil. This wet low-permeability clay-soil mix is then pushed back into the open trench with a bulldozer. The backfill mixture displaces the less dense trench slurry and creates a containment wall with very low permeability. A cap typically consists of a geomembrane that limits the infiltration of surface water runoff into the contaminated soil mass, and a soil cover that limits potential direct contact with the affected soil. The cap would be constructed with a subsurface drainage layer that would divert stormwater infiltration away from the cap. A cap can be constructed using standard earth-moving equipment. 7.5.4 Excavation Excavation (with subsequent treatment and reuse) would reduce or eliminate risk by removing contaminant mass. Therefore, excavation can potentially meet all remedial objectives for the Liberty Hill Road properties. The process would require the following key elements: (1) excavation of impacted soil; (2) on-site reuse or off-site disposal of treated soil; (3) excavation dewatering and treatment of effluent, as necessary; and (4) backfilling and restoration of excavation areas. The removal of affected soil would be performed using standard excavation equipment. Emissions of fugitive dust, volatile compounds, and odors would require control measures during excavation. Dust and odor control measures were assumed to consist of spraying with water or foam and using dust screens to contain particulates.



Dewatering may be required during excavation activities. The dewatering effluent was assumed to require treatment due to the presence of BTEX and PAH compounds in groundwater at the Site. 7.5.5 Soil Treatment –Thermal Desorption The most appropriate ex-situ treatment and disposal technology identified for managing excavated soil was thermal desorption. Thermal desorption is a physical separation process that uses either indirect or direct heat exchange to vaporize VOCs and SVOCs from soil. A gas is used as the transfer medium for the vaporized components. The separated organic components in the gas phase may either be recovered through condensation or can be destroyed in a second stage thermal oxidizer. Thermal desorption could be conducted either on-site or off-site. The primary advantages of on-site processing include reduced transportation costs and potential to reuse the treated soil to backfill the excavations. The primary disadvantages of on-site treatment are limited throughput and potential impacts to the neighborhood, such as noise and odors, resulting from the operation of the treatment system.



8. Detailed Evaluation of Remedial Action Alternatives

8.1 Development of Remedial Action Alternatives Four Remedial Action Alternatives (RAAs) were developed to address the RAP objectives (Section 7.2). These RAAs consist of combinations of the remedial technologies retained following the screening evaluation. In this section, we distinguish between ‘tar-impacted soil’ and ‘tar-saturated soil’ when we describe the goals 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. Therefore, one of the RAAs, RAA2, was designed to evaluate the effect of removal of primarily the tar-saturated soil. The RAAs retained for the detailed evaluation consist of the following:

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

This alternative consists of excavating the tar-impacted soil identified at the Site and treating the soil off-site using thermal desorption technology. An AUR would not be required for 69, 77, 83, or 87 Liberty Hill Road.

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

This alternative consists of excavating the tar-impacted soil to a depth of 15 feet and excavating the tar-saturated soil below 15 feet, with the excavated soil shipped off-site for thermal desorption treatment. This option is a variant of RAA1, reducing the volume of the remedial excavation while still removing the majority of contaminant mass in soil at the Site. An AUR would be required for 87, 83, 77, and 69 Liberty Hill Road, unless property boundaries were modified.



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

This alternative consists of excavating tar-impacted soil to a depth of 15 feet and containing the remaining tar-impacted soil below this depth. The containment system would consist of an impermeable cap installed at a depth of 15 feet, backfill with 15 feet of clean imported fill, and a clay-soil slurry wall encircling the tar-impacted soil from 15 feet to the bottom of the tar-impacted soil (50 feet). An AUR would be required for 87, 83, 77, and 69 Liberty Hill Road, unless property boundaries were modified.

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

A variant of RAA3, this alternative consists of excavating the tar-impacted soil to a depth of 3 feet and containing the remaining tar-impacted soil below this depth. The containment system would consist of an impermeable cap installed at a depth of 3 feet, backfill with 3 feet of clean, imported fill, and a clay-soil slurry wall encircling the tar-impacted soil at a depth of 3 to 50 feet. An AUR would be required for 87, 83, 77, and 69 Liberty Hill Road, unless property boundaries were modified.

Details of each RAA are presented in the next section. 8.2 Remedial Action Alternatives Descriptions 8.2.1 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 10. 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 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 Appendix I. 8.2.2 RAA2 – Excavate Tar-impacted Soil to 15 feet and Tar-saturated Soil

Below 15 Feet Deep and Treat Soil Off-site with Thermal Desorption This alternative is similar to RAA1, except that below a depth of 15 feet, only tar-saturated soil will be removed and transported off-site for treatment. The estimated excavation limits are shown in Figure 11. The reduced extent of the excavation would significantly reduce the volume of soil to be excavated and transported off-site for treatment, as well as the amount of deep excavation support and duration of dewatering required. Under this alternative, approximately 2,500 tri-axle dump trucks will be required to transport the estimated 50,000 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 83 percent of the source material and would cost approximately $7,700,000 (48 percent of the cost of RAA1). The duration of the construction phase is estimated to be one construction year (e.g., April through December). We estimate that New Hampshire Groundwater Quality Criteria would be achieved in groundwater near Jewett Brook in approximately 120 years following soil removal.



8.2.3 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

This alternative consists of excavation of the tar-impacted soil at the Site to a depth of 15 feet. A 3-foot-thick, 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 Figure 12. This alternative would remove 6 percent of the source material and contain the remaining 94 percent of the source material with the slurry wall and cap. The estimated cost of this alternative is $8,500,000 (approximately 53 percent of the cost of RAA1). We anticipate the containment wall will be constructed using a long-reach excavator, although a crane-mounted clamshell bucket may be required for excavation in the dense till. 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 15-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 2,200 tri-axle dump trucks will be required to transport the estimated 44,000 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 restored for residential reuse, however an AUR will be required to prohibit activities that may disturb soil greater than 15 feet deep and impact the cap or containment 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. 8.2.4 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 would consist of a containment system similar to RAA3 (Fig. 12), except the containment wall will be installed from a depth of 3 to 50 feet deep. 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 upper three feet of Site soil will be excavated and tar-impacted soil will be shipped off-site for treatment. 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 geotextile drainage mat or layer of crushed stone will be installed above the geomembrane to facilitate drainage from the cap. 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. This alternative would remove 0.5 percent of the source material and contain the remaining 99.5 percent of the source material using the containment system. The estimated cost of this alternative is $5,500,000 (approximately 35 percent of the cost of RAA1). 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. 8.3 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

8.4 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 19 (lower score preferred).



8.5 Selected Remedial Action Alternative Based on the scoring relative to the detailed evaluation criteria, 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) was selected as the most appropriate remedial action alternative with the most favorable balance of benefits and cost. Compared to the full excavation scenario (RAA1), it results in removal or containment of the same mass of contamination, the time to achieve restoration of downgradient groundwater quality is approximately the same, and it achieves the RAP objectives at less than half the cost of RAA1. Our ranking of RAA4 relies on assumptions about the design, configuration, effectiveness, and implementability of the containment system. For this evaluation, our assumptions were based on discussions with construction contractors, a preliminary evaluation of groundwater flow characteristics at the Site, our experience designing and installing similar systems at other sites, and our research of applications of these technologies at other sites. In Appendix J, we have provided brief project descriptions and contact information for several projects where slurry walls were used successfully to contain contaminated soil and control the migration of dissolved contaminants in downgradient groundwater. Prior to implementing the selected remedy, we propose to prepare a more rigorous 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. 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 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.



9. Conclusions and Recommendations 9.1 Conclusions

1. The lateral and vertical extent of COPCs in soil has been established. Concentrations of benzene, naphthalene, and several other PAHs exceed the residential (S1) standards in subsurface soil samples collected from multiple borings at the Site. None of the concentrations detected in soil samples exceeded the UCLs. The area with COPC concentrations in excess of the S1 standards generally coincides with the area where visual evidence of tar was observed.

2. Lateral extent of COPCs in groundwater has been established to the east, along Liberty Hill Road, to the south at the 87 Liberty Hill Road property, and to the north and northwest at the 63 Liberty Hill Road property. However, additional investigation activities are planned to evaluate conditions west of Jewett Brook on the golf course property.

3. GW1 standards were exceeded in groundwater samples collected in November 2006 from six shallow wells, ten intermediate wells, and one deep well. GW1 exceedances were limited to five compounds: benzene, naphthalene, styrene, toluene, and 1,2,4 trimethylbenzene. Locations where GW1 exceedances were observed were within the area where tar impacts were encountered and at downgradient locations.

4. No current exposure pathways to visitors or trespassers at the Site were identified because COPCs attributable to coal tar were not detected at concentrations greater than residential S1 standards in surface soil samples collected at the Site, were not detected in drinking water, and were not detected in ambient or indoor air. Therefore, there is no current pathway of exposure for visitors, trespassers, or residents of abutting properties. However, potential exposures of coal tar-related COPCs to people may occur during excavation work, landscaping activities that involve digging into the soil, or utility repair in the area with coal tar impacts, and these activities should be postponed until remedial requirements are evaluated.

5. COPCs were encountered in soil in the upper ten feet in portions of the backyards at 83 and 77 Liberty Hill Road and in coarser grained lenses within the till to depths up to 50 feet.

6. COPCs were detected in groundwater at the Site. COPCs were detected in till groundwater to depths up to 100 feet, but were not detected in drinking water wells at the Site. COPCs detected in groundwater include primarily BTEX and naphthalene



in areas where tar was observed in soil and in areas downgradient from tar-affected soil.

7. BTEX and naphthalene were detected in a surface water sample collected from a pool in an otherwise dry side channel of Jewett Brook. Surface water at this location was not flowing and water in the channel appeared to be result of discharge of groundwater to the channel. Results of the November 2006 round of surface water sampling were consistent with results of the April 2006 sampling round.

8. Since submittal of the SIR, KeySpan purchased the four properties where tar impacts are present to facilitate remediation. This document proposes a remedy that eliminates potential future exposures to tar in soil at the Site, and that contains the source material to eliminate further discharge of dissolved phase contaminants to groundwater downgradient of the source material.

9. A Stage I Ecological Screening of Jewett Brook indicates a condition protective of the environment exists, based on data collected to date, and a Stage II Environmental Risk Characterization is not required. However, a round of surface water samples is proposed during a seasonal low flow period in the summer of 2007 to confirm these conclusions.

10. Four remedial alternatives were evaluated and ranked. The selected alternative (RAA4) consists of excavation of the tar-impacted soil at the Site to a depth of three feet, construction of a soil-clay slurry wall to a depth of 50 feet around the remaining tar-impacted soil, and construction of an impermeable cap. This alternative would remove 0.5 percent of the contaminant mass and contain the remaining 99.5 percent of the mass with the slurry wall. 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.

11. Implementation of the selected alternative would result in reuse of the properties at 83

and 77 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.



9.2 Recommendations 9.2.1 Recommended Remedial Action Alternative The recommended remedial action alternative to address the source material at the Site is RAA 4, which includes excavation of tar-impacted soil to 3 feet below ground surface, containment of tar-impacted soil below 3 feet depth with a slurry wall, and treatment of excavated soil off-site with thermal desorption. 9.2.2 Delineation of Groundwater Management Zone We recommend delineating the GMZ following installation of the monitoring wells across Jewett Brook and receipt of analytical results. This well installation is planned for early May 2007. GEI will submit a GMZ permit application to NHDES within 60 days of obtaining results for groundwater samples from the newly installed wells. The GMZ permit application will include site information, site plans, and tables summarizing groundwater data, as specified in Env-Or 607-03. 9.2.3 Design Plans and Construction Specifications 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 by the end of August 2007. These plans will used by the selected contractor to implement the proposed remedial alternative. A public meeting will be held following submittal, in September 2007, to update the community on the remedial plans. 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. The recommended remedial alternative consists of excavation of the upper three feet of soil, installation of a 50-foot deep slurry wall around the soil with tar impacts, and construction of a low permeability cap on top of the contained soil. 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.



10. 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.



11. References 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.

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

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



12. 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 Boston Gas Company d/b/a KeySpan Energy New England LNAPL light non-aqueous phase liquid LRPP Local Resource Protection Priority 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 PCBs polychlorinated biphenyls PID photoionization detector PVC polyvinyl chloride



RAA Remedial Action Alternative RAP Remedial Action Plan RCMP Risk Characterization and Management Policy 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

Documents

Remedial Action Plan - Lower Liberty Hill Site Liberty... · GEI Consultants, Inc. i Table of Contents Executive Summary v 1. Introduction 1 1.1 Site Information and Description 1