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WEHRAN o ENGINEERS AND SCIENTISTS 3 - U .

SDMS DocID 464408

VOLUME I

REMEDIAL INVESTIGATION SOMERSWORTH MUNICIPAL LANDFILL SOMERSWORTH, NEW HAMPSHIRE

WEHRAN ENGINEERS AND SCIENTISTS GOLDBERG-ZOINO & ASSOCIATES, INC. WESTON GEOPHYSICAL CORPORATION ENVIRONMENTAL RESEARCH AND TECHNOLOGY, INC. CAMBRIDGE ANALYTICAL ASSOCIATES

VOLUME I

REMEDIAL INVESTIGATION SOMERSWORTH MUNICIPAL LANDFILL SOMERSWORTH, NEW HAMPSHIRE

Prepared for:

New Hampshire Department of Environmental Services Waste Management Division Concord, New Hampshire

Prepared by:

Goldberg-Zoino & Associates, Inc. Manchester, New Hampshire

and Wehran Engineers and Scientists

Methuen, Massachusetts •"

May 1989 GZA File No. D-5162 WE Project No. 05127

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Wehran Engineering Corporation 100 Milk Street Methuen, Massachusetts 01844 Tel: 508-682-1980 Fax: 508-682-1980 Ext. 2006

May 25, 1989

Mr. Richard H. Pease, P.E. On-Scene Coordinator The State of New Hampshire Department of Environmental Services Waste Management Division 6 Hazen Drive, P.O. Box 95 Concord, NH 03301

RE: Remedial Investigation Report Somersworth Municipal Landfill WE Project No. 05217

Dear Dick:

Enclosed please find ten (10) copies of the final Remedial Investigation Report for the above referenced project, including Section 8.0, Public Health Risk Assessment, which was attached as an addendum to the draft report.

We would like to take this opportunity to thank you and other representatives of New Hampshire Department of Environmental Services and United States Environmental Protection Agency for your contribution to the entire remedial investigation effort. Your work, particularly in the area of the environmental sampling and analytical program were particularly critical to the progress and successful completion of the project.

Sincerely,

VEHRAN EN6I ING CORPORATION

Charles L. Head, P.E.' Senior Prcfject .Manager Gotl^berg f oinq'; and Associates

Assqiciate Goldberg Zoino and Associates

Patrick G. Gillespie, P.E. Vice President, New England Regional Offices

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SOMERSWORTH REMEDIAL INVESTIGATION

EXECUTIVE SUMMARY

1.0 INTRODUCTION 1-1

1.1 STUDY OBJECTIVES 1-1

1.2 SITE BACKGROUND INFORMATION 1-2

1.2.1 Site Description 1-2 1.2.2 Remedial Investigation Study Area 1-3 1.2.3 Site History and Operations 1-3

1.2.4 Previous Site Investigations 1-6

1.3 HISTORICAL ASSESSMENT OF PROBLEM 1-8

2.0 SITE FEATURES INVESTIGATION 2-1

2.1 DEMOGRAPHIC SETTING 2-1

2.2 LAND USE 2-1

2.3 CLIMATOLOGY 2-3

3.0 HAZARDOUS SUBSTANCES SURVEY 3-1

4.0 HYDROGEOLOGIC INVESTIGATION PROGRAM 4-1

4.1 GEOLOGIC RECONNAISSANCE AND FRACTURE TRACE ANALYSIS 4-2 4.1.1 Geologic Reconnaissance 4-2

4.1.2 Fracture Trace Analysis 4-3

4.2 RESIDENTIAL WELL SURVEY 4-3

4.3 GEOPHYSICAL EXPLORATIONS 4-3

4.3.1 Seismic Refraction Survey 4-4 4.3.2 Electromagnetic Survey 4-4 4.3.3 Magnetometer Survey 4-5 4.3.4 Electrical Resistivity Survey 4-5

4.4 TEST PIT EXPLORATIONS 4-6

4.5 TEST BORINGS 4-7

4.5.1 Drilling Procedures 4-7 4.5.2 Soil Sampling 4-7 4.5.3 Bedrock Drilling and Sampling 4-8

4.6 GROUNDWATER MONITORING WELL INSTALLATIONS 4-8

TABLE OF CONTENTS (continued)

4.7 IN-SITU HYDRAULIC CONDUCTIVITY TESTS 4-10

4.7.1 In-situ Overburden Hydraulic Conductivity Tests 4-10

4.7.2 In-situ Bedrock Pressure Tests 4-10

4.8 LABORATORY SOILS TESTS 4-11

4.8.1 Laboratory Soil Gradation Analyses 4-11

4.8.2 Cation Exchange 4-11

4.9 SURFACE WATER STATIONS 4-11

4.10 SOIL AND SEDIMENT SAMPLING AND ANALYSIS 4-12

4.11 GROUNDWATER AND SURFACE WATER SAMPLING

AND ANALYSIS 4-15

5.0 SITE GEOLOGY AND HYDROLOGY 5-1

5.1 SURFICIAL AND BEDROCK GEOLOGY 5-1

5.1.1 Bedrock Geology 5-1

5.1.2 Surficial Geology 5-6

5.2 SURFACE WATER HYDROLOGY 5-12

5.3 GROUNDWATER HYDROLOGY 5-14

5.3.1 Hydrogeologic Setting 5-14 5.3.2 Hydraulic Properties 5-15 5.3.3 Groundwater Levels and Flow Directions 5-17 5.3.4 Hydraulic Gradient and Groundwater

Seepage Velocities 5-19

6.0 AIR MONITORING PROGRAM 6-1

6.1 INITIAL AIR MONITORING 6-1

6.2 REMEDIAL INVESTIGATION AIR MONITORING PROGRAM 6-1

7.0 DISTRIBUTION AND MIGRATION OF CONTAMINANTS 7-1

7.1 OBSERVED CONTAMINANTS 7-1

7.1.1 Volatile Organic Compounds (VOCs) 7-2 7.1.2 Acid and Base/Neutral Extractable

Organic Compounds (ABN's) 7-3 7.1.3 Metals 7-4 7.1.4 Leachate and/or Groundwater

Quality Indicators 7-5


7.2 OBSERVED DISTRIBUTION OF CONTAMINANTS 7-6

7.2.1 Surface Water and Sediments 7-6 7.2.2 Groundwater 7-8 7.2.3 Soils 7-13 7.2.4 Air 7-15 7.2.5 Summary 7-15

7.3 CONTAMINANT TRANSPORT 7-17

7.3.1 Groundwater Contaminant Transport and Attenuation Mechanisms 7-17

7.3.2 Site Contaminant Migration 7-21 7.3.3 Potential Receptors to

Groundwater Contamination 7-28

8.0 RISK ASSESSMENT 8-1

8.1 PUBLIC HEALTH 8-1

8.1.1 Introduction 8-1

8.1.1.1 Site Description 8-1 8.1.1.2 General Risk Assessment Scope

and Approach 8-2

8.1.2 Exposure Pathways 8-2

8.1.2.1 Sources and Contaminant Transport 8-2 8.1.2.2 Exposure Points, Exposure

Routes, Receptor Populations 8-3 8.1.3 Indicator Chemical Selection 8-6

8.1.3.1 Generation of Mean Statistics 8-7 8.1.3.2 Background Considerations 8-7 8.1.3.3 Frequency of Occurrence

Considerations 8-7 8.1.3.4 Toxicity Considerations 8-8

8.1.4 Dose Response Assessment 8-8

8.1.4.1 Carcinogens 8-8 8.1.4.2 Noncarcinogens 8-8 8.1.4.3 ARARS 8-8 8.1.4.4 Toxicity Profiles 8-9

8.1.5 Exposure Assessment 8-9

8.1.5.1 Exposure Profiles 8-9 8.1.5.2 Exposure Point Concentrations 8-9


8.1.5.3 Exposure Equations and Assumptions 8-10

8.1.5.4 Exposure Estimates 8-11 8.1.5.5 Comparison of Exposure Point

Concentrations with ARARS 8-12

8.1.6 Risk Characterization 8-13

8.1.6.1 Noncarcinogenic Effects 8-13 8.1.6.2 Carcinogenic Effects 8-15 8.1.6.3 Sources of Uncertainty 8-16

8.2 ENVIRONMENTAL RISK ASSESSMENT 8-18

8.2.1 Environmental Characterization 8-18 8.2.2 Threatened and Endangered Species 8-20 8.2.3 Risk Characterization 8-20

9.0 IDENTIFICATION OF POTENTIALLY APPLICABLE REMEDIAL

TECHNOLOGIES 9-1

9.1 GENERAL RESPONSE ACTIONS 9-1

9.2 POTENTIALLY APPLICABLE REMEDIAL TECHNOLOGIES 9-2 9.2.1 Land Use Restrictions 9-2 9.2.2 Alternate Water Supply 9-3 9.2.3 Continued Monitoring 9-3 9.2.4 Surface Barriers 9-3 9.2.5 Removal and Containment of Contaminated

Sediments 9-4 9.2.6 Subsurface Barriers 9-5 9.2.7 Excavation 9-6 9.2.8 Groundwater Extraction 9-7 9.2.9 Liquid Treatment 9-7 9.2.10 Hazardous Solids Treatment 9-9 9.2.11 Hazardous Solids Disposal 9-9 9.2.12 Gas Migration Control 9-9

9.3 PRELIMINARY SCREENING OF REMEDIAL TECHNOLOGIES 9-11

10.0 SUMMARY AND CONCLUSIONS 10-1

10.1 BACKGROUND 10-1

10.2 HYDROGEOLOGIC CONDITIONS 10-2


10.3 NATURE AND DISTRIBUTION OF ENVIRONMENTAL CONTAMINATION 10-3

10.4 RISK ASSESSMENT 10-6

11.0 RECOMMENDATIONS FOR ADDITIONAL EXPLORATIONS AND

ANALYSIS 11-1

11.1 ADDITIONAL EXPLORATIONS 11-1

11.2 POSSIBLE ADDITIONAL SOURCE AREA 11-2

11.3 CONTINUED SITE MONITORING 11-2

BIBLIOGRAPHIC REFERENCES

VOLUME II - TABLE OF CONTENTS

TABLES

TABLE 1 REMEDIAL INVESTIGATION TASKS

TABLE 2 SUMMARY OF GROUNDWATER ELEVATIONS

TABLE 3 SUMMARY OF SURFACE WATER ELEVATIONS

TABLE 4 SUMMARY OF HYDRAULIC CONDUCTIVITIES - IN-SITU ANALYSIS

TABLE 5 SUMMARY OF HYDRAULIC CONDUCTIVITIES KOZENY-CARMAN ANALYSIS

TABLE 6 SUMMARY OF CHEMICAL ANALYSIS PERFORMED

TABLE 7 SUMMARY OF VOLATILE ORGANIC COMPOUNDS OBSERVED GROUNDWATER

TABLE 8 SUMMARY OF VOLATILE ORGANIC COMPOUNDS OBSERVED SURFACE WATER

TABLE 9 SUMMARY OF VOLATILE ORGANIC COMPOUNDS OBSERVED - SOIL AND SEDIMENT

TABLE 10 SUMMARY OF METALS OBSERVED CONCENTRATIONS GREATER THAN MAXIMUM CONTAMINANT LEVELS GROUNDWATER AND SURFACE WATER

TABLE 11 SUMMARY OF METALS OBSERVED CONCENTRATIONS GREATER THAN MAXIMUM ANTICIPATED BACKGROUND CONCENTRATIONS - SOIL AND SEDIMENT

TABLE 12 SUMMARY OF ACID AND BASE/NEUTRAL EXTRACTABLE COMPOUNDS OBSERVED - GROUNDWATER AND SURFACE WATER

TABLE 13 SUMMARY OF ACID AND BASE/NEUTRAL EXTRACTABLE COMPOUNDS OBSERVED - SOIL AND SEDIMENT

TABLE 14 SUMMARY OF LEACHATE INDICATORS OBSERVED

TABLE 15 PROBABLE EXPOSURE POINTS

TABLE 16 SAMPLING POINTS WITHIN IDENTIFIED EXPOSURE POINTS

TABLE 17 CHEMICALS DETECTED

TABLE 18 GROUNDWATER ANALYSIS

TABLE 19 SOIL ANALYSES

TABLE 20 SURFACE WATER ANALYSES

TABLE 21

TABLE 22

TABLE 23

TABLE 24

TABLE 25i

1 TABLE 26

j TABLE 27

TABLE 28

TABLE 29

TABLE 30

TABLE 31

TABLE 32!

TABLE 33

j TABLE 341

TABLE 35I TABLE 3 6I

TABLE 37

TABLE 38

TABLE 39

TABLE 40TABLE 41

TABLE 42

VOLUME II - TABLE OF CONTENTS (continued)

SEDIMENT ANALYSES

TOXICITY VALUES FOR CARCINOGENIC EFFECTS

EPA WEIGHT OF EVIDENCE CATEGORIES FOR POTENTIAL CARCINOGENS

TOXICITY VALUES FOR NONCARCINOGENIC EFFECTS

POTENTIAL ARARS FOR INDICATOR CHEMICALS

EXPOSURE PROFILES FOR RECEPTOR GROUPS

EXPOSURE POINT CONCENTRATIONS

EXPOSURE ASSUMPTIONS AND EQUATIONS FOR INGESTION OF GROUNDWATER VIA PRIVATE RESIDENTIAL WELLS

EXPOSURE ASSUMPTIONS AND EQUATIONS FOR INGESTION AND DERMAL CONTACT WITH SOIL - PLAYGROUND

EXPOSURE ASSUMPTIONS FOR SURFACE WATER CONTACT DURING WADING (PETER'S MARSH BROOK)

EXPOSURE ASSUMPTIONS FOR INGESTION OF FISH

BIOCONCENTRATION FACTORS FOR INDICATOR CHEMICALS

GROUNDWATER INGESTION-NONCARCINOGENS-AREA 5

GROUNDWATER INGESTION-NONCARCINOGENS-AREA 4

SOIL INGESTION-NONCARCINOGENS-AREA 2 AND 3 SOIL INGESTION-NONCARCINOGENS-AREA 4

FISH CONSUMPTION-NONCARCINOGENS-AREA 4

SURFACE WATER-WADING-DERMAL NONCARCINOGENS-AREA 4

GROUNDWATER INGESTION-CARCINOGENS-AREA 5

GROUNDWATER INGESTION-CARCINOGENS-AREA 4 SOIL CONTACT DERMAL-NONCARCINOGENS AND CARCINOGENSAREA 4

SURFACE WATER-WADING-DERMAL CARCINOGENS-AREA 4

TABLE 43

TABLE 44

TABLE 45

TABLE 46

I TABLE 47I

TABLE 48I

TABLE 49i

FIGURES I

FIGURE 1

FIGURE 2

FIGURE 3

i FIGURE 4

FIGURE 5i ^ FIGURE 6; FIGURE 7

FIGURE 8

FIGURE 9

VOLUME II - TABLE OF CONTENTS (continued)

FISH CONSUMPTION-CARCINOGENS-AREA 4

COMPARISON OF EXPOSURE POINT CONCENTRATIONS TO ARARS

RISK CHARACTERIZATION SUMMARY

COMPARISON OF SURFACE WATER CONCENTRATIONS TO AQUATIC TOXICITY VALUES

GENERAL RESPONSE ACTIONS AND ASSOCIATED REMEDIAL TECHNOLOGIES

SITE CHARACTERISTICS THAT MAY AFFECT REMEDIAL TECHNOLOGY SELECTION

WASTE CHARACTERISTICS THAT MAY AFFECT REMEDIAL TECHNOLOGY SELECTION

LOCUS PLAN

EXPLORATION LOCATION PLAN

SUBSURFACE PROFILE A-A'

SUBSURFACE PROFILE B-B' AND CC'

SUBSURFACE PROFILE D-D'

BEDROCK ELEVATION CONTOUR GROUNDWATER ELEVATION CONTOUR PLAN

TOTAL VOLATILE ORGANIC COMPOUNDS IN GROUNDWATER AND SURFACE WATER EXCLUDING BEDROCK MONITORING WELLS

TOTAL VOLATILE ORGANIC COMPOUNDS IN GROUNDWATER; BEDROCK MONITORING WELLS

FIGURE 10 ESTIMATED ZONE OF GROUNDWATER CONTAMINATION

FIGURE 11 EXPOSURE POINTS

APPENDICES

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E

APPENDIX F

VOLUME II - TABLE OF CONTENTS fcontinued^

LIMITATIONS

FRACTURE TRACE ANALYSIS

SUMMARY OF RESIDENTIAL WELL SURVEY

TEST BORING LOGS PREPARED BY GZA

TEST PIT LOGS PREPARED BY WEHRAN

TEST BORING LOGS PREPARED BY OTHER INVESTIGATORS

APPENDICES

APPENDIX G

APPENDIX H

APPENDIX I

APPENDIX J

APPENDIX K

APPENDIX L

VOLUME III - TABLE OF CONTENTS

LABORATORY SOIL TEST RESULTS

SUMMARY OF ANALYTICAL DATA

WESTON GEOPHYSICAL REPORT

TOXICITITY PROFILES

DERIVATION OF TOXICOKINETIC FACTORS

EXECUTIVE SUMMARY

The Somersworth Municipal Landfill accepted municipal and industrial refuse for on-site disposal between approximately the mid 1930's and 1981. Groundwater quality studies initiated at the landfill site in 1980 indicated that the groundwater beneath the site was being contaminated by volatile organic compounds (VOCs) leaching from the landfill. Succeeding investigations documented both inorganic and organic contamination of groundwater and surface water in the area. The site was siibsequently proposed to the EPA's National Priority List (NPL), which is prepared in accordance with the National Contingency Plan (NCP) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, commonly referred to as the "Superfund" legislation).

The NPL listing triggered remedial investigative activities under the direction of the EPA, beginning with the preparation of a Remedial Action Master Plan (RAMP), which was completed in September 1983. In 1984, Wehran Engineers and Scientists was engaged to complete a Remedial Investigation/Feasibility Study for the Somersworth Municipal Landfill. Work on the Remedial Investigation phase was initiated in November 1984 by Wehran in cooperation with Goldberg-Zoino & Associates, Inc. (GZA), Weston Geophysical Corporation, Can±)ridge Analytical Associates, Inc. (CAA), and Environmental Resource Technology, Inc. (ERT). The Remedial Investigation was initiated under the State of New Hampshire Department of Environmental Services, Water Supply and Pollution Control Commission (NH WSPCC), under the direction of the U.S. Environmental Protection Agency (EPA), and continued under the New Hampshire Department of Envrionmental Services - Waste Management Division (NH DES - WMD).

The Somersworth Municipal Landfill is located in the central portion of Somersworth, New Hampshire, approximately one mile to the southwest of the City proper. The approximately 26-acre waste disposal area (referred to as "the site" or "the landfill") is situated entirely on land owned by the City of Somersworth. The City has owned and managed the operation of the landfill since approximately 194 5. At present, the City is a member of the Lamprey Regional Solid Waste Disposal Cooperative, which operates an incinerator in Durham, New Hampshire. Although the landfill is still active, it currently accepts only those materials that cannot be incinerated. These materials are now disposed in the western portions of the landfill in an area known as the "stump dump."

The former Somersworth municipal si pply well No. 3 is located approximately 2,300 feet to the north-northwest of the landfill as shown on Figure 2. Discussions with.the Somersworth City Engineer indicate that this well is no longer in use and is currently being dismantled by the City. A second well, Somersworth municipal

Somersworth - May 22. 1989 - File No. D-5162 - Executive Summary Page 1

supply well No. 4, is located approximately 800 feet southwest of the landfill. Well No. 4 has never been used as a water supply source and, according to the City Engineer, there are no plans in 1987 to use it as a water supply source in the future.

The landfill is situated adjacent to, and within approximately 400 feet of Peter's Marsh Brook. Previous investigators (CDM, 1983) have indicated that all surface runoff from both the active and inactive portions of the landfill eventually reaches Peter's Marsh Brook. This brook is a tributary of Tate's Brook which is in turn a tributary of the Salmon Falls River. Both the City of Somersworth, New Hampshire and neighboring Berwick, Maine withdraw water from the Salmon Falls River for drinking water supply. The Somersworth and Berwick intakes on the river are located approximately 1.5 miles to the north-northeast of the landfill.

Previous studies undertaken by others at the Somersworth Municipal Landfill indicated that these public water supplies, as well as private residential wells located in the vicinity of the site, were potentially threatened by groundwater contamination emanating from the landfill. Primary wastes deposited in the landfill which have engendered groundwater contamination are anticipated to have included municipal trash and industrial wastes, including some chemical wastes.

Site Geology and Hydrology

Surficial soil deposits are generally of glacial origin and are underlain by metamorphic bedrock. Natural soils encountered in the test borings generally consisted of the following four basic types of deposits:

stratified sand with significant variations in silt and gravel content (kame deposits);

dense silty, gravelly sand (glacial till deposits);

peat (recent wetland deposits); and

clayey silt, frequently including sand and/or gravel (possible vestigial glacio-marine deposits).

At the Somersworth landfill site, the kame deposits were observed to be prevalent.

A review of topographic maps indicates that the Somersworth Municipal Landfill is located completely within the drainage basin of Peter's Marsh Brook. As Peter's Marsh Brook is a secondary tributary to the Salmon Falls River, the site is also within the

Somersworth - Mav 22. 1989 - File No. D-5162 - Executive Summary Page 2

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watershed of the Salmon Falls River which serves as a water supply to both Somersworth, New Hampshire and Berwick, Maine. Field observations Indicate that surface water runoff in the immediate vicinity of the site drains into Peter's Marsh Brook.

At the Somersworth Municipal Landfill site and surrounding area, groundwater is stored and transmitted through the pore spaces of the overburden soil deposits, and through the fractures within the bedrock. At this site, because of the apparent direct hydraulic communication between the overburden and upper zone of fractured bedrock, the saturated soil deposits and fractured bedrock can be collectively referred to as an unconfined aquifer. The unconsolidated soil deposits comprising the overburden aquifer materials within the site study area basically consist of gravelly and silty sand kame deposits, and fibrous peat encountered within the swampy wetlands associated with Peter's Marsh Brook. Other overburden materials observed within the site study area are not considered an important or significant part of the aquifer.

Bedrock fractures were observed to be most predominant within the upper 5 to 10 feet of the bedrock surface, although groundwater data obtained from monitoring wells installed in bedrock indicate that fractures which extend to at least 30 feet below the bedrock surface are in direct hydraulic communication with the overlying unconsolidated depos its.

Groundwater movement within the aquifer occurs regionally in a westerly, then west-northwesterly direction across the landfill toward Peter's Marsh Brook and surrounding wetlands. A review of

topographic maps of the study area and its surrounding environs indicates that it is probable that Willand Pond, located

approximately one mile south-southwest of the landfill, serves as a major source of groundwater recharge. Rainfall recharge also

likely occurs along the uplands located to the east and west of the study area. Groundwater is anticipated to flow regionally from Willand Pond and the upland recharge areas toward the landfill.

It is anticipated that the wetland area surrounding Peter's Marsh Brook located immediately northwest of the landfill is a point of discharge (surfacing) for groundwater within the study area. Evidence of this is provided by:

strongly convergent groundwater flow northwest of the landfill with no substantial increase in saturated thickness (although saturated thickness data are limited); an increase of almost one foct of hydraulic head with depth, observed within companion cluster monitoring wells at location B-8 located within the wetland area north of the landfill; and


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an approximate one-half order of magnitude increase in flow volume of Peter's Marsh Brook between Blackwater Road and the

area in the vicinity of surface water station S-6, with limited additional surface drainage during most of the year.

Groundwater discharged within this wetlands area would subsequently flow with the surface waters of Peter's Marsh Brook toward the Salmon Falls River.

Distribution of Contaminants

During the course of the Remedial Investigation, samples of surface sediments, subsurface soils, groundwater, surface water, and air were obtained from the study area for evaluation of possible chemical contamination. Five basic types of chemical analyses were performed on samples of the various environmental media. These analyses included methods for the detection of volatile organic compounds (VOCs), acid and base/neutral extractable organic compounds (ABN's), metals, polychlorinated biphenyls (PCB's), and

pesticides. In addition, analyses for several inorganic contaminants considered to be indicators of landfill leachate, as

well as measurements of certain physical properties considered as leachate indicators of water quality, were conducted as part of the

groundwater sampling and analysis program. The contaminants that were identified at the site include VOCs, ABN's, metals, and typical landfill leachate indicators. Neither PCB's nor pesticides were detected in any of the samples analyzed.

VOCs were observed to be the most significant chemical contaminants, in terms of both distribution and concentration. A

total of 25 VOCs were identified in the site area in the various media. In general, the greatest frequency, concentration, and

total number of VOC contaminants were observed in groundwater within approximately 800 feet of the northwest corner of the landfill at total concentrations as high as approximately 13,000

micrograms per liter (parts per billion). VOC contaminants have also been observed in the surface water of Peter's Marsh Brook,

west and northwest of the landfill; however, total concentrations of VOCs in these surface waters are typically less than 100

micrograms per liter. Although VOCs were detected in one sample of a total of five samples obtained from the Salmon Falls River, downgradient of its confluence with Peter's Marsh Brook, these results are considered suspect. The highest concentrations of VOCs in soils were observed in samples obtained from test pits excavated within the landfill area.

ABN contaminants were observed with considerably less frequency, and typically at lower concentrations than VOCs. An exception to this is a composite soil sample obtained while drilling boring B-


4 located immediately south of the landfill within which eight base/neutral extractable compounds were detected.

Metals contaminants at concentrations above anticipated background levels were also observed with considerably less frequency than VOCs. In groundwater, only arsenic, chromium and lead were observed at concentrations above both their respective Maximum Contaminant Level criteria and anticipated background levels. Zinc, copper, and nickel were also commonly observed at levels above anticipated background concentrations at locations considered both up- and downgradient of the landfill. Therefore, no pattern of distribution is readily apparent.

Results of initial air quality screening by the project team, as well as results of air quality screening during the soil boring program, indicated no detectable VOCs within air in the vicinity of the landfill. Detection limits were approximately l ppm.

Fate of Contaminants

The estimated zone of groundwater contamination is shown on Figure 10. Groundwater contamination downgradient of the Somersworth Municipal Landfill is at this time considered primarily attributed to the Somersworth Municipal Landfill. It is noted however, that hazardous materials may have been stored on, or transferred through adjacent properties including a scrap metal yard south of Blackwater Road, a dry cleaning operation, and the National Guard Armory. It is not clear what effect, if any, activities relating to possible hazardous wastes at these sites may have had on water quality in the vicinity of the site.

Water quality data indicate that the zone of highest groundwater contamination extends as a plume northwesterly from the landfill approximately 1,000 feet. The centerline of this contaminant plume is estimated to lie in proximity to monitoring clusters B-6 and B8. Contaminant concentrations appear to decrease on either side of the plume centerline; however, analyses of groundwater samples obtained from monitoring clusters B-9 and B-10 indicate that the zone of contaminated groundwater extends at least 200 feet west and 700 feet east of Peter's Marsh Brook. Water quality data also indicate that the zone of contaminated groundwater extends at least 100 feet south of the landfill perimeter.

Contamination entering the groundwater beneath the landfill source area would be expected to migrate by advective-dispersive transport west-northwesterly in the direction of regional groundwater flow toward Peter's Marsh Brook and associated wetlands. The plume centerline is anticipated to be approximately coincident with a line extending from the center of the landfill through monitoring clusters B-6 and B-8.


The downgradient extent and ultimate fate of groundwater contamination is difficult to assess due to limited groundwater } quality data northwest of monitoring cluster B-8. Results of analytical contaminant transport analyses, however. Indicate that the contaminant plume is at steady state; discharge of dissolved contaminants with groundwater into Peter's Marsh Brook and adjacent wetlands has limited contaminant migration downgradient of geophysical terrain conductivity exploration EM line 19 shown on Figure 10. As such, the primary receptor to contaminant migration within groundwater at the Somersworth Municipal Landfill is regarded at this time as Peter's Marsh Brook. This conclusion should be svibstantiated with additional data collection as recommended in Section 11.1.

Contaminants discharged to Peter's Marsh Brook with groundwater must pass through a layer of peat, observed to be approximately 15

J to 25 feet thick. Because of the large percentage of organic carbon typically contained within peat, adsorption of VOC and ABN contaminants by the peat is anticipated to be a significant

I attenuation mechanism. Increased microbial activity within the ' peat is anticipated to result in increased biological decay or

transformation, especially as the solute transport is retarded by ! adsorption. Finally, volatilization of organic compounds is likely I to be significant as discharged groundwater mixes with surface

water. The contribution of all three of these mechanisms to contaminant attenuation is not quantifiable with the limited site data; however, although some seasonal fluctuation in the specific contaminants and contaminant concentrations is probable, contamination within Peter's Marsh Brook is not anticipated to

i increase significantly over levels detected during the Remedial ' Investigation considering that the contaminant plume is estimated

to have been at steady state for approximately 10 to 30 years.

I To conservatively estimate the potential impact of contaminants transported in the surface waters of Peter's Marsh Brook to downgradient receptors, primarily the Berwick and Somersworth water

\ intakes in the Salmon Falls River, a dilution analysis based on ' stream flow data was performed. The resultant dilution factor is

approximately 35:1; that is, contaminant concentrations in the I Salmon Falls River are anticipated to be less than 3 percent of I concentrations observed in Peter's Marsh Brook downgradient of the

landfill. In actuality, volatilization, photodegradation and biodegradation, as well as added dilution from the Little River and Tate's Brook not considered in the analysis, are significant attenuation mechanisms, rendering the 35:1 dilution factor very conservative.

In addition to Peter's Marsh Brook, few probable receptors to groundwater contamination were identified in the site study area. Groundwater production wells within or in proximity to the


estimated zone of contamination are considered receptors. Only three groundwater production wells are known to exist in the site study area, including residential well RW-2 located immediately south of the landfill, and the Somersworth municipal supply well Nos. 3 and 4. All three of these wells have been decommissioned at this time, with the Somersworth municipal supply well No. 3 being physically dismantled.

Risk Assessment

An assessment of the risk posed by the Somersworth Municipal Landfill to public health and the environment was conducted as part of the remedial investigation. The risk assessment considered a number of exposure points, or areas where people may be exposed to site contaminants. Quantitative estimates were developed for dermal and ingestion exposures from soil to visitors to the playground, dermal and ingestion exposures from soil to visitors to the Peter's Marsh Brook area, dermal exposures from surface water to persons wading in Peter's Marsh Brook, and ingestion exposures to persons ingesting fish taken from Peter's Marsh Brook. In addition, potential future exposures via groundwater ingestion as drinking water were estimated for the areas of Blackwater Road and Peter's Marsh Brook.

A number of exposure points were not considered quantitatively, for a variety of reasons. Somersworth Well No. 4 and the Salmon Falls River were considered as potential future exposure points, but exposures were not quantified, as the remedial investigation suggests that the contaminant plume will not reach these locations. Somersworth Well No. 3 was not considered an exposure point because it has been dismantled. On- site air and air nearby the site are considered potential exposure points, although data available to date do not indicate detectable contaminant levels. As a result, these exposure points were not quantified.

An evaluation of average and maximum concentrations found at exposure points showed that concentrations of some chemicals exceeded potentially Applicable or Relevant and Appropriate Requirements (ARARs). Measured concentrations in groundwater in both the Blackwater Road area (Area 5) and the Peter's Marsh Brook area (Area 4) exceed the MCL for arsenic. Surface water concentrations (Table 20) of arsenic exceed the Ambient Water Quality Criteria (AWQC) for the Protection of Human Health (including both ingestion of water and aquatic organisms). The worst-case exposure point concentration (maximum) for 1,1dichloroethane (1,398 ug/1) in Area 4, exceeds the New Hampshire drinking water action level (810 ug/1). Average groundwater concentrations of 1,2-dichloroethane, 1,1-dichloroethylene, trichloroethylene and benzene in Area 4 also exceed the MCL.


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Average surface water concentrations of 1,2-dichloroethane, tetrachloroethylene and benzene in Peter's Marsh Brook and Tate's Brook exceed AWQC. The average measured concentration of chromium and 1,1-dichloroethylene in groundwater in Area 5 equals the MCL, and the maximum exceeds it. Both the average and maximum

1,2-dichloroethylene concentrations in Area 4 exceed the MCLG. The maximum methyl ethyl ketone concentration (1,530 ug/1 ) exceeds the

lifetime health advisory of 170 ug/1.

A quantitive evaluation of the risk posed by the site showed showed that, based on the data available and a number of assumptions, current exposure levels for residents along Blackwater Road are not likely to pose a risk of chronic effects, as calculated hazard indices are less than 1. If private wells were reopened or installed in this area, the exposure would result in a hazard index

greater than 1, due to arsenic. The estimated upper bound excess risk of cancer for residents along Blackwater Road based on current

exposure levels, are on the order of 5.2x10'' or 5.2 in 100,000 in the most-probable case and 3.2x0' (3.2 in 10,000) for the worst

case. These estimated risks are primarily due to potential arsenic exposures from ingesting fish from this area as well as dermal contact with surface water in Peter's Marsh Brook. Future estimated risks of cancer from ingestion of drinking water in the

Blackwater Road area were 8.4x10"' (most-probable) and 2.1x10' (worst case). Estimated risks excluding arsenic were 1.4x10"* and 1.1x10"', respectively.

If private wells were installed in the area of Peter's Marsh Brook, north/northwest of the site, exposures could result in chronic effects in the exposed population, primarily due to exposures to arsenic and l,1-dichloroethylene. Future excess cancer risks associated with groundwater ingestion in this area were 6.9x10"' (most-probable) and 9.9x10* (worst case) based primarily on exposures to arsenic, 1,2-dichloroethane, 1,1-dichloroethylene and 1,1-dichloroethane.

The assessment of risk to the environment was preliminary, as a wetlands assessment will be conducted as part of the feasibility study. Based on available information, as discussed in Section 8.2, the site does not appear to pose a risk to aquatic organisms in Peter's Marsh Brook.

There are a number of sources of uncertainty that should be considered in evaluating the conclusions of the risk assessment. Little or no sampling of air, fish, and surface soils was conducted and represents a limitation to the risk assessment. In addi+ion, a number of the assumptions used to estimate exposure may be questionable and cannot be easily verified. Lastly, toxicity values appropriate for risk assessment are not available for all chemicals of interest at the site.


1.0 INTRODUCTION

This report presents the results of a Remedial Investigation of the Somersworth Municipal Landfill in Somersworth, New Hampshire. The study was completed by Wehran Engineers and Scientists in cooperation with Goldberg-Zoino & Associates, Inc. (GZA), Weston Geophysical Corporation, Cambridge Analytical Associates, Inc. (CAA), and Environmental Resource Technology, Inc. (ERT). The Remedial Investigation was undertaken for the State of New Hampshire Department of Environmental Services, Waste Management Division (NHDES - WMD) under the direction of the U.S. Environmental Protection Agency (EPA). This Remedial Investigation has been prepared in accordance with the Agreement for Consultant Services for this project dated October 24, 1984, and the Contract Amendments to that agreement dated December 19, 1985; July 8, 1986; and August 20, 1986.

Please note that the analyses and conclusions presented in this report are subject to the limitations found in Appendix A.

1.1 STUDY OBJECTIVES

The Remedial Investigation of the Somersworth Municipal Landfill site emphasizes data collection and site characterization to determine the presence, nature, and extent of contamination in the environment, including groundwater, surface water, soil, sediment, and air. Public health and environmental risk due to the site contamination are also addressed. Specific Remedial Investigation objectives include the following:

1. Define the hydrogeologic regime in and around the site;

2. Characterize the nature and extent of contaminant migration;

3. Quantitatively assess public health and environmental risk as a result of the presence and migration of contaminants; and

4. Preliminarily identify potential source control and treatment technologies applicable to the site.

Study work tasks were developed to investigate subsurface and surface conditions and evaluate the significance of contamination observed at the landfill. The work tasks are outlined in Table 1, along with identification of the project team member(s) responsible for implementation of each task.

The results of the Remedial Investigation will be used for the subsequent development and evaluation of remedial alternatives during a Feasibility Study.

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1.2 SITE BACKGROUND INFORMATION

The Somersworth Municipal Landfill accepted municipal and industrial refuse for on-site disposal between approximately the inid-1930's and 1981. Groundwater quality studies initiated at the landfill site in 1980 indicated that the groundwater beneath the site was being contaminated by volatile organic compounds (VOCs) leaching from the landfill. Succeeding Investigations documented both inorganic and organic contamination of groundwater and surface waters in the site area. The site was subsequently proposed to the EPA's National Priority List (NPL) prepared in accordance with the National Contingency Plan (NCP) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, commonly referred to as the "Superfund" legislation).

The NPL listing triggered remedial investigative activities under the direction of the EPA, beginning with the preparation of a

Remedial Action Master Plan (RAMP), which was completed in September 1983. Work on the ensuing Remedial Investigation was

initiated in November 1984, and will be formally completed upon acceptance of the final Remedial Investigation report.

The following subsections discuss the physical features of the site study area, site history and operations, previous site

investigations, and the nature and extent of the problem as perceived prior to commencement of the Remedial Investigation. Information presented below has been obtained primarily from review of documents currently in the public domain produced by others. Additionally, City of Somersworth officials were contacted to

obtain certain background information. A complete list of references used in this report is included as a bibliography.

1.2.1 Site Description

The Somersworth Municipal Landfill, shown on Figure 1, is located in the central portion of Somersworth, New Hampshire,

approximately one mile to the southwest of the City proper. The landfill is situated immediately north of Blackwater Road, about 1,500 feet to the west of Blackwater Road's junction with High

Street (Route 9) and approximately 300 to 400 feet west-southwest of Maple Street Extension. The site and current site features are shown in more detail on Figure 2.

The approximately 26-acre waste disposal area (referred to as "the site" or "the '"andfill") is situated entirely on land owned by the City of Somersworth. The City has owned and managed the operation of the landfill since approximately the mid-1930's. At present, the City is a member of the Lamprey Regional Solid Waste Disposal Cooperative, which operates an incinerator in Durham, New Hampshire. Although the landfill is still active, it currently

Somersworth - May 22. 1989 - File No. D-5162 - Section 1 - Page 2

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accepts only those materials that cannot be incinerated, such as stumps, major household appliances, old furniture, leaves, brxish, etc. These materials are now disposed in the western portions of the landfill in an area known as the "stump dump." The

northwestern corner of the landfill appears currently inactive and materials disposed there are generally covered with a layer of sandy soil. Vehicle access to this portion of the landfill is gained through an entrance gate located on Blackwater Road approximately 2,100 feet to the west of its intersection with Maple Street Extension.

Approximately 10 acres of the easternmost portion of the landfill have been reclaimed as a city recreation area known as Forest Glade Park. This area presently includes tennis and basketball courts, two baseball fields, and a playground. Access to the park is

gained by a paved road which traverses the eastern end of the park extending from Blackwater Road to Maple Street Extension. A

portion of the site, immediately to the west of Forest Glade Park, appears to have been covered with a thin layer of topsoil underlain

by a fine sandy-silty clay that was reportedly intended to function as an "impermeable" cap. The terrain in this area remains fairly uneven and has a thin vegetative cover generally consisting of

weeds and grasses. A small stockpile of the "cap" material was observed in the northwestern portion of this area. Most of the

remainder of the landfill between Forest Glade Park and the stump dump has been covered with a sandy material and seeded.

The landfill and the City-owned property on which it is located are generally abutted by private undeveloped property to the north,

Blackwater Road to the south. National Guard Armory property, the City Fire Station and an apartment building to the east, and

Peter's Marsh Brook to the west. The westernmost reaches of the landfill do not extend to the Peter's Marsh Brook boundary but lie

within approximately 100 to 400 feet of it. As indicated on Figure 2, numerous residential properties are located within proximity of the site along Blackwater Road and the Maple Street Extension.

Other prominent features in the area include the Forest Glade Cemetery located approximately 200 feet to the north-northeast of the landfill, and two areas previously mined for sand and gravel, one which borders the landfill to the north, and a second located approximately 1,000 feet to the northwest.

The former Somersworth municipal supply well No. 3 is located approximately 2,300 feet to the north-northwest of the landfill as shown on Figure 2. Discussions with the Somersworth City Engineer indicate that this well is no longer in use and is currently being dismantled by the City. A second well, Somersworth municipal supply well No. 4, is located approximately 800 feet southwest of the landfill. Well No. 4 has never been used as a water supply source and, according to the City Engineer, there are no plans in 1987 to use it as a water supply source in the future.


I I / The surface of the landfill was observed to slope gently from a

point of highest elevation (approximately 218 ft. MSL) near the I northeast comer of the recreation area toward the site's southern

and western boundaries. Within the recreation area, topographic relief is approximately 10 feet; the elevation of the area in which the playground is located is approximately 215 feet Mean Sea Level (MSL), while the elevation within the park area adjacent to Blac]cwater Road is approximately 208 MSL.

From the eastern portions of the landfill the ground surface slopes gently downward toward the western portion of the site before reaching several sand mounds that lie along its western perimeter. The largest of these mounds lies in the northwestern comer of the site and has a high point of approximately 207 feet MSL. The area of lowest elevation within the site is situated along the west-central boundary. The elevation at this point is approximately 187 feet MSL. Topographic relief across the landfill is thus approximately 31 feet.

1.2.2 Remedial Investigation Study Area

The study area for the Remedial Investigation extends beyond the boundaries of the landfill to include important hydrogeologic features of the site. The Remedial Investigation study area extends to Blackwater Road to the south. Maple Street Extension to the east, the former Somersworth Municipal Supply Well No. 3 to the north, and to points approximately 200 to 300 feet west of Peter's Marsh Brook. Pursuant to the Remedial Investigation scope of work, while residential, recreational, municipal, and State (National Guard Armory) activities unrelated to the landfill have occurred within this area, the Remedial Investigation was focused on the landfill area.

1.2.3 Site History and Operations

The landfill originated as a burning dump in the northeast corner of the site that was probably used, according to local residents, as early as the mid-1930's. In that period, the site operations reportedly consisted of dumping the refuse in piles and burning the debris. Access to the burning dump was from an entrance road located off Maple Street Extension to the northeast of the site and from several dirt roads that entered from Blackwater Road.

In 1958 the operation was converted to a landfill, and open burning stopped. The landfill was intended for disposal of household trash, business refuse, and industrial wastes generated in the City of Somersworth. Landfill operations generally consisted of excavation of natural soils immediately beyond the limits of the working area and subsequent filling in of the excavated area with


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refuse. A tractor was then used to compact "the garbage and nibbish" and at the end of each day sand was "poured over the compacted rubbish, eliminating any health hazards and putting an end to the existence of rats" (Somersworth City Report, 1958). The sand cover was reportedly obtained from the original excavation.

Although expansion of the landfill occurred in a generally westerly direction, available information suggests that the growth of the landfill was somewhat Irregular. Refuse filling was apparently

extended first toward areas with available material for excavation and cover. Generally only one or two layers of refuse were placed in the working areas, reaching a maximum height above original

grade of approximately 20 feet. The exact areal and vertical limits of the refuse deposits are not known. For example,

discussions with City officials indicated that refuse may never have been placed within the southern, low-lying portion of the recreation area, or perhaps was placed there in considerably lesser thickness than within the northern portions of the site.

Sometime between 1962 and 1976, a garage was built in the southwest corner of the site and a formal entrance gate established.

Discussions with City of Somersworth officials indicate that the eastern portion of the site was not used for landfilling after

approximately 1975. At about that time the City acquired federal funds to assist in the financing of a recreation park. The City subsequently determined that, if the eastern portion of the

landfill was closed and covered, it would provide a suitable location for the park. As a result, landfilling activity within that portion of the site was phased out and preparations for the

construction of the park were initiated sometime around 1975.

By 1978 the eastern portion of the landfill had been covered with soil and seeded (CDM, 1983). Discussions with City officials indicated that the cover material provided for the construction of

the park consisted primarily of sand which was overlain by a thin layer of topsoil. This cover material was placed directly over the sandy materials which were used to cover the refuse during

landfilling. Construction of the recreation park was completed in late 1978 (letter from City Engineer to GZA, June 3, 1987). As use of the eastern portion of the site was phased out, landfilling activity in the western portion of the site increased, primarily within the northern half of that area. An aerial photograph dated July 31, 1981 suggests that in general by that date, landfilling operations had expanded westerly to the approximate current limits of the landfill (EPA, 1981). The adoption of the Hazardous Waste Management Act b^ the State of New Hampshire in July 1979 effectively banned the disposal of industrial wastes at the site. Prior to that time, it was permissible to dispose of many industrial wastes at the landfill (CDM, 1983). Sometime in 1980-1981, the City decided to terminate landfill operations and participate in the Lamprey Regional Solid


I Waste Cooperative. To that end, in approximately April 1981, a

t private contractor began collecting the City's solid waste and transporting it to the Cooperative's incinerator in Durham, New Hampshire (letter from City Engineer to Waste Management Division, 1981).

To close the landfill (in compliance with New Hampshire Waste Management Division (WMD) regulations governing solid waste disposal), the City was required to prepare a site closure plan. That plan was submitted by the City to the WMD in a letter dated June 18, 1981. In accordance with State approved guidelines, the plan included the installation of four monitoring wells around the site; regular, periodic monitoring of groundwater and surface water quality; and the construction of an erosion resistant, domed, "impervious" cover on the landfill to limit precipitation from permeating the refuse. Coincident with the submittal of the site closure plan, the City requested, and was granted, permission to continue their stump dump operation in the western portion of the site.

The implementation of the closure plan began in June 1981 with the construction of four monitoring wells at the site by Soil Exploration Corporation of Stow, Massachusetts. The locations of these monitoring wells, which were installed near the site's northern and western boundaries, are shown on Figure 2 and labeled with the prefix "MW-." Logs of the monitoring well test borings are included in Appendix F.

At approximately the same time, the City began construction of a cap over a portion of the landfill located along the northern side of the site to the west of the recreation area. Material for this cap consisted of a "sandy silt clay containing a minimum of 15 percent passing a 200 sieve" obtained from a site in Rollingsford, New Hampshire (letter from City of Somersworth to WMD, 1981) . This material was reportedly approved by the WMD as suitable cover material. An area of approximately 350 feet by 400 feet along that northern portion of the site was covered with an approximately 1to 2-foot thickness of this material. Construction of the cover was discontinued with the verbal approval of the WMD when the site was placed on the US EPA's Interim List of 418 top-priority disposal sites (personal communication with Somersworth City Engineer, May 27, 1987).

1.2.4 Previous Site Investigations

Data concerning the site were accumulated by several investigators including Soil Exploration Corporation; the Mitre Corporation; Ecology and Environment, Inc.; Camp, Dresser & McKee, Inc. (CDM) ; and the US EPA. Data collected from these previous investigations are summarized below.


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' / Soil Exploration Comoration Data

Soil Exploration Corporation conducted a subsurface exploration program under contract to the City of Somersworth in June 1981. This program included the installation of four groundwater monitoring wells around the landfill. These wells were designated as MW-1 through MW-4 and are shown on Figure 2. The boring and well installation logs are provided in Appendix F.

Ecoloov and Environment. Inc. Data

Documents prepared by Ecology and Environment, Inc. (E&E) concerning the site include:

i . Potential Hazardous Waste Site Identification and Preliminary ! Assessment (April 29, 1982).

Potential Hazardous Waste Site Inspection Report (July 26, I 1982).

Hazard Ranking System Form and Documentation Records ! (September 1982).

Camp. Dresser & McKee. Inc. (CDM) Data

In February 1983 CDM prepared a Remedial Action Master Plan (RAMP). That document was prepared from existing information in accordance with the intent of the National Contingency Plan (Federal Register Vol. 47, No. 137, July 16, 1982).

U.S. EPA Data

In February 1985 the US EPA prepared a report titled "Site Analysis, Somersworth Landfill, Somersworth, New Hampshire, Interim Report." That document was largely based on aerial photographs.

Mitre Corporation Data

Mitre Corporation conducted a telephone survey of industries in the Somersworth area to determine industrial waste quantities generated by these industries. These data are compiled in Mitre Corporation's 1978 report entitled "Solid Waste Management Alternatives for Dover and Somersworth, New Hampshire: Detailed Report."


• 1.3 HISTORICAL ASSESSMENT OF THE PROBLEM

1 This section provides a discussion of the nature and extent of the ^ problem as perceived prior to initiation of the Remedial

Investigation. This discussion is Included as a preface to evaluation of the Remedial Investigation data discussed in subsequent sections.

The landfill is situated adjacent to, and within approximately 400 feet of Peter's Marsh Brook. Previous investigators (CDM, 1983) have indicated that all surface runoff from both the active and inactive portions of the landfill eventually reaches Peter's Marsh

j Brook. This brook is a tributary of Tate's Brook which is in turn I a tributary of the Salmon Falls River. Both the City of

Somersworth, New Hampshire and neighboring Berwick, Maine withdraw water from the Salmon Falls Riiver for drinking water supply. The 1 Somersworth and Berwick intakes on the river are located approximately 1.5 miles to the north-northeast of the landfill.

j The landfill is also situated approximately 2,300 feet to the south ' of the City of Somersworth Municipal Supply Well No.3. Given the

landfill's proximity to these potential groundwater and surface J water receptors, concern existed that either the Somersworth i municipal supply well No. 3 or the Salmon Falls River may become

contaminated by leachate generated at the landfill, although contaminants attributable to the landfill had not been detected in these municipal water supplies. Somersworth municipal supply well

' No. 4, located approximately 800 feet southwest of the landfill, has not been used as a municipal water supply source primarily due

J to insufficient yield, and therefore there was apparently less ' concern about potential contamination of this well.

Although there are no records of the amount or types of wastes I dumped at the Somersworth landfill (CDM, 1983), it is likely that

prior to the adoption of the Hazardous Waste Management Act in 1979, local industries in the Somersworth area disposed some or

I all of their hazardous wastes at the site. Local industries in • the Somersworth area include tanneries, bleacheries, shoe

manufacturers, and metal finishing companies.

Water quality samples were obtained from the aforementioned monitoring wells MW-1 through MW-4 by the City of Somersworth during the period from July 1981 to December 1982. Chemical analyses performed on these samples by Peck Environmental Laboratory, Inc. of Hampton Falls, New Hampshire indicated that numerous volatile organic compounds (VOCs) including carbon tetrachloride, ethyl benzene, toluene, 1,2-trans-dichloro-ethylene, trichloroethylene, and chloroform were present in the groundwater beneath the site. The highest concentrations of VOCs were detected in the groundwater samples obtained from monitoring well MW-2, which is located within the landfill, and monitoring well MW-


I 1. 4, which is located immediately to the west of the landfill, near

Peter's Marsh Brook. In addition to the samples obtained from these monitoring wells, water samples were obtained and analyzed I from the City of Somersworth municipal water supply well No.3 and a culvert located near the cemetery situated to the northeast of the site. VOCs were not detected at either of these locations (CDM, 1983). I Field investigations performed by Ecology and Environment, Inc. for the US EPA in April 1982 indicated the presence of carbon I tetrachloride, toluene, and ethyl benzene in samples obtained from the aforementioned MW-series monitoring wells (E&E, 1984). In July 1982, Ecology and Environment obtained surface water samples from areas located to the north and west of the site. In the analyses of these samples for VOCs, Ecology and Environment tentatively identified chloroform and toluene in two of the samples taken from an area located to the north of the site (E&E, 1982).


2.0 SITE FEATURES INVESTIGATION

These subsections discuss prominent site features. This information is based on a review of previous studies, published literature, and a site reconnaissance.

2.1 DEMOGRAPHIC SETTING

The Somersworth Municipal Landfill is located in a generally urban setting on the outskirts of the City of Somersworth. The site is situated approximately one mile to the southwest of the City proper. "New Hampshire Population Projections," published in 1985 by the New Hampshire Office of State Planning, suggests that the current population of Somersworth is approximately 11,400. The population of Berwick, Maine, situated immediately to the north of Somersworth across the Salmon Falls River, is approximately 4,150 (Citation World Atlas, 1982). Demographic details of the Study Area are discussed in Section 8.0, as part of the risk assessment performed for this study.

2.2 LAND USE

Numerous residential properties are located to the north, south, and east of the subject site along Maple Street Extension, Blackwater Road, and High Street, respectively. The General Linen Service Company is located approximately 1,500 feet to the east of the site at the intersection of Blackwater Road and High Street (Route 9) . Conversations with the operations manager of the General Linen Service Company on November 21, 1986 indicate that no dry cleaning operations have occurred at this site for approximately five years, and that the facility is currently only used as a depot.

Properties abutting the site to the east include an apartment building, the City Fire Station, and a National Guard Armory• From conversations on November 21, 1986 with Armory personnel, the project team understands that five underground storage tanks are located on the National Guard Armory property. Four of these tanks are reportedly in use as of that date, including one 2,500-gallon heating oil tank, one 2,000-gallon heating oil tank, and two 2,000gallon gasoline tanks. Another 2,000-gallon heating oil tank was abandoned in about 1975; however, the remaining oil was reportedly never removed (personal communication with Armory Personnel, 1986). Ages of these tanks were estimated by Armory personnel to be between 12 and 30 years. Additionally, waste oils, antifreeze, solvents, and battery acid are also stored on the property. A floor drain in the maintenance building of the Armory complex reportedly discharges wash water and detergent from a pressure cleaner into a dry well. This dry well is located to the west of


the armory complex, approximately a few hundred feet from the original southeast corner of Somersworth Municipal Landfill.

An automobile salvage/scrap metal yard was observed behind one of the homes along the south side of Blackwater Road due south of the landfill. Aerial photographs indicate that the salvage yard has been in operation since before 1962. An aerial photograph dated 1953 suggests that this area may have been mined for sand and gravel during the early 1950's. Project team personnel have observed from the adjacent property that junk automobiles including detached tires and batteries, as well as other metal debris including several empty drums were on this approximately 1-acre site in 1987.

To the southwest of the site lies an undeveloped area that is comprised largely of wetlands surrounding Peter's Marsh Brook. The Somersworth municipal supply well No. 4 is situated within this area, located approximately 800 feet to the southwest of the landfill. Discussions with Somersworth City officials indicate that this well was never used for supply purposes due to problems with its construction, low yield, and subsequent vandalism. No use of this well is planned in the future.

Peter's Marsh Brook lies to the west of the site and flows in a general northwest direction within the study area. Peter's Marsh Brook is a tributary of Tate's Brook which is in turn a tributary of the Salmon Falls River. The confluence of Tate's Brook and the Salmon Falls River occurs approximately 1.7 miles due north of the site. Approximately 0.5 miles downstream (southeast) from this confluence is where the Cities of Somersworth and neighboring Berwick, Maine withdraw water from the Salmon Falls River for drinking water supply.

The Forest Glade Cemetery is located directly north of the site on the west side of Maple Street Extension. This property is comprised of gently sloping terrain to the west with topographic relief from approximately 225 to 190 feet (MSL).

Directly north of the landfill just west of the Forest Glade Cemetery, exists a sand and gravel mining area which is owned and operated by Mr. Turcotte and T&S Construction of Somersworth, New Hampshire. A somewhat larger sand and gravel mining area comprised of approximately 10 acres of land exists approximately 1,500 feet to the north of the Icindfill. This property is owned by Mr. Rouleau, also of Somersworth.

The former Somersworth municipal supply well No.3 exists north of Rouleau's sand pit, approximately 2,300 feet to the north-northwest of the site. Discussions with City officials indicate that prior to 1984 when well No.3 was decommissioned, the well supplied approximately 10 percent of the City's total water supply, and was


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mainly used during periods of peak water demand. Water from the well was reportedly high in iron and manganese content throughout its history, and the expense of treatment was a major contributing factor in the decision to decommission it. While in operation, well No.3 was reportedly pumped at a maximum possible rate of approximately 140 gallons per minute (gpm) , well below its original projected yield of approximately 400 gpm (personal communication. City of Somersworth Engineer, 1986). With additional concerns regarding possible contamination from the landfill, the City decided to abandon well No. 3, and in 1987 was in the process of dismantling it.

2.3 CLIMATOLOGY

The average monthly temperatures and rainfall amounts for Durham, New Hampshire for the period 1951 to 1980 are shown below. Durham is located approximately 8.5 miles southwest of the City of Somersworth and represents the nearest climatic data station of the National Climatic Data Center from which these data were obtained.

Temperature Precipitation Month (degrees J:I finches1

January 23.1 3.51 February 25.4 3.12 March 34.1 3.66 April 45.2 3.80 May 55.5 3.57 June 64.8 3.00 July 70.1 3.00 August 68.1 3.31 September 60.5 3.37 October 50.1 3.91 November 39.4 4.70 December 27.3 4.28

Precipitation minimums typically occur in June and July. Although the area is subject to frequent convective (thunderstorm) activity during the summer months, this activity is sporadic and does not play a significant role in yearly precipitation totals (Storm Records Center, 1987). Conversely, two major storm tracks affect New England weather during the fall, winter and early spring months and are the dominant factors in the regional precipitation pattern. The greatest monthly precipitation typically occurs in November and is nearly one inch greater than the greatest monthly total occurring during the spring months. Annual snowfall in the region averages about 50 inches (Bradley, 1964).


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The average annual temperature at Durham is approximately 47 degrees Fahrenheit ("F) . January is the coldest month with an the average annual temperature of approximately 23°F, whereas July is the warmest month with has an average temperature of 70''F.

Located within the middle latitudes of the northeast coastal region, the site lies within the influence of constant conflicts between cold, dry air masses flowing out of the subpolar region to the northwest and the warm, moist, tropical marine air masses from the south. Frequently warm, moist air masses are forced aloft over wedges of relatively dry, continental air, resulting in rain, snow or cloudiness. Under the influence of the prevailing westerlies, weather disturbances and storms in New England usually move northeastward, and are followed by several days of clear, fair weather characterized by warm southwesterly winds in the summer and cold northwesterly winds in the winter (Bradley, 1964).

Comparison of average monthly precipitation figures with average monthly temperatures indicates that groundwater recharge peaks in the spring months due to the melting of snow accumulated during the winter months. Similarly, larger than average groundwater recharge typically occurs during the fall as precipitation increases and evapotranspiration decreases.

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3.0 HAZARDOUS SUBSTANCES SURVEY

The following section presents the available information concerning the types and quantities of wastes that nay have been deposited within the landfill. The information discussed below is not derived from records of the types or quantities of wastes which were deposited in the Somersworth landfill. No such records, in any form, are known to exist. Because data are not available concerning materials known to have been disposed of in the landfill, no attempts have been made to quantify the wastes present at the site. A limited amount of information is available concerning the annual rates of generation of some wastes which were probably disposed of in the landfill. This information pertains only to certain years, however, and to infer rates of waste generation during other years based on these data would be highly speculative. In addition, many gaps exist in these data and the Information is considered to be wholly insufficient to allow any useful or meaningful estimate of the quantities of wastes that may be present at the site.

Wastes that have been accepted and deposited within the Somersworth Municipal Landfill Include solids and liquids from both domestic and industrial sources. Wastes were burned and/or landfilled on-site. After the open burning phase of operations, which occurred from approximately the mid-1930's to 1958, wastes were generally placed using a fill and cover method of landfilling that began in the northeastern portion of the site and generally expanded in westerly and southerly directions. Since approximately 1981, the landfill has accepted only those wastes not suitable for incineration, such as stumps, construction debris, household appliances, and brush. The greatest thickness of wastes is believed to occur within the northeastern portion of the site where refuse has been placed and compacted to a thickness of approximately 20 feet.

The Strafford Regional Planning Commission has conducted several telephone surveys of industries in the Somersworth area to determine industrial waste quantities and composition. The information obtained in these surveys as compiled by the Mitre Corporation in their 1978 report entitled "Solid Waste Management Alternatives for Dover and Somersworth, New Hampshire: Detailed Report." Results of these surveys indicate that the industrial wastes consist primarily of paper and plastic, with lesser amounts of wood, rags, leather, etc. Industries that produce significant quantities of metal scrap reportedly either recycle those materials themselves or sell it to a scrap dealer. The telephone survey identified only one industry which acknowledges the disposal of chemical wastes at the landfill. Reported quantities were on the order of eighty 35-gallon drums per week.


I I ' ' The types of chemicals disposed of were not reported.

I V. Information about the wastes present within the landfill also may i be Inferred from an analysis of the observed contamination

emanating from the landfill. In the case of an uncontrolled waste site such as this one, a study of the contaminants Icnown to be emerging from the site would In fact, appear to be the most significant concern. For this reason toxicity, bloaccumulatlon, persistence, transformation characteristics, mobility, and other pertinent characteristics of the wastes are discussed In Section

! 8.0.

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4.0 HYDROGEOLOGIC INVESTIGATION PROGRAM

A two-phase field exploration and testing program was conducted as part of the Remedial Investigation. Phase I explorations were

conducted in June 1985. Following an evaluation period. Phase II explorations were initiated in October 1986 and completed In November 1986. The primary goals of the field exploration and

testing programs were to obtain data for analyses which would:

1. Define the hydrogeologic regime in and around the site study area including estimation of the areal and vertical extent of unconsolidated soil deposits, the nature and sxibsurface topography of bedrock, groundwater conditions, and the hydraulic properties of unconsolidated deposits and bedrock;

2. Identify pathways of contaminant migration; and

3. Characterize the nature and extent of contaminant migration patterns from the former Somersworth landfill refuse disposal area.

Programs designed and implemented by the project team to obtain these data included:

1. A geologic reconnaissance and fracture trace analysis conducted within the vicinity of the site study area;

2. A limited residential water well survey of residences located along Blackwater Road and Maple Street Extension and elsewhere in the vicinity of the site;

3. Geophysical explorations consisting of seismic refraction, total field magnetometer, electromagnetic, and electrical resistivity surveys;

4. Excavation of 16 test pits within and around the limits of the landfill with installation of observation wells in 10 of the test pits;

5. Drilling of 27 test borings at 13 test boring cluster locations which included soil sampling and preliminary volatile organics screening;

6. Installation of groundwater monitoring wells within all test borings;

7. In-situ hydraulic conductivity tests within selected boreholes drilled into the overburden soils and bedrock;

8. Laboratory grain size and cation exchange analyses performed on selected soil samples;


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9. Installation of 11 surface water stations and near-surface well points hereinafter collectively referred to as surface

water stations;

10. Measurement of groundwater elevations In 10 test pit observation wells, 27 monitoring wells Installed as part of this Remedial Investigation, 4 monitoring wells installed previously, and measurement of surface water elevations at 11 surface water stations;

11. Soil and sediment sampling and analyses for chemical contaminants at selected soil test borings and surface water stations;

12. Groundwater sampling from 27 monitoring wells Installed as part of this Remedial Investigation, 4 monitoring wells previously installed in the site study area, selected residential wells, and the former Somersworth municipal supply well No. 3 for chemical contaminant analyses; and

13. A qualitative air monitoring program conducted during and after the hydrogeologic field exploration phase of the project.

The following subsections describe each of these programs in more detail with the exception of the air monitoring program which is discussed in Section 6.0. The programs described below were

conducted in a manner which generally meet or exceed the requirements of the Investigation Work Plan for this project.

4.1 GEOLOGIC RECONNAISSANCE AND FRACTURE TRACE ANALYSIS

GZA completed a geologic reconnaissance and fracture trace analysis (reconnaissance-level) to assess prominent bedrock fracture patterns in the vicinity of the Somersworth landfill as part of the Remedial Investigation. The objective of the geologic reconnaissance and fracture trace analysis was to Identify major lineaments crossing the landfill site. Such lineaments could represent zones of preferential groundwater flow in bedrock and, as such, may represent pathways for preferential contaminant migration from the site.

4.1.1 Geologic Reconnaissance

The location of the Somersworth landfill proper on relatively thick stratified sands and gravels limited observation of bedrock, and therefore precluded execution of a detailed bedrock geologic reconnaissance of the study area. The only observed outcrops in close proximity to the subject site were a small outcrop observed


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off Knox Lane in Berwick, Maine, and a series of outcrops within the bed of the Cocheco River near the hydroelectric power station

on Watson Road in Dover, New Hampshire. Fault and brittle fracture data were collected from these outcrop localities by GZA during the

Phase I explorations in 1985. The field mapping was carried out to determine the fundamental fracture fabric on the study area and

to provide a data base for correlation with the photollneament/fracture trace analysis. Detailed descriptions of bedrock llthologies and structure are presented in Section 5.1.3, and in Appendix B.

4.1.2 Fracture Trace Analysis

Remote sensing was used to perform a fracture trace analysis for the Somersworth landfill and its environs. The remote sensing analysis was based upon review of base Information at several different map scales. Topographic lineaments were Inferred from USGS topographic maps at a scale of 1:62,500 (Dover 15' and Berwick, ME-NH 15' quadrangles) and at a scale of 1:24,000 (Dover East and Dover West 7.5' quadrangles). Tonal and/or textural lineaments were Inferred from high altitude color Infrared (CIR) photography (September 1973) at a scale of approximately 1:62,500.

Lineament overlays were prepared for each of the above sets of base information. Lineaments were then classified relative to their orientation to magnetic north. Lineaments are shown on Figures B2 and B-3 of the fracture trace analysis report Included as Appendix B.

4.2 RESIDENTIAL WELL SURVEY

During the course of the Remedial Investigation, the project team conducted a residential well survey to identify the number of domestic drinking water wells in the study area. While the majority of homes in the area are connected to the City of Somersworth municipal water supply system, a limited number of residents in the general area also have private domestic wells. A summary of the number, locations, and owners of these wells is Included in Appendix C.

4.3 GEOPHYSICAL EXPLORATIONS

A two-phase geophysical investigation v as conducted at the Somersworth landfill as part of the Remedial Investigation by Weston Geophysical Corporation of Westboro, Massachusetts. Phase I geophysical Investigations were conducted in December 1984 and Included seismic refraction, electrical resistivity, electromagnetic terrain conductivity, and magnetic surveys.


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The Phase I investigations were designed to collect information about the geology and hydrogeology of the site and to determine, to the extent possible, the extent of contaminant migration. The Phase II geophysical investigations, conducted in May 1985 and August 1986 and Included seismic refraction and electromagnetic terrain conductivity surveys. These investigations were generally performed in order to refine data obtained during the first phase of the geophysical investigation, particularly in regard to the extent of contaminant migration from the landfill.

The final geophysical report, which describes methods, locations, data, and interpretations of the data, is Included In Appendix H. A summary of the individual methodologies of the progreun is provided below.

4.3.1 Seismic Refraction Survev

The seismic refraction survey conducted during Phase I of the geophysical explorations was used to estimate depths to geological interfaces, to identify general classes of overburden materials, and to identify the possible presence and extent of fracture zones in the bedrock. Seismic refraction survey data regarding depths to various geologic interfaces was used to supplement and verify similar Information obtained from the test boring explorations.

Seismic refraction data were obtained with an analog data acquisition system utilizing spread lengths of 400 feet with 10and 20-foot geophone spacings and 600 feet with 15- and 30-foot geophone spacings. Travel time measurements made at each geophone location were used to determine the compressional (P) wave velocities and evaluate subsurface layering in terms of depths and velocities. A total of 9,020 linear feet of seismic refraction profiling data were obtained along 12 lines encircling the landfill. Locations of the seismic lines are shown on Figure 2 of the geophysical report.

4.3.2 Electromagnetic Survey

The objective of the electromagnetic terrain conductivity (EM) survey was to identify possible zones of high conductivity within the subsurface surrounding the landfill. Highly conductive areas are believed to be indicative of contaminated groundwater and/or the presence of clay layers, and thus this technique may assist in definition of the contaminant plume.

The EM survey was conducted with EM-31 and EM-34 non-contacting terrain conductivity meters. The conductivity meter has a self-contained dipole transmitter which generates an electromagnetic source field in the earth. A self-contained dipole receiver


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detects a secondary electromagnetic field which is linearly related to the terrain conductivity. EM-31 conductivity measurements are continuous and recorded on a chart recorder. EM-34 conductivity measurements were made In the horizontal and vertical dipole modes with 20-meter coll spacings and 25- to 50-foot station spacings. A total of 15,815 feet of electromagnetic terrain conductivity profiling data were obtained along a minimum of 9 survey lines as part of the Phase I and Phase II geophysical explorations. Locations of the EM lines are shown on Figure 2 of the geophysical report.

4.3.3 Magnetometer Survev

The magnetometer survey was used to develop a magnetic intensity contour map of the landfill area. Once the regional magnetic signature of the study area is filtered from the acquired data, residual positive magnetic anomalies may Indicate the locations of buried metallic objects such as may Include metal containers or drums, and therefore, may suggest areas where hazardous wastes could have been landfilled.

The magnetic survey utilized a model G-816 proton procession land magnetometer. Magnetic readings were obtained at 10-foot station spacings along parallel survey lines spaced 100 feet apart. A total of 5,380 linear feet of magnetic profiling data were obtained along 9 parallel survey lines across the landfill. Locations of the magnetic lines are shown on Figure 7 of the geophysical report.

4.3.4 Electrical Resistivitv Survev

Electrical resistivity soundings (point tests) were conducted to characterize the stratigraphic arrangement of overburden materials. Sounding data supplement the seismic refraction and EM data by providing depths and thicknesses of relatively resistive and non-resistive layers.

Electrical resistivity measurements were made utilizing vertical electrical sounding procedures. Vertical electrical sounding measurements are made by expanding the electrode array away from a central point. The measured resistivity values are apparent since they represent the average resistivity of the various layers within a half-space whose dimensions are defined by the electrode separation. As the electrode or "A" spacing increases, the effective depth of penetration increase;S. The resulting plot of apparent resistivity values versus electrode spacing therefore Indicates the variation of resistivity with depth. The Lee modification of the Wenner electrode configuration was used for point test measurements. A total of 4 electrical resistivity point tests were performed at various locations around the perimeter of

Somersworth - Mav 22. 1989 - File No. D-5162 - Section 4 - Page ^

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the landfill during the Phase I geophysical explorations. These r tests are Identified as PT-1 through PT-4 and their locations are shown on Figure 2 of the geophysical report.

4.4 TEST PIT EXPLORATIONS

Sixteen test pits were excavated within the site study area as part of the Phase I exploration program. Twelve test pits were excavated within the landfill boundary (TP-4, TP-5, TP-6, TP-8, TP-9, TP-10, and A-1 through A-6). All test pits were excavated utilizing a track-mounted Caterpillar 235 backhoe. The purpose of excavating test pits TP-1 through TP-10 was to observe near surface conditions in and around the refuse disposal area. Test pits A-1 through A-6 were excavated at locations within the refuse disposal area identified as having positive magnetic anomalies by geophysical survey. The purpose was to explore the possibility of a subsurface cache of drums. The backhoe and other heavy construction equipment were supplied and operated by personnel from Midway Excavators, Inc. of Hampton, New Hampshire. Test pits were observed and logged by Wehran personnel. Logs of the test pits are Included in Appendix E.

Test pits TP-1 through TP-10 were located by Wehran's field survey crew using a transit and tape. Test pits A-1 through A-6 were

( located by Wehran's test pit observer using taped distances from ^ staked and flagged magnetic survey stations. Locations of the test

pits are shown on Figure 2.

Prior to backfilling the test pits, excavated soil and refuse were field screened for the presence of volatile organic compounds (VOCs) with a Photovac Tip photoionization detector. An explanation of field screening procedures is included in Section 4.10. Results of the field screening are included on the test pit logs. In addition to the field screening, soil samples were obtained from 8 selected test pits (TP-5 through TP-10, A-5, and A-6) for laboratory chemical analyses. The depths, conditions, chemical analyses, and other detailed information are docvimented on the test pit logs (Appendix F). Results of the chemical analyses are included in Appendix I.

Observation wells were installed within test pits TP-1 through TP10 for the purpose of observing groundwater elevations. The observation wells were constructed utilizing a 2-foot long porous polyolefin (Vyon) tube connected to a 1-inch diameter polyvinyl chloride (PVC) riser pipe within the general backfill to the test pit. Test pit observation well installation details are Included on the test pit logs.


f. 4.5 TEST BORINGS

Test borings were performed using truck-mounted drill rigs at a total of 13 separate test boring cluster locations in the site study area during the Phase I and Phase II field programs. The test borings were drilled to observe soil, bedrock, and groundwater conditions below the ground surface. A test boring cluster consists of a group of several individual test borings designed to allow the installation of groundwater monitoring wells at discrete elevations at a single location.

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Test borings B-1 through B-4 and test boring clusters B-5 through B-7 were performed as part of the Phase I exploration program in June 1985 and Included the drilling of 11 borings. Test boring clusters B-8 through B-13 weire performed as part of the Phase II exploration program from October 1986 to November 1986, and Included the drilling of 16 borings. All test borings were } observed and logged by a GZA representative. Locations of the test borings are included on Figure 2. Logs of the test borings are included in Appendix D.

j 4.5.1 Drilling Procedures

! Test borings were advanced through overburden soils with both ( 4-lnch (HW) and 3-inch (NW) Inside diameter (I.D.) casing using

standard drive and wash techniques. The HW casing was advanced 1 through upper granular soils into any existing clayey strata whereupon NW casing was telescoped through the HW casing to advance the test borings to deeper levels and bedrock. Where clayey strata I was not encountered, as was the case for most borings, HW casing was advanced to refusal. Drilling fluid was not recirculated in any of the test borings. Water for drilling and borehole testing operations was obtained both from the City of Dover and Somersworth I municipal water supply system.

To limit the potential for cross-contamination, between boring I locations the drill rigs and their associated equipment were moved to a designated on-site decontamination area. There they were cleaned with water and rinsed with methanol prior to the initiation t of the drilling program and before moving to each new boring location. This procedure was also implemented at the end of the Phase I and Phase II exploration programs.

4.5.2 Soil Sampling

\ Soil samples were obtained at 5-foot intervals within the first borehole drilled (R- or L- designation) at each test boring

. cluster location. Sampling within companion boreholes at each I cluster location was generally limited to samples of granular soils


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at in-situ hydraulic conductivity test Intervals. Samples were recovered using a 1-3/8-lnch ID split-spoon sampler driven 18 to

24 inches with a 140-pound weight falling 30 Inches. The number of blows required to drive the seunpler each 6-lnch Increment was recorded and is shown on the boring logs. The number of blows required to drive the sampler from 6 to 18 Inches from the point of penetration is termed the Standard Penetration Resistance (also referred to as the Standard Penetration Test N-value, or SPT N-value) of the soil and is an Index measure of soil density and consistency. The split-spoon sampler was washed with clean water and rinsed with methanol after each sample was taken to limit the potential for cross-contamination of soil samples.

Soil samples were visually classified and logged in the field by a GZA representative and then sealed in 8-ounce glass jars with Teflon-lined caps. Soils were classified using the nomenclature of the Burmister system of soils classification. A summary of the Burmister classification system is enclosed with the test boring logs in Appendix D.

4-?.? Bedrock Drilling and Sampling

Bedrock was cored to a depth of approximately 30 feet below the bedrock surface at test boring cluster locations B-5 through

B-9 and B-11 through B-13. Confirmatory 5-foot bedrock cores were obtained from each of the L-serles test borings during the Phase

I drilling program. Confirmatory 5-foot bedrock cores were obtained from L-series test borings only at the clusters in which R-series test borings were not performed during the Phase II explorations. Rock cores were obtained using a doiible tiibe, NX-size (3-inch O.D.) core barrel fitted with a diamond drill bit. Coring was initiated after the borehole was advanced to "refusal" conditions and the casing was seated into rock. The Rock Quality Designation (RQD) was determined for each bedrock core sample run upon recovery of the sample. RQD is a standard index of rock condition and is defined as the summation of all pieces of core greater than 4 inches in length divided by the total length of the core run, expressed as a percentage. RQD values are indicated on the appropriate boring logs in Appendix D. A summary of the method used for the classification of bedrock cores, including a table of RQD percentages and corresponding diagnostic descriptions, is enclosed with the test boring logs in Appendix D.

4.6 GROUNDWATER MONITORING WELL INSTALLATIONS

During Phase I and Phase II of the exploration program, multi-level monitoring well clusters were constructed at locations B-5 through B-13 by installing PVC wells within closely spaced Boreholes. At monitoring clusters B-5 and B-8, a "U" suffix after the test


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c boring/well number indicates that the monitoring well was placed In granular soils geologically overlying clayey strata. Similarly, the "L" suffix at clusters B-5 and B-8 indicates that the monitoring well was placed in granular soils geologically underlying the clayey strata. The "L" designation at all other test borings, however. Indicates the placement of a fully penetrating monitoring well within the overburden aquifer materials at these locations. An **R" suffix denotes monitoring wells placed within the upper 30 feet of bedrock. Water table monitoring wells were Installed at test boring locations B-8, B-9, B-10, and B-13 as part of the Phase II explorations. These wells, given a "WT-" designation, were designed to Intercept the uppermost portions of the water table.

WT-serles monitoring wells were typically screened from aibove the observed groundwater level to a depth of approximately 10 feet. The two U-Series monitoring wells at cluster locations B-5 and B8 were screened from above the observed groundwater level to approximately 6 to 12 inches into the aforementioned clayey strata. The two corresponding L-series wells at these cluster locations were screened from just above the bottom of the clay to the top of bedrock. All other L-Series wells were typically screened from above the observed groundwater level to the top of bedrock. Bedrock wells (R-series) were generally screened from approximately 2 to 4 feet below the weathered zone, as estimated in the field

^ from in-situ bedrock pressure testing, to the bottom of the core hole. Screen lengths within bedrock wells were typically about 20 feet.

Monitoring wells were constructed of 1-1/2-inch Schedule 80 threaded PVC pipe; no PVC glues or solvents were employed in the assembly of the pipe sections. Well screens were constructed of 0.01-inch machine slotted sections of PVC. Solid PVC riser pipe was installed above the screened interval. The annulus between the borehole wall and the well screen was backfilled with clean silica sand to approximately 2 feet above the top of the well screen. Cement/bentonite grout was subsequently used to backfill the annulus between the borehole wall and the solid PVC riser pipe to just below the ground surface. Where well screens were Installed near the ground surface (WT-serles wells), silica sand was placed around the well screen to approximately 6 inches above the screen, and a bentonite seal was constructed above the filter sand to the ground surface.

Concrete surface seals and locking protective casings were provided for each monitoring well. Installation details for well cluster locations B-1 through B-13 are included on the test boring logs in Appendix D.

Somersworth - May 22, 1989 - File No. D-5162 - Section 4 - Page 9

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4.7 IN-SITU HYDRAULIC CONDUCTIVITY TESTS

A program of borehole testing was conducted as part of the Remedial Investigation exploration program to obtain estimates of the hydraulic conductivity (permeability) of subsurface soils and bedrock encountered within the study area. The methods and procedures used to estimate hydraulic conductivity and the zones in which these tests were performed are briefly described.

4.7.1 In-situ Overburden Hydraulic Conductivitv Tests

In-situ falling head hydraulic conductivity tests were conducted within the more pervious portions of the overburden soils during the advancement of test borings drilled during the Phase I and Phase II explorations. These tests were generally performed within the L-series test borings at each well cluster location. A total of 15 in-situ hydraulic conductivity tests were performed within the overburden soils, at well cluster locations B-1 through B-7, and B-10 through B-13. Additional tests attempted at locations B-8, B-9, and B-11 could not be completed. Very dense soils, or sands flowing into the drill casing, or poor sample recoveries, or horizontal stratification within the samples precluded the acquisition of meaningful hydraulic conductivity data at these locations.

The in-situ overburden hydraulic conductivity tests were wick tests generally performed by introducing water into the borehole and monitoring the rate at which the water level in receded toward the initial static level. This rate was then converted to an effective hydraulic conductivity for horizontal flow using theoretical formulas developed by Hvorslev (Lambe and Whitman, 1979). A svxmmary of the results of the in-situ overburden hydraulic conductivity tests and analytical methods used is included in Table 4.

4.7.2 In-situ Bedrock Pressure Tests

The hydraulic conductivity of the upper 30 feet of bedrock was evaluated by performing bedrock pressure tests in the cored portions of all R-series test borings. Pressure testing was performed by isolating 5-foot lengths of the core hole using an 11-foot long, double-ended, inflatable rubber packer apparatus, and pumping water under pressure into the isolated rock zone. Relevant test data and the recorded flow into the rock zone were used, with the methods outlined in Groundwater Manual (1981), to estimate an effective hydraulic conductivity of the rock within that zone. Pressure test results were evaluated in the field and used to position the PVC well screen within the core hole.


Pressure testing was not performed within the 5-foot confirmatory . boreholes within the appropriate L-series borings as the packer

I - apparatus requires a minimum core length of 11 feet. Results of ^ the bedrock pressure tests are included in Table 4. Table 4 also

contains a description of the procedures, assumptions, and limitations of bedrock pressure testing.

I 4.8 LABORATORY SOILS TESTS

I Soil samples obtained from test borings were selected for laboratory analyses discussed in the following subsections. Results of all laboratory soils tests are Included in Appendix G.

I 4.8.1 Laboratory Soil Gradation Analyses

I I Laboratory soil gradation analyses were performed on soil

samples obtained from intervals where in-situ falling head hydraulic conductivity tests were performed. Gradation analyses were performed at GZA's soils laboratories in Manchester, New Hampshire and Newton, Massachusetts in accordance with applicable ASTM standards presented in Appendix G. Results are summarized

I graphically and are also included in Appendix G.

(^ The soil gradation analyses were performed primarily for a

I quantitative evaluation of the hydraulic conductivity of the

f granular overburden soil deposits using the Kozeny-Carman equation (Freeze and Cherry, 1979). Hydraulic conductivity estimates based on the Kozeny-Carman equation are presented in Table 5. An explanation of the Kozeny-Carman procedures, assumptions, and limitations is also included in Table 5.

1 4.8.2 Cation Exchange

Laboratory cation exchange analyses were performed on 4 selected soil samples by Arnold Greene Testing Laboratories of Natick, Massachusetts. The purpose of these analyses was to obtain information regarding the cation exchange capacity of major soil units observed in the site study area for possible correlation with ionic adsorption of chemical contaminants, primarily metals. Results of the cation exchange analyses are included in Appendix G.

4.9 SURFACE WATER STATIONS

Staff gauges were installed at 7 surface water stations, labeled S-1 through S-7, during Phase I of the exploration program. These surface water points were installed to provide locations for


obtaining surface water quality and elevation data. The staff ( gauges generally consist of sections of wooden 2x4's driven into v^ the groiind below the standing water. The elevations of these

gauges were later estedslished by Timothy A. Pare, Land Development Consultant, using standard differential leveling techniques.

Four additional surface water stations designated S-8 through S-11 were Installed during Phase II of the exploration program. Stations S-8, S-9, and S-10 consist of well points with a 3-foot long continuous-slot steel screen with steel riser pipe, hand-driven in areas where surface water was anticipated to be seasonal. Station S-11 consists of a staff gage driven into the bed of Peters Marsh Brook. The surface water stations Installed during Phase II were used to obtain surface and near surface water elevations only; no surface water samples were obtained at these locations. The elevations of stations S-8 through S-11 were also established by Timothy A. Pare, Land Development Consultant, using level survey techniques.

With the exception of surface water station S-7 which is located at the confluence of Tate's Brook and the Salmon Falls River, locations of the surface water stations are shown on Figure 2. Surface water elevations measured at these locations are provided in Table 3.

4.10 SOIL AND SEDIMENT SAMPLING AND ANALYSIS

Selected soil samples were obtained from test borings and test pits performed during the exploration program and analyzed to provide information about the areal and vertical extent of soil contamination in the study area. Additionally, sediment samples were collected from surface water stations located in Peters Marsh Brook. These samples were analyzed to provide information about the areal extent of contaminated surface water sediments.

Analyses performed on soil samples included routine field screening of all soil samples obtained from test borings and test pits for VOCs. Laboratory analyses performed on soil and sediment samples Included quantitative VOC analyses, metals analyses, acid and base/neutral extractable compound analyses, and pesticides and PCB's analyses.

Soil samples obtained for quantitative VOC analyses were collected in 40 milliliter glass vials with Teflon-lined caps. Soil samples obtained for metals analyses were collected in 4-ounce plast. c cups with plastic caps, and soil samples obtained for ABN and PCB/pesticide analyses were collected in 12-ounce glass jars. Soil samples for laboratory analyses were placed in an ice-filled cooler immediately upon collection and kept refrigerated until delivery to the analytical laboratory. Sample handling was performed in


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accordance with EPA approved "chain of custody" protocols as described in the Quality Assurance Project Plan (QAPP). Analyses of soil samples were performed by Cambridge Analytical Associates, Inc. (CAA) of Boston, Massachusetts, in accordance with procedures and protocols established in the QAPP. Soil sample containers were provided by CAA.

A summary of the type, location, and number of the chemical analyses performed on soil and sediment samples during the exploration program is provided in Table 6. Results of these analyses are enclosed in Appendix I. Particular aspects of this sampling program are discussed below.

Test Borings

Samples obtained from the test borings were collected from split-spoon samples generally recovered at 5-foot depth intervals as described previously in Section 4.5.2. To limit the potential for cross-contamination, the split-spoon sampler was decontaminated between samples in accordance with procedures outlined in the Remedial Investigation Plan. The sampler was initially washed and rinsed and placed in a clean location prior to each day's sampling activities. After each sampling attempt, the split-spoon was disassembled, scrubbed, and rinsed in water in order to remove any excess soil residue or gross contamination which may have collected on the spoon during sampling. The disassembled spoon was then sprayed with methanol, rinsed with clean water, reassembled, and placed in a clean location ready for the next sample.

GZA screened each soil sample recovered from the first test boring executed at each well cluster location for volatile organic compounds (VOCs) using an Analytical Instriiment Development, Inc. (AID) photoionization detector Model 580. The AID meter responds readily to most synthetic organic contaminants but does not register natural components of air, such as oxygen, nitrogen, carbon dioxide, or methane. The AID meter lower detection limit is approximately 1 part per million (ppm) referenced to a butadiene in air standard. The field screening procedure involved opening the split-spoon sampler as soon as it was retrieved from the borehole, halving the sample lengthwise, and parting the halves to an approximately 45 degree angle. The probe of the AID meter was then placed within this gap and the readings recorded. Results of VOC field screening of test borings are included on the test boring logs in Appendix D.

Non-cohesive soil samples from each split-spoon sample taken were obtained for quantitative VOC analyses as outlined in the QAPP. Samples from within the same boring were composited by CAA prior to analysis, thus providing an indication of soil contamination at each well cluster location. Results of these analyses are included in Appendix I.


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GZA also collected soil samples from the selected test borings and submitted these to a separate laboratory for VOC screening

analyses. These sauries were obtained from split-spoon samples considered representative of the overburden soils at each well

cluster location. Soil samples collected during the Phase I and Phase II exploration programs were analyzed by GZA's Newton, Massachusetts leiboratory, and by Eastern Analytical, Inc. of

Concord, New Hampshire, respectively. These analyses were performed to provide GZA with information regarding possible soil contamination at each well cluster location during each respective phase of drilling. This information was generally used as a

preliminary assessment of the vertical and areal extent of contamination within the study area. Results of these analyses are also included in Appendix I.

Separate samples of non-cohesive soils collected during the Phase I and Phase II drilling programs and composited in the field by GZA personnel were analyzed for acid and base/neutral extractable organic compounds (ABN's), polychlorinated biphenyls (PCB's) pesticides, and metals. These samples consisted of composites of all soil samples obtained from within each individual boring at predetermined locations as described in the Remedial Investigation Plan.

Sediment Sampling and Analyses

On August 9, 1985, CAA personnel collected sediment samples from surface water stations S-1 through S-8. Sediment samples were collected using a stainless steel scoop in accordance with procedures discussed in section 2.4.4 of the QAPP. One sample from each station was analyzed for VOCs. Sediment samples obtained at Stations S-1, S-4, and S-6 were also analyzed for metals, ABN's, and pesticides and PCB's.

Test Pit Sampling and Analyses

During the test pit exploration program, excavated soil and refuse from each test pit was screened using Photovac TIP photoionization detector. Soil samples from selected test pits were obtained based on the photoionization results and subjected to laboratory analyses. The TIP meter operates under the same principle as the AID meter described earlier in Section 4.10. The screening procedure generally Involved placement of the probe of the instrument within several inches of freshly excavated soil or refuse and recording the measurements on the test pit log. Results of VOC field screening of test pits are included on the test pit logs in Appendix F and discussed in Section 7.0.


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Soil samples obtained from the test pits were typically procured directly from the test pit walls or from soils excavated from the test pits. Sample containers appropriate to the type of analysis to be performed were filled using a clean metal spatula. Soil samples for laboratory VOC analyses were obtained from test pits TP-5 through TP-10, and A-6 during the test pit exploration program. Additional samples were obtained from test,pits TP-9 and A-5 and analyzed for metals, ABN's, and pesticides and PCB's.

4.11 GROUNDWATER AND SURFACE WATER SAMPLING AND ANALYSIS

During the period from approximately July 1985 to December 1986, several rounds of water sampling and analyses were performed by the NH WSPCD and CAA on completed groundwater monitoring wells, nearby residential wells, the Somerswoirth municipal supply well No. 3, and surface water sampling stations established during Phase I of the exploration program. The groundwater and surface water sampling and analytical program was designed to characterize the nature and distribution of groundwater and surface water contamination in the site study area.

Sampling and analysis of water samples for VOCs was performed by the NH WSPCD. Sampling and analysis of water samples for metals, ABN's, PCB's, and pesticides was performed by CAA. Discussions with the NH WSPCD and CAA indicated that groundwater and surface water samples were obtained and analyzed by the NH WSPCD and CAA in accordance with procedures and protocols established and documented in the QAPP.

A summary of the type, location, and number of chemical analyses performed on water samples during the Remedial Investigation is provided in Table 6. Results of these analyses are included in Appendix I.

Discussions with officials of the NH WSPCD indicate that field screening measurements of temperature, pH, and specific conductance were routinely made by NH WSPCD personnel during their water sampling program. Discussions with CAA Indicated that CAA's temperature, pH, and specific conductance measurements of groundwater and surface water samples were made at their laboratory in Boston, Massachusetts. A summary of the NH WSPCD's field screening results for temperature, pH, and specific conductance is provided in Appendix I.


c 5.0 SITE GEOLOGY AND HYDROLOGY

An understanding of the area's hydrogeologic setting is essential to an evaluation of the distribution and potential migration of

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contaminants. These subsections present an assessment of hydrogeologic conditions In the site study area.

5.1 SURFICIAL AND BEDROCK GEOLOGY

The geology of the Somersworth Municipal Landfill and surrounding area has been described in detail in a number of previous studies. The surficial geology of the New Hampshire seacoast region, which includes the Somersworth Municipal Landfill site, was mapped by Bradley (1964) as part of a USGS Water Supply paper. A discussion of ice-contact deposits of the Great Bay Region of New Hampshire with regard to a model of the deglaciation of the region was published by R.B. Moore (1982). Major structural features of the bedrock in the region have been described by Billings (1956) and Lyons et al (1986).

It is the intent of these subsections to describe the geology of the study area by combining the findings of previous studies with the geologic information obtained during this study. Sxibsurface profiles (located on Figure 2) representing generalized

stratigraphic relationships among the overburden deposits and bedrock are presented on Figures 3 through 5. Detailed descriptions of soil samples recovered during Phase I and Phase II explorations are included on the test boring logs presented in

Appendix D and test pit logs in Appendix E. Logs of MW-series test borings are included in Appendix F.

5.1.1 Bedrock Geology

The bedrock geology of the Somersworth Municipal Landfill site area and surrounding areas has been described in several previous studies. Major structural features of the bedrock in the region

have been described by Billings (1956) and most recently Lyons et al (1986). Novotony (1963) and (1969) described the bedrock

geology of the seacoast region of New Hampshire. Also, a detailed study of rocks comprising the Merrimack Trough in southeastern New Hampshire is provided by Bothner et al (1984). In addition to the review of this literature, GZA performed a reconnaissance-level fracture trace analysis which is included in Appendix B. A summary of important findings is presented below.


Tectonic Setting

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Southeastern New Hampshire is underlain by dominantly neta-sedlmentary rocks of the Merrimack Trough (Billings, 1956). On the new Preliminary Geologic Map of New Hampshire, Lyons et al (1986) assign these rocks Ordoviclan to Proterozoic Z ages based on isotopic age dates from the Massabessic Gneiss Complex (Fltchburg Pluton of Billings, 1956) and the Exeter Dlorite.

The Somersworth Landfill is underlain by rocks of the Bezrwick Formation, the structurally highest and youngest of the formations comprising the Merrimack Group as mapped by Billings (1956) and Lyons et al (1986). In a more detailed study on field relationships between the Berwick Formation and the Massabessic Gneiss, Bothner et al (1984) describe Berwick rocks as well bedded, laminated, purple-gray biotite granofels with calc-sllicate layers, stringers (discontinuous veinlets), and pods (pockets).

Bedrock Litholoaies

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GZA obtained approximately 270 feet of rock core during the subsurface explorations conducted as part of this study. The dominant rock type recovered consists of a moderately hard to hard, fresh to slightly weathered, light gray to purple-gray, fine to

medium-grained, micaceous sugar-textured quartzite to (juartzbiotite granofels. Biotite is the dominant sheet silicate within the rocks with lesser amounts of muscovite and chlorite observed. Feldspar was observed to be a minor constituent in some of the samples. Garnet was observed in isolated bedding planes; pyrrhotite or massive pyrite was observed to be an important accessory mineral.

Bedding was observed to range in thickness from approximately 2 to 10 centimeters (cm) and is generally parallel to the weakly developed foliation in the rocks. A characteristic feature of the rock observed within the study area are small-scale, generally foliation parallel, vein-quartz segregations that range in thickness from 1 millimeter to a few centimeters. They can locally comprise up to an estimated 40 percent of the rock. Actinolite is closely associated with the vein quartz and often the quartz completely surrounds lenticular actinolite clots. Typically the actinolite is fine-grained. Biotite clots are also locally present in these vein quartz segregations.

Another important lithology observed in core samples recovered from borings B-8R, B-llR, and B-13R consists of a medium, fresh to slightly weathered, light green-white, fine-grained calc-silicate. Characteristic mineralogy of these rocks consists of diopside, actinolite, epidote, plagioclase, calcite, and quartz.

Somersworth - May 22. 1989 - File No. D-5162 - Section 5 - Page 2 I

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within test boring B-12R, a moderately hard, fresh to moderately weathered, fine- to medium-grained basalt to diabase was

encountered from approximately 36 to 40 feet below the ground surface. These rocks were generally highly fractured with the fractures commonly coated with a thin veneer of calcite. The aforementioned quartzItes to granofels were observed both overlying and underlying this mafic dike.

Bedrock Structure

On a local scale, bedrock structural fabrics were difficult to assess due to the lack of outcrop in the study area. The only observed outcrops in close proximity to the subject site included a small outcrop observed off Knox Lane in Berwick, Maine, approximately 2 miles north-northeast of the subject site, and a series of outcrops within the bed of the Cocheco River near the hydroelectric power station on Watson Road in Dover, New Hampshire, approximately 3.2 miles southwest of the Somersworth Landfill. At the first locality, a pink-white, coarse-grained, two mica granite cut by numerous pegmatite veins was observed. A master joint set was observed to strike at approximately 060 degrees with steep northwesterly dips. These joints were observed to be spaced at approximate 2-foot intervals and to often contain epidote slickenside striae. A secondary joint set was observed to be approximately oriented at 305 degrees with steep directionally

variable dips.

Outcrops of the meta-sedimentary Berwick Formation were observed at the aforementioned hydroelectric station on Watson Road. At this location, foliation was observed to strike 075 degrees and dip 26 degrees to the north. Dominant fracture orientations were measured at 043 degrees and 306 degrees with steep dips.

Structural data obtained at the outcrop level is limited due to the lack of exposure within the subject site area. Consec[uently, correlation of outcrop data to lineament analysis is tenuous at best. Observations made, however, do support a strong northeast preferential orientation of bedding planes, secondary foliation, and fractures (joints). In addition, a minor to perhaps major northwest orientation of joints and late (i.e., geologically insignificant but possibly hydrologically significant) brittle faults was also identified. This orientation was observed for several small scale faults located within the series of outcrops at the aforementioned hydroelectric station.

Structural observations from rock core recovered from sxibsurface explorations were limited due to the nature of rock core Itself. In general, bedding parallel foliation and younging direction reversals indicate that an episode of isoclinal folding has affected the rocks. Fracture morphology within the rock cores is discussed in the next section.


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Based on data collected as part of the fracture trace analysis (Appendix B), bedding and foliation planes within the bedrock underlying the site likely strike to the northeast. Although

limited, field data confirmed the presence of a primary fracture and small scale fault pattern which approximated the northeast preferential orientation of foliation. Field observations also revealed a secondary structural orientation trending to the northwest as evidenced in fractures and occasional small scale faults. Both of these prominent orientations identified by field data were observed using remote imagery. However, it appears that a number of features identified by remote imagery that trend to the northwest may have been biased due to the effects of recent glaciation. Neither field data nor remote imagery revealed the presence of major structural features or lineaments which would cross the site.

Bedrock Quality

In general, the quartzites and granofels recovered from the bedrock cores appeared to be fresh to slightly weathered, and massive to moderately fractured with occasional highly fractured zones. In many instances the fractures paralleled the bedding parallel foliation which ranged in dip from 30 to 70 degrees from the horizontal. Significant differences in fracture orientation

were observed within the bedrock cores, so that no generalizations can be made. The calc-silicate rocks were generally fresh and

massive, whereas the basaltic rocks recovered from boring B-12R were generally slightly to highly weathered and moderately to highly fractured.

The rock quality designation (RQD) for each core run performed during the Phase I and Phase II exploration programs was calculated in the field. These values are included on the boring logs in Appendix D. The RQD is defined as the summation of rock core pieces greater then 4 inches in length divided by the total length of the core run and is expressed as a percentage. An RQD value of 75 percent or greater is generally indicative of competent rock.

Zones of highly fractured rock characterized by RQD values of less than 10 percent (exclusive of the first five feet of rock encountered in each boring which was often observed to be deeply weathered) were not encountered within any of the borings performed during the Phase I and Phase II subsurface explorations.


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Bedrock Topography

Bedrock elevations in the vicinity of the Somersworth Landfill have been estimated based on the following data:

Bedrock elevations in Remedial Investigation-phase borings confirmed by rock coring;

Depths to bedrock from the seismic refraction survey performed by Weston as part of this Remedial Investigation.

Figure 6 is a bedrock elevation contour plan of the study area prepared based on the above information using a computer-assisted regional variable technique termed Krlglng (Golden Software, Inc., 1987). It is noted that this interpretation of bedrock topography is based upon limited and widely spaced subsurface data. Actual bedrock topography is probably more complex than indicated on Figure 6.

Bedrock relief across the area was observed to be approximately 76 feet, with decreasing elevation in a general north-northwesterly direction, from approximately 189 feet MSL at boring location BIIR (in west side of site) to approximately 117 feet MSL at boring location B-7R (in north side of site). Bedrock elevation also decreases in a general westerly direction from approximately 182 feet MSL at boring B-12 to approximately 139 feet MSL at boring B13. Based on the interpretation of bedrock data, shown on Figure 6, the general bedrock topography underlying the landfill area is quite irregular, including numerous isolated knobs and basins.

The Somersworth landfill proper is apparently underlain by an east-west trending elongate basin extending from the area just west of B-5 to the area just east of B-9. Relief across this structure is of approximately 20 to 25 feet, from about elevation 153 feet MSL to 130 feet MSL. However, relief is much greater across this structure in the vicinity of boring B-12, grading from approximately 182 feet MSL at boring B-12 to 130 feet MSL in the apparent center of the basin, directly beneath the central portion of the Somersworth landfill proper.

Based on geophysical data, a small. Isolated, basin apparently exists in the vicinity of monitoring well B-6. The base elevation of this structure is approximately 138.1 feet MSL. The elevation of this structure rises abruptly to the east to approximately elevation 160 MSL in the vicinity of monitoring well B-2 and to the west-southwest to approximately elevation 154 feet MSL in the vicinity of monitoring well B-9.

A bedrock high appears to exist in the swampy lowlands just north of the landfill proper, of borings B-2 and B-10. Elevations of bedrock in this area range from approximately 165 to 175 feet MSL.


c This bedrock high apparently extends to the east of B-10 toward the vicinity of boring B-11. An isolated bedrock knob also appears to exist in the vicinity of boring B-12, at approximately 182 feet

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MSL.

5.1.2 Surficial Geoloov

Surficial soil deposits in the study area, with the exception of recent topsoil, and organic wetland deposits to the southwest, west, and northwest of the site, are believed to be linked, directly or indirectly, to a single major advance and retreat of the continental ice sheet during the last (Late Wisconsin) stage of the Pleistocene epoch approximately 10,000 to 20,000 years before present. Subsurface explorations performed during the Remedial Investigation generally support the description of surficial deposits of the New Hampshire seacoast region detailed by Bradley (1964).

Natural soils encountered in the test borings generally consisted of the following four basic types of deposits:

stratified sand with significant variations in silt and gravel content (kame deposits);

dense silty, gravelly sand (glacial till deposits);

peat (recent wetland deposits); and

clayey silt, frequently including sand and/or gravel (possible vestigial glacio-marine deposits).

In addition to these soil units, secondary deposits of topsoil, windblown silt, and fill material were also encountered within the study area, generally overlying the uppermost of the natural granular soils.

The thickest overburden deposits encountered were those composed of the aforementioned stratified gravelly or silty sands. Frequently, these deposits were encountered from the natural ground surface to bedrock. In several isolated instances, clayey silt and/or silty, gravelly sand deposits were observed to underlie the stratified sands.

Varying thicknesses of peat were encountered within borings performed in the vicinity of Peter's Marsh Brook and adjacent wetlands. In those areas, peat deposits comprised the uppermost stratigraphic soil unit. Deposits of peat were typically underlain by a relatively thin layer of sandy and/or gravelly clay, which was in turn underlain by the stratified gravelly or silty sands.


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The surficial geology of the study area is presented below, initiated with a discussion of the Pleistocene history and morphological processes of deposition, followed by a discussion of the characteristics of the soil deposits observed within the study area.

Pleistocene History and Processes of Deposition

In recent geological history the rock masses of New England have been subjected to a long interval of weathering and erosion, predominantly through several periods of continental glaciation. The most recent stage of continental glaciation occurred within the Late Wisconsin and had a dramatic influence in shaping the landforms as they exist today.

Regional evidence indicates that, during glaciation, overburden materials were removed and the bedrock often scraped bare and abraded. Much of the removed rock and soil particles, ranging from

clay to boulder size, were caught up and carried along within the moving ice mass. Where these materials were redeposited underneath the glacier, with little or no sorting or layering of the sediments by water, the resultant dense deposits are referred to as glacial

till. The discontinuous layer of dense silty gravelly sand sporadically encountered in the study area directly overlying

bedrock is believed to be of this origin. It is also evident, given the stratigraphic position at the bottom of the soil profile, that the deposits of glacial till are the oldest deposits encountered in the study area.

A large portion of a glacier's sediment load is transported in the meltwater streams that exist within and on the surface of a glacier. Much of the sand and gravel load carried in these streams is deposited in considerable thicknesses on the surface of the ice, around the ice front, and between and adjacent to stagnant ice blocks by normal fluvial depositional processes. These deposits remain, typically in slightly modified form, after the ice has melted away and, having been deposited in contact with the glacier, are referred to as "ice-contact" or "kame" deposits. Because of the erosive action and variable energy of the meltwater streams in which these deposits were born, the material generally consists of fine to coarse sands, significant amounts of waterworn rounded gravel, and minor amounts of silt. Typically, the material is somewhat stratified, and deltaic depositional sequences are also commonly observed. The stratified, variably silty or gravelly sands, encountered in the test borings and exposed in the cut banks of the numerous sand and gravel mining operations in the area are considered typical "ice-contact" deposits. Bradley (1964) has mapped the sand and gravel deposits of the area that includes the landfill as a "large kame plain" that underlies much of Somersworth and extends into Dover and Rollingsford on the south and Rochester on the north.


c A significant portion of the ice-contact deposits in the study area likely accumulated during retreat or down-wasting of ice in the last major period of glaciation because of the great Increase in meltwater activity. The melting back of the continental ice sheet also had a pronounced effect on sea levels in the New Hampshire coastal region. Rising sea levels from the great influx of neltwaters into the sea, coupled with the isostatically depressed land surface, had the effect of inundating the coastal region with tidal saltwater marshes, bays and open sea. Previous research (Moore, 1982) suggests that in the New Hampshire coastal region, the continental ice sheet retreated in contact with the rising sea. The marine deposits associated with the generally serene waters of the Inland bays and estuaries are typically composed of very fine sand, silt, and clay which were allowed to settle out of fluid suspension. Bradley (1964) has reported that '*ln most of southeastern New Hampshire, marine deposits underlie lowlands and valleys to a distance of about 20 miles inland from the present coastline."

In the study area, the marine inundation is believed to be represented by discontinuous vestigial deposits of silty clay. The high granular soil content of some of the marine deposits in the study area and the superposition of silty sand deposits on more uniform marine clays is believed to reflect the proximity of the presvimed bays or estuaries in the lowlands or valleys to the melting ice masses that were simultaneously adding to the adjacent ice-contact deposits. In these areas, meltwater streams issuing from the down-wasting ice sheet would periodically carry coarser sand and/or gravel sediments into the adjacent marine environments.

After deglaciation, the depressed land surface gradually rose to its present level in isostatic adjustment to the loss of the overlying ice mass, emptying the temporary bays and estuaries of seawater. Certain of these lowlands and valleys, however, were emptied of seawater only to be refilled by freshwater. Over the course of several thousands of years some of these areas slowly accumulated significant thicknesses of peat and organic silt such as those observed within the wetlands of the study area.

Description of Soil Strata

The following subsections discuss in detail characteristics of each of the major soil strata and refuse observed within the site study area. Strata descriptions are presented as generally observed irom the bedrock to the ground surface to maintain consistency with the discussion of the Pleistocene history and processes of deposition above.


I I Siltv Gravelly Sand ^Glacial Till) - Deposits of dense, silty

gravelly sand were encountered in test boring clusters B-2, B-5 ('y and B-13. The thickness of these deposits was observed to vary

from approximately 2 feet at boring cluster location B-2 to ! approximately 25 feet at boring cluster location B-13. SPT N-

values (blows per 12" of penetration) of the silty gravelly sand deposits typically ranged from approximately 42 to 68, indicating that these deposits are generally dense to very dense. Haxinxim and minimum SPT N-values recorded were 108 and 31, respectively.

The glacial till deposits generally were observed to consist of gray to brown, fine to coarse sand with varying amounts of gravel and silt, visual observation indicates the gravel content of these deposits varies between approximately 10 to 50 percent, and that in some seunples the gravel is actually the dominant soil component. In general, the silt content was observed to vary from approximately 10 to 20 percent. In one sample of the glacial till from boring B-13R, however, clayey silt was the dominant soil component observed.

Stratified Sands (Kame Deposits) - Deposits of stratified sands of variable silt and gravel content were observed at all Phase I and Phase II boring locations with the exception of boring cluster B9. Typically, the thickness of the stratified sand deposits

( encountered was approximately 26 feet. With the exception of B-9, thicknesses were observed to vary from a minimum of approximately

V 9 feet at boring location B-12 to a maximum of approximately 71 feet at boring location B-7. SPT N-values of the stratified sand deposits usually ranged from approximately 8 to 35, indicating that they are generally loose to dense. Maximum and minimum SPT N-values recorded were 142 and 2, respectively.

The deposits generally were observed to consist of fine to medium sand with widely varying amounts of gravel and silt. Visual observation indicates that the gravel content varied from trace (less than 10 percent) to over 50 percent. In samples where the gravel was observed to be the dominant constituent, the sand was generally medium to coarse and constituted approximately 10 to 35 percent of the samples. Silt content of these particular samples was observed to be usually trace levels. In some instances, however, the silt content visually was observed to be approximately 10 to 20 percent. In these samples, the sand fraction was usually fine to fine to medium, and the gravel content was typically trace to 20 percent.

Sandy and/or Gravelly Clay - Deposits of clay, frequently containing significant amounts of sand and/or gravel, were encountered at test boring cluster locations B-5, B-6, B-8, and B9. This deposit was also reportedly encountered in MW-4.


c Generally, the thickness of these deposits was approximately 12 feet, ranging from a thickness of approximately 4 feet at test boring cluster B-8, to cibout 20 feet at test boring cluster B-5. SPT-N values for these deposits generally ranged from weight-ofrods (W.O.R.) to 10, indicating these materials are generally very soft to stiff. Maximum and minimum SPT-N values recorded were 30 and 0, respectively. In general, the higher SPT-N values were observed in samples in which the clayey strata was interbedded with sand and gravel.

With the exception of test boring cluster B-5, all of the borings in which clay was observed are located in or immediately adjacent to the wetlands area that lies to the northwest of the site. Bedrock elevations at these locations were typically between 140 and 155 feet MSL. These elevations are not significantly lower than adjacent bedrock elevations where only stratified sand deposits were encountered, and in some areas the stratified sand deposits were noted to have accumulated over bedrock surfaces of significantly lower elevation. These data suggest that the governing topography for the formation of the marine environments in which the clay deposits formed was not the bedrock surface but rather the surface of the stratified sand deposits which the clays

, were deposited on and/or against.

In general, the clayey strata at the site was observed to consist / of gray silt and clay to clay and silt, with minor amounts of sand

I 1 and gravel. Visual observation indicates that the sand fraction I of the samples recovered ranged from trace to 20 percent and

consisted of dominantly fine to medium sand. Gravel content was ' observed to be typically less than 10 percent. In some instances, I a very soft, gray silty clay with trace fine sand and trace gravel

was observed. i

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Peat - Peat was encountered overlying the above-mentioned deposits of clay at test boring locations B-6, B-8, and B-9, and directly overlying stratified sand deposits in test boring B-13. A maximum I thickness of 21 feet of peat was observed at test boring location B-8, while the minimum thickness of peat encountered within the test borings where it was observed was approximately 7 feet at MW4.

Peat was also encountered at the ground surface during the I installation of surface water stations S-1, S-2, and S-4. Shallow peat probes performed in the vicinity of stations S-6 and S-12 during the installation of these surface water stations indicate

1 that the peat reaches a depth of over 5 feet in that area.

I Somersworth - May 22. 1989 - File No. D-5162 - Section 5 - Page 10

In general, the peat was observed to consist of a very soft, light to dark brown, fibrous peat with abundant fragments of roots, wood, and humus. These materials often were observed to grade down into ( a very loose, black, non-fibrous peat with trace fine sand and roots.

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' Refuse - Within the limits of the landfill, natural soils were observed to be overlain by landfill refuse. Information concerning the nature of refuse within the landfill was generally obtained from 12 of the 16 test pits which were excavated within the site study area. One half of these twelve test pits (TP-4, TP-5, TP-6, TP-8, TP-9, and TP-10) were performed within the landfill boundary to obtain Information concerning the thickness and composition of the landfill refuse, and the natural soils underlying the boiuidary landfill refuse. The remaining six test pits (A-1 through A-6)

j were performed within the landfill to investigate areas of i anomalously high magnetism which were identified during the

geophysical explorations. The locations of the test pits are shown ! on Figure 2.

Eight of the test pits which were performed within the landfill (TP-5, TP-6, TP-8, TP-9, TP-10, A-2, A-5, and A-6) were excavated

1 to depths which completely penetrated the refuse, extending into the natural underlying soils. The average thickness of refuse

} / encountered within these test pits was approximately 14 to 15 feet. The minimum thickness of refuse encountered in these test pits excavations was approximately 6 feet, in test pit A-2. The maximum thickness of refuse identified in the test pit exploration program

I was encountered in test pit TP-4, performed within the northeastern I portion of the site, which reached a depth of approximately 23 feet

without encountering natural soil strata. Generally, the thickness 1 of the refuse deposits was observed to decrease toward the southern I and western areas of the site.

Test pits conducted within the landfill generally encountered materials typical of municipal garbage and household trash, and i various other debris. Including plastic, glass, and wood products, bricks, and various types of scrap metal. Crushed and deteriorated 55-gallon drums and 5-gallon cans were also encountered in several i test pits. One 55-gallon drum was encountered in each of test pits TP-4, TP-5, TP-9, and A-1, and one 5-gallon metal container was encountered in each of test pits A-4 and A-5. In test pits A-2 and I A-6, no cause for the observed magnetic anomalies was identified.


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Natural soils and refuse encountered in several of the excavations (TP-4, TP-5, TP-6, TP-8, TP-9, TP-10, A-1, and A-5) were observed to be blackened and/or contain ashes, indicative of decomposition of the refuse, or past burning practices, or possibly both. The natural soils encountered underlying the landfill refuse were generally composed of the same stratified sands of varied granular composition encountered in a majority of the test borings.

Water level readings obtained in stand pipes installed within test pits TP-5 and TP-6 indicate that refuse has, at least within southerly portions of the landfill, been placed 1 to 4 feet below groundwater levels. In more northerly portions of the landfill, stand pipe data indicate groundwater levels are slightly below the base of refuse. The data are very limited however, and prior to implementation of a remedial technology, the refuse groundwater contact area should be evaluated with a careful program of test pit excavations performed on a grid throughout the landfill area.

5.2 SURFACE WATER HYDROLOGY

A review of topographic maps indicates that the Somersworth Municipal Landfill is located completely within the drainage basin of Peter's Marsh Brook. As Peter's Marsh Brook is a secondary tributary to the Salmon Falls River, the site is also within the watershed of the Salmon Falls River which serves as a water supply to both Somersworth, New Hampshire, and Berwick, Maine. Field observations indicate that surface water runoff in the immediate vicinity of the site drains into Peter's Marsh Brook, either directly by precipitation runoff into the wetland area that surrounds the brook, or indirectly by surface flow into a catch basin near the entrance to the landfill which channels runoff into a swale that extends from that point westerly along the north side of Blackwater Road into Peter's Marsh Brook.

An unnamed intermittent tributary to Peter's Marsh Brook is located to the north of the site. This stream flows in a generally east to west direction from a culvert under Maple Street Extension immediately to the south of the Forest Glade Cemetery through the wooded area which lies immediately to the north of the Turcotte sand and gravel pit, joining Peter's Marsh Brook at surface water stations S-4 and S-5. In the small ravine that separates the unexcavated eastern portion of the Turcotte sand and gravel pits from the adjacent cemetery, this stream was observed to flow only during periods of stormw^ter runoff. Further downstream in the wooded and wetland areas to the north of the Turcotte sand and gravel pit, water was observed in the stream throughout the year.

The headwater of Peter's Marsh Brook is Willand Pond, which is located approximately one mile to the south-southeast of the site. Willand Pond has a surface area of approximately 65 acres. The


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drainage divide which separates the drainage basins of the Cocheco River and the Salmon Falls River approximately surrounds the pond

on its southern, eastern, and western sides. Peter's Marsh Brook originates at the northern end of the pond. From there the brook meanders through a wetland corridor in a northerly direction, and joins Tate's Brook at a point located approximately 3,000 to 4,000 feet northwest of the site. Note that wetlands in New Heunpshire are regulated by the U.S. Army Corps of Engineers and the US EPA, as well as the State Government.

Stream flow gaging performed by GZA on June 17, 1987 measured flow of Peter's Marsh Brook at Blackwater Road to be approximately 0.8 cubic feet per second (cfs). Flow was observed to increase significantly after the brook enters the large wetland area northwest of the site; stream gaging performed by GZA on the same date in the vicinity of surface water stations S-6 and S-11 measured flow to be approximately 6 cfs.

From the confluence of Peter's Marsh Brook and Tate's Brook, it is approximately 1.4 stream miles to the confluence of Tate's Brook and the Salmon Falls River. The Salmon Falls River is the boundary between the States of New Hampshire and Maine. The river flows in a generally northwest to southeast direction and joins the Cocheco River just to the southeast of Dover, New Hampshire. The Piscataqua River is formed by the confluence of those two rivers and the Salmon Falls River drainage basin is therefore a sub-basin of the Piscataqua River drainage basin.

No USGS or other recognized gauging stations are located on the Salmon Falls River near the City of Somersworth. Information provided by Berwick, Maine Town officials and other engineering firms (CDM, Kimball Chase) indicates that the flow of the Salmon Falls River is largely controlled by the Milton Three Pond Dam in Milton, New Hampshire, located approximately 15 miles northwest (upstream) of Berwick, Maine and Somersworth, New Hampshire. The USGS 7-day 10-years permissible low flow for the Salmon Falls River at this locality is reportedly 35 cfs. The average flow for the Salmon Falls River at the Milton Station for the years 1974 and 1984 was reportedly 160 cfs and 281 cfs, respectively. Records from another USGS gauging station on the Salmon Falls River located approximately 5 miles upstream of Somersworth indicate that the average flow of the river there is approximately 200 cfs. These gauging stations are located upstream from an apparent significant input to the Salmon Falls River, namely the Little River; the confluence of these two rivers is approximately 3.5 miles northwes -. of Berwick-Somersworth. The flow of the Salmon Falls River near the area of Berwick-Somersworth may be significantly greater than the aforementioned values due to the increased flow to the system from the Little River and several other smaller tributaries downstream from the described gauging stations. No gauging station is believed to exist on the Little River.


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i ' Both the City of Somersworth and the Town of Berwick withdraw water from the Salmon Falls River for municipal water supply. Discussions with Town officials of Berwick indicate that the river supplies water to approximately 625 residents in the downtown area. The Town also withdraws water from the river for fire protection, water storage, and other purposes. Reportedly, the Town withdraws approximately 300,000 to 400,000 gallons per day (9 to 12 million gallons per month or 0.5 to 0.6 cfs) from the river.

Discussions with City of Somersworth officials indicate that the Salmon Falls River currently provides approximately 25 to 30 percent of the City's drinking water supply. Approximately 9.3 million gallons of water are withdrawn monthly from the river at the Somersworth intakes. Officials also indicated that prior to 1986, when the Somersworth municipal supply well No.l was rehabilitated to increase its capacity, the City removed approximately 16 to 17 million gallons per month from the river.

5.3 GROUNDWATER HYDROLOGY

The following discussion of the groundwater hydrology in the vicinity of the site is based primarily on field data obtained during the Remedial Investigation subsurface exploration program. Where available and appropriate, data from subsurface explorations

{ conducted by others prior to initiation of the Remedial Investigation were also reviewed and incorporated.

5.3.1 Hydrogeologic Setting

At the Somersworth Municipal Landfill site and surrounding area, groundwater is stored and transmitted through the pore spaces of the overburden soil deposits, and through the fractures within the bedrock. Where water is stored and transmitted readily through soil matrix interstices or bedrock fractures the saturated soil or bedrock is generally referred to as an aquifer. In the site study area the upper boundary of the overburden aquifer is the phreatic water table and the aquifer is thus termed a water table or unconfined aquifer.

The unconsolidated soil deposits comprising the overburden aquifer materials within the site study area basically consist of two major soil types. The first soil type consists of the gravelly and silty sand kame deposits which, as discussed in Section 5.1, include fine to medium sand, medium to coarse sand with varying amounts of rounded gravel, and rounded gravel with varying amounts of sand. Lesser but variable amounts of silt were also observed within these granular deposits. The second major soil type observed in the site study area consists of the fibrous peat encountered within the swampy wetlands associated with Peter's Marsh Brook. Other


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materials observed within the site study area consist of minor, isolated occurrences of glacial till and silty clay. These materials are not considered an important or significant part of the aquifer.

Data obtained from bedrock monitoring wells Installed in the study area generally indicated that fractures extending to at least 30 feet below the bedrock surface are in direct hydraulic communication with the overlying unconfined aquifer (a maximum core penetration of 30 feet precluded exploration of deeper bedrock characteristics). Bedrock fractures were, however, observed to be predominant in the upper 5 to 10 feet of bedrock. Because of the apparent hydraulic communication between the fractured bedrock and the overlying aquifer (suggested by the general lack of any impermeable layer between the two zones, and almost identical groundwater flow patterns within the overburden and upper fractured bedrock), the upper 30 feet of fractured bedrock is, in this hydrogeologic setting, considered part of the unconfined overburden aquifer.

5.3.2 Hydraulic Properties

Three important characteristics of an aquifer include the hydraulic conductivity (K), the saturated thickness (b), and the porosity (n) . Hydraulic gradient which is also an important hydraulic property, is discussed subsequent to definition of these characteristics. Hydraulic conductivity is a measure of the ease with which water will move through a particular aquifer material, and is a function of both the properties of the water and the soil or bedrock matrix through which it flows. For an unconfined aquifer, saturated thickness is typically defined as the distance from the phreatic groundwater surface to a relatively impermeable lower boundary, such as massive, competent bedrock or a clay silt aquitard. The porosity of a soil is a ratio of the volume of void space within a soil, to total unit volume and is used in estimating groundwater seepage velocities.

Data sources used to estimate hydraulic conductivity in the study area include:

1. Grain size distribution; and 2. Borehole permeability tests

Both data sources were used to estimate hydraulic conductivities of the unconsolidated granular soil deposits, whereas only the borehole permeability tests were used to estimate the hydraulic conductivities of bedrock. Procedures used to conduct grain size distribution and borehole permeability tests are described or referenced in Section 4.0. Results of borehole permeability tests are stommarized on Table 4. Results of laboratory grain size


I [ analyses are included in Appendix G and results of Kozeny-Carmen

hydraulic conductivity analyses, performed using the results of c leUsoratory gradation analyses, are summarized on Table 5. U n / / ^ [ Based on the data summarized in TeUsles 4 and 5, the hydraulic'^^'-''^

conductivities of the gravelly and silty sand kame deposits appear - to range from approximately 1 to 150 feet per day (ft/day). The ^ y ^ ^ ^ I lower hydraulic conductivity values would be associated with the c/* > dense, fine, silty sand portions of the kame deposits, whereas the higher values would be associated with the looser, coarse, gravelly 1 sand portions of the kame deposits. In general, based on the data included in Tables 4 and 5, a more average range of hydraulic conductivity of the kame deposits is approximately 30 to 60 ft/day.

I Estimates of the hydraulic conductivity of peat were obtained from hydrogeologic literature and past experience, due to extreme 1 difficulties with field testing and sampling soft, saturated fibrous peat. Casagrande (1966) notes a hydraulic conductivity range of approximately 3 to 30 ft/day for similar fibrous peat I materials, which is in agreement with past experience.

The hydraulic conductivity of the glacial till soils is estimated I from data presented in Tables 4 and 5 to range from approximately g,.' '' 0.1 to 5 ft/day. Hydraulic conductivity testing was not perfoxnned :}.x.ic on the clayey soils. ' c^fe

1 ( Hydraulic conductivity within bedrock is a function of several ^§i^i-^ factors Including fracture density, orientation, and aperture "^"T^IQ'width. All of these factors can be highly variable, with fracture "I density and aperture width typically decreasing with depth due to [ M ^ ' ^ f a decrease in the effects of bedrock weathering, and increase in o^' i lithostatic pressure. Therefore, bedrock aquifers are generally ^ c 1 anisotropic with widely varying values of hydraulic conductivity. .v63 ic

Data from bedrock pressure testing conducted within boreholes drilled in the study area Indicate bedrock hydraulic conductivities

! as high as approximately 4 ft/day in upper, highly fractured zones. Within massive, unfractured bedrock, hydraulic conductivity values were observed to be less than approximately 0.05 ft/day. Average 1 bedrock hydraulic conductivity values of approximately 0.1 ft/day were recorded within 30 feet of the bedrock surface.

1 Saturated Thickness

1 Saturated thickness of overburden soils was observed to vary across the study area from approximately 3 feet in the vicinity of boring cluster B-12 to approximately 68 feet in the vicinity of boring cluster B-7. To the area west and northwest of I the landfill, saturated thickness values were observed to range


I 1 from approximately 25 feet in the vicinity of boring B-2 to / approximately 40 feet near boring B-3. Areas with apparently '^ limited saturated thickness include the vicinity of boring cluster

B-11 east of the landfill with an observed value of approximately 9 feet, and boring cluster B-12 as noted above.

Porosity

Porosities of sand deposits typically range from approximately 0.25 to 0.45. The lower porosity values are typical of finer, dense, or non-uniformly graded deposits, whereas the higher porosity values are typical of coarser, loose, or uniformly graded deposits. For the sand deposits observed within the site study area, an average range of porosity values from 0.30 to 0.40 appears reasonable based on standard grain-size and standard penetration test information.

5.3.3 Groundwater Levels and Flow Directions

Groundwater elevations were monitored at a total of forty-one monitoring wells in the vicinity of the study area. These monitoring wells include:

( . Twenty-seven B-series monitoring wells installed during Phase I and Phase II of the Remedial Investigation field program at 13 separate cluster locations;

Ten observation wells installed within test pits excavated during Phase I of the Remedial Investigation field program; and

Four MW-series monitoring wells installed previously by the Town of Somersworth.

Groundwater and surface water levels measured on December 29, 1986 were used to prepare the groundwater elevation contour map shown on Figure 7. Groundwater movement is in the direction of lower hydraulic head represented as elevation contours on Figure 7. With respect to the site and surrounding study area, hydraulic head losses occur both horizontally and vertically within the aquifer.

Groundwater elevation contours shown on Figure 7 indicate groundwater movement within the aquifer occurs regionally in a westerly, then west-northwesterly direction across the landfill toward Peter's Marsh Brook and surrounding wetlands. A review of topographic maps of the study area and its surrounding environs Indicates that Willand Pond, located approximately one mile south-southwest of the landfill, may serve as a source of groundwater recharge. This assessment is based primarily on its proximity to


I the upper reaches of the Peter's Marsh Brook watershed. Rainfall recharge also likely occurs along the uplands located to the east

y and west of the study area. Groundwater is anticipated to flow regionally from Willand Pond and the upland recharge areas toward

«. the landfill.

{ Although groundwater elevation contours depicted on Figure 7 reflect contouring of overburden monitoring well data, contouring of bedrock well data would result in a nearly Identical flow field.

I This is an indication that the upper fractured bedrock is in direct \ hydraulic communication with the overburden deposits, and that

groundwater flow within bedrock is in the same horizontal direction as in the overburden deposits.

1 I It is anticipated that the wetland area surrounding Peter's Marsh

Brook located immediately northwest of the landfill is a point of discharge (surfacing) for groundwater within the study area. Evidence of this is provided by:

strongly convergent groundwater flow northwest of the landfill

1 with no substantial increase in saturated thickness (although saturated thickness data are limited);

1 an increase of almost one foot of hydraulic head with depth observed within companion cluster monitoring wells at B-8 located within the wetland area north of the landfill; and

an approximate one-half order of magnitude increase in flow ! volume of Peter's Marsh Brook between Blackwater Road and the area in the vicinity of surface water station S-6, with

I limited additional surface drainage during most of the year.

1 Groundwater discharged within this area would subsequently flow with the surface waters of Peter's Marsh Brook toward the Salmon Fall River.

In addition to monitoring cluster B-8, hydraulic head was observed I to increase with depth at monitoring clusters B-9, B-11 and B-13 indicating upward, discharging groundwater flow. At monitoring cluster B-6, hydraulic head was observed to decrease slightly with

1 depth on one occasion, indicating a downward component of groundwater flow. At the remaining four cluster installations, no significant vertical differences in hydraulic head were observed.

I It is noted that the monitoring well network was not established for the purposes of measuring vertical gradients. Due to the long 1 screens used to construct these monitoring wells, only limited indications of vertical flow can be gained from the data, especially at locations B-6 and B-9 where the change in head was equal to, or less than one-half foot.

Somersworth - Mav 22^ 1989 - File No. D-5162 - Section 5 - Page 18

I. 5.3.4 Hydraulic Gradients and Groundwater Seepage Velocities

The hydraulic gradient, or change in hydraulic head per unit distance of flow in a given direction, represents the driving force in groundwater dyneunics. Within the study area, both horizontal and vertical hydraulic gradients were observed to vary with location.

Groundwater elevation contours shown on Figure 7 indicate that, in general, horizontal hydraulic gradients decrease from Maple Street Extension west to Peter's Marsh Brook. Within the site study area, hydraulic gradients were observed to range from approximately 0.014 feet per foot (ft/ft) to 0.002 ft/ft. The average hydraulic gradient in eastern portions of the landfill is approximately 0.012 ft/ft to 0.014 ft/ft. A hydraulic gradient of approximately 0.004 ft/ft was observed from the central portion of the landfill in the vicinity of TP-9 north-northwesterly toward monitoring cluster B6. Between monitoring clusters B-6 and B-8, a hydraulic gradient of approximately 0.006 ft/ft was observed. Because of the wetland, it is anticipated that the hydraulic gradient decreases northwest of monitoring cluster B-8.

Groundwater movement through a soil is a function of the driving gradients and of the soil and fluid characteristics. The average

( velocity with which water travels through a soil unit, defined as the seepage velocity, can be determined by the following relationship:

V = Ki/n

where v = average seepage velocity k = hydraulic conductivity (permeability) 1 = hydraulic gradient n = soil porosity


K Estimated seepage velocities within the study area are anticipated to vary considerably given the heterogeneity of the aquifer. Of Importance to this study is the consideration of average horizontal seepage velocities from the landfill westerly toward to Peter's Marsh Brook, and then northwesterly toward the area in the vicinity of monitoring well cluster B-8. Using average hydraulic parameter (hydraulic conductivity, porosity, and gradient) values discussed above, the following approximate seepage velocities have been determined:

Estimated Seepage Area VglggJtYi V

_-4 Central portion of landfill west-northwesterly to B-6 <0.5 to 1 ft/day

B-6 Northwesterly to B-8 >0.5 to <2 ft/day

I'


I

I

(

6.0 AIR MONITORING PROGRAM

The following subsections outline the air monitoring task which has been performed at the site by the project team.

6.1 INITIAL AIR MONITORING

In November 1984, representatives of the project team conducted an initial site reconnaissance of the Somersworth Municipal Landfill. During the Initial site reconnaissance, project team personnel utilized an HNU Systems, Inc. Model PI-101 organic vapor analyzer to evaluate air quality conditions throughout the project site. No volatile organic compounds (VOCs) were observed in the ambient air at the site during this Site reconnaissance. The Initial air monitoring results were used by the project team to aid in the development of the Remedial Investigation air monitoring program.

6.2 REMEDIAL INVESTIGATION AIR MONITORING PROGRAM

Based on the data obtained during the initial site reconnaissance, it was determined that the air monitoring program's primary objective would be to ensure adherence to appropriate safety

considerations (i.e., protection levels) for personnel Involved in various site investigations. During the test boring and monitoring well installation phase of this project, the ambient air at the site was monitored daily by GZA personnel using a Thermo Electron Instruments (TEI) Model 580 organic vapor meter (OVM) . The TEI OVM responds readily to most volatile organic contaminants but does not register methane or natural components of air such as oxygen, nitrogen or carbon dioxide. The TEI OVM detection limit is approximately 1 part per million (ppm) by volume, referenced to a butadiene-in-air standard. The TEI OVM was calibrated at the site at the beginning of each day with the butadiene-in-air standard. No VOCs were detected by the TEI OVM in the ambient air at the site during the field work phase of this project.


Y 7.0 DISTRIBUTION AND MIGRATION OF CONTAMINANTS

^ The discussion of distribution and migration of contaminants within the site study area is separated into three subsections, including:

1. Contaminants observed within the samples obtained from the site study area;

2. Observed distribution of contaminants (data review only); and

3. Mechanisms and patterns of contaminant migration within the site study area.

7.1 OBSERVED CONTAMINANTS

During the course of the Remedial Investigation, samples of surface sediments, subsurface soils, groundwater, surface water, and air were obtained from the study area for evaluation of possible chemical contamination. Sampling and analytical protocols are discussed in Section 4.0 of this report.

Five basic types of chemical analyses were performed on samples of the various environmental media. These analyses included methods for the detection of volatile organic compounds (VOCs), acid and

< base/neutral extractable organic compounds (ABN's), metals, polychlorinated biphenyls (PCB's), and pesticides. In addition, analyses for several Inorganic contaminants considered to be indicators of landfill leachate, as well as measurements of certain physical properties considered as general indicators of water quality, were conducted as part of the groundwater sampling and analysis program. The contaminants that were identified at the site include VOCs, ABN's, metals, and typical landfill leachate indicators. Neither PCB's nor pesticides were detected in any of the samples analyzed.

The analytical water quality program implemented for the Remedial Investigation focused on analyses for VOCs. Most of the groundwater and surface water samples obtained during the Remedial Investigation field exploration program were analyzed for VOCs. Additionally, composite soil samples were obtained from most soil borings, test pits, and surface sediment sampling points for VOC analysis. Substantially fewer ABN, metals, PCB, and pesticide analyses were performed in accordance with the Remedial Investigation work plan. At most groundwater and surface water sampling points, pH, specific conductance, and temperature measurements were obtained. A summary of the chemical analyses performed on groundwater, surface water, subsurface soil, and surface sediment samples during the Remedial Investigation is shown in Table 6. A compilation of all analytical data obtained is included as Appendix I.


(

7.1.1 Volatile Organic Compounds

VOCs are so named because these compounds vaporize in air at typical ambient temperatures. VOCs Include numerous members of the three major classes of organic compounds - aromatlcs, allphatics, and heterocyclics - and are among the most common chemicals used in the manufacturing industry today. As a result of their natural tendency to change phase from liquid to gas at ambient temperatures, VOCs are often easily detected and differentiated by standard gas chromatography techniques. The EPA-approved methods for analysis of VOCs that were used during the Remedial Investigation Included gas chromatography (GC) and mass spectrometry (MS).

A total of 25 VOCs were identified within the study area in the various media that were sampled. A svimmary of the VOCs observed in groundwater and surface water samples is included in Tables 7 and 8, respectively. A summary of VOCs observed in soils and sediments is included in Table 9. Total VOC concentrations obseirved at each groundwater and surface water sampling point are shown on Figures 8 and 9. VOCs most frequently observed within the study area are presented below.

Benzene, ethylbenzene, xylene, and toluene are aromatic organic compounds. These particular compounds are common components of petroleum products (gasoline, diesel fuel, etc.), paints, paint thinners, and adhesives, and are widely used as Industrial solvents.

Acetone, methyl ethyl ketone (2-butanone), and methyl isobutyl ketone are carbonyl organic compounds and are Included as members of the subgroup termed ketones. Ketones are common constituents of resins, paints, lacquers, coatings, paint strippers, certain adhesives, and may also be used as industrial solvents.

1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, dichloroethylene, l,1-dichloroethylene, trichloroethylene, and tetrachloroethylene are halogenated aliphatic organic compounds. Trichloroethylene, tetrachloroethylene and 1,1,1-trichloroethane are among the most widely used degreasing agents in industry, as well as common constituents of various cleaners, polishes, and deodorizers. The other halogenated compounds observed within the study area are commonly used as industrial solvents.

Tetrahydrofuran and diethyl ether are aliphatic organic compounds termed ethers. Tetrahydrofuran is commonly used as an industrial solvent to dissolve synthetic resins, particularly polyvinyl chloride.

Somersworth - May 22, 1989 - File No. D-5162 - Section 7 - Page 2

In order to facilitate discussion of VOC contaminant distribution, ( common nomenclature used in the discussion is defined below.

Total VOC' s - The sum of the concentrations of each of the Individual VOCs detected in the 6C/MS analysis of a single szunple. In the calculation of total VOC concentrations, if the concentration of a single compound Is detected at trace levels, typically signified by <5 micrograms per liter, the total VOC concentration has been conservatively estimated using the detection limit value reported for that particular compound.

Maximum Total VOC's - Represents the maximum total VOC concentration calculated from analyses of all the samples obtained over time from a single sampling station.

7.1.2 Acid and Base/Neutral Extractable Organic Compounds

ABN's do not vaporize as readily as VOCs in air at typical ambient temperatures. Consequently these compounds must be Isolated and concentrated by solvent extraction as part of their analysis. Once this is completed, the extract is analyzed by normal GC and MS techniques for analyte identification. ABN's were observed to be less prevalent than VOCs within the study area, however, it is important to note that far fewer ABN analyses were

( performed on samples obtained during the Remedial Investigation than VOC analyses. A s\immary of the ABN's observed in the groundwater, surface water, soil, and sediment samples that were obtained from the study area during the Remedial Investigation is included in Tables 12 and 13.

ABN's most frequently observed in water samples analyzed from the site include phenol, 4-methylphenol, and 2-methylphenol, all of which belong to the phenols group of aromatic organic compounds. Phenols are commonly used as disinfectants, and in the manufacture of certain resins and many medical and industrial organic compounds and dyes. Other ABN's detected in analyzed water samples include diethylphthalate and benzoic acid. The former is widely used in plastics manufacturing while the latter is a common preservative in soft drinks.

Members of a subclass of base/neutral extractable compounds called polynuclear aromatic hydrocarbons (PNA's) were detected in soil samples from three locations at the site. PNA's detected include fluorene, fluoranthene, phenanthrene, anthracene, pyrene, chrysene, and benzanthracene. PNA's are common constituents of coal tar, creosote, fuel oils, diesel fuels, gasolines, and lubricants, and are also typical byproducts of internal combustion engines and coal burning.


V,

Laboratory data from the ABN analyses performed lists concentrations of ABN's below ten times the detection limit as "trace" levels, an arbitrarily chosen criterion. Reported trace levels ranged from about 2 to 6 micrograms per liter (ug/1), however, where detection limits were high, trace levels up to 15 ug/1 were recorded.

7.1.3 Metals

Analyses performed for metals during the Remedial Investigation included tests for the presence of antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, zinc, and total cyanide. Although the free cyanide ion itself is not a metal, cyanides are commonly used in the metal plating industry as complexing agents to lower the concentration of the free metal ion being plated. Hence, where plating wastes are present both metals and cyanides may be in the environment. For the convenience of this and following discussions, the term "metals" Includes cyanide as well as the above-listed elements.

Since most metals are naturally occurring elements, certain environmental media, notably soils, will contain natural background concentrations of these constituents. Metals commonly detected in soil samples obtained within the study area Include arsenic, chromiiim, copper, lead, nickel, and zinc. Anticipated background levels of metals in soils have been estimated based on published data and are summarized in Table 11; however; in cases where metals data indicates anomolously high metals concentrations compared to metals data collected from locations anticipated to be upgradient of the landfill, it has been noted in the text.

Natural background concentrations of metals in groundwater and surface water are typically much lower than natural background levels in soils. Published data (Davis and DeWeist, 1966; Holland, 1978; Freeze and Cherry, 1979) indicate that typical background concentrations in groundwater and surface water of barium, chromivuQ, copper, lead, nickel and zinc may be as high as 50-200 ppb, but typically will be less. Arsenic, cadmium and selenium background levels would be expected to be less than 10 ppb. Other metals analyzed for in the water samples obtained within the study area, including beryllium, silver, and thallium, are considered trace constituents and generally would be expected to be present at background levels of less than 1 ppb. Natural background concentrations of mercury would be expected to be less than 0.05 ppb (Friberg et al, 1979).


I J The Maximum Contaminant Levels (MCL's) for metals were established

y by the National Safe Drinking Water Act of 1974, and subsequently I Incorporated into the State of New Hampshire Drinking Water ' Regulations (1986). Although not necessarily an Indicator of

groimdwater or surface water contamination, MCL's are a useful indicator of water quality for the risk assessment described in Section 8.0. A siunmary of the appropriate MCL's, coupled with identification of the groundwater and surface water samples where metals were detected in excess of the MCL's during the Remedial Investigation, is Included as Table 10. For metals which have no MCL, alternate criteria are indicated on the table.

I 7.1.4 Leachate and/or Groundwater Quality Indicators

I Substances that commonly are found in landfill leachate Include iron, manganese, chloride, sulfate, nitrate/nitrite, and phosphorus. Because these compounds are generally conserved, analyses for these substances are performed to help define the

I extent of leachate contamination from a landfill. Other groundwater quality parameters routinely used to identify leachate contamination are measurements of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and total organic carbon (TOC).

COD is a measure of the oxygen required for oxidation of the , ^ organic material present in a water sample and is therefore also \ • a rough indicator of the total organic content of that sample. * COD is affected both by organics that are highly susceptible to

biodegradation and organics that are generally resistant to I biodegradation, and is somewhat dependent upon the oxidation state \ of those organics. TKN is a measure of nitrogen content that

includes both organic nitrogen and ammonia nitrogen; TOC is a direct measure of the organic carbon compounds present in a water sample, independent of the oxidation state of those organics.

State of New Hampshire Drinking Water Regulations list Secondary Maximiom Contaminant Levels (SMCL's) for several of the above-listed compounds (i.e., chloride, iron, manganese, sulfate, and nitrate/nitrite) that are considered secondary contaminants in drinking water. These SMCL's are listed in Table 14 which is a summary of the leachate indicator parameters identified within the study area. The leachate indicator analyses data are enclosed in Appendix I.


c 7.2 OBSERVED DISTRIBUTION OF CONTAMINANTS

The observed distribution of contaminants is discussed in the following subsections for each of the relevant environmental media. Results of analyses performed on soils and sediments are reported in terms of micrograms of contaminant per kilogram of soil (ug/kg), or microgreuDS of contzuninant per gram of soil (ug/g). Results of analyses performed on groundwater and surface water samples are reported in terms of micrograms of conteuninant per liter of water (ug/1), or milligrams of contaminant per liter of water (mg/1). Values of ug/kg and ug/g are equivalent to parts per billion (ppb) and parts per million (ppm) respectively. Furthermore, because only very small concentrations of contaminants were detected in the water samples, the density of these waters will be very close to 1.00 gm/cm and therefore values of ug/1 and mg/1 are essentially the same as ppb and ppm respectively.

7.2.1 Surface Water and Sediments

Surface water and surface sediment samples for quantitative chemical analyses were obtained in portions of Peter's Marsh Brook both upstream and downstream of the landfill, an unnamed intermittent stream that is located to the north of the site, and at one location in the Salmon Falls River. Contaminants observed within surface water samples are discussed first, followed by a discussion of contaminants observed within sediment samples.

Surface Water Samples

Table 8 and Appendix 1.1.4 summarize the VOCs observed in the surface water samples obtained within the study area. Several VOCs were observed in surface water samples obtained from stations S-4, S-5, and S-6. These stations are all located within Peter's Marsh Brook and its unnamed tributary downgradient of the landfill. The total VOC concentrations observed in samples obtained during five rounds of surface water sampling at stations S-5, and S-6, and four rounds at station S-4, ranged from none detected to 118 ug/1. The fluctuation of VOC concentrations with time may be due, in part, to seasonally dependent variables such as volume of groundwater discharge to the brook, volume of surface water runoff, and ambient water and air temperature. Total VOCs observed in surface water are shown on Figure 8.

VOCs were also observed in a sample obtained from sampling station S-7 located within the Salmon Falls River at its confluence with Tate's Brook on May 17, 1985. Since S-7 VOC data are very similar in terms of compounds observed and contaminant concentrations to data obtained from four other sampling points at the Somersworth Municipal Landfill surface water stations S-5 and S-6, and monitoring wells MW-1 and MW-2 and to two other sampling points at


[

I the nearby Dover Municipal Landfill (RW-18 and RW-21) on May 17, 1985, these data are considered suspect. Additionally, four subsequent sampling rounds at surface water station S-7 over the Ic following one and one-half years indicate no detectable VOC contamination at station S-7, further suggesting that the May 17, 1985 data are questionable. Subsequent sampling rounds at MW-1, MW-2, S-5 and S-6 Indicated detectable contamination at each of these seunpling points.

I Disregarding the suspect May 17, 1985 sampling round data, eight

I different VOCs were detected in samples obtained from the above-listed stations. The most prevalent compound in terms of both frequency of occurrence and concentration was dichloroethylene (c&t) observed at a maximum concentration of approximately 25 ug/1

I at S-4. Trichloroethylene, 1,1-dichloroethane, dichloromethane, benzene, toluene, tetrahydrofuran, and diethyl ether were also observed, typically at trace (< 5 ug/1) levels.

Tables 10 and 12 and Appendices 1.2.2, 1.3.2, and 1.4.2 stunmarize the observed distribution of ABN's and metals in the surface water samples obtained within the study area. ABN's and metals analyses were performed on samples from three of the seven surface water stations, namely S-1, S-4, and S-6. Results indicated that two ABN's, phenol and 4-methylphenol, were present at trace concentrations in a single sample from surface water station s-6.

( No other ABN's were detected in any of the surface water samples ^ obtained.

! Results of metals analyses indicated metal concentrations above MCL's in samples obtained from two locations, each involving one

} constituent. Mercury was detected in a sample obtained from surface water station S-1 at a concentration of 0.0053 mg/1,

w slightly above the MCL of 0.002 mg/1. Cyanide was detected in a sample obtained from station S-6 at 0.012 mg/1. The MCL for 1 cyanide is 0.01 mg/1.

1 Sediment Samples

Table 9 and Appendix 1.1.6 summarize the observed distribution of VOCs in the surface sediment samples obtained within the study area. Several VOCs were detected in sediment

!

1 samples obtained from surface water stations S-4, S-5, and S-6. These compounds include xylenes, which were detected in samples from each of the above-listed locations, methylcyclohexane, toluene, ethylbenzene, and carbon disulfide. The latter four compounds were identified only in the sediment sample obtained from surface water station S-5 and are listed here in order of I decreasing concentration. The maximum concentration of xylenes observed was 130 ug/kg at station S-5.


c Tables 11 and 13 and Appendices 1.2.4, 1.3.4, and 1.4.4 siimmarize the observed distribution of ABN's and metals in the sampled surface sediment within the study area. ABN and metals analyses were performed on the sediment samples obtained from stations S-1, S-4, and S-6. Results indicated that no ABN's were present in those samples and that metals were not present above their anticipated background levels.

7.2.2 Groundwater

Groundwater samples were obtained from all B-serles and MW-series monitoring wells, from the Somersworth municipal supply well No.3, and from several residential wells at locations listed in Appendix C.

A sximmary of the chemical analyses performed on the groundwater samples obtained from these wells is listed in Table 6. VOC, ABN, and metals contamination was observed in many of the groundwater samples obtained from monitoring wells screened within both the overburden soils and the bedrock of the study area. VOCs were observed to comprise a major portion of the overall groundwater contamination. The following discussion describes groundwater contamination detected in the study area.

( VOCs

Table 7 and Appendices I.1.1, 1.1.2, and 1.1.3 summarize the VOCs observed in the groundwater samples obtained within the study area during the Remedial Investigation. Figures 7 and 8 illustrate the total VOC concentrations observed at the monitoring well and surface station sampling points for each sampling round performed.

The highest concentrations of VOC contamination were observed in samples obtained from monitoring well clusters B-6 and B-12. Total VOC concentrations observed at these locations ranged between approximately 2,000 and 13,000 ug/1 during the monitoring period. At no other locations were total VOC concentrations observed to equal or exceed 1,000 ug/1. Relatively high concentrations of V OCs were observed in samples obtained from monitoring well locations B-2, B-3, B-8, B-9, B-13, MW-2, and MW-4, all located within approximately 700 feet of the northwest corner of the landfill. Maximum total VOC concentrations associated with samples obtained from these locations ranged from approximately 100 to 800 ppb. Lower levels of VOCs were observed in samples obtained from monitoring wells B-l, B-4, B-5, B-10, MW-l, MW-3, and RW-2. Maximum total VOC concentrations observed in samples obtained at


I !

I f these well locations ranged from approximately <5 to 100 ppb. I VOCs were not detected in samples obtained from the remaining

groundwater sampling points including B-7, B-11, RW-1 (the Somersworth municipal supply well No.3), RW-4, RW-5, RW-6, RW-7, and RW-8.

I A single VOC (toluene) was detected at a concentration of less than 5 ppb in a sample obtained from residential well RW-3, however, the analytical laboratory reported that result as a "possible laboratory contamination." No VOCs have been detected in three ! subsequent rounds of szunpling at RW-3.

A total of 33 VOCs were observed in groundwater samples obtained \ within the study area. The most commonly observed VOCs are listed

below in decreasing order of frequency of occurrence.

I I

Maximum Monitoring Well Concentrat ion Associated with

Compound Observed (uq/11 Maximum Concentration

. dichloroethylene (c&t) 5,175 B-6R

. trichloroethylene 2,000 B-12R

. 1,1-dichloroethane 1,399 B-6R

. benzene 23 B-6R

. toluene 872 B-6L i^ . diethyl ether 144 B-6R

. tetrahydrofuran 146 MW-4

. trichloromethane 21 B-5L ; . acetone 1,840 B-6L • . chlorobenzene 8 B-6L

A detailed pattern in the lateral distribution of the Individual V OCs is not readily apparent from a qualitative review of the data. It was observed, however, that, with the exception of VOCs detected in one sample obtained from monitoring cluster B-5, all other contaminated samples were obtained from monitoring wells considered downgradient of or adjacent to the landfill.

Trends are apparent in the vertical distribution of various VOCs. At some monitoring clusters that contain monitoring wells screened within both the overburden soils and the bedrock, a stratification of the VOC contamination was observed. This phenomenon was observed to be most prominent at monitoring well clusters located Immediately downgradient o^ the landfill where total VOC concentrations are relatively high. Specifically, at monitoring cluster B-6, and to a lesser extent at monitoring clusters B-9 and B-12, certain VOCs appeared in notably higher concentrations in the bedrock monitoring wells than the overburden monitoring wells. These VOCs include the following compounds:


I

Ir * . 1,l-dlchloroethane

. 1,1-dlchloroethylene

. dichloroethylene (c&t)

. trichloroethylene I . tetrachloroethylene These compounds have relatively low solubilities in water and have specific gravities greater than one (in a pure form they sink).

I I At monitoring cluster B-6, VOCs that generally were observed In

notzJsly higher concentrations in the overburden wells as opposed to the bedrock wells include the following compounds:

. ethylbenzene

. toluene

. xylenes I . methyl ethyl ketone

. methyl isobutyl ketone

I These compounds generally have relatively low solubitillties in water and have specific gravities less than one (in a pure form they float).

I This apparent stratification of the VOCs generally was not observed at monitoring well clusters located at distances further downgradient from the landfill. For example, at monitoring well locations B-8 and B-13, dichloroethylene (c&t), trichloro-ethylene, and tetrachloroethylene were observed at approximately equal or

I higher concentrations in samples obtained from the overburden I monitoring wells compared to samples obtained from the bedrock

monitoring wells. f t ABN's i

Table 13 and Appendices 1.3.1 and 1.4.1 summarize the

I ABN's observed in groundwater samples obtained during the Remedial

I Investigation. Acid and base/neutral extractable compounds were observed at two monitoring well locations in the study area. A total of eight ABN's were detected in the groundwater samples obtained from downgradient monitoring wells B-6L and B-6R, and B9WT and B-9R. Trace levels of three acid extractable compounds phenol, 4-methylphenol, and benzoic acid - were observed in samples

I obtained at monitoring cluster B-9. Phenol and methylphenol were

I also observed in a sample obtained from monitoring well B-6L at concentrations of 23 ug/1 and 430 ug/1, respectively. N-nitrosodiphenylamine was observed in a sample obtained from monitoring well B-6R at a concentration of 42 ug/1. The remaining ABN compounds identified at monitoring well cluster B-6 were observed at trace concentrations.

I Somersworth - Mav 22. 1989 - File No. D-5162 - Section 7 - Page 10

/ Metals

Table 10 and Appendix 1.2.1 summarize the metals observed in the groundwater samples obtained during the Remedial Investigation. Metals analyses performed on samples obtained from B-series monitoring wells indicate that arsenic, chromium, copper, lead, nickel, and zinc are common constituents in the groundwater within the study area. Results also indicate that only arsenic, chromium, and lead were observed at concentrations above both their respective MCL criterion and anticipated background levels. Arsenic was observed equal to or above the MCL in samples obtained from monitoring clusters B-1, B-4, B-5, B-6, B-10, B-11, and B-13. The highest concentration detected was 0.38 mg/1 in a sample obtained from monitoring well B-4L. Chromiiim was observed equal to or above the MCL in samples obtained from monitoring clusters B-9, B-10, B-11, and B-13. The highest concentration of chromium detected was 0.11 mg/1 at monitoring wells B-IOL and B-13L. Finally, lead was observed above the MCL in a sample obtained from B-9WT, at a concentration of 0.12 mg/1.

Copper, nickel, and zinc were observed at concentrations exceeding their respective anticipated background levels of 0.1 mg/1 based on previously discussed published data, and on a comparison with other metals data obtained from the landfill area. Levels of all three metals appear high in samples obtained at monitoring clusters

^ B-10, B-11, and •B-13. In addition, both zinc and nickel were observed above the anticipated background levels at monitoring cluster B-6, and of the three, zinc alone was observed above the anticipated background level at monitoring clusters B-5, B-8, and B-9. These monitoring locations represent both up- and downgradient sampling points from the landfill and, therefore, no pattern of distribution is readily apparent.

Leachate Indicators

Table 14 and Appendix 1.7.1 summarize the observed distribution of leachate indicators. Leachate quality indicator analyses were performed on groundwater samples obtained from all of the B-series and MW-series monitoring wells with the exception of B-3L, B-7L, B-7R, and MW-4. Residential well RW-2 was also tested for leachate indicators. These analyses included tests for six inorganic substances (iron, manganese, chloride, sulfate, nitrate/nitrite, and total phosphorous) as measures of total organic content, chemical oxygen demand, and ammonia nitrogen content (TOC, COD, and TKN, respectively).

Concentrations of most of the leachate indicators were observed to vary non-systematically across the study area, limiting meaningful Interpretation of their distribution. Of the five Inorganic leachate indicators for which State of New Hampshire SMCL's are available (currently there is no MCL for phosphorus), three were


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observed at concentrations above their respective SMCL criteria. Iron was observed at concentrations above its SMCL criterion in all of the groundwater samples analyzed for the leachate parameters. Manganese was also observed at concentrations above Its SMCL criterion in 25 of the 28 groundwater samples analyzed for the leachate parameters. Chloride was observed at concentrations above the MCL in only two of the groundwater samples tested.

Although iron and manganese were generally present at concentrations which may reflect the presence of landfill leachate (Freeze and Cherry, 1979), available information indicates that natural iron and manganese in this area of New Hzmpshire are typically present in very high concentrations. Specific to the southeastern New Hampshire area, Bradley (1964) indicated that "...iron in water (groundwater) is a fairly common problem." In fact, the high natural iron content of water from Hussey Springs (Dover, New Hampshire supply well No. 6) in the Willand Pond area of Dover-Somersworth, New Hampshire was probably one of the principal causes for its abandonment as a public supply source (Bradley, 1964). Additionally, high iron and manganese concentrations have historically been recorded at Somersworth municipal supply well No. 3, which, as indicated in Section 2.0, contributed significantly to its decommissioning.

Naturally high iron and manganese contents in the groundwater may be related to the reducing (i.e. low oxygen) conditions produced in the peat-rich soils and swamps. Both iron and manganese are much more soluble in their reduced states (Fe * , Mn " ) than in their oxidized states (Fe'*, Mn'VMn**) (KrausKopf, 1972). Furthermore, the abundance of decaying vegetation produces large quantities of organic acids which may complex the iron and manganese and Increase their concentration in solution (Holland, 1978). This information indicates that the generally high iron and manganese concentrations observed at groundwater sampling points within the study area do not necessarily correlate with contamination by leachate emanating from the Somersworth landfill.

Water quality data provided in Bradley (1964) indicate that background levels of chloride may be as high as approximately 40 mg/1. At the Somersworth Municipal Landfill, the highest chloride concentrations were observed in samples obtained from downgradient monitoring wells B-6L, B-6R, and MW-3 at 280 mg/1, 112 mg/1, and 275 mg/1, respectively, which is considered to Indicate the presence of landfill leachate. Chloride levels above the anticipated background level of 40 mg/1 or less, were also observed in samples obtained from downgradient monitoring wells B-IL, B-9R, B-12R, B-13L, MW-1, MW-2, and RW-2, and from upgradient monitoring wells B-5U and B-llR.


c Levels of COD, TKN, and TOC were observed to vary significantly across the site; however, consistently high values of all three parameters were recorded at downgradient monitoring clusters B-6, B-8, and B-9. On the average, the lowest values of these parameters were observed at upgradient monitoring clusters B-5 and B-11.

7t2f3 goils

Chemical analyses were performed on soil samples collected from 20 separate locations Including both test borings and test pits. A summary of the locations from which soil samples were obtained and the analyses performed on these samples is Table 6. Table 11 and Appendix 1.1.5 summarize the observed distribution of V OCs in the soil samples that were obtained during the Remedial Investigation.

Test Poripqs

Composite soil samples were obtained from each boring performed during the Remedial Investigation. Because of the drive-and-wash techniques used to advance all borings during the field exploration program, results of soil analyses are considered only as an indicator of the possible presence, and not necessarily the

( absence, of contaminants within these soil samples.

Analyses of the composite soil samples obtained from the test borings indicated the presence of VOCs in test borings B-1, B-2, B-3, B-8, B-9, B-12 and B-13, all considered to be downgradient or adjacent to the landfill. The VOCs observed in the soil samples obtained from the test borings include:

. xylenes

. toluene

. ethylbenzene

. methyl ethyl ketone

. acetone

. carbon disulfide

The highest VOC concentrations were observed from soil samples obtained from test borings B-8 and B-9 where methyl ethyl ketone was detected in boring samples at levels of 70 ug/kg and 130 ug/kg, respectively. Carbon disulfide was also detected in soil sample B-8 at a concentration of 15 ug/kg. VOC concentrations within the remaining test borings were observed to be generally lower, with total VOC concentrations ranging from 5 ug/g in a sample obtained from boring B-12 to 60 ug/kg in a sample obtained from boring B-1.


c

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Appendix 1.2.3 suximarizes the observed distribution of metals in the soil samples obtained during the Remedial Investigation. Cadmixim and arsenic were the only metal observed in soils at

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concentrations above anticipated background levels based on published data summarized in Table 11; however the concentrations of zinc of 180 ug/g observed in a sample obtained from boring B-2 appears high based on a comparison with other zinc data. Cadmium was detected at concentrations of approximately 1.0 ug/g and 1.8 ug/9 in soil samples obtained from borings B-1 and B-8, respectively. Arsenic was detected near or above anticipated background levels in soil samples obtained at B-1, B-4, B-8, B-9, and S-4.

Table 13 and Appendices 1.3.3 and 1.4.3 siimmarize the observed distribution of ABN's in the soil samples obtained during the Remedial Investigation. Acid extractable compounds were not observed in any of the soil samples obtained from the test borings, and base/neutral extractable compounds were observed only in samples obtained from test borings B-4 and B-12. Total base/neutral concentrations observed were 11,530 ug/kg in a sample obtained from boring cluster B-4 and 540 ug/kg in a sample obtained from boring cluster B-12. Nine different base/neutral compounds were detected, most of which are PNA's.

Test Pits

VOC analyses were performed on soil samples obtained from test pits TP-5, TP-6, TP-8, TP-9, TP-10, A-5, and A-6,

all of which were excavated within the limits of the landfill. Metals and ABN analyses were performed on soil samples obtained from test pits TP-9 and A-5.

VOCs were observed in the soil samples obtained from test pits TP-8, A-5, and A-6 in the following approximate total VOC concentrations:

Test Pit Total VOC Concentrations

TP-8 2,780 ug/kg A-5 1,600 ug/kg A-6 580 ug/kg

Individual VOCs that were observed include xylenes, toluene, ethylbenzene, methyl ethyl ketone, trans-1,2-dichloroethylene, and acetone.


I ! r Metals were not observed in concentrations above anticipated I background levels in the soil samples obtained from test pits TP

I - 9 and A-5. ABN's were observed in the soil sample obtained from

I test pit TP-9, but not in the seunple obtained from test pit A-5. Fluoranthene and pyrene were detected in TP-9 at trace concentrations of 1,200 ug/kg and 540 ug/kg, respectively.

7.2.4 Air

Results of initial air quality screening by the project team, as well as results of air quality screening during the soil boring program Indicated no VOCs detected. Detection limits were approximately 1 ppm.

1 7.2.5 Summary

Analyses of surface water and sediment samples obtained from surface water stations within the site study area indicate that 1 surface water and sediment contamination generally occurs within portions of Peter's Marsh Brook located downstream of the landfill and within the lower reaches of an unnamed tributary of the brook

I near their confluence. The most prominent VOC detected in the surface water samples was dichloroethylene (c&t).

I f I , Results of ABN's and metals analyses performed on samples from

I • ' surface water stations S-1, S-4, and S-6 indicate that ABN's were

detected at trace levels at surface water station S-6. Mercury was detected at a concentration slightly above the MCL in a surface water sample obtained from station S-1. Cyanide was detected at a concentration slightly above the MCL in a surface water sample obtained from station S-6.

I I Chemical contamination observed in sediment samples obtained at

surface water stations in the study area was observed to include only VOCs. VOCs were observed in sediment samples obtained from surface water stations S-4, S-5, and S-6. Xylenes were detected in all of the samples obtained from each of these stations.

I VOC, ABN, metals, and leachate Indicator contamination in groundwater was observed to be most prevalent at locations considered downgradient of the landfill, especially within the

1 vicinity of the northwest corner of the landfill. The highest concentrations of VOCs were observed in groundwater samples obtained from monitoring wells B-6L and B-6R, located approximately

^ 200 feet from-the northwest corner of the landfill, where total VOC ] concentrations ranged from approximately 2,500 ug/1 to 13,000 ug/1.


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Relatively few ABN compounds were observed in groundwater samples obtained from monitoring wells within the study area. ABN's were detected in samples obtained from monitoring well clusters B-6 and B-9, both located northwest and downgradient of the landfill.

Concentrations of metals zUsove anticipated background levels and MCL criteria were observed in groundwater samples obtained from many monitoring wells within the study area. Only arsenic, chromium, and lead were observed at concentrations above both their respective MCL criterion and anticipated background levels. Zinc, copper, and nickel were also observed at levels above anticipated background concentrations at locations considered both up- and downgradient of the landfill. Therefore, no pattern of distribution is readily apparent.

Of the leachate indicators, iron and manganese concentrations were observed to be very high, however, these levels may reflect naturally occurring iron and manganese in this area. Therefore, these results are inconclusive. Chloride levels were observed to be highest in samples obtained from downgradient monitoring cluster B-6 and monitoring well MW-3. Similarly, levels of COD, TKN, and TOC were observed to be consistently high at downgradient monitoring clusters B-6, B-8, and B-9.

Chemical analyses performed on composite soil samples obtained from test borings indicate the presence of VOCs and ABN's in soil at locations considered downgradient of the landfill. The highest VOC

concentrations were observed from soil samples obtained from test boring B-8 and B-9 where methyl ethyl ketone was observed at levels of 70 ug/g and 130 ug/g, respectively. Base neutral compounds, primarily PNA's, were detected in soil samples obtained from borings B-4 and B-12 at concentrations of 11,530 ug/kg and 540 ug/kg, respectively. Cadmium, arsenic, and zinc were the only metal observed in soils at concentrations above anticipated background levels.

Chemical analyses performed on soil samples obtained from test pits detected total VOC contaminant concentrations between approximately 580 ug/kg and 2,780 ug/kg in three of seven test pits sampled. Metals were not observed above anticipated background levels in the soil samples obtained from two test pits sampled. ABN's, at a trace total concentration of approximately 1,800 ug/kg, were detected in one of two test pits sampled.

Results of initial air quality screening by the project team, as well as results of air quality screening during the soil boring program and a qualitative air monitoring program conducted subsequent to the soil boring program indicated no detectable VOCs within air in the vicinity of the landfill. Detection limits were approximately 1 ppm.


I I / 7.3 CONTAMINANT TRANSPORT

I Contaminants released to the environment may migrate via a variety ^ of transport mechanisms through various media - air, groundwater,

and surface water - potentially affecting environmental or human receptors. Hence, evaluation of the migration of conteuninantsI represents a key element in the Remedial Investigation process.

Hydrogeologic and water quality data collected during the Remedial Investigation field investigation progreun Indicate that most contaminants beyond the limits of the landfill are observed within groundwater. Therefore, the primary mechanism of contaminant transport from the landfill source area is anticipated to occur in the groundwater. Conteuninant transport is also anticipated to occur in surface water subsequent to recharge by conteuninated groundwater, primarily in Peter's Marsh Brook west and northwest of the landfill. Groundwater contaminant transport and attenuation mechanisms are discussed in detail below.

7f?ra, Groundwater Contaminant Transport and Attenuation Mechanisms

Contaminants at the site may enter the groundwater flow regime via percolation of liquid wastes disposed on the ground surface,

( infiltration of precipitation through contaminated solids, and ^ direct subsurface discharges during the period of operation (i.e.,

leaking drums). Once contaminants enter the groundwater, transport mechanisms include advection and dispersion. Advection Involves the transport of dissolved constituents by the bulk motion of groundwater flow. Ignoring attenuating mechanisms, dissolved constituents will flow with groundwater in the direction of decreasing hydraulic head at an average rate equal to the groundwater seepage velocity. Dispersion is the spreading process associated with the combination of molecular diffusion and the tortuosity of groundwater flow paths. Contaminant transport via molecular diffusion is a relatively slow process driven by concentration gradients, and is consequently not a factor at the site relative to advective transport processes. Mechanical dispersion is governed by soil characteristics represented by dispersion coefficients which are difficult to measure and may not ever be totally described for the complete hydrogeologic setting at the site. Contaminant migration via dispersion is believed to be less important than advective transport.


c Immiscible Liquid Contaminants

The transport of non-aqueous phase (immiscible) liquids

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can be considerably more complex than the migration of dissolved constituents. Many of these liquids are solxible in water at very low concentrations, typically less than 100 to 1,000 mg/1 at common ambient temperatures. Consequently, many of these liquids can persist in a non-aqueous phase for very long durations in a groundwater environment.

Immiscible liquids which are lighter than water may float on the surface of the saturated zone and may be transported in the direction of groundwater flow at varying rates depending upon the specific properties of the fluid. The presence of a floating layer of light non-aqueous phase liquids (LNAPL's) can often be detected within groundwater monitoring wells using standard sampling equipment and protocol. Toluene and xylene are examples of common light non-aqueous phase liquids. While these compounds were commonly observed in groundwater samples obtained at the Somersworth Municipal Landfill, no floating layers were detected.

Dense non-aqueous phase liquids (DNAPL's) typically migrate vertically downward very rapidly through both the vadose zone and the unsaturated zone. Recent research indicates that DNAPL's may form product pools at topographic low points of underlying aguitards (Cherry, 1987). Since DNAPL's can be deflected or retained by low hydraulic conductivity beds such as silt lenses, and can migrate along the surface of an aquitard in the direction of decreasing elevation (even if it opposes the direction of groundwater flow), DNAPL pools are extremely difficult to locate. Additionally, because DNAPL pools are typically of limited thickness as a result of product spreading under the influence of gravity, it is improbable that a DNAPL pool would be detected using standard sampling equipment and protocol.

The halogenated aliphatic hydrocarbons discussed in Section 7.1 are common DNAPL's thought to have been disposed at the Somersworth Municipal Landfill. These compounds were detected in solution in many groundwater and surface water samples obtained from the site study area. Therefore, it is possible that undetected DNAPL pools could exist at the base of the aquifer within proximity of the landfill. Such pools, if present, could likely be present either in subsurface bedrock basins, or within bedrock fractures. The potential effect that DNAPL pools may have with regard to transport and persistence of groundwater contamination at the Somersworth Municipal Landfill is discussed in Section 7.3 2.


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Contaminant Attenuation

There are a number of processes which operate to reduce contaminant concentrations as they migrate through the groundwater flow regime. These Include the above-mentioned dispersion, which acts as a dilution process to reduce contaminant levels; adsorption, an immobilization (either temporary or permanent) of constituents by attachment to solid substrates; biodegradation, the transformation of organic conteuninants via metabolism by microorganisms present in soils; and chemical transformation. Including oxidation/reduction reactions and precipitation reactions.

Adsorption is perhaps the most significant attenuation mechanism for contaminants migrating through saturated soils. Primary adsorption sites Include organic matter, which is present at variable levels within essentially all soils, and colloidal particles. The magnitude and rate of adsorption is a function of the chemical properties of the contaminant, the nature and availability of the solid substrate, and the concentration of the contaminant. For organic compounds, adsorption typically Increases with molecular weight within homologous series. In other words, lower molecular weight compounds, such as cezrtain volatiles, generally display increased mobility in comparison to heavier extractable organics. For some polar organic and Inorganic compounds, adsorption can entail the formation of relatively strong bonds with substrates normally found in natural soils such as clay minerals or humic substances.

With respect to transport of organic compounds, adsorption tends to be reversible and acts to impede or retard the advective solute front and, hence, is important in consideration of potential contaminant transport times. The degree of impedance or retardation is defined as the Retardation Factor, R:

V R =

where V ^ groundwater seepage velocity Vj = advective transport velocity

Studies have shown that for some organic compounds the retardation factor can be estimated by the following relationship:

f. b*Kd R = 1 + '

n

where P b . \ h « bulk dry soil density Kd = distribution coefficient n s= soil porosity


c The distribution coefficient (Kd) is defined as the mass of solute on the solid phase per unit mass of solid phase, per concentration

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of solute in solution (Freeze and Cherry, 1979). Consequently, the larger the distribution coefficient the less mobile the solute. For many organic compounds, Kd can be estimated by:

Kd « foe * Koc

where foe « fraction of organic carbon in the soil matrix Koc « organic carbon partition coefficient

The bulk dry soil density, soil porosity, and fraction of organic carbon are all properties of the soil itself. The organic carbon partition coefficient is a function of the individual compound, however, and consequently may vary considerably among compounds, resulting in a range of retardation factors for compounds observed at the site. When more than one compound is migrating in groundwater, contaminant plume segregation and variable arrival times at receptors are often the result.

Adsorption may also retard the migration of metals; however, the distribution coefficient, and consequently the retardation factor, is partially a function of the cation exchange capacity of the soil media, the valence of the metal contaminant, and pH of the groundwater. Metals tend to be more soliible and more mobile in groundwater with a low pH. For many metals, adsorption, and thus retardation factors, may be very high at pH values greater than 8 or 9. For some metals, notably zinc, copper, and cadmium, adsorption may be almost complete at low concentrations in groundwater with a pH above 8 (Palmer et al, 1987).

Oxidation/reduction and precipitation reactions may also significantly retard the migration of metals, including iron and manganese. Many metals, including iron, copper, lead, zinc, cadmium, mercury and arsenic form very insoluble sulfides. Therefore, the presence of significant amounts of HjS (as a gas or in solution) will tend to precipitate sulfides of these metals, thiis immobilizing them and reducing their concentrations in solution (Barnes, 1979). Reduced iron and manganese may also be precipitated as hydrated oxides from solution via oxidation reactions in more oxygen rich environments (Krauskopf, 1972). The precipitated iron and manganese oxides may in turn adsorb other metals such as copper, lead, zinc, nickel & cadmium (Jenne, 1968; Krauskopf, 1972).


c The oxidation and resultant precipitation of iron is most likely responsible for the observed red coloration of the surface soils downgradient of the landfill. At this location, groundwater is in a reduced state due to interaction with the organic rich soils and is thought to discharge to the surface. At the surface these groundwaters are oxidized, and essentially all iron in solution is precipitated as hydrated iron oxides.

Biological transformation of organic compounds by micro-organisms In the soil column has received substantial attention in recent years as a potentially significant mechanism of attenuation. The rates and byproducts of biodegradation can be highly varieible depending upon the nature of the cont2minants present, the species of micro-organisms, availability of nutrients, and general groundwater chemistry. Certain aromatic compounds have been known to be susceptible to biological degradation; recent research has indicated that many halogenated aliphatic compounds may also be biologically transformed under certain conditions.

Additional mechanisms of attenuation may operate as groundwater discharges to surface water environments. Principal among these for volatile contaminants is volatilization which can result in substantial reductions of concentrations under favorable enviroTunental conditions. Photodecomposition and hydrolysis are other attenuating mechanisms which may result in the degradation of certain contaminants.

7.3.2 Site Contaminant Migration

Groundwater contamination downgradient of the Somersworth Municipal Landfill is at this time considered primarily attributed to the Somersworth Municipal Landfill. It is noted however, that hazardous materials may have been stored on, or transferred through adjacent properties including a scrap metal yard south of Blackwater Road, a dry cleaning operation, and the National Guard Armory. It is not clear what effect, if any, activities relating to possible hazardous wastes at these sites may have had on water quality in the vicinity of the site.

Contamination is anticipated to migrate from the landfill source area to the groundwater beneath the landfill by several different mechanisms, including primarily the following:

1. Direct disposal of liquid wastes to the landfill surface during the period of operation, with subsequent infiltration to the groundwater beneath the landfill;

2. Intermittent infiltration of liquid wastes as containers within the refuse corrode; and


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3. Leaching ofunsaturatedprecipitation infiltration.

contaminants soil (vadose

from the refuse, and from zone) beneath the refuse

the by

Mass loading of contaminants to the groundwater beneath the landfill via these mechanisms is regarded as highly variable. This is the result of the uncontrolled nature of waste disposal, both temporally and aerially. Additionally, there is a high degree of inherent variability of factors controlling leachate generation. Including regional climatology, permeability and adsorptlve characteristics of landfilled refuse, and solubility of various chemical contaminants.

Contaminant loading during the approximately 40- to 45-year operational period of the landfill has likely resulted from all three of the above-described mechanisms. Although waste disposal was terminated in 1981, observation of contaminants in relatively high concentrations immediately downgradient of the landfill indicates that contaminant loading due to the latter two mechanisms may have continued to the present time. This opinion is supported by observations of contaminants within vadose zone samples obtained from test pits excavated within the landfill. Additionally, although Intact drums containing liquid wastes were not encountered in the limited number of test pits excavated at the landfill, studies by previous Investigators (Mitre Corporation, 1978)

Indicate that intact drums containing liquid wastes may have been placed within the landfill during the period of operation, and

therefore could continue to be a source of contamination. The variability of contaminant mass loading discussed above, and the lack of specific information available pertaining to characteristics of the various potential contaminant sources within the refuse, precludes an assessment of the length of time over which the landfill will continue to be a source of contamination.

The disposal of significant volumes of dense, non-aqueous phase liquids could engender a secondary source of groundwater contamination. As discussed in Section 7.3.1, bulk disposal of these wastes may have resulted in the formation of DNAPL pools at the base of the aquifer. Recent research has Indicated that groundwater flowing over DNAPL pools, or through DNAPL residual in the vadose or saturated zones, slowly dissolves the contaminant mass (Cherry, 1987). Depending on the volume and surface area, DNAPL pools may persist as potential sources of groundwater contamination for long durations (Cherry, 1987).


c Zone of Contamination

The estimated zone of groundwater contamination is shown

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on Figure 10. Water quality data Indicate that the zone of highest groundwater contamination extends as a plume northwesterly from the landfill approximately 1,000 feet. The centerline of this contaminant plume is estimated to lie in proximity to monitoring clusters B-6 and B-8. Contaminant concentrations appear to decrease on either side of the plume centerline; however, analyses of groundwater samples obtained from monitoring clusters B-9 and B-10 indicate that the zone of contaminated groundwater extends at least 200 feet west and 700 feet east of Peter's Marsh Brook.

Geophysical terrain conductivity values, contoured on Figures 5 and 6 of the geophysical report included as Appendix H, also suggest the presence of a plume of groundwater contamination extending northwest of the landfill. The highest terrain conductivity values were detected in the vicinity of monitoring cluster B-6, with elevated terrain conductivity values along Peter's Marsh Brook west and northwest of the landfill. Similar to water quality data, the terrain conductivity data indicate a decrease in contaminant concentrations to the east and west of Peter's Marsh Brook.

Water quality data also indicate that the zone of contaminated groundwater extends at least 100 feet south of the landfill perimeter. Although this area is not directly downgradient of the landfill, its proximity to the landfill may result in groundwater contamination due to minor seasonal fluctuations in the regional groundwater flow pattern, local variance in flow direction not reflected on the larger-scale groundwater elevation contour plan, and on hydrodynamic dispersion along the plume boundary.

Nevertheless, the southerly extent of the zone of groundwater contamination is anticipated to be limited due to the governing

regional northwesterly groundwater flow regime.

VOC contamination has been detected on one occasion at upgradient monitoring cluster B-5 located approximately 600 feet northwest of the intersection of Blackwater Road and Maple Street Extension.

Because of the one time occurrence and the clearly upgradient location of this sampling point, the landfill is not considered the

source of contamination in the sample obtained at B-5. Three sampling rounds have been performed at monitoring cluster B-5 over one and one-half years subsequent to the sampling round from which the contaminated sample was obtained indicating transient

contamination from an unidentified source, or suspect data.


c Fate of Contaminants in Groundwater

Superimposed on the estimated zone of groundwater

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contamination shown on Figure 10 are groundwater contours and flow lines. The northern and southern flow lines form approximate flow boundaries to the streamtube beneath the landfill area, referred to below as the "landfill streamtxibe. ** Conteunination entering the groundwater beneath the landfill source area would be expected to migrate primarily within the landfill streamtube by advectivedispersive transport west-northwesterly in the direction of regional groundwater flow toward Peter's Marsh Brook and associated wetlands. The plume centerline is anticipated to be approximately coincident with the center flow line shown on Figure 10. As Indicated eibove, contaminant migration outside the landfill streamtube boundaries may be the result of minor seasonal fluctuations in the regional groundwater flow pattern, local variance in flow direction not reflected on the larger-scale groundwater elevation contour plan, as well as hydrodynamic dispersion at the limits of the contaminant plume. These factors and others, such as low flow conditions within Peter's Marsh Brook and the presence of discontinuous low permeability clay strata, may also result in underflow beneath Peter's Marsh Brook as evidenced by contamination detected in samples obtained at monitoring cluster B-9.

The actual downgradient extent and ultimate fate of groundwater contamination is difficult to assess due to limited groundwater quality data northwest of monitoring cluster B-8. Water quality data support the contention that the contaminant plume has migrated at least as far northwest as monitoring cluster B-8. Geophysical terrain conductivity values from EM line 19, located approximately 700 feet downgradient of monitoring cluster B-8, suggest the presence of shallow contamination in the immediate vicinity of Peter's Marsh Brook, but no contamination to the east. Although these data are inconclusive, the higher conductivity values observed in the immediate vicinity of Peter's Marsh Brook may reflect contaminated sediments, not necessarily contaminated groundwater. In aggregate, these water quality and geophysical data indicate that the downgradient limit of the contaminant plume currently lies between monitoring cluster B-8 and EM line 19 as Indicated on Figure 10. It should be noted however, that EM line 19 does not extend west of Peter's Marsh Brook.

Two basic scenarios were considered with regard to groundwater contaminant transport in the study area. Either the contaminant plume is transient with ccntaminant concentrations Increasing at distances downgradient of the landfill, or the contaminant plume is at steady state, with a relatively stationary contaminant front due to discharge of contaminants into Peter's Marsh Brook and/or other attenuation mechanisms. Due to the relatively limited amount


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C of hydrogeologic and water quality data collected during the Remedial Investigation, and the complex and extensive hydrogeologic environment observed at the site, conclusive evidence supporting either a transient or a steady state scenario is not available. Nevertheless, review and analyses of data collected during execution of the Remedial Investigation provide an indication of the operative transport mechanics and fate of chemical conteuninants In groundwater at the Somersworth Municipal Landfill. The results of the data review and analyses are discussed below. It is recommended that these results, and the ensuing judgments and conclusions, be further substantiated with additional ditta collection as described in Section 11.1.

Hydraulic data indicate that a steady state scenario is more likely. As discussed in Section 5.3, Peter's Marsh Brook and the surrounding wetlands are considered a major discharge area for regional groundwater flowing from points south and east. Review of the estimated horizontal flow pattern shown on Figure 10 indicates that groundwater within the landfill streamtube is discharged to Peter's Marsh Brook and adjacent wetlands in an area extending from immediately north of Blackwater Road northerly to the vicinity of EM line 19. The estimated zone of groundwater contamination, also shown on Figure 10, appears confined primarily within the landfill streamtube. The lack of an indication that contaminants have migrated north of EM line 19 suggests that discharge of dissolved groundwater contaminants to surface water strongly inhibits contaminant migration in groundwater northwest ( of EM line 19.

The steady state scenario is also supported by a site specific contaminant transport analysis. In particular, contaminants that migrate by advective transport at, or near the mean seepage velocity are considered in this analysis. Contaminants of this type have a low affinity for adsorption and hence are termed "very highly mobile"; the distribution coefficient (Kd) of these contaminants is close to zero, with the resulting retardation factor close to or equal to one (refer to Section 7.3.1 for an explanation of these terms). At the Somersworth Municipal Landfill, only a few observed contaminants fall into this category. Organic contaminants considered very highly mobile include acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) (Griffin and Roy, 1985). Of slightly less mobility but still considered highly mobile are benzene, 1,1-dichloroethane, 1,2dichloroethane, 1,1-dichloroethylene, and 1,2-dichloroethylene (Griffin and Roy, 1985; Cherry, 1987). Chloride is the primary Inorganic contaminant observed in samples obtained from the site study area that is regarded as very highly mobile.

Since the highly mobile contaminants migrate by advectivedispersive transport at a rate approximately equal to the mean groundwater seepage velocity, the hydraulic parameters presented


c in Section 5.3 were used to estimate the time for a non-retarded contaminant front to travel northwest from the landfill with regional groundwater flow. The results of the analysis were compared with water quality data to determine if observed contaminant behavior is consistent with the predicted contaminant behavior.

A major limitation to the analysis is the uncontrolled and undocumented waste disposal practices which render temporal and areal source characterization unquantlfleible. Therefore, it was assumed that waste disposal practices have remained consistent since termination of open burning in 1958, at which point actual landfilling operations commenced. Additionally, it was assumed that the area in the vicinity of test pit TP-9 represents the approximate center of landfill activities since 1958.

Using the average hydraulic parameters discussed in Section 5.3, the non-retarded contaminant front would be expected to reach monitoring cluster B-6 within approximately 4 to 8 years after contaminant disposal near the center of the landfill. The non-retarded advective transport time from monitoring cluster B-6 to downgradient monitoring cluster B-8 is estimated to be approximately 1 to 3 years. Approximately 30 years have passed from Initiation of landfill operations, and perhaps as much as 52 years since initiation of an open burning dump in the northeast corner of the site. Therefore, based on transport times, concentrations of highly mobile contaminants in the vicinity of ( monitoring cluster B-8 in 1987 would be anticipated to be approximately the same (assuming constant source) or greater (assuming decaying source) than concentrations of the highly mobile contaminants in the vicinity of monitoring cluster B-6.

Water quality data indicate that this is not the case. In general, total VOC concentrations were observed to decrease by one to two orders of magnitude between monitoring cluster B-6 and monitoring cluster B-8, suggesting significant contaminant attenuation between these two points. Of the very highly mobile contaminants, including acetone, MEK, MIBK, and chloride, the following sharp reductions in contaminant concentrations were observed in the results of the December 1986 sampling round:

G-6 B-8 Contaminant L R WT u L R

Acetone 1,840 144 15 18 MEK 1,480 - - - - 5 MIBK 164 - - - -

Chloride 280,000 112 ,000 12 ,000 40,000 NA 22,000


c In the above table, "NA" indicates not analyzed, "-" Indicates none detected, and results are reported in ug/1 (ppb). It should also be noted that chloride concentrations observed in samples obtained

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from monitoring cluster B-8 are in a range considered indicative of background levels, whereas chloride concentrations observed in samples obtained from monitoring cluster B-6 are elevated. Similar reductions In the concentrations of the other mobile VOC contaminants, teUsulated in Appendix I.1.1, were observed as well. Therefore, since consideration of only the highly mobile conteuninants limits the significance of adsorption as a primary attenuation mechanism, contaminant attenuation due to surface water discharge, or Irreversible biochemical decay, is considered more likely. In either case, downgradient plxime migration in groundwater appears to be strongly inhibited.

Geophysical terrain conductivity data support the steady state hypothesis as well. Since geophysical terrain conductivity is insensitive to the presence of most organic compounds, the terrain conductivity data are considered inconclusive with regard to migration of VOCs; however, terrain conductivity has been shown to be directly correlated with specific conductance of groundwater (Shope, 1986), which in turn is directly proportional to ion concentrations in groundwater, including chloride. Results of the geophysical explorations indicate that terrain conductivity values are highest within approximately 200 feet of the west and northwest perimeter of the landfill, and decrease substantially downgradient of that area. Terrain conductivity values along EM line 19, located approximately 700 feet northwest of monitoring cluster B8, exceed anticipated background levels only in the immediate vicinity of Peter's Marsh Brook, which may be the result of contaminated sediments, not necessarily contaminated groundwater.

The pattern of migration of contaminants in the bedrock is less clear. Water quality data confirm the presence of contamination within groundwater samples obtained from most downgradient bedrock monitoring wells. Hydraulic data indicate that, at least on a macroscopic scale, direct hydraulic communication between the overburden deposits and the bedrock fractures occurs. Therefore, regional groundwater flow in bedrock is anticipated to be in a direction approximately coincident with regional overburden groundwater flow. Since no large fracture lineaments have been detected in the vicinity of the site, no strongly preferential bedrock flow pattern is anticipated; however, the secondary northwesterly trending regional fracture pattern identified in the fracture trace analysis aligns closely with the regional groundwater flow direction. As such, advective contaminant migration in northwesterly trending bedrock fractures appears likely.


c On a local scale, contaminant migration in bedrock fractures is controlled by: fracture orientation and tortuosity, aperture width and orientation, fracture roughness, the porosity matrix of the rock, as well as the diffusion/adsorption reactions between each individual contaminant and the rock. This information (in the required detail) is not attained3le by conventional site exploration programs (Cherry, 1985). Water quality data indicate that the most substantial bedrock contamination occurs in the vicinity of monitoring cluster B-6, which supports the contention that the primary route of contaminant migration in bedrock is similar to that in the overburden deposits. Additionally, the significant contaminant attenuation observed between monitoring cluster B-6 and monitoring cluster B-8 is true of both bedrock as well as overburden water quality, which suggests that groundwater discharge or biochemical degradation may also be Important attenuation mechanisms in bedrock. Nevertheless, contaminant migration in the highly anisotropic bedrock flow field, particularly in deep fractures below the zone of bedrock exploration, could result in contaminant dispersion perpendicular to the regional groundwater flow regime and contaminant migration in bedrock northwest of EM line 19, and/or beyond the estimated zone of groundwater contamination depicted on Figure 10.

7.3.3 Potential Receptors to Groundwater Contamination

Results of analytical contaminant transport analyses indicate that the contaminant plume is at steady state; discharge of dissolved contaminants with groundwater into Peter's Marsh Brook and adjacent wetlands has severely limited contaminant migration downgradient of EM line 19. As such, the primary receptor to contaminant migration within groundwater at the Somersworth Municipal Landfill is regarded as Peter's Marsh Brook.

Contamination detected within samples obtained from surface water stations downgradient of the landfill in Peter's Marsh Brook has been observed to consist primarily of VOCs, although, as noted in Section 7.2, minor ABN and metals contamination has also been detected. Total VOC concentrations within these samples are typically less than 100 ug/1, and are significantly lower than total VOC concentrations in groundwater samples obtained at monitoring clusters B-6 and B-8 located adjacent to Peter's Marsh Brook. Since the above-described analyses indicate that the contaminant plume has reached steady state for a considerable length of time, the reduction of contaminant concentrations between adjacent groundwater and surface water monitoring points provides evidence of contaminant attenuation as groundwater is discharged to Peter's Marsh Brook.


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Contaminants discharged to Peter's Marsh Brook with groundwater must pass through a layer of peat, observed to be approximately 15 to 25 feet thick. Because of the large percentage of organic

carbon typically contained within peat, adsorption of VOC and ABN contaminants by the peat is anticipated to be a significant attenuation mechanism. Increased microbial activity within the peat is anticipated to result in increased biological decay or transformation, especially as the solute transport is retarded by adsorption. Finally, volatilization of organic compounds is likely to be significant as discharged groundwater mixes with surface water. The contribution of all three of these mechanisms to contaminant attenuation is not quantifiable with the limited site data; however, although some seasonal fluctuations in the specific contaminants and contaminant concentrations is probable, contamination within Peter's Marsh Brook is not anticipated to Increase significantly over levels detected during the Remedial Investigation considering the length of time the contaminant plume is estimated to have been at steady state.

To conservatively estimate the potential impact of contaminants transported in the surface waters of Peter's Marsh Brook to downgradient receptors, primarily the Berwick and Somersworth water Intakes in the Salmon Falls River, a dilution analysis based on stream flow data provided in Section 5.2 has been performed. The following assumptions were made:

1. The average flow in Peter's Marsh Brook in the vicinity of monitoring clusters B-6 and B-8 to the Salmon Falls River is 6 cfs.

2. The average flow in the Salmon Falls River at the Somersworth and Berwick water Intakes is 200 cfs.

3. The only contaminant attenuation mechanism is dilution.

The resultant dilution factor is approximately 35:1, that is, with the conservative assumptions provided above, contaminant concentrations in the Salmon Falls River are anticipated to be less than 3 percent of concentrations observed in Peter's Marsh Brook downgradient of the landfill. In actuality, volatilization, photodegradation, and biodegradation as well as added dilution from the Little River and Tate's Brook are significant attenuation mechanisms, rendering the 35:1 dilution factor very conservative.

In addition to Peter's Marsh Brook, few probable receptors to groundwater contamination were Identified in the site stu'ly area. Groundwater production wells within or in proximity to the estimated zone of contamination are considered receptors. The only groundwater well believed to be within this zone, however, is residential well RW-2, which reportedly has been abandoned and replaced with City water. The decommissioned Somersworth municipal


supply well No. 4, located immediately south of the estimated zone ( of landfill contamination is also a potential receptor, especially

considering the pumping gradients and resultant zone of Influence of a typical municipal production well. It is the project team's understanding, however, that this well has never been used for water supply purposes and that at this time there are no plans to use this well in the future.

The former Somersworth municipal supply well No. 3 is being dismantled in 1987 and for this reason alone it is not considered a potential receptor. Additionally, water quality data from groundwater samples obtained at this well have Indicated only iron and manganese at elevated levels; however, high concentrations of these inorganic contaminants appear to be natural in this area. No other contaminants have been observed. Since these data are consistent with the steady State scenario of contaminant pliime discharge into Peter's Marsh Brook between Blackwater Road and EM line 19, it is questionable whether the Somersworth municipal supply well No.3 was at risk prior to this time. Nevertheless, the project team considers its abandorunent prudent given its proximity and downgradient location to the landfill.

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8.0 RISK ASSESSMENT

8.1 PUBLIC HEALTH

gfltl iptroduc^ipn

This risk assessment for the Somersworth Municipal Landfill in Somersworth, New Hampshire was developed using available data discussed in other sections of the Remedial Investigation. The purpose of this risk assessment is to characterize public health risks associated with contaminants found on-site, as well as contaminants that have migrated off-site.

8.1.1.1 Site Description.

The Somersworth Municipal Landfill, herein referred to as the landfill or the site, covers an area of approximately 26 acres and is located one mile southwest of the City of Somersworth. The landfill was originally used as a burning dump, as early as the mid 1930's. Since there are no existing records of the type and amount of wastes disposed of at the Somersworth Municipal Landfill, it is assumed that local industries disposed of some or all of their hazardous waste materials at the site in the earlier years of the landfill operation. These industries include tanneries, bleacheries, shoe manufacturers and metal finishing companies.

Section 1.2.1 of the Draft Remedial Investigation describes the history of the landfill in more detail. Currently, the landfill

is active and accepts materials that cannot be Incinerated. These materials are disposed in what is referred to as the "stximp dump" which accepts stumps, major household appliances, old furniture, leaves, brush, etc. This area is located in the western portion of the landfill.

The eastern-most portion of the landfill has been developed into a lO^acre city recreational area known as Forest Glade Park, which consists of a playground, tennis courts, basketball courts and baseball fields. South of the landfill is a residential area along Blackwater Road. The western areas of the landfill lie approximately 100 to 400 feet from Peter's Marsh Brook which flows in a general northwest direction and is a tributary of Tate's Brook which is a tributary of Salmon Falls River which is a source of drinking water for the City of Somersworth, NH, and the Town of Berwick, Maine. North- northwest of the landfill is the location of the former Somersworth municipal water supply well No. 3. Previous investigations have indicated that this well is no longer in use and is being dismantled. The Somersworth municipal supply well No. 4 located southwest of the landfill has never been used as a water supply source (see Figure 11), and currently there are no future plans to use it as a water supply source.

Somersworth - May 22^ 1989 - File No. D-5162 - Section 8 - Page 1

8.1.1.2 General Risk Assessment Scope and Approach

This baseline risk assessment characterizes the risk to pxiblic health posed by the landfill, assuming it is left in its current state. The approach to this risk assessment consisted of an initial identification of exposure pathways, including an identification of exposure points, receptor populations, and exposure routes. The available data were then used to develop exposure point concentrations for all contaminants identified at the site. This information was used, in addition to dose- response information, to select indicator chemicals through a qualitative approach. Only those chemicals that were detected very infrequently or that clearly would not contribute to risk posed by the site were excluded from the more detailed exposure and risk assessment.

Quantitative estimates of exposure were then developed for the indicator chemicals using the exposure point concentrations and various exposure assumptions. The exposure estimates were used to characterize the carcinogenic and non-carcinogenic risks posed by the site, using available unit risk values for carcinogens, and Reference Dose (RfD) values for noncarcinogens. The approach used for this risk assessment is consistent with that described in the Superfund Public Health Evaluation Manual (1986) and in the Superfund Exposure Assessment Manual (1988).

8.1.2 Exposure Pathways

Exposure pathways that may result from the Somersworth Municipal Landfill include a source and chemical release mechanism; a contaminant transport mechanism and media; an exposure point or point of possible human contact with contaminants; and a route(s) of exposure. These four parameters when combined together represent a potentially "complete" exposure pathway. Exposure pathways may also be incomplete, but have the potential to be complete in the future.

8.1.2.1 Sources and Contaminant Transport

Sources of contaminants at the landfill consist primarily of contaminated soil, drums, and refuse that still exist at the site. Groundwater under the site appears to be a source, as evidenced by contamination observed on the periphery of the landfill. In addition, off-site cont€unination of groundwater, surface water and sediment can also be considered sources.

Contaminants have been released from the on-site source areas by leaching, surface runoff, and perhaps volatilization or particulate entrainment. They have then migrated in groundwater, surface water,and perhaps, air.


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Both the on-site source areas and the areas to which contaminants have migrated represent potential points of exposure, as described in the next section.

8.1.2.2 Exposure Ppjnt?, EXPPgUre RpUtgP. Receptor Populations

Exposure points in and around the Somersworth Municipal Landfill are considered to be those areas in which a receptor may come in contact with contamination resulting from the landfill either directly or indirectly. Exposure points were identified by considering the landfill and the areas around it, the extent and media of the contamination in those areas, and the uses of these areas by nearby populations. . As a result, ten potential exposure points were identified. The site itself was divided up into two exposure points. One exposure point was the portion of the landfill that has been converted to a park. This area has some cover, and receives different use than the remainder of the landfill, which was considered as a separate exposure point. These two exposure points are referred to as the playground (Area 2), and the landfill (Area 3), respectively. As there were ponded areas on both the playground and the landfill, these were also identified as potential exposure points. Exposure points outside the landfill include Somersworth Well No. 3 (being dismantled) , Somersworth Well No. 4, private residential wells on Blackwater Road (Area 5), Salmon Falls River, the Peter's Marsh Brook area (Area 4), and the downwind area. Most of these areas are identified on Figure 11. Area 1 indicated on this figure represents locations selected to

represent background, or areas not impacted by the site.

Table 15 identifies these exposure points, the exposed population, and the exposure routes. The existing extent and possible future extent of contamination surrounding the landfill were used in the

evaluation of exposed populations.

Background Areas (Area 1)

Several locations were identified as background areas. These areas were upgradient wells for groundwater and upstream samples for

surface water and sediment. For soil, an area east of the landfill was selected that did not appear to be impacted by the landfill.

Playground fArea 2)

Visitors to the playground (old section of landfill) are potential receptors, including children and adults who utilize the tennis courts, basketball courts, baseball fields, and the playground itself. According to the Parks and Recreation Department of


Somersworth, the two baseball fields are used 5 nights a week for practice during good weather. There are two minor league teams which play games there, and spectators who watch the games. Tennis lessons are provided at the tennis court and the tennis club utilizes the courts in the evenings, as well as other tennis players in the area. Day care groups in the surrounding area use the park facilities in the mornings and school children use the park in the afternoon. Although no soil samples were taken from the playground (older section of landfill) and very few from the rest of the landfill, these areas may be of concern due to accessibility and use. In some places on the playground and in the landfill, cover material is only 0.5 feet thick. If this material is worn down to the underlying refuse, direct exposure to contaminants is possible. Unfortunately, soil samples were taken from the bottom of test pits, or were composite samples from borings. As a result, the extent of contamination at or near the surface is unknown. As a conservative estimate, the data available for the landfill were used for the playground exposure point concentrations, although they may not be representative of surface conditions.

Landfill rArea 3)

A site visit by Wehran personnel on July 19, 1988, indicated that access to the landfill is currently unrestricted and there is Incomplete fencing around the site. In addition, there is a lack of "No Trespassing" signs around the landfill, and dirt bike tracks were observed. Receptors to the landfill itself may include children and adults (particularly adolescents) who may use the area for recreational purposes, such as riding dirt bikes and other activities associated with unrestricted access to open areas. Visitors to the landfill may be exposed to contaminated soil at or near the surface through dermal contact, ingestion and inhalation of particulates, as indicated in Table 15.

Ponded Areas

During the site visit, ponded areas were identified on both the playground and the landfill. On the playground, this represented a wet area after heavy rainfall. However, on the landfill, the ponded areas were more substantial. These ponded areas represent exposure points, with the potential receptors being those identified above as visiting the landfill and the playground.

Peter's Marsh Brook Area (Area 4)

Another exposure point or area was identified northwest of the landfill. This area is largely marsh and is in the direction of groundwater flow from the site towards Peter's Marsh Brook.


Relatively high levels of soil and groundwater contamination were found in this area, as well as surface water and sediment contamination in Peter's Marsh Brook.

Receptors to this area could be visitors to the marshy area, and exposure to contaminated soil could result. However, the area is not conducive to recreational use and frequency of use is expected to be lower than for the playground. Another exposure pathway in this area may be the bioacciimulation of contaminants by fish or wildlife and the subsequent ingestion by humans. According to the conservation officer in the area, deer hunting is limited by the availability of deer. There are abundant woodcock and partridge associated with the wetlands and they are hunted frequently when in season. Peter's Marsh Brook, which is located 100-400 feet from the landfill, is approximately 0.5 to 2 feet deep. It is a heavily fished stream with large populations of native trout. The stream is thought to be a spawning ground for trout by the conservation officer in the area.

Due to the groundwater contamination in the area, and the potential for the installation of private wells, this area was also Identified as a future exposure point for ingestion of drinking water.

Another potential exposure pathway in this area is exposure to contaminants in surface water and sediment during wading in Peter's Marsh Brook or Tate's Brook. The exposure routes are considered to be limited to dermal contact. No ingestion is assumed, as swimming is not expected given the shallow depth of the brook.

Somersworth Wells No. 3 and 4

Somersworth Municipal Well No. 3 will not be considered as an exposure point in this risk assessment because it was dismantled in 1987. Somersworth Well No. 4 is considered only as a future exposure point because currently the well is not used as a drinking supply. Exposure at this point was not quantified because the Remedial Investigation does not suggest migration of the contaminant plume to Well No. 4 and there are currently no plans to utilize this well. In addition, any exposures through use of this well would be lower than those evaluated for groundwater use in the Peter's Marsh Brook Area.

Blackwater Road (Area 5)

The groundwater in the area of Blackwater Road was also evaluated as an exposure point, primarily due to the close proximity of residents in this area to the landfill. All private residential wells within close proximity of the landfill have been changed to public water supplies. However, areas of residential and industrial growth will be evaluated (i.e., those along Blackwater


Road) as future exposure points, considering the possibility of reopening of existing wells, or the installation of new wells.

Salmon Falls River

Salmon Falls River was also identified as a potential exposure point. Peter's Marsh Brook feeds into Tate's Brook, which eventually leads to Salmon Falls River at a distance of about one mile from the landfill. No contamination associated with the landfill has been found in the downstream areas of Tate's Brook or in the Salmon Falls River. As such, the Salmon Falls River is considered a future exposure point. Exposure routes would Include Ingestion, as the intakes for the Towns of Berwick, Maine, and Somersworth, New Hampshire are about 1/2 mile downstream of the confluence of Tate's Brook and the Salmon Falls River. Exposure could also result from recreational use of the river by dermal contact and ingestion.

The Salmon Falls River will not be quantified as an exposure point since the data obtained from sampling is considered suspect (see Section 7.2.1) and there is no indication that there is currently contamination in the river originating from the landfill. This location is considered a potential future exposure point, but no exposure point concentrations were estimated.

On-site Air and Downwind Areas

Exposure to nearby residents may also take place via inhalation of vapors or particulates from the landfill. Limited monitoring data is available for this exposure pathway, and the data indicated no detectable levels of VOCs as measured by an organic vapor meter (see Section 7.2.4). Nevertheless, the pathway is considered complete, but was not quantified.

Table 16 summarizes the sampling points included in each exposure point identified above.

8.1.3 Indicator Chemical Selection

A number of contaminants were detected at Somersworth Municipal Landfill as shown in Table 17. This table also indicates the basis for excluding chemicals from the evaluation. Those contaminants potentially posing the most risk were chosen as indicator compounds or chemicals. These chemicals will serve as the basis of the risk characterization. The selection of the indicator chemicals was based on concentration, toxicity, frequency of detection as well as the sample location.

All known and possible carcinogens with available potency values were included as indicator compounds. In order to select indicator


chemicals for other compounds, mean concentrations were developed for each medium using the available data for the sampling points within each exposure point identified in Table 16. Section 8.1.3.1 describes the development of these mean concentrations, which were compared to mean concentrations for background areas as described in Section 8.1.3.2 and some substances were excluded, as they could not be attributed to the landfill. The remaining substances were examined for their potential toxicity, and some were excluded on that basis.

8.1.3.1 Generation of Mean Statistics

Arithmetic means were used to calculate summary statistics for the background locations and exposure points identified in Section 8.1.2.2. The Somersworth Municipal Landfill analytical data provided in Appendix I shows non-detectable concentrations of numerous parameters in the samples analyzed. These ND or non- detects were treated as values of 0 (zero) for calculating mean concentrations. Arithmetic means were taken for each contaminant including all sampling points by media within each area shown in Table 16. In Tables 18 through 21, the mean concentrations are shown based on zero for non-detected values.

Samples which detected contamination below the detection limit of the instrument or just above the detection limit were quantified by laboratory analysis as trace values. In these cases, the trace values were used to generate the summary statistic as recommended by the Superfund Public Health Evaluation Manual (Draft) 1988.

8.1.3.2 Background Considerations.

Chemicals were excluded as indicator chemicals which had mean concentrations less than background values. Chemicals were also excluded which were detected only in Area 5 (along Blackwater Road) and thus may have had sources other than the landfill. Table 17 provides the basis for exclusion of substances as indicator chemicals.

8.1.3.3 Freguencv of Occurrence Considerations

The occurrence of the chemicals found at the site was evaluated by exposure point. Therefore, the occurrence of a particular chemical relates to the area it is located in as well as the medium, rather than its presence at the site as a whole. Table 16 summarizes the analyses completed at each area for a particular medium. Summary tables (Tables 18 through 21) for each medium sampled contain the number of detections per number of samples (shown as a ratio, i.e., 2:5). The maximum concentration of the chemical and the average concentration found in that


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particular area are also shown. The tables are arranged so that a direct comparison of the presence of the chemicals in their respective areas can be made through the different media associated with the landfill site. The consideration of the presence of the chemicals in a particular area and medium was one basis for indicator chemical selection. Only those substances that were detected in two or less samples were excluded.

8.1.3.4 Toxicity Considerations

Xylenes were the only substance excluded as an indicator chemical based on toxicity. These compounds would not appear to contribute substantially to risks posed by the site at concentrations observed.

8.1.4 Dose Response Assessment

Section 8.1.3 described the chemicals found at the site and those selected as indicator chemicals. This section describes the toxic effects associated with the indicator chemicals, the toxicity values to be used in the risk assessment, and the Applicable or Relevant and Appropriate Requirements (ARARs) potentially applicable for these indicator chemicals.

8.1.4.1 Carcinogens

All known or possible carcinogens were included in the risk assessment as indicator chemicals and are shown in Table 22, including their potency and their EPA weight of evidence for carcinogenicity. The EPA Weight of Evidence describes the degree to which the data supports the carcinogenicity of a particular compound to humans. Table 23 describes the EPA Weight of Evidence categories.

8.1.4.2 Noncarcinogens

Reference dose (RfD) values were used as the basis for evaluating chronic toxicity due to the chemicals found at the site. If no RfD values were available, chronic acceptable intake (AIC) values were used. These values, as shown in Table 24, represent the daily exposure level below which significant adverse effects are not expected, assuming a lifetime of exposure.

8.1.4.3 ARARs

Table 25 summarizes the ARARs potentially applicable to the Somersworth Municipal Landfill. These values will be used as


points of comparison for exposure point concentrations in the risk characterization.

8.1.4.4 Toxicity Profiles

Toxicity profiles were prepared for all indicator chemicals. These profiles are found in Appendix J.

8.1.5 Exposure Assessment

The human populations around the Somersworth Landfill site could be exposed to a variety of contaminants through several exposure routes, as discussed in Section 8.1.2.2. The most significant exposure pathways were chosen for quantification, and exposure profiles developed. The exposure profiles were developed for most probable and realistic worst-case conditions. These two conditions were then used to estimate the body dose levels of contaminants for each scenario. By varying the exposure parameters, such as the frequency of contact with contaminants, the exposure period and the duration of the contact, as well as the environmental contaminant level; these two separate exposure profiles were developed. The most- probable case scenario utilized the average level detected and the realistic worst-case scenario utilized the maximum level of a contaminant detected within each exposure point.

8.1.5.1 Exposure Profiles

Exposure points and exposure routes associated with the Somersworth landfill were described in Section 8.1.2. From those descriptions, exposure profiles were developed.

Table 26 summarizes exposure profiles which represent likely combinations of exposure pathways for a given receptor group, although other combinations of pathways representing different receptor groups are possible. Other combinations would generally be subsets of those pathways presented, and the exposed population would hence have a lower total exposure. The exposure points and pathways for each profile are discussed in Section 8.1.2.2.

8.1.5.2 Exposure Point Concentrations

Section 8.1.3.1 describes the development of summary statistics from the monitoring data obtained by Wehran Engineering and Goldberg and Zoino Associates in the Remedial Investigation. Data (groundwater, surface water, sediment, soil), were collected over a period ranging from May 1985 to January, 1987.

Somersworth - Mav 22, 1989 - File No. D-5162 - Section 8 - Page 9

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Exposure point concentrations are the mean and maximum values measured at each exposure point and medium. The exposure point

concentration for the most probable case is generally a range calculated using two assumptions regarding non-detected values.

The lower end of the range assiimes zero as all non-detected values and the upper end of the range assumes the detection limit for non-detected values. The realistic worst case concentration is the maximum value reported within an exposure point. The exposure point concentrations utilized in this risk assessment are provided in Table 27 which were taken directly from Tables 18 through 21. The 0 MP values in this table indicate the most probable exposure point concentration using zero for non-detected values. The 5 MP values Indicate the most probable exposure point concentration using the detection limit of 5 (ug/1) for non-detected values of volatile organics.

8.1.5.3 Exposure Eguations and Assumptions

Exposure to the contaminants of concern were calculated by multiplying the concentrations of the contaminant in its respective medium by a variety of exposure coefficients or factors which were appropriate for that particular exposure point (playground, landfill, Peter's Marsh Brook and Blackwater Road). The following discussion provides the assumptions and methods of calculation for exposure estimates by media and exposure route.

Table 28 shows the assumptions and equation for estimating exposure via ingestion of drinking water. These assumptions are based on a lifetime exposure to the contaminant with a 2 liter/day consumption of drinking water. This equation and assumptions were used to calculate the future drinking water exposures for the future residents along Blackwater Road and in the area of Peter's Marsh Brook.

Table 29 describes the assumptions used to calculate ingestion and dermal exposures to soil on the playground area. The receptor population is assumed to be 2-30 years old. The frequency of events (visits) is unknown, but due to the area's accessibility and proximity to residential areas, a relatively high frequency was assumed. The percent skin surface exposed was assumed to be hands and feet (5%) for the most-probable case, and hands, lower legs, and feet (10%)for the worst-case. The amount of soil deposited on the skin surface is unknown. The assumptions are based on recommendations provided in the EPA Draft Exposure Assessment Manual (1988).

Table 30 provides the assumptions used for estimating dermal exposure via surface water while wading in Peter's Marsh Brook. The age group was assumed to be limited to ages 6-15, since both older and younger persons are not likely to visit this location.


The frequency of exposure is un3aiown, but in the most-probable case it was assumed to be twice a week in the summer months, and four times a week for the worst-case. The duration of a wading event is unknown, but one hour and two hour durations were assumed for the most probable and worst case, respectively. The body surface area exposed was assumed to be 5% (hands and feet, most-probable) and 10% (hands, lower legs, and feet, worst- case) . No water Ingestion was assumed to occur while wading.

Exposure to soil via ingestion and dermal contact in the Peter's Marsh Brook area was estimated using the ages exposed, the average weight over the exposure period, the years of exposure, and the frequency of events from Table 30, and the equation and other assumptions from Table 29.

Table 31 provides the exposure assumptions for ingestion of fish that may have bioaccumulated chemicals from contaminated surface water or sediment. The age group considered for this exposure pathway was 6 through 70, considering that younger children may not be likely to consume fish. The total amount of fish ingested per day is typically 6.5 grams (g). No information is available concerning the frequency of catches from Peter's Marsh Brook or Tate's Brook.

As an alternative assumption, an average portion size of 300 g was used, with a frequency of 12 meals per year. This is about 10 g/day as an average fish consumption; or comparable to 6.5 g/day. The worst- case frequency was assumed to be 24 meals per year.

In order to estimate exposure via fish consumption, chemical concentrations in fish are needed. Since no analytical data on contamination levels in fish are available, bioconcentration factors (BCF) were used to estimate such concentrations. These factors represent steady-state partitioning between water and fish tissue, and are generally based on laboratory studies of fish accumulation over some time period. Their utility for predicting concentrations in the field is questionable, and is dependent on the chemical and particular study from which the the BCF value was generated. However, the use of BCF values represents a simple tool for providing a rough estimate of fish concentrations and they have been used for this risk assessment . The BCF values used are shown in Table 32.

8.1.5.4 Exposure Estimates

Quantitative exposure estimates were developed for the exposure pathways and routes indicated on Table 26 using the exposure point concentrations provided in Table 27 and the exposure assumptions and equations provided in Tables 28 through 31.


Chronic exposures were estimated as the average daily exposures over the period of exposure. Lifetime exposures represent the average daily exposure over a lifetime (70 years) and were used to estimate carcinogenic risk. Estimates of chronic exposure due to soil ingestion and dermal contact at the playground were based on the 2-8 year old group, as this age group had the assumed highest frequency of visits and the largest quantity of soil Ingested.

Estimates of chronic exposure by exposure pathway/route are found in Tables 33 through 38 for the indicator chemicals with non-carcinogenic effects. Estimates of lifetime exposure for carcinogenic indicator chemicals are found in Tables 39 through 43.

8.1.5.5 Comparison of Exposure Point Concentrations with ARARs

Tables 18 through 21 and Table 27 provide the mean and maximum concentrations of the indicator chemicals by media at the exposure points. These values can be compared to potential ARARs in Table 25, to provide one indication of the risk posed by the site. This comparison is shown in Table 44.

Table 44 indicates that average concentrations in groundwater in both Areas 4 and 5 exceed the MCL for arsenic. The surface water concentration of arsenic exceeds the Ambient Water Quality Criteria (AWQC) for the Protection of Human Health (including both ingestion of water and aquatic organisms).

The maximum groundwater concentration for 1,1-dichloroethane (1,398 ug/1) in Area 4 exceeds the New Hampshire drinking water action level. Average groundwater concentrations of 1,2dichloroethane, 1,1-dichloro-ethylene, trichloroethylene and benzene in Area 4 exceed the respective MCLs.

Average surface water concentrations of 1,2-dichloroethane, tetrachloroethylene and benzene in Peter's Marsh Brook and Tate's Brook exceed AWQC.

The average concentrations of chromium and 1,1-dichloroethylene in groundwater in Area 5 equal their MCLs, and their maximum exceeds it.

Both the average and maximum 1,2-dichloroethylene concentrations in Area 4 exceed the proposed MCLG. The maximum methyl ethyl ketone concentration (1,530 ug/1 ) exceeds the lifetime health advisory of 170 ug/1.


8.1.6 Risk Characterization

8.1.6.1 Noncarcinogenic Effects

In order to assess the potential adverse effects associated with exposure to noncarcinogens, the estimated chronic exposures were compared to their reference dose (RfD) or acceptable intake (chronic) (AIC) values as shown in Tables 33 through 38 for the different exposure pathways and routes. This comparison is presented in the columns entitled Body Dose/RfD and is shown as a ratio of the estimated exposure to the RfD. For example, in the case of future Ingestion, exposure via groundwater in the area of Peter's Marsh Brook (Area 4) (most-probable) for toluene was estimated to be 1.54x10' mg/kg/day. The ratio would then be:

EX 1.54x10"' mg/kg/day = = 5.14x10"'

TV 3.0x10"

Where: EX = the estimated chronic exposure in mg/kg/day; and

TV = the appropriate toxicity value, either an RfD or AIC in mg/kg/day

Since it is thought that exposures to multiple chemicals below their acceptable dose, or the RfD, may result in adverse effects,

i the potential for noncarcinogenic effects from exposure to multiple I chemicals is evaluated by using the hazard index.

A noncarcinogenic Hazard Index (HI) for a particular exposure point is defined as the sum of the ratios of the estimated daily intake of any indicator chemical (IC) to the relevant acceptable daily intake (RfD or AIC) for all ICs present at the exposure point. Summing of the IC ratios assumes that the chemicals have the same toxicological endpoints. An HI of less than one (unity) indicates that the estimated total intake of ICs does not exceed the acceptable intake and that, therefore, the potential for adverse health effects is not likely (given the assumptions used in calculating the HI).

If, on the other hand, the HI exceeds one, then the estimated intake of ICs exceeds the acceptable intake and a potential for adverse health effects may exist.


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The hazard index can be represented as follows:

HI = V CEX, \

TV,

Where: CEX, - the estimated chronic exposure for the i* chemical in mg/kg/day; and

TV, = the appropriate toxicity value for the i**' chemical in mg/kg/day

The ratio from all exposure pathways and routes applicable to a given receptor are summed and are shown on Tables 33 through 38.

The hazard indices for the different receptor groups at the Somersworth Landfill are summarized in Table 45. These values are tarken directly from Tables 33 through 38, which show these calculations by chemical, and the total by exposure pathway. The hazard indices for the purposes of screening assume no difference in mechanism of action between the chemicals. While this is not the case, it was assumed as a simplifying assumption in order to see if additional refinement of the hazard index was necessary. Table 45 shows that hazard indices based on current exposure levels to residents along Blackwater Road are well below 1, even including all indicator chemicals in the hazard index, thus indicating that the chronic effects due to exposures from the site are not likely.

Future drinking water exposures could result if residential wells along Blackwater Road were reopened, or if new wells in this were installed. The hazard index for this future exposure route was greater than 1 for the most probable and worst cases, including all chemicals. This hazard index is primarily due to exposure to arsenic with a hazard index alone of 4.6 and 11 for the most probable and worst case estimates. The hazard index for all of the remaining chemicals was less than 1.

Future drinking water exposures in Area 4, in the area north/northwest of the site may pose a risk of chronic toxicity. Again, these hazard indices are primarily due to exposure to arsenic. In the most probable case, the hazard index for all of the other chemicals was less than 1. However, in the worst case, the hazard was primarily due to 1,1-dichloroethylene (16), while the hazard index for arsenic was 6. These results suggest that chronic effects may occur if this exposure route becomes complete in the future, that is if residential wells are installed in this area.


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8.1.6.2 Carcinogenic Effects

Eight of the compounds selected as ICs from the Somersworth Landfill are also considered to be probable or known

human carcinogens. These compounds are: o arsenic o 1,2-dichloroethane o 1,4-dichlorobenzene o 1,1-dichloroethane o 1,1-dichloroethylene o benzene o trichloroethylene o tetrachloroethylene

The upper bound of the carcinogenic risk posed by these compounds was calculated by multiplying the estimated daily intake (average lifetime) tff each IC by the carcinogenic potency factor for that IC. The upper bound of excess lifetime cancer risk was calculated

for the most-probable and worst-case exposure for each IC at every exposure point and pathway as follows:

Upper bound carcinogenic risk for a given exposure pathway

= 'rSL, LEX, PV, 1. * '1 . - . . . . _ .. . th where LEX, = the estimated lifetime exposure for the i

chemical in mg/kg/day; and

PV, = the appropriate potency value for the i* chemical in (mg/kg/day)"^

The calculated upper bound carcinogenic risks for each exposure pathway are provided in Tables 39 through 43. The risks for relevant receptor groups are then summed to evaluate a total risk for that population. Table 45 provides a summary of estimated carcinogenic risks by exposure pathway and receptor groups.

Table 45 shows a total upper bound excess risk of cancer based on current exposure levels, to residents along Blackwater of 3.4x10' (most probable) and 1.4x10"* (worst-case). These risks are primarily due to potential exposures from ingesting fish from this area. The estimated risks are primarily due to arsenic exposure. The total risks excluding arsenic for the most probable and worst case, respectively, were 1x10"' and 2x10" '"

Future drinking water exposures in the area of Blackwater Road could pose upper bound excess risks of cancer of 8.4x10"' (most probable) and 2.1x10" (worst-case). These risks are primarily due to exposure to arsenic (see Table 39) although estimated upper bound excess risks of cancer posed by chemicals other than arsenic were 1.4x10"* (most-probable) and 1.1x10"' (worst-case).


Future drinking water exposures in Area 4 could pose upper bound excess risks of cancer of 6.9x10"' (most-probable) and 9.9x10-2 (worst-case). These risks can be attributed (see Table 40) primarily to exposure to arsenic, 1,2-dichloroethane, 1,1-dichlorethylene, and 1,1-dichloroethane.

8.1.6.3 Sources of Uncertainty

A number of sources of uncertainty in this risk assessment have been identified in the previous sections. These sources of uncertainty are generally site-related, although uncertainty also arises from assumptions and procedures common to all risk assessments. Generic sources of uncertainty will not be addressed here. This site-specific factors contributing to uncertainty are discussed briefly below.

Data Adeguacy

There are a number of limitations to the site characterization that limit the adeguacy of the risk assessment. One of the most important limitations is the unavailability of adequate background data. For the purposes of this risk assessment, it has been assumed that available background data is representative.

In addition, in some cases, sampling data indicated the presence of other sources in the area. Specifically, the concentration of mercury was relatively high in the upstream sample of Peter's Marsh Brook (it exceeded its MCL). The source of this contamination is unknown. Similarly, soil contamination with some of the polycyclic aromatic hydrocarbons was found in Area 5. Such contamination may be due to automobile traffic. As a result, these chemicals could not be attributed to the site and were not included in the risk assessment.

Another limitation is the data availability from soil sampling. For risk assessment purposes, soil sample depths of 0 x 2 feet are preferred. However soil samples were taken from the bottom of test pits and the samples were composited. It was assumed that these samples were representative of surface conditions, even though some cover is present, but the accuracy of this assumption is unknown.

In addition to the depth of soil samples, sampling points were limited. No samples were taken from the playground area, the most important exposure point. As a result, soil data from the rest of the landfill were usea to represent soil contamination on the playground. Little data are available on two routes of exposure, inhalation and fish ingestion. Air sampling has been limited, and no sampling of fish from Peter's Marsh Brook was conducted. Inhalation exposures were not estimated in the limited monitoring because no air contamination has been attributed to the site. Fish


Ingestion exposures were estimated, but the use of bioconcentration factors to estimate fish concentrations adds to the uncertainty of the exposure assessment.

Exposure Assumptions

Tables 28 through 31 provide the asstunptions used in the exposure assessment. In some cases these values have a high degree of uncertainty. In particular, the assumptions regarding frequency and duration of exposure have little basis in fact. They are more based on reasonable assumptions about how receptors might use the area in question, and certainly a wide range in uses can be expected.

Another exposure assumption that has a high degree of uncertainty is the soil contact rate. There is some basis in the literature for the value used, but the information is limited. In addition, the extent to which both soil and water contaminants are available for absorption is not well understood. Assumptions regarding absorption have been made (as described in Appendix K), but these values may not be representative.

Another factor that may affect the exposure estimates is that the concentrations at the various exposure points were assumed to remain constant over time, based on the assertion in the RI that further migration of the plume was not expected. If this is not the case, exposure estimates may be under- or over-estimated, and potential exposure points may not have been evaluated.

Risk Characterization Assumptions

Most of the uncertainties related to risk characterization are common to all risk assessments. They relate to the methods available for evaluating the potential for adverse effects based on dose response data from laboratory animals exposed at relatively high concentrations. However, there are some limitations to this risk assessment due to the unavailability of dose-response data for some chemicals. The implicit assumption is that risk is primarily due to those chemicals that have adequate toxicological data, as other substances are excluded from the quantification of risk. In fact, these chemicals may be contributing to the public health risk posed by the site, although the extent is unknown.

Another important limitation to this risk assessment is f.ie contribution of arsenic to the risk posed by the site. Exposure point concentrations were not corrected for background. Therefore, the actual risk attributable to the site by arsenic has not been specifically identified.


8.2 ENVIRONMENTAL RISK ASSESSMENT

As part of the remedial investigation, an assessment is required of the adverse effects on the environment that have resulted or may result from the site. In the case of the Somersworth Municipal Landfill, the Wetlands Assessment, which is a major component of the enviroiunental assessment, will be conducted as part of the feasibility study. As a result, this document contains a brief discussion of the area and an evaluation of possible impacts on biota.

8.2.1 Environmental Characterization

The Somersworth Municipal Landfill covers an area of approximately 26 acres and is located one mile southwest of the City of Somersworth. The eastern-most portion of the landfill has been developed into a 10 acre city-recreational area know as Forest Glade Park. South of the landfill, several residential properties are located along Blackwater Road. The western areas of the landfill lie approximately 100 to 400 feet from Peter's Marsh Brook, which flows in a general ^northwest direction and is a tributary of Tate's Brook which is a tributary of Salmon Falls River.

According to Bruce Bonefant, a biologist for the New Hampshire Fish and Game Department and John Boland, a fisheries biologist for the Maine Fish and Game Department, the following represents a general inventory of fish native to Peter's Marsh Brook, Tate's Brooks and the Salmon Falls River:

Peter's Marsh Brook and Tate's Brook

o Native Trout

Salmon Falls River

o Yellow Perch o White Perch o Chain Pickerel o Brown Bull Head o Golden Shiner o Common Shiner o Fall Fish o Brook Trout o Brown Trout o Large Mouth Bass o Small Mouth Bass o Common Sucker o American Eel


Mr. Bonefant was of the opinion that due to tidal influences on the Salmon Falls River, both Peter's Marsh Brook and Tate's Brook may serve as spawning grounds for the river.

Also, according to Mr. Bonefant and Phillip Bozenhard, a wildlife biologist for the Maine Fish and Game Department, the following represents a general inventory of wildlife and vegetation native to the area:

Wildlife

o White-tailed Deer o Woodcock o Partridge o Raccoon o Cottontail Rabbit o Skunk o Porcupine o Gray Squirrel o Chipmunk o Deer Mouse o Norway Rat o Green Frog o Pickerel Frog o Snapping Turtle o Musk Turtle o Painted Turtle o Common Water Snake o Salamander o Newt o Mink o Otter o Muskrat o Wild Duck o Mallard Duck o Duck o Turtle Dove o Redwing Black Bird

Vegetation

o Cattail o Speckled Alder o White Pine o White Oak o Hemlock o Various Grasses


8.2.2 Threatened and Endangered Species

According to the New Hampshire Natural Heritage Inventory, there are no known rare plants, animals or exemplary natural communities in the area of the Somersworth Municipal Landfill (Appendix L).

8.2.3 Risk Characterization

It is not possible, for the most part, to quantify the risk to biological species because little is known about their exposure patterns as well as the exposures at which adverse effects may be expected. However, effect levels for aquatic life have been developed through laboratory toxicity studies. In some cases, these data have been used by EPA to develop Water Quality Criteria for the Protection of Aquatic Life. These criteria, or the lowest effect levels reported by EPA in the Quality Criteria for Water 1986 (the Gold Book), are shown in Table 46. A comparison of these values with concentrations in surface water shows that all measurements of contaminants in Peter's Marsh Brook are below Ambient Water Quality Criteria and reported lowest effect levels. This comparison suggests that the site is not likely to pose a risk to aquatic organisms.


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9.0 IDENTIFICATION OF POTENTIALLY APPLICABLE REMEDIAL TECHNOLOGIES

Overall approach:

1. Identify general response actions 2. Identify potentially applicable technologies, screen

these technologies and develop remedial alternatives 3. Screen public health, environmental and cost factors

Identification of general response actions and potentially applicable remedial technologies is the focus of this section. The screening of the remedial technologies, development of remedial alternatives and the initial screening of remedial alternatives for public health, environmental and cost factors is the focus of the Feasibility Study.

9.1 GENERAL RESPONSE ACTIONS

The National Oil and Hazardous Substances Contingency Plan (NCP) outlines a process for identifying, developing and evaluating remedial action alternatives for a given site. The process begins with project scoping for the Remedial Investigation, the data gathering and site characterization phase. As part of project scoping, general response actions to remedy known problems at the site are identified (based upon existing data) as a basis for determining data gaps and preliminary remedial technologies. Table 19 is a list of general response actions and associated remedial technologies. A "no action" response is included as a baseline against which other response actions can be rated as to mitigative effectiveness.

General response actions are classified as source control measures or management of migration measures. Source control measures prevent or minimize migration of contamination by removing, stabilizing and/or containing the hazardous substances. Source control technologies include land disposal of contaminated soils or sludges, incineration/ treatment of liquids or sludges, and on-site soil aeration. Management of migration measures are appropriate when hazardous substances have migrated from the original source of contamination beyond site boundaries, and pose a significant threat to public health, welfare or the environment. Management of migration measures include groundwater treatment, barrier construction, gradient crntrol and/or provision of an alternate drinking water supply.

Although management of migration remediation is feasible, source control remediation is usually preferable when contaminant migration has been inhibited and high concentration source areas


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are still present on-site. Once the contaminants begin to migrate and disperse downgradient from source areas, removing the contaminants becomes increasingly difficult.

Generally, a reduction in contamination source strength can be accomplished by either of two ways. First, contamination sources can be removed either by on-site treatment or removal for off-site treatment/disposal. Second, the volume of leachate from contaminant sources can be reduced while leaving the sources in situ. This is accomplished by isolating the contaminants as much as possible from the groundwater flow system so that the contaminants enter the groundwater system at a rate which does not have a significant adverse effect on human health or the environment.

Under the "no action" response action, natural processes would be relied upon to eventually reduce all contaminant concentrations to below no adverse response levels. Natural processes include adsorption, biodegradation, volatilization and dilution. The feasibility of the "no action" response action is determined by developing and assessing probable and worst case scenarios and associated health risk assessments.

9.2 POTENTIALLY APPLICABLE REMEDIAL TECHNOLOGIES

For each general response action identified, technologies exist to implement that response action, recognizing that there may be compatible and incompatible combinations of source control and management of migration measures. A list of candidate technologies appropriate for the Somersworth site is found below. Some technologies may be modified or eliminated if they prove to be difficult to implement, may not achieve the objective in a reasonable time or the technology may not have a proven performance record.

9.2.1 Land Use Restrictions

Land use restrictions are used primarily to prevent accidental human exposure to potentially hazardous environments. Restriction can range from limited passive measures, such as posting warning signs, to the construction of physical barriers, to prohibition of specific activities (e.g. mining, installation of wells), to relocation of the human population. Land use restrictions do not affect contamination transport or potential impacts of contaminants on natural resources and the environment. Environmental impacts directly attributable to land use restrictions are negligible.


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9.2.2 Alternate Water Supply

Because consumption or other use of contaminated local waters pose a major potential hazard to residents of the affected areas, provision of an uncontaminated water supply to those areas is a significant infrastructural technology. This technology does not affect contaminant transport, potential impacts of contaminants upon natural resources and the environment, or potential human contact with surface discharges of contaminants. Environmental impacts directly attributable to provision of alternate water supplies are generally negligible.

9.2.3 Continued Monitoring

Continued monitoring can be used to determine whether contaminants continue to enter the environment and/or if they are being redistributed within the environment. Monitoring can reduce the potential for human contact with contaminants by identifying areas of new or increased contamination. The results of continued monitoring can serve as a basis for future decisions about the implementation of more extensive remedial actions. Continued monitoring does not affect contaminant transport or potential impacts of contaminants on natural resources and the environment. Environmental impacts directly attributable to continued monitoring are negligible.

9.2.4 Surface Barriers

Surfacecontaminated

barriers areas to

or seals prevent

(caps) i accidental

nvolve human

covering exposure

of to

contaminants, minimize the exposure or transport of contaminants by erosion, and minimize subsurface migration of contaminants by reducing infiltration. Caps typically incorporate a layer of low permeability material such as clays, cement, synthetic liners or a combination of these. The low permeability layers often are stabilized by covering with topsoil and vegetation. Surface drainage controls to prevent runon and speed runoff of rainwater are typically included in the design of the cap. Capping does not restore areas which are already contaminated, environmental impacts attributable to capping can range from small to moderate.

Two kinds of capping materials are discussed below: clay and synthetic membranes. Other varieties of capping materials (e.g. asphalt, concrete) were judged to have relatively high susceptibility to weathering or to cracking during potential settlement of the landfill; these other materials are, therefore, not considered.


Both clay and synthetic caps usually consist of a sand compacted onto a graded surface, overlain by a layer of low permeability (clay or synthetic fabric), with a protective blanket of loam on top. The clay later may also be underlain by a filter layer of silt. Surface water diversion and collection systems carry runoff from the capped area. On steeper slopes, cobbles or boulders may be required for erosion control. The capped area is also revegetated with grass to prevent erosion. Long-term maintenance is usually required to prevent growth of deep-rooted plants which could damage the seal. A gas collection system consisting of vents in the cap may also be required. The gas may be discharged to the air or, if necessary, through a filter system to control release of contaminants.

Clay caps are proven effective; they have longevity and durability, assuming proper design, installation and maintenance. Installation is straight forward, because similar operations are required to place each of the layers. Construction is usually accomplished in a timely manner with conventional earthmoving equipment. When properly installed, a clay cap is not highly susceptible to cracking from settlement and frost heave.

Synthetic membrane caps are also highly effective. However, they can be more time consuming and difficult to install than clay caps. Installation is accomplished with hand labor, excavation equipment and seaming machines. Seams in the membrane require careful checking and sealing. There is limited long-term experience with synthetic membrane caps for landfills.

9.2.5 Removal and Containment of Contaminated Sediments

Remedial techniques for contaminated sediments generally involve removal and subsequent disposal or treatment of the sediments. Sediment removal methods include well-established excavation and dredging techniques. Dredged materials ("spoil") management includes techniques for drying, physical processing, chemical treatment and disposal. Treated sediments, or those that have not been severely contaminated, may be used as construction fill and in reclamation projects. Plans to remove and treat contaminated sediments must be designed and implemented on a site-specific basis. Dredging in wetlands may require revegetation of the area.

A knowledge of the physical properties and distribution of contaminated sediments is highly desirable, if not essential, in selecting a dredging technique and in planning the dredging operation. Information on grain size, bed thickness and source and rate of sediment deposition is particularly useful in this context. Such information can be obtained through a program of bottom sampling or core sampling of the affected sediment.


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' , Mechanical dredging of contaminated sediments should be considered under conditions of low, shallow flow. Dredging should be used in

1 conjunction with stream diversion techniques to hydraulically i isolate the area of sediment removal. Under any other conditions,

mechanical excavation with draglines, clamshells or backhoes may j crate excessive turbidity and cause uncontrolled transport of ] contaminated sediments further downstream. Stream diversions with

temporary cofferdams, followed by dewatering and mechanical excavation of the contaminated sediments, are typical elements of

I a mechanical dredging operation for streams, creeks or small ^ rivers. Mechanical excavation can also be used to remove

contaminated sediments that have been eroded from disposal sites during major storms and deposited in floodplains or along river ( banks above the level of base flow.

. Instream mechanical dredging (wet excavation) of contaminated j sediments is feasible only for relatively shallow, stagnant flows ' or for isolated ponds and basins where streamed agitation and

excessive turbidity will not cause uncontrolled downstream j contamination. For contaminated sediments in deep bodies of water

or in those with any appreciable flow, low turbidity hydraulic dredging operations are required. Low turbidity dredging is any hydraulic dredging operation that uses special equipment (dredge vessels, pumps) or techniques to minimize the re-suspension of bottom materials and subsequent turbidity that may occur during the operation. Conventional hydraulic dredging may cause excessive

j agitation and re-suspension of contaminated bottom materials, which ! decreases sediment removal efficiency and which may lead to

downstream transport of contaminated materials, thereby I exacerbating the original pollution.

There are several well-established techniques for the processing and reuse or disposal of uncontaminated dredge spoil. Techniques for managing contaminated dredge spoil, however, are influenced by the hazardous nature of the spoil material. Special consideration must be given to handling these sediments in a safe, efficient

; manner. Contaminated spoil treatment and disposal options may be limited because of this fundamental consideration.

9.2.6 Subsurface Barriers

Subsurface barriers, also called "cutoff walls", involve the placing of a subsurface wall material of low permeability adjacent to or surrounding a zone of contamination. A partial wall can be used to direct the f.low of contaminated groundwater away from the sensitive areas, whereas an encompassing wall can be used to contain the contaminants. Both options may be used to reduce the flow of uncontaminated groundwater through the zone of contamination.


In general, cutoff walls provide good containment capability but are subject to leaks due to poor embedment and impermeable strata or bedrock. Cutoff wall integrity may also be comprised due to degradation by contaminants or natural constituents of the groundwater.

Cutoff walls do not restore areas which are already contaminated, but do restrict the spread of contamination.

Four general kinds of cutoff wall technology are compared below: grout curtain, slurry wall, vibrated beam, and sheet pile.

Installation of a grout involves the injection of cement or chemical grout, often mixed with bentonite, through vertical pipes installed into the ground. Typically, a minimum of three (3) rows of pipes is required at staggered spacing to assure continuity of the wall.

The construction of a slurry wall involves the excavation of a trench to bedrock using bentonite slurry for temporary stabilization. The trench is then backfilled; a soil/bentonite mix or concrete and bentonite are often used for backfill, but concrete alone, asphaltic emulsions and synthetic materials are also employed. Slurry walls have been in general use for about 20 years. The technology of construction is well developed, but longterm performance data on their use for containment of contaminants are not available. On the other hand, slurry walls have a good performance record when used for groundwater control.

The vibrated beam cutoff wall is installed by using vibratory force to advance a steel beam into the ground, allowing injection of a relatively thin wall of asphalt (or cement and/or bentonite) as the beam is withdrawn. The wall is constructed by successive placement of adjacent segments. The technology is most applicable to clean, fine to medium sands. Maintaining alignment of the beam and continuity of adjacent segments is difficult in very coarse or non-homogeneous materials. The technology is unproven and does not have a long performance record.

Sheet pile cutoff walls consist of interlocking steel wall sections assembled at the surface and driven into the ground. Sheet pile systems have a shorter lifetime than other cutoff wall systems due to deterioration of the steel. Maintenance of the alignment of the wall is difficult in coarse materials and very coarse materials (boulders and cobbles) may make installation impossible.

9.2.7 Excavation

Excavation of buried contaminants or contaminated soil can restore areas which are contaminated and significantly reduce the


potential for migration of contaminants. The technology is usually most effective where contaminants are highly concentrated in or near the area of original deposition. Contaminants which have migrated beyond the area of excavation are not affected. I<aboratory analyses may be required during excavation to define the precise limits of excavation. Because the excavated material is hazardous, excavation is always used in conjunction with a treatment or disposal technology. Contaminated wastes and soil can be excavated by various types of tracked or wheeled equipment such as scrapers, front end loaders, backhoes, draglines or clamshells. , Backhoes, draglines and clamshells are more commonly used for excavation of landfilled waste and contaminated soil.

The strength of the fill material may be a significant factor, as the fill may not provide sufficient bearing capacity for heavy equipment. Wastes and contaminated soils are generally highly contaminated relative to ambient soils, so spills or leaks must be minimized. Extensive arrangements must be made for stockpiling and subsequent treatment and/or removal or the excavated material. Drummed wastes may require special handling to avoid ignition or explosion.

9.2.8 Groundwater Extraction

Interceptor wells can be used to collect contaminated groundwater, restricting the migration of contaminants and sometimes restoring areas which are already contaminated. Pumping of the interceptor well superimposes a "cone of depression" upon the natural groundwater gradient, and flow to the well is from all directions. This permits some flexibility in siting. Because the extracted groundwater is hazardous, extraction is always used in conjunction with a treatment or disposal technology. Laboratory analyses may be required during extraction to determine the duration of extraction and to assure that the characteristics of the contaminants remain compatible with the selected treatment or disposal technology.

The pumping rate and well placement required to achieve the desired alteration of groundwater flow patterns are controlled by many local groundwater and geologic conditions. These include the transmissivity of earth materials in the screened interval and hydraulic conductivity and extent of relatively impermeable layers.

9.2.9 Ljguid Treatment

Liquid treatment employs physical or chemical processes either to reduce the concentration of contaminants in water or to otherwise render the contaminants harmless. This technology is


i used in conjunction with groundwater extraction as discussed above, which provides the waste stream for the treatment process. The treated water may either the reinjected into the ground or discharged to surface water. Minor contaminated groundwater treatment technologies include air stripping, steam stripping, carbon absorption.

Air stripping consists of a system to mix large volumes of air with the contaminated water, typically in a column packaged with an inert medium, to promote the transfer of volatile organic compounds (VOCs) from the water into the air. Water is piamped into the top of the column. It cascades down over the medium while air is blown upward through the column. The air discharged from the stripper contains VOCs, may be considered a "new source" of volatile organic emissions and may, therefore, require further treatment for odor or air pollution control before discharge into the atmosphere. The technology has good durability and has been effective in removing VOCs from water. Other contaminants are not removed, and so wastewater may require further treatment.

Steam stripping is similar to air stripping except that steam is used with or in place of air as the gas is pumped into the stripping column. Steam stripping uses heat to promote the transfer of VOCs from liquid into the gas. The gases and condensate may be passed through carbon filters prior to discharge. Relative to air stripping, this technology is more effective in removing VOC contaminants, but durability and ease of installation are reduced. Other contaminants are not removed. Additional mechanical equipment is required and boilers and distribution systems are needed.

Carbon adsorption involves passing groundwater through a bed of granular activated carbon where contaminants are adsorbed by the carbon. The technology is effective for a wide range of contaminants. Carbon adsorption achieves a high level of contaminant removal and is capable of yielding water that is of drinking quality. Installation difficulty is comparable to other treatment technologies, but operation and maintenance is somewhat more difficult. The system requires a higher level of mechanical attention because the activated carbon requires periodic regeneration or replacement. Further operation requires more frequent performance monitoring to detect carbon exhaustion. Exhausted carbon may require disposal as a hazardous waste.

Biological treatment of contaminated groundwater is viable when the organic content of the water is relatively high. It can he used as a pretreatment before a physical/chemical process.


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i 9.2.10 Hazardous Solids Treatment

1 Solids treatment employs physical or chemical processes either i to reduce the concentration of contaminants in the solids or to

otherwise render the contaminants harmless. Potentially applicable treatment methods may be divided into four groups:

1. Solidification/stabilization, which improves the handling characteristics of the wastes and may detoxify the

\ contaminants or limit their solubility. j

2. Biological treatment, which may detoxify the wastes through microbial alteration.

3. Physical treatment, which separates hazardous constituents from the waste stream.

4. Incineration, which uses high temperatures to destroy or otherwise alter the characteristics of the contaminants.

9.2.11 Hazardous Solids Disposal

Solids disposal involves containment or immobilization of wastes excavated from the site or produced during the treatment of contaminated liquids or soils. Disposal of hazardous solids on-site involves construction of an RCRA designed impermeable contaminant for disposal of wastes from the excavation (unless a waiver is granted). Disposal off site involves removal of the contaminated materials to a permitted secure hazardous waste disposal facility.

9.2.12 Gas Migration Control

Approaches to control gas from landfilled materials can be grouped into two categories: control of methane, and control of volatile toxics.

Control of methane gas is important at sites where biodegradable organics are present. Anaerobic decomposition of organics produces methane gas which forms an ignitable mixture with air. Methane diffuses readily along paths of least resistance and may travel laterally and collect in underground structures, thus, presenting an imminent hazard. Methane is not usually an explosion hazard in the soil, s;'.nce its concentration is usually much greater than the upper explosive limit. Approaches to the control of methane migration are aimed principally at stopping lateral subsurface migration rather than controlling emissions to the atmosphere. Control of volatile toxic compounds, on the other hand, is concurrently aimed at limiting both the lateral movement and


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atmospheric emissions of toxic vapors. Gas collection and emission control treatment are mandatory for volatile toxics, while their

use in sites generating methane is primarily for fuel recovery.

Before gas migration controls can be properly installed at a hazardous waste site, it is important to determine the type of wastes present, the depth of fill, and surface geology of the site and adjacent areas. Also, field measurement to determine gas concentrations, positive or negative pressures, and soil permeabilities should be used to establish optimum design of vent

systems.

Pipe vents consist of vertical or lateral perforated pipes installed in the landfill for collecting gases or vapors. The may be installed in and around the landfill alone, or in combination with trench vents for the control of lateral gas migration. Pipe vents are usually surrounded by a layer of coarse gravel to prevent clogging by solids or water. They may discharge directly to the atmosphere or be connected to a negative pressure collection

system.

Trench vents are constructed by excavating a deep, narrow trench surrounding the waste site or spanning a section of the area perimeter. The trench is backfilled with gravel, forming a path of least resistance through which gases migrate upward to the atmosphere or to a collection manifold. By diverting flow in this manner, the trench vents form a barrier against lateral migration of methane or toxic vapors. Trench vents are used in combination with liners to form an effective barrier against gas migration. Trenches can be open or capped with clay and fitted with collection laterals and riser pipes venting to the atmosphere or connected to a negative pressure fan or blower. Also, air can be injected into trench vents to form a blanket that controls gaseous migration.

Barriers against the migration of gases and vapors are employed in a number of ways at waste disposal sites, usually in conjunction with other remedial measures. An effective barrier against gas flow must consist of a material with low gas permeability. Materials found to prevent gas migration include compacted clay, concrete slurry walls, gunite, and synthetic liners.

Gas from waste disposal sites frequently contain malodorous and toxic substances and, thus, require treatment before release to the atmosphere.

Several basic types of gas treatment are applicable* adsorption by carbon; thermal oxidation; and ranking. Carbon adsorption systems are either non-regenerative or regenerative. Thermal oxidation systems include the use of a flare or afterburner, despending on the desired control requirements.


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\ i i J PRELIMINARY SCREENING OF REMEDIAL TECHNOLOGIES

Remedial technology screening is based on several factors, the first of which being site conditions they may limit or promote the use of certain remedial technologies. Table 48 identifies site characteristics that should be evaluated. Technologies whose use is clearly precluded by site characteristics should be eliminated from consideration.

Certain waste characteristics may Influence the effectiveness or feasibility of the remedial technologies. Table 49 presents these waste characteristics. Technologies clearly limited by waste characteristics should be eliminated from consideration.

Screening is also based upon the level of technology development, performance record, and inherent construction, operation, and maintenance problems. Technologies that are unreliable, perform oorly, or are not fully demonstrated, should be eliminated.

Technologies that have passed the technology screening are combined to form overall site remedial action alternatives. As part of the development of preliminary remedial action alternatives, each of the following must, at a minimum, be evaluated to the requirements of the Feasibility Study guidance developed by the USEPA.

a. Alternatives for treatment and/or disposal at an off-site facility approved by the USEPA, as appropriate.

b. Alternatives which attain applicable and relevant federal public health or environmental standards.

c. As appropriate, alternatives which exceed applicable and relevant public health or environmental standards.

d. Alternatives which do not attain applicable or relevant public health or environmental standards but will reduce the likelihood of present or future threat from the hazardous substances. This must include an alternative which closely approaches the level of protection provided by the applicable or relevant standards and meets CERCLA (Comprehensive Environmental Response, Compensation and Liability Act) objective of adequately protecting public health, welfare and environment.

Sine 3 groundwater contamination is a frequent problem, the corrective action requirements of Subpart F of the RCRA (Resource Conservation and Recovery Act) regulations (40 CFR Part 264) will be applicable in this case and should be included in alternatives developed under category (B). Under the RCRA regulations, corrective actions must attain a groundwater cleanup standard

Somersworth - May 22. 1989 - File No. D-5162 Section 9 - Page 11

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established for each facility. For a limited number of potential contaminants, a standard is specified in the regulations at levels

corresponding to National Interim Primary Drinking Water Standards developed pursuant to the Safe Drinking Water Act. An alternate concentration limit (ACL) may be established for any contaminant upon a determination that the ACL will "...not pose a substantial

present or potential hazard to human health or the environment as long as the alternate concentration limit is not exceeded" [40 CFR 264.94(b)]. In the absence of an ACL or a standard based on Safe

Drinking Water Act determinations, the groundwater protection standard is background. Groundwater cleanup to upgradient

background conditions should be included in alternatives developed under category (C).

Generally, ACLs can be based on a demonstration that there is a lack of exposure or that levels of exposure are adequate to protect human health. In considering ACLs, it is appropriate to consider attenuation, degradation and dilution of the contaminants before they reach possible receptors. Engineering approaches can be used to augment natural dilution and attenuation processes.

Additionally, institutional controls to assure that groundwater within the current or probable reach of the plume of contamination will not be withdrawn, or will be withdrawn only at points at which contaminants are at concentrations that are safe, may be considered as a basis for controlling exposure. In conjunction with the controls described above, there may be limited circumstances where treatment o the water before use can be guaranteed as a means of preventing exposure to harmful levels. The decision criterion is in all cases, however, whether an alternate concentration level will pose a substantial hazard to human health or the environment. Alternatives that do not meet the RCRA Subpart F requirements for background MCLs (maximum contaminant limit) or ACLs but significantly reduce public health threats (for example, engineering controls to attenuate or dilute concentrations to acceptable levels at the receptor point), should be presented in category (D).

Cost screening should be undertaken for all remedial alternatives remaining from the public health and environmental screening. The cost screening can be divided into three basic tasks:

1. Estimation of costs 2. Present worth analyses; and 3. Cost screening production

Cost screening factors eliminate alternatives that have costs an order of magnitude greater than those of other alternatives but do not provide greater environmental or public health benefits or greater liability.


10.0 SUMMARY AND CONCLUSIONS

This section summarizes the background research and data collection conducted for the Remedial Investigation and presents conclusions regarding the site hydrogeology and the distribution and migration of contaminants in the environmental media. The conclusions are based primarily on the data obtained during the Remedial Investigation.

10.1 BACKGROUND

The Somersworth Municipal Landfill accepted municipal and industrial refuse for on-site disposal between approximately 1945 and 1979. At present, the City is a member of the Lamprey Regional Solid Waste Disposal Cooperative, which operates an incinerator in Durham, New Hampshire. Although the landfill is still active, it currently accepts only those materials that cannot be incinerated. These materials are now disposed in the western portions of the landfill in an area known as the "stump dump."

The former Somersworth municipal supply well No.3 is located approximately 2,300 feet to the north-northwest of the landfill as shown on Figure 2. Discussions with the Somersworth City Engineer indicate that this well is no longer in use and is currently being dismantled by the City. A second well, Somersworth municipal supply well No. 4, is located approximately 800 feet southwest of the landfill. Well No. 4 has never been used as a water supply source and, according to the City Engineer, the City does not, at present, plan on use of the well as a water supply source in the future.

The landfill is situated adjacent to, and within approximately 400 feet of Peter's Marsh Brook. Previous investigators (CDM, 1983) have indicated that all surface runoff from both the active and inactive portions of the landfill eventually reaches Peter's Marsh Brook. This brook is a tributary of Tate's Brook which is in turn a tributary of the Salmon Falls River. Both the City of Somersworth, New Hampshire and neighboring Berwick, Maine withdraw water from the Salmon Falls River for drinking water supply. The Somersworth and Berwick intakes on the river are located approximately 1.5 miles to the north-northeast of the landfill.

Previous studies undertaken by others at the Somersworth Municipal Landfill indicated that the Somersworth and Berwick public water supplies, as well as private residential wells located in the vicinity of the site, were potentially threatened by groundwater contamination emanating from the


landfill. Primary wastes deposited in the landfill which have engendered groundwater contamination are anticipated to have included municipal trash and industrial wastes, including some chemical wastes.

10.2 HYDROGEOLOGIC CONDITIONS

The geology of the Somersworth landfill site is generally characteristic of the southeastern New Hampshire coastal region. Surficial soil deposits are generally of glacial origin and are underlain by metamorphic bedrock. Natural soils encountered in the test borings generally consisted of the following four basic types of deposits:

- stratified sand with significant variations in silt and gravel content (kame deposits);

- dense silty, gravelly sand (glacial till deposits);

- peat (recent wetland deposits); and

- clayey silt, frequently including sand and/or gravel (possible vestigial glacio-marine deposits).

At the Somersworth landfill site, the kame deposits were observed to be prevalent.

At the Somersworth Municipal Landfill site and surrounding area, groundwater is stored and transmitted through the pore spaces of the overburden soil deposits, and through the fractures within the bedrock. The saturated soil deposits and fractured bedrock are collectively referred to as an unconfined aquifer. The unconsolidated soil deposits comprising the overburden aquifer materials within the site study area basically consist of gravelly and silty sand kame deposits, and fibrous peat encountered within the swampy wetlands associated with Peter's Marsh Brook. Other overburden materials observed within the site study area are not considered an important or significant part of the aquifer.

Fractured bedrock is considered part of the unconfined aquifer. Bedrock fractures were observed to be most predominant within the upper 5 to 10 feet of the bedrock surface, although groundwater data obtained from monitoring wells installed in bedrock indicate that fractures which extend to at least 30 feet below the bedrock surface are in direct hydraulic communication with the overlying unconsolidated depos its.


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Groundwater elevation contours shown on Figure 7 indicate groundwater movement within the aquifer occurs regionally in a westerly, then west-northwesterly direction across the landfill toward Peter's Marsh Brook and surrounding wetlands. A review of topographic maps of the study area and its surrounding environs indicates that it is probable that Willand Pond, located approximately one mile south-southwest of the landfill, serves as a major source of groundwater recharge. Rainfall recharge also likely occurs along the uplands located to the east and west of the study area. Groundwater is anticipated to flow regionally from Willand Pond and the upland recharge areas toward the landfill.

It is anticipated that the wetland area surrounding Peter's Marsh Brook located immediately northwest of the landfill is a point of discharge (surfacing) for groundwater within the study area. Evidence of this is provided by:

- strongly convergent groundwater flow northwest of the landfill with no substantial increase in saturated thickness (although saturated thickness data are limited);

- an increase in hydraulic head with depth, observed within companion cluster monitoring wells at location B-8 located within the wetland area north of the landfill; and

- an approximate one half order of magnitude increase in flow volume of Peter's Marsh Brook between Blackwater Road and the area in the vicinity of surface water station S-6, with limited additional surface drainage during most of the year.

Groundwater discharged within this wetlands area would subsequently flow with the surface waters of Peter's Marsh Brook toward the Salmon Falls River.

10.3 NATURE AND DISTRIBUTION OF ENVIRONMENTAL CONTAMINATION

Four broad categories of contaminants were tested for within various media at the site study area. These categories include volatile organic compounds (VOCs) , acid and base/neutral extractable organic compounds (ABN's), metals, anr* polychlorinated biphenyls (PCB's) and pesticides. PCB's and pesticides were not observed in any of the samples obtained from the various media analyzed specifically for those compounds.


( . VOCs were observed to be the most significant chemical \ contaminants, in terms of both distribution and concentration.

» A total of 25 VOCs were Identified in the site area in the ^ various media. In general, the greatest frequency,

concentration, and total number of VOC contaminants were * observed in groundwater within approximately 800 feet of the i northwest comer of the landfill at total concentrations as

high as approximately 13,000 micrograms per liter (parts per billion). VOC contaminants have also been observed in the surface water of Peter's Marsh Brook, west and northwest of the landfill; however, total concentrations of VOCs in these surface waters are typically less than 100 micrograms per liter. Although VOCs were detected in one sample of a total of five surface water samples obtained from the Salmon Falls River, downgradient of its confluence with Peter's Marsh Brook, these results are considered suspect. The highest concentrations of VOCs in soils were observed in samples obtained from test pits excavated within the landfill area.

ABN contaminants were observed with considerably less i frequency, and typically at lower concentrations than VOCs.

An exception to this is a composite soil sample obtained while j drilling boring B-4 located immediately south of the landfill j within which eight base/neutral extractable compounds were

detected.

i Metals contaminants at concentrations above anticipated

background levels were also observed with considerably less frequency than VOCs. In groundwater, only arsenic, chromium

j and lead were observed at concentrations above both their t respective Maximum Contaminant Level criteria and anticipated

background levels. Zinc, copper, and nickel were also commonly observed at levels above anticipated background concentrations at locations considered both up- and downgradient of the landfill. Therefore, no pattern of distribution is readily apparent.

Results of initial air quality screening by the project team, as well as results of air quality screening during the soil boring program, indicated no detectable VOCs within air in the vicinity of the landfill. Detection limits were approximately 1 ppm.

For the purpose of this evaluation, the landfill was considered to be the major source of contamination within the site study area. Although hazardous materials jay have been stored on, or transferred through adjacent properties including a private scrap metal yard south of Blackwater Road, a dry cleaning operation, and the National Guard Armory, this Remedial Investigation focused on the Somersworth Municipal Landfill site pursuant to the approved scope of work.


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Therefore, there is no direct indication that these adjacent properties are, or are not additional sources of contamination observed in some of the samples obtained during the Remedial Investigation field program.

Water quality data indicate that the zone of highest groundwater contamination extends as a plume northwesterly from the landfill approximately 1,000 feet. The centerline of this contaminant plume is estimated to lie in proximity to monitoring clusters B-6 and B-8. Contaminant concentrations appear to decrease on either side of the plume centerline; however, analyses of groundwater samples obtained from monitoring clusters B-9 and B-10 indicate that the zone of contaminated groundwater extends at least 200 feet west and 700 feet east of Peter's Marsh Brook. Water quality data also indicate that the zone of contaminated groundwater extends at least 100 feet south of the landfill perimeter.

Contamination entering the groundwater beneath the landfill source area would be expected to migrate by advectivedispersive transport west-northwesterly in the direction of regional groundwater flow toward Peter's Marsh Brook and associated wetlands. The plume centerline is anticipated to be approximately coincident with a line extending from the center of the landfill through monitoring clusters B-6 and B8.

The downgradient extent and ultimate fate of groundwater contamination is difficult to assess due to limited

groundwater quality data northwest of monitoring cluster B-8. Results of analytical contaminant transport analyses, however,

indicate that the contaminant plume is at steady state; discharge of dissolved contaminants with groundwater into Peter's Marsh Brook and adjacent wetlands has limited contaminant migration downgradient of geophysical terrain conductivity exploration EM line 19 shown on Figure 10. As such, the primary receptor to contaminant migration within groundwater at the Somersworth Municipal Landfill is regarded at this time as Peter's Marsh Brook.

Contaminants discharged to Peter's Marsh Brook with groundwater must pass through a layer of peat, observed to be approximately 15 to 25 feet thick. Because of the large percentage of organic carbon typically contained within peat, adsorption of VOC and ABN contaminants by the peat is anticipated to be a significant attenuation mechanism. Increased microbial activity within the peat is anticipated to result in increased biological decay or transformation, especially as the solute transport is retarded by adsorption. Finally, volatilization of organic compounds is likely to be significant as discharged groundwater mixes with surface


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i water. The contribution of all three of these mechanisms to . • contaminant attenuation is not quantifiable with the limited ' site data; however, although some seasonal fluctuations in the ' specific contaminants and contaminant concentrations is

probable, contamination within Peter's Marsh Brook is not anticipated to increase significantly over levels detected during the Remedial Investigation, considering that the contaminant plume is estimated to have been at steady state for approximatley 10 to 30 years.

To conservatively estimate the potential impact of contaminants transported in the surface waters of Peter's Marsh Brook to downgradient receptors, primarily the Berwick

i and Somersworth water intakes in the Salmon Falls River, a dilution analysis based on stream flow data was performed.

1 The resultant dilution factor is approximately 35:1; that is, I contaminant concentrations in the Salmon Falls River are

anticipated to be less than 3 percent of concentrations observed in Peter's Marsh Brook downgradient of the landfill. In actuality, volatilization, photodegradation and biodegradation, as well as added dilution from the Little River and Tate's Brook not considered in the analysis, are significant attenuation mechanisms, rendering the 35:1 dilution factor very conservative.

In addition to Peter's Marsh Brook, few probable receptors to groundwater contamination were identified in the site study area. Groundwater production wells within or in proximity to the estimated zone of contamination are considered receptors. Only three groundwater production wells are known to exist in the site study area, including residential well RW-2 located immediately south of the landfill, and the Somersworth municipal supply well Nos. 3 and 4. All three of these wells have been decommissioned at this time, with the Somersworth municipal supply well No. 3 being physically dismantled.

10.4 RISK ASSESSMENT

An assessment of the risk posed by the Somersworth Municipal Landfill to public health and the environment was conducted as part of the remedial investigation. The risk assessment considered a number of exposure points, or areas where people may be exposed to site contaminants. Quantitative estimates were developed for dermal and ingestion exposures from soil to visitors to the playground, dermal an''. ingestion exposures from soil to visitors to the Peter's Marsh Brook area, dermal exposures from surface water to persons wading in Peter's Marsh Brook, and ingestion exposures to persons ingesting fish taken from Peter's Marsh Brook. In addition, potential future


exposures via groundwater ingestion as drinking water were estimated for the areas of Blackwater Road and Peter's Marsh Brook.

A number of exposure points were not considered quantitatively, for a variety of reasons. Somersworth Well No. 4 and the Salmon Falls River were considered as potential future exposure points, but exposures were not quantified, as the remedial Investigation suggests that the contaminant plume will not reach these locations. Somersworth Well No. 3 was not considered an exposure point because it has been dismantled. On- site air and air nearby the site are considered potential exposure points, although data available to date do not indicate detectable contaminant levels. As a result, these exposure points were not quantified.

An evaluation of average and maximum concentrations found at exposure points showed that concentrations of some chemicals exceeded potentially Applicable or Relevant and Appropriate Requirements (ARARs). Measured concentrations in groundwater in both the Blackwater Road area (Area 5) and the Peter's Marsh Brook area (Area 4) exceed the MCL for arsenic. Surface water concentrations (Table 20) of arsenic exceed the Ambient Water Quality Criteria (AWQC) for the Protection of Human Health (including both ingestion of water and aquatic organisms). The worst-case exposure point concentration (maximum) for 1,1- dichloroethane (1,398 ug/1) in Area 4, exceeds the New Hampshire drinking water action level (810 ug/1). Average groundwater concentrations of 1,2-dichloroethane, 1,1-dichloroethylene, trichloroethylene and benzene in Area 4 also exceed the MCL. Average surface water concentrations of 1,2-dichloroethane, tetrachloroethylene and benzene in Peter's Marsh Brook and Tate's Brook exceed AWQC. The average measured concentration of chromium and 1,1-dichloroethylene in groundwater in Area 5 equals the MCL, and the maximum exceeds it. Both the average and maximum 1,2-dichloroethylene concentrations in Area 4 exceed the MCLG. The maximum methyl ethyl ketone concentration (1,530 ug/1 ) exceeds the lifetime health advisory of 170 ug/1.

A quantitive evaluation of the risk posed by the site showed showed that, based on the data available and a number of assumptions, current exposure levels for residents along Blackwater Road are not likely to pose a risk of chronic effects, as calculated hazard indices are less than 1. If private wells were reopened or installed in this area, the exposure would result in a hazard index greater than 1, due to arsenic. The estimated upper bound excess risk of cancer for residents along Blackwater Road based on current exposure levels, are on the order of 5.2x10" or 5.2 in 100,000 in the


.-« f most-probable case and 3.2x10" (3.2 in 10,000) for the worst « case. These estimated risks are primarily due to potential

arsenic exposures from ingesting fish from this area as well as dermal contact with surface water in Peter's Marsh Brook. Future estimated risks of cancer from Ingestion of drinking water in the Blackwater Road area were 8.4x10*' (most-probable) and 2.1x10" (worst case). Estimated risks excluding arsenic were 1.4x10' and 1.1x10" , respectively.

If private wells were installed in the area of Peter's Marsh Brook, north/northwest of the site, exposures could result in chronic effects in the exposed population, primarily due to exposures to arsenic and 1,1-dichloroethylene. Future excess cancer risks associated with groundwater ingestion in this area were 6.9x10"' (most-probable) and 9.9x10"^ (worst case) based primarily on exposures to arsenic, 1,2-dichloroethane, 1,1- dichloroethylene and 1,1-dichloroethane.

The assessment of risk to the environment was preliminary, as a wetlands assessment will be conducted as part of the feasibility study. Based on available information, as discussed in Section 8.2, the site does not appear to pose a risk to aquatic organisms in Peter's Marsh Brook.

There are a number of sources of uncertainty that should be considered in evaluating the conclusions of the risk assessment. Little or no sampling of air, fish, and surface soils was conducted and represents a limitation to the risk assessment. In addition, a number of the assumptions used to estimate exposure may be questionable and cannot be easily verified. Lastly, toxicity values appropriate for risk assessment are not available for all chemicals of interest at the site.

Somersworth - Mav 22. 1989 - File No. D-5162 - Section 10 - Page R

11.0 RECOMMENDATIONS FOR ADDITIONAL EXPLORATIONS AND ANALYSES

i Recommendations for further site explorations and analyses considered necessary by the project team to complete the Feasibility Study are discussed below. This work includes additional subsurface explorations to better assess the extent of the contamination plume within the area of Peter's Marsh Brook northwest of monitoring cluster B-8, and to characterize additional possible contaminant source areas within close proximity to the site. It is beyond the intent of this section to provide a detailed scope of work for additional subsurface explorations and analyses. Instead, general recommendations are provided.

11.1 ADDITIONAL EXPLORATIONS

The downgradient extent and ultimate fate of groundwater contamination is difficult to assess due to limited groundwater quality data northwest of monitoring cluster B-8. Results of analytical contaminant transport analyses, however, indicate that the contaminant plume is at steady state; discharge of dissolved contaminants with groundwater into Peter's Marsh Brook and adjacent wetlands has significantly limited contaminant migration downgradient of EM line 19. As such, the primary receptor to contaminant migration within groundwater at the Somersworth Municipal Landfill is regarded at this time as Peter's Marsh Brook.

I The project team recommends that this conclusion be substantiated with additional water quality data obtained from monitoring wells installed northwest of monitoring cluster B-8, near the axis of

• Peter's Marsh Brook. At this time, it is envisioned that two to ' three additional monitoring clusters would be installed between EM

line 19 and Route 16A. Monitoring clusters should include at least I one well screened in bedrock and one well screened in the i overburden deposits. These additional monitoring clusters could

also function as long-term downgradient monitoring points associated with any site remediation.

Water level readings obtained in stand pipes installed within test pits TP-5 and TP-6 indicate that refuse has, at least within

j southerly portions of the landfill, been placed 1 to 4 feet below I groundwater levels. In more northerly portions of the landfill,

stand pipe data indicate groundwater levels are slightly below the base of refuse. The data are very limited however, and prior to

• implementation of a remedial technology, the refuse groundwater contact area should be evaluated with a careful program of test pit excavations performed jn a grid throughout the landfill area.


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11.2 POSSIBLE ADDITIONAL SOURCE AREA

Groundwater contamination downgradient of the Somersworth Municipal Landfill is at this time considered primarily attributed to the Somersworth Municipal Landfill. It is noted however, that hazardous materials may have been stored on, or transferred through adjacent properties including a scrap metal yard south of Blackwater Road, a dry cleaning operation, and the National Guard Armory. It is not clear what effect, if any, activities relating to possible hazardous wastes at these sites may have had on water quality in the vicinity of the site. Because of the proximity of these potential source areas to the Somersworth Municipal Landfill, any remedial action undertaken at the landfill site may not be entirely sufficient without delineation of additional potential source areas. Characterization of additional potential source areas would require as a minimum an investigation into the history of operations and land use, as well as additional subsurface explorations, installation of monitoring wells, water quality analyses, and hydrogeologic analyses.

11.3 CONTINUED SITE MONITORING

It is recommended that NH WSPCD continue to sample and analyze monitoring wells and surface water stations in the site study area, as well as the residential wells along Blackwater Road. At a minimum, sampling should be performed quarterly for VOCs until the need for a full monitoring program is evaluated during the Feasibility Study. The purpose of continued sampling would be:

1. to provide up-to-date information concerning contaminant distribution on and around the site as it might affect human and environmental receptors; and

2. to further define baseline conditions as a precursor to any remedial actions which may be implemented at the site; and, if implemented, to monitor the effectiveness of the remedial actions.


BIBLIOGRAPHIC REFERENCES

Billings, M.P., 1956, The Geology of New Hampshire: Part II, Bedrock Geology: State of New Hampshire, Division of Economic Development, Concord, NH, 200 p., geologic map.

Blackey, F.E., Cotton, J.E., and Toppin, K.W., 1983, Water Resources Data New Hampshire and Vermont; Water Year 1983: US Geological Survey Water - Data Report NH-VT-83-1.

Bothner, W.A., et al, 1984, Geologic Framework of the Massabessic Anticlinorium and the Merrimack Trough, Southeastern New Hampshire, in Hanson, L.S., ed., The New England Intercollegiate Geologic Conference, 76th Annual Meeting, Guidebook to Fieldtrips, Trip B-5, pp. 186-206.

Bradley, E., 1964, Geology and Ground-Water Resources of Southeastern New Hampshire: Department of the Interior, United States Geologic Survey Water Supply Paper No. 1695, 80 p., geologic map.

Cherry, J.A., 1987, Contaminant Migration Processes: A Field Perspective: Lecture Notes for Distinguised Seminar Series on Ground Water Science, National Water Well Association, Dublin, Ohio.

Cherry, J.A., 1984, Contaminant Migration in Groundwater: Processes and Problems: Proceedings of the 1985 Boston Society of Civil Engineers. Lecture Series "Controlling Hazardous Wastes", Boston, MA, 28 p., references.

Davis, S.N., and Dewiest, R.J.M., 1966, Hydrogeology: John Wiley and Sons, Inc., New York, 463 p.

Dunne T. , and Leopold, L.B., 1978, Water in Environmental Planning: W.H. Freeman and Company, San Francisco, CA, 818 p.

Freeze, F.A., and Cherry, J.A., 1979, Groundwater: Prentice-Hall, Inc., Englewood Cliffs, NJ, 604 p.

Friberg, L., Nordberg, G.F., and Vouk, V.B., eds., 1979, Handbook on the Toxicology of Metals: Elsevier/North Holland Biomedical Press, Amsterdam.

Friedman, J., 1950, Stratigraphy and Structure of the Mt. Pawtuckaway Quadrangle, Southeastern New Hampshire: Geological Society of American Bulletin, Vol. 61, pgs. 449-492.

Goldman, S.J., Jackson, K., and Bursztynsky, T.A., 1986,

Bibliography - Page 1

i Erosion and Sediment Control Handbook: McGraw-Hill Book Company, New York.

Goldthwait et al, 1951, The Geology of New Hampshire: Part I, Surficial Geology: New Hampshire State Planning and Development Commission, Concord, NH, 83 p., surficial geologic map.

Griffin, R.A., and Roy, W.R., 1985, Interaction of Organic Solvents with Saturated Soil-Water Systems: Open File Report prepared for the Environmental Institute for Waste Management Studies, The University of Alabama.

Jury, W.A., Spencer, W.F., and Farmer, W.J., 1984, Behavior Assessment Model for Trace Organics in Soil: III Application of Screening Model: Journal of Environ. Quality, Vol. 13, No. 4, pp. 573-579.

Karickhoff, S.W., 1981, Semi-empirical Estimation of Sorption of Hydrophobic Pollutants on Natural Sediments and Soils: Chemosphere, Vol. 10, No. 8, pp. 833-846.

Lambe, T.W., and Whitman, R.V., 1979, Soil Mechanics, SI Version: John Wiley and Sons, Inc., New York, 553 p.

Lyons, J.B., Bothner, W.A., Moench, R.H., Thompson, J.B., Jr., 1986, Interim Geologic Map of New Hampshire: Office of State Geologist, Open File Map OF-86-1, Scale = 1:250,000.

McDonald, M.G., and Harbaugh, A.W., 1984, A Molecular Three Dimensional Finite-Difference Ground-Water Flow Model: Scientific Publications Co., Washington D.C., 528 p. Prepared by: US Department of the Interior US Geologic Survey, National Center, Reston, Virginia.

McWhorter, D.B., and Sunada, D.K., 1977, Ground-Water Hydrology and Hydraulics: Water Resources Publications, Fort Collins, CO, 290 p.

Moore, R.B., 1982, Calving Bays vs. Ice Stagnation — A Comparison of Models for the Deglaciation of the Great Bay Region of New Hampshire: Northeastern Geology, Vol. 4, No.l, pp. 39-45.

New Hampshire Office of State Planning, 1985, New Hampshire Population Projections, Total Populations for Cities and Towns, 1980-2010: State of New Hampshire, Concord, NH, 6 p.


Prickett, T.A., Naymik, T.G., and Lonnquist, C.G., 1981, A "Random-Walk" Solute Transport Model for Selected Groundwater Quality Evaluations: Illinois State Water Survey, Champaign, Bulletin 65, 1981.

Schwarzenbach and Westall, 1981, Variation in Log Kp for Selected Organic Compounds in Various Types of Natural Sediments: Environmental Science and Technology, 15, 13601367, American Chemical Society; reprinted in Thurman, E.M., 1986, Organic Geochemistry of Natural Waters: Martinus Nijhoff/Dr. W. Junk Publishers, Dordrecht, Netherlands.

Sittig, Marshall, 1985, Handbook of Toxic and Hazardous Chemicals and Carcinogens, Second Edition: Noyes Publications, Park Ridge, NJ, 950 p.

Smith, L.R., and Dragun, J., 1984, Degradation of Volatile Chlorinated Aliphatic Priority Pollutants in Groundwater: Environmental International, Vol. 10, pp. 291-298.

State of New Hampshire, Department of Environmental Services, Water Supply and Pollution Control Division, Bureau of Water Supply Engineering; 1986, Drinking Water Regulations: Concord, NH, 83 p.

U.S. Department of the Interior, Water and Power Resources Service, 1981, Groundwater Manual.

U.S. Environmental Protection Agency, 1985, Site Analysis, Somersworth Landfill, Somersworth, New Hampshire: Environmental Monitoring Systems Laboratory, Warrenton, VA, 16 p.

Wang, H.F., and Anderson, M.P., 1982, Introduction to Groundwater Modeling: W.H. Freeman and Company, San Francisco, CA, 237 p.

Yeh, G.T., 1981, Analytical Transient One-, Two-, and Three-Dimensional Simulation of Waste Transport in the Aquifer System, Oak Ridge National Laboratory, Environmental Sciences Division, Publication No. 1439, Contract No. W-7405-eng-26.


COMMUNICATION REFERENCES

Letter for Somersworth City Engineer to GZA, June 3, 1987.

Letter from Somersworth City Engineer to Waste Management Division, June 18, 1981.

Telephone communication with Somersworth City Engineer, May 27, 1987.
