HMM A S S O C I A T E S , INC. LETTER

' \ C I \ f h R s ( \ \ I R O \ \ U \ T M ( ( > c\ Pt \ \ \ E R S

DATE: June 5, 1990

TO: Richard GoehlertU.S. EPAJ. F. Kennedy BuildingHSN-CAN 5Boston, MA 02203

RE: Savage Well Site

SUBJECT: Draft FS Section 1.0

For Your InformationPer Your Request

FROM: Mark HeubergerHMM Associates, Lie.196 Baker AvenueConcoid,MA 01742

JOB NO.: 2176-160

For Your Review/CommentsFor Your Authorization

REMARKS:

Enclosed is Section 1.0, Introduction, of the Draft Feasibility Study for the Savage Well Site.The Section is organized as follows:

1.1 Purpose and Organization of Report1.2 Summary of Site Characteristics1.3 Contaminants and Media of Concern1.4 Risk Assessment1.5 Remediation Goal

The final Section 1.0 will include a revised discussion of Fate and Transport based on recent andongoing work and incorporating comments received on the Fate and Transport section of theDraft RI.

Signature

COMMENTS:

Date

Signature Date

2176-160/HAZ/3699 - 6/5/90196 Baker Avenue • Concord • Massachusetts • 01742 • (508) 371-4000 • FAX: (508) 371-2468Three Executive Park Drive • Bedtord • New Hampshire • 05102 • (6031 647 1010 • FAX (603) 626-4642

SAVAGE WELL SITE

DRAFT FEASIBILITY STUDY REPORT

1.0 INTRODUCTION

1.1 PURPOSE AND ORGANIZATION OF REPORT

This report will present the results of the Feasibility Study (FS) conducted by HMM

Associates, Inc. (HMM) at the Savage Well Site in Milford, New Hampshire. The specific

objective of the Savage Well Site FS is to propose a means to return the groundwater to its

beneficial uses in a time frame that is reasonable given: 1) the land-use characteristics of the

site; 2) the nature and extent of contamination; 3) the nature of the sources of contamination; and

4) the nature of the current impact to human or environmental receptors posed by the

contamination.

The FS is the second component of the Remedial Investigation/Feasibility Study (RI/FS)

process for National Priority List (NPL) sites under the Comprehensive Environmental

Response, Compensation, and Liability Act (CERCLA)*. The Remedial Investigation (RI)

provided data relevant to site characterization, the nature and extent of contaminants in various

media, and the risk posed by the contaminants to public health and the environment. The FS

develops remediation goals for the site from the findings of the remedial investigation and the

baseline risk assessment. Based on those findings it specifies the contaminants of immediate

concern, the potential exposure pathways of concern, the potential exposure pathways of

concern, and the concentrations of contaminants for each exposure pathway that are deemed to

be appropriately protective of human health and the environment and to comply with applicable

or relevant and appropriate requirements (ARARs) for the site.

* NOTE: This Feasibility Study has been conducted in accordance with 1) the October, 1988

"Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA"

(EPA/540/G-89/004) and 2) the newly revised March, 1990 National Contingency Plan (NCP).

The Feasibility Study also takes into consideration recent EPA records of decision and policies,

including the October 28, 1989 EPA memorandum entitled "Considerations in GroundwaterRemediation at Superfund Sites" and the October, 1989 EPA publication (540/4-89/005) entitled

"Performance Evaluation of Pump-and-Treat Remediations".

2176-160/HAZ/3560 1-1

The remediation goals so developed are based on "reasonable maximum exposure

scenarios," i.e. on the maximum exposures reasonably likely to occur, rather than on the

worst-case exposure assumptions. It then identifies potentially suitable technologies, evaluates

them and assembles them into remedial alternatives designed to meet the remediation goals.

As provided in the March, 1990 revised NCP, the analysis of technologies and remedial

alternatives for meeting the remedial goals should be appropriate for the complexity of

site-specific conditions. As discussed in Section 2.0, the remedial objectives for the Savage

Well Site are relatively straightforward, involving only one class of contaminants of concern

(chlorinated hydrocarbons) in one environmental medium (groundwater). The contaminant

sources likely exist locally as dense non-aqueous phase liquid (DNAPL). Accordingly, there are

a limited number of remedial options that could be applied to the Site to deal with the

contaminants as they exist. The FS has therefore been focused upon the alternatives most likely

to provide solutions to identified site contamination.

The FS Report is organized according to the sequence in which remedial alternatives were

developed, as described below.

Section 1.0 provides a summary of the results of the RI and an overview of the FS

objectives. Section 2.0 presents the Identification and Screening of Technologies by: 1)

developing the remedial action objectives and general response actions for each contaminant and

media of interest; 2) identifying the volumes or areas to which response action might be applied;

and 3) identifying and screening technology types and process options to eliminate those that

cannot be technically implemented at the site.

Section 3.0 describes the development and screening of alternatives by: 1) combining

technology types and process options to form alternatives; and 2) screening the alternatives

relative to effectiveness, implementability, and cost.

Finally, Section 4.0 presents a detailed evaluation of the alternatives retained from the

initial screening with respect to the following criteria:

• Overall protection of human health and the environment.

• Compliance with applicable or relevant and appropriate requirements (ARARS).

• Long-term effectiveness and permanence.

• Reduction of toxicity, mobility, or volume of contaminants.

• Short-term effectiveness.

2176-160/HAZ/3560 1-2

• Implementability.

Cost. ^' , \\\C' .

• State Acceptance.V / ' / , "~1 ~1

• Community Acceptance. I ". •" ' ! r

1.2 SUMMARY OF SITE CHARACTERISTICS

1.2.1 Background

The Savage Well Site is located in the western portion of the Town of Milford, New

Hampshire, a community of approximately 12,000 residents located in Hillsborough County, in

the south central portion of the state. The site location is depicted on Figure 1-1. Also indicated

on Figure 1-1 is the area included within the Site Base Map (Plate I) and the general area of

investigation, encompassing approximately 2.7 square miles.

The Savage well is a private water well that has not been used as a water supply since

February 1983 when the New Hampshire Water Supply and Pollution Control Commission

(WSPCC) detected volatile organic compounds in the well during routine water quality

monitoring. The five volatile organic compounds (VOCs) detected were Tetrachloroethylene

(PCE), Trichloroethylene (TCE), 12-Dichloroethylene (DCE) 1,1,1 Trichloroethane (TCA), and

1,1 Dichloroethane (DCA).

Four of the five compounds, with the exception being DCA, also were detected in a nearby

mobile home park water well. A municipal water line serving the trailer park has been installed

as completed remedial action at this site. The Town of Milford has completed the

interconnection with Pennichuck Water Works in order to replace water that might have been

drawn from the Savage Well Site area. Municipal sources of water supply now supply the entire

site area, with the exception of the Milford Drive-In Theater. Production wells at the Hitchiner

and Hendrix facilities continue to utilize local groundwater for industrial process and cooling

water. Production wells are also used at the George Brox, Inc./Granite State Concrete property,

at the Milford Fish Hatchery, and at Souhegan Valley Aquaculture, a private fish hatchery.

The New Hampshire WSPCC, in conjunction with the Division of Public Health Services,

undertook a standard regulatory inspection of four major industrial facilities in the Savage Well

Site area, OK Tool Company, Hitchiner Manufacturing Company, Hendrix Wire and Cable, and

New England Steel Fabricators (NESFAB), and several smaller commercial establishments in

the area. Environmental site assessments were performed by OK Tool Company and Hitchiner

2176-160/HAZ/3560 1-3

2276

mlhmFIGURE 1-1

LOCATION MAP - SAVAGE WELL SITE, MILFORD, NH

' Manufacturing Company. In 1985 WSPCC produced a report of its hydrogeological study of the

area, including information contained in the hydrogeological studies performed by HitchinerManufacturing Company and OK Tool Company.

The Savage Well site was placed on the National Priority List (NPL) of hazardous waste

sites under the provisions of CERCLA. The site was included on the NPL primarily because the

Savage Well was formerly a drinking water supply. However, the well is no longer a potential

potable water supply because Hitchiner Manufacturing Company purchased the well in 1985 for

industrial water supply purposes, and the area is supplied with potable water from an alternate

source.

A group of local industries, consisting of OK Tool Company, Hitchiner Manufacturing

Company, Hendrix Wire and Cable, and New England Steel Fabricators, were identified by EPA

as Potentially Responsible Parties (PRPs). Under the provisions of CERCLA and SARA, the

PRP Group agreed to investigate the nature and extent of the contamination detected in the

Savage Well. In accordance with a consent decree signed by the PRP Group and EPA, the PRP

Group agreed to conduct a remedial investigation/feasibility study (RI/FS) in accordance with

the work plan prepared by EPA Region I. HMM was retained by the PRP Group as a consultant

to aid them in completing the RI/FS. A Project Operations Plan (POP) was prepared by HMM,

approved by EPA, and served as the guideline for site characterization activities performed

during the RI/FS.

Figure 1-2 is a map of a portion of the study area showing the locations of various features

of interest. The Savage Well, currently owned by Hitchiner Manufacturing Company as an

industrial water supply, is located in the eastern portion of the map. Figure 1-3 shows the

location of groundwater monitoring wells and pumping wells discussed in the text. The Site

Base Map, included as Plate I, indicates groundwater and surface water monitoring points, as

well as topography and cultural features.

The RI describes the relevant site characteristics in detail. For ease of reference, they are

briefly recapitulated here. They are divided into naturally occurring and anthropogenic

characteristics.

2176-160/HAZ/3560 1-5

o

1.2.2 Naturally Occurring Characteristics

Surficial Features

The Savage Well Site is located within a broad river valley underlain by a thick, highly

permeable aquifer, and is characterized by a variety of industrial, commercial, residential, and

agricultural uses which are all potential sources of contamination to the aquifer.

The predominant landform feature of the Savage Well Site is the floodplain of the

Souhegan River Valley, a relatively flat land surface extending through the majority of the site

area (see Plate I). Much of the study area lies within the flood plain of the Souhegan River and

is designated within Zone A, the area of 100-year flood, on the National Flood Insurance

Program Flood Insurance Rate Map. The Souhegan River traverses from west to east throughout

the length of the site area. At the eastern edge of the site, the River takes a pronounced

southward bend before resuming its generally west to east orientation. The boundaries of the

floodplain are approximately coincident with North River Road, to the north of the river, and

Tucker Brook, to the south. Surface elevations within this area are generally within the range of

270 feet (in the western portion of the site) to 250 feet (in the eastern portion of the site). The

Souhegan River flows into the site area through a narrow gorge to the west of the site in Wilton

and the topography to the west of the site becomes more pronounced at the edge of the river

valley, with elevations at the western edge of the site rising to greater than 370 feet. The

southwestemmost portion of the site also exhibits a change in topography coincident with the

edge of the river valley, with elevations rising to greater than 390 feet.

Several small hills, formed as glacial depositional features, are present within the

floodplain. These include a landform located near the center of the site, immediately southwest

of the Savage Well, which has been used for sand and gravel quarrying.

Three principal surface water features traverse the site: 1) the Souhegan River, as

discussed above; 2) Tucker Brook, which flows from the southwest comer of the site, through

the southern portion of the site where it is associated with several wetland areas, and eventually

into the Souhegan River at the eastern end of the site; and 3) a process water discharge stream,

originating from the Hitchiner and Hendrix facilities, which flows southwest to . 'rtheast across

the central portion of the site and into the Souhegan River. (In March 1990, Hendrix installed a

process water recycling system and thereby ceased process water discharges. Moreover,

Hendrix is currently using storm water discharges for irrigation, thereby eliminating all point

source discharges to the stream.) Additionally, several small streams flow from the northwest

and discharge into the northern banks of the Souhegan River.

2176-160/HAZ/3560 1-8

Regional Geology

The town of Milford and the Savage Well Site lie in the west-central portion of a geologic

district known as the Massabesic-Merrimack-Rye Terrain.

The surficial geology of the region has been described by the USGS on the 1970 Surficial

Geologic Map of the Milford Quadrangle, Hillsborough County, New Hampshire. The surficial

deposits include: 1) glacial till deposits of two types; a brown silty compact till referred to as

lower till, and a non-compact gray sandy till referred to as upper till; 2) glacial lake and glacial

stream deposits consisting of sand, silt, gravel and minor amounts of clay which was deposited

in glacial Lake Merrimack; 3) stream-terrace deposits of sand and gravel cut into glacial lake

and glacial stream deposits; 4) alluvium deposits of silt, sand, and gravel in flood plains along

present streams; and swamp deposits of peat, silt, and sand.

Site Geology - Unconsolidated Aquifer

The unconsolidated aquifer is a thick (up to 130+ feet) sequence of glacial outwash

deposits, locally overlain by alluvium and stream terrace deposits along the Souhegan River and

by thin (less than five feet) layers of organic \ch loam at the surface. The glacial outwash

deposits consist primarily of noncohesive stratified fine to coarse sands and gravels. Lenses of

silt and fine sand have been observed at some locations but are not common.

Underlying the stratified sands and gravels is a very dense glacial till consisting of a

poorly sorted mixture of fine to medium sand, gravel, silt, clay and angular rock fragments. The

till layer typically varies in thickness from 2 to 15 feet and is present as a continuous layer or as

isolated lenses along the bedrock surface. In the westernmost portion of the site in the vicinity

of OK Tool, the till is observed to be thicker (up to 33 feet) and to consist of two types. A

coarser, less compact gray to brown till directly, but not always continuously, overlies a

characteristically olive-green dense lower till.

Site Geology - Bedrock Characteristics

The thickness and boundaries of the unconsolidated aquifer are directly related to

variations of the bedrock surface elevation.

2176-160/HAZ/3560 1-9

Two significant bedrock features identified at the site are: 1) a narrow bedrock trough

trending west to east from the vicinity of the OK Tool facility and terminating in a broader basin

structure in the vicinity of MW-16, MW-17 and MW-20 and 2) a large broad depression to the

northwest of the site situated between the Souhegan River and North River Road. Downgradient

of the trough feature, the bedrock surface is relatively broad and flat, dipping only slightly to the

east. The bedrock surface rises steeply toward the south-southeast of the site where bedrock

outcrops have been observed. The bedrock elevation also approaches the land surface elevation

in the northwest and the northeast sections of the site.

The bedrock underlying the glacial outwash deposits consists of medium to coarse grained

granite and diorite gneiss. The degree of surficial weathering and fracturing is variable

throughout the site. At locations in the eastern portion of the site and in the vicinity of MW-11,

13, and 14 there is no surficial weathering and fracturing observed. With the exception of the

westernmost portion of the site, surficial weathering and fracturing is typically less than 10 feet

in thickness and the intensity decreases with depth. In the westernmost portion of the site, at

MW-2 and MW-4, the weathered and fractured zone is approximately 30 and 40 feet thick,

respectively.

Hydrogeology - Unconsolidated Aquifer

Groundwater in the unconsolidated aquifer flows generally from west to east. The

gradients in the western part of the site, as calculated from the August, 1989 sampling round, are

0.008 upgradient of OK Tool and 0.013 upgradient of Hitchiner and Hendrix. The gradients are

less steep downgradient of the facilities. The gradient calculated from OK Tool (MI-27) to

MW-20 is 0.0027, from MW-20 to the Savage Well is 0.0029, and from the Savage Well to the

Souhegan River is 0.0028.

Hydraulic conductivities for the unconsolidated deposits were estimated from in-situ

falling head permeability tests and from grain size distribution curves. The hydraulic

conductivities in the sand and gravel deposits ranged from 3.3 feet per day at MW-14B (39 to 41

feet below ground surface) to 100 feet per day at MW-12A (14 to 16 feet below ground surface).

The average hydraulic conductivity for the sand and gravel using the Hvorslev Method

(1951) for evaluating falling head permeability tests is 32.7 feet per day with a standard

deviation of 26.8 feet per day. Two till hydraulic conductivities were calculated to be 1.9 and

0.6 feet per day. One hydraulic conductivity value calculated for a silt lens was 0 1 feet per day.

The average hydraulic conductivity of the sand and gravel aquifer, calculated using the Hazen

Method for analyzing grain size distribution curves, is 65 feet per day with a standard deviationof 47 feet per day.

2176-160/HAZ/3560 1-10

As part of previous studies of the site, NAI, Inc. estimated the hydraulic conductivity of

the sand and gravel to be 136 feet per day using slug test data, Roy F. Weston, Inc. estimated it

to be 11 feet per day using slug test data, and NHWSPCC estimated it to be 159 feet per day

using pump test data.

Using an average hydraulic conductivity from the two methods presented in this study of

49 feet per day, the hydraulic gradients presented above, and an assumed effective porosity of

0.2, the rate of groundwater flow is estimated to be 1.96 feet per day west of OK Tool, 3.19 feet

per day west-southwest of Hitchiner and Hendrix, and 0.74 feet per day downgradient of these

facilities.

Using the hydraulic conductivity of 235 feet per day derived from the January, 1990 pump

test of the Hitchiner production well, these flow rates are estimated to be 9.4 feet per day, 15.3

feet per day, and 3.3 feet per day, respectively.

Hydrogeology - Bedrock

In order to evaluate the hydraulic characteristics of the bedrock, permeability tests were

performed at the deep bedrock wells MW-2, 4, 11 and 14 using pneumatic packers. These wells

were advanced approximately 50 feet into bedrock and were constructed by casing off the

unconsolidated aquifer materials and the uppermost portion of the bedrock, while leaving the

majority of the bedrock well open.

The bedrock packer test data indicates no measurable hydraulic conductivity throughout

the tested bedrock zones at MW-2 or MW-14. At bedrock well MW-4, where drilling did not

penetrate beyond surficial weathered and fractured zone, the calculated hydraulic conductivities

within the open bedrock well varied between 0.45 and 1.18 feet per day. At bedrock well

MW-11, the calculated hydraulic conductivity values for the open bedrock interval varied

between 1.31 feet per day at a depth interval varied between 1.31 feet per day at a depth interval

of 81.3 to 98.8 feet and a maximum of 0.08 feet per day at a depth interval of 102.3 to 122.8 feet.

Bedrock wells MW-16, MW-30, and MW-31 were drilled to intersect transmissive (i.e.,

water-bearing) zones. Estimates of water yield were made during the drilling process and again

during sampling.

Two water-bearing zones were intersected in MW-16R, one in the interval from 105 to

124 feet below the ground surface, and the second in the interval from 130 to 138 feet. Each

interval was estimated to yield approximately 1.25 gallons per minute (gpm). No discrete

water-bearing intervals (i.e., >1 gpm) were identified at MW-30, which was drilled to a total

depth of 303 feet. At MW-31, the first water-bearing zone was identified at a depth of 270 to

273 feet, with an estimated yield of 75 gpm.

2176-160/HAZ/3560 1-11

Measured groundwater elevations at the site indicate that downward vertical gradients

exist between the overburden and the bedrock at MW-2, MW-11 and MW-16, all in the western

portion of the site. Upward vertical gradients exist at MW-4 and at MW-14, in the southwest,

and MW-31 in the east.

Stream-Aquifer Interaction - Hitchiner-Hendrix Discharge Stream

A comparison of the water level measurements in the upper portion of the

Hitchiner-Hendrix Discharge Stream with the groundwater elevations in the area show that the

surface water levels are approximately three to five feet above the water table. This suggests

that surface water generally discharges to the groundwater in that portion of the stream.

A comparison of the water levels in the central portion of the stream and the groundwater

elevations at that location indicate that the central portion of the Hitchiner-Hendrix Discharge

Stream receives flow from and discharges to the groundwater depending upon the gradient

between the surface water level and the groundwater elevation.

In the downstream portion of the Discharge Stream the surface water level was almost

always observed to be greater than the groundwater elevation. This suggests that surface water

generally discharges to the groundwater at this location.

A comparison of calculated and estimated discharge rates at water level recording stations

WLR-3 and WLR-4 (see Plate I) indicate that the stream is losing between 32,000 and 995,000

gallons per day, or an average of 394,000 gallons per day. Previous investigations by

NHWSPCC indicated that the stream was losing between 97,000 and 116,000 gallons per day.

Groundwater elevation fluctuations occur seasonally, and as a result of groundwater

pumping (see below). Surface water level fluctuations also occur seasonally as a result of

variations in runoff, and as a result of variations in the process water discharges from the

Hitchiner and Hendrix facilities.

Stream-Aquifer Interaction-Souhegan River

Based on comparison of staff gauge levels in the Souhegan River with groundwater levels

in adjacent piezometers and monitoring wells, some general observations on the relationship

between flows can be made. In the western portion of the site, the flow gradient along the

Souhegan River and the hydraulic gradient of the aquifer are relatively steep and the river

appears to lose water to the groundwater system on the south side of the river. Through the

2176-160/HAZ/3560 1-12

central portion of the site, as the flow gradient decreases, there is a transition zone where no

clear hydraulic gradient exists between the River ar> ' the groundwater, and finally, in the eastern

portion of the site, the river appears to gain water from the groundwater system.

The USGS previously performed flow measurements and stream gauging during June and

August, 1988 at stations located near WLR-1, SG-2 and WLR-5 (See Plate I). The results of

three sets of measurements indicate that the upper portion of the Souhegan River was losing

between 420,000 and 16.5 million gpd, and that the lower portion of the river was gaining

between 1.3 million and 11 million gpd.

Comparisons of calculated and estimated discharge rates from data collected during the RI

indicates some variations in river-aquifer interactions. Data collected at WLR-1 and SG-2,

located along the upstream portion of the River, indicates that this portion of the River behaves

as both a losing stretch and a gaining stretch. Ten sets of discharge values indicate gains, four

indicate losses, and five indicate little or no change in discharge (less than 5 cfs). The average

gain is approximately 3.5 cfs, or 2 million gallons/day.

Comparison of discharge measurements along the central portion of the Souhegan River,

at stations SG-2 and SG-3, indicate a generally losing stretch. Twelve measurements indicated

losses, six measurements indicated gains and two indicated no appreciable difference. The

average loss was approximately 7.32 cfs, or approximately 4.7 million gpd.

Discharge data for the downstream portion of the river between SG-3 and WLR-5 indicate

a consistently gaining stretch, consistent with interpretations based on groundwater contours,

with 20 sets of discharge values indicating gains, 2 sets indicating losses and 5 sets indicating no

appreciable difference. The average gain between SG-3 and WLR-5 was approximately 13 cfs,

or approximately 8.4 million gpd.

The data indicates that over the length of the study area, between WLR-1 and WLR-5, the

River is a generally gaining stretch, with 16 of 22 discharge values indicating gains.

The river-aquifer relationship is variable depending on fluctuating contribution from

rainfall/runoff and is influenced by various groundwater pumping locations and surface water

discharges. The main channels of rivers are usually gaining stretches, however the upper

stretches of the Souhegan from WLR-1 through SG-2 and SG-3 are at times losing stretches, in

part due to high flows from steeper stretches to the north and in part due to the combined effects

of high pumping at Fish Hatchery wells to the north and at industrial wells to the south. The

lower stretch of the river, having recovered from these influences and receiving flows from

several tributaries, is a consistently gaining stretch.

2176-160/HAZ/3560 1-13

Groundwater Pumping

Hitchiner withdraws approximately 320,000 gallons of water per day for non-contact cooling

and process water. Hendrix has a production well which, prior to March 1990, formerly

withdrew approximately 150,000-225,000 gallons of water per day which was also used for

non-contact cooling. Groundwater flow lines in the vicinity of these wells will be affected as a

result of this pumping. In addition, the upper portion of the Hendrix-Hitchiner Discharge Stream

may be losing water to the groundwater as a result of induced infiltration from the pumping

wells.

In addition to the effects on groundwater flow produced by the industrial production wells,

groundwater flow at the site may also be influenced by production wells at the Fish Hatchery

located on the north side of the Souhegan River. Two production wells FH-13 and FH-10 (See

Figure 1-3) are both pumping at a rate of 800 gallons per minute, 24 hours per day. This

amounts to 1,152,000 gallons per day for each well. These wells have been operating at this rate

since the spring of 1988 when well FH-10 was put on line. Other wells in this vicinity had

previously been pumping at lower rates (i.e., < 500 gpm) since approximately 1970.

A pumping test was performed in 1988 on production well FH-10 which is located 800

feet from the river. Well FH-13 is located 200 feet from the river. The data from the pump test

suggests that the drawdown from the well has the potential to extend to and perhaps beyond the

Souhegan River thereby possibly influencing the groundwater flow in the vicinity of the river.

Additionally, pumping wells located north of the river at Souhegan Valley Aquaculture, in

operation since the Fall of 1989, pump at a rate of approximately 150 gallons per minute.

Vertical and horizontal hydraulic gradient data indicate that these wells induce migration of

groundwater beneath the river from the site.

1.2.3 Anthropogenic Characteristics

Surficial Land Use

Land uses within the site area are varied, including residential, agricultural, commercial,

light industrial, and heavy industrial uses. Industrial uses are concentrated along Elm Street

(Route 101) in the western part of the site and include Hitchiner Manufacturing, Inc., Hendrix

Wire and Cable, and New England Steel Fabricators (NESFAB), at the western end of Elm

Street (see Figure 1-2). The OK Tool facility, also located in this area of the site, is no longer

used for industrial operations. A number of smaller commercial and industrial operations,

2176-160/HAZ/3560 1-14

including gas stations, autobody shops, and light manufacturing operations, are located

throughout the length of Elm Street. Agricultural uses, consisting of cornfields and a sod farm,

dominate the central and western portions of the site, extending from Elm Street to the Souhegan

River. Residential properties exist along Old Wilton Road, along the eastern end of Elm Street,

and along North River Road, to the north of the Souhegan River. Additionally, a mobile home

trailer park is located between Elm Street and the Milford Drive-in. Land uses on the north side

of the river include agricultural properties, the Milford Fish Hatchery, and a private fish hatchery.

Surface Water Use

There are no current uses of surface water as a drinking water supply. The Souhegan

River is used for recreational purposes (i.e. fishing, canoeing) and for irrigation of agricultural

properties (i.e. the sod farm). The river also receives NPDES - permitted discharges from

various locations.

Ground Water Use

The primary current uses of groundwater at the site are limited to industrial water supply

and fish hatcheries.

The Savage Well, a gravel packed overburden production well with a yield of

approximately 500 gallons per minute, was formerly used as a water supply for the Town of

Milford from 1960 to 1983. By comparison, the site area has been developed for industrial use

since approximately 1940.

1.3 CONTAMINANTS AND MEDIA OF CONCERN

1.3.1 Air

Ambient air monitoring detected low levels of acetone, TCA, methylene chloride, and

PCE at the site. The highest concentrations detected for each of the compounds were below the

proposed New Hampshire Ambient Air Level Guidelines. Therefore, no contaminants of

concern are identified in terms of remedial objectives.

2176-160/HAZ/3560 1-15

1.3.2 SoU

Analysis of soil and soil gas samples from thirteen suspected contaminant source areas

throughout the study area indicated the presence of volatile organic compounds in ten of the

thirteen areas, with the highest concentrations detected in the area between the OK Tool building

and the Souhegan River.

The results of the analyses did not indicate any source areas with VOC concentrations

high enough to pose a threat of continued release of contaminants to the groundwater or to

warrant source removal or remediation activities with respect to VOC contamination.

Additional work was completed subsequent to submission of the Draft RI to determine whether

source areas may exist underneath the OK Tool, Hitchiner, and Hendrix buildings.

The results of the additional soils investigation have identified higher levels of

tetrachloroethylene (PCE) beneath the OK Tool building slab than had been previously

identified in soils sampled elsewhere at the site during the RI. The eight samples collected

beneath the slab had PCE levels ranging from 83 ug/kg to 2,400 ug/kg. The highest levels, 2,400

ug/kg in SL-1 and 1,300 ug/kg in SL-2, were detected in soils located immediately adjacent to

the excavation of a former floor drain. Sample SL-8, located approximately 70 feet from the

excavation at the easternmost edge of the building, had PCE at a level of 900 ug/kg.

Trichloroethylene (TCE) was detected at 19 ug/kg in soil sample SL-8. The presence of

methylene chloride, identified in five of the samples, has been determined to be the result of

laboratory contamination.

Two of the soil samples collected from the stockpiles located north of the OK Tool

building were found to contain PCE at levels below the detection limit while the third contained

PCE at 44 ug/kg. The sample collected from the storm drain contained PCE at 840 ug/kg, TCE

at 160 ug/kg, and 1,2-DCE at 320 ug/kg.

The four samples collected beneath the Hitchiner facility contained no detectable VOC's

with the exception of Acetone, detected at 22 ug/kg in SL-9.

Sampling of soils beneath the Hendrix building indicated detectable levels of PCE in three

of four samples. PCE was detected at 100 ug/kg in SL-16, collected from a floor drain, at 110

ug/kg in SL-13, and at 5 ug/kg in SL-14.

One sample from each sub-floor area was also analyzed for the complete Hazardous

Substance List (HSL) parameters including acid and base/neutral extractable organic compounds

(ABNs), polychlorinated biphenyls (PCBs), and metals. The results do not appear to indicate asource for these contaminant parameters at any of the locations.

2176-160/HAZ/3560 1-16

The results of the additional soils investigation do not appear to indicate the presence of

VOCs in vadose zone soils at levels high enough to serve as a long-term source for groundwater

contamination. Elevated levels of PCE (i.e., in the 1 to 2 mg/kg range) were identified in soils

beneath the O.K. Tool floor slab, but these levels are significantly lower than levels of PCE

detected in groundwater immediately downgradient of O.K. Tool. Thus, the sampling results forthe soils beneath O.K. Tool do not suggest a contaminant source area which warrants source

control remedial action specific to the soils.

Metal debris is present in soils at depths of one to five feet below the ground surface

throughout an area measuring approximately 100 feet by 50 feet, located between the northwest

comer of the OK Tool building and the Souhegan River. A second area of metal debris exists

along the north side of the nearby state-owned lot, adjacent to the Souhegan River. Laboratory

analyses of soils from test pits and borings in the areas of metal debris indicate comparatively

elevated levels of a number of metals, including arsenic, barium, chromium, copper, iron, lead,

manganese, nickel, and vanadium.

PCBs were detected in soils in the vicinity of the O.K. Tool Building at levels of 0.633 to

3.48 mg/kg, and at a level of 24.0 mg/kg in a soil sample collected adjacent to the

Hitchiner-Hendrix discharge stream.

The results of the health risk assessment (see Section 1.5) for exposures to soils at the site

through ingestion or dermal absorbtion did not indicate unacceptable risks (i.e., the risks were

within the range used by EPA for remediation target levels). Therefore, the soils do not appear

to warrant remediation based on health risks.

1.3.3 Surface Water

The detection of VOCs in surface water within the study area was limited to samples

collected from the NPDES-permitted Hitchiner-Hendrix discharge stream. The single exception

to this was the detection of low levels of PCE, TCE, and 1,2-DCE in the surface water body

directly southwest of the Well, referred to herein as Savage Pond. The VOCs detected in Savage

Pond are likely derived from the groundwater contaminant plume.

The highest total VOC concentrations, in excess of 400 ug/1, occur in samples collected

from permitted outfalls at the Hitchiner facility (SW-5, which discharges to the ponded area at

the upstream end of the stream) and Hendrix facility (SW-19). VOC concentrations decrease

rapidly downstream from the outfalls. The most prevalent contaminants detected in surface

water along the Hitchiner-Hendrix discharge stream are acetone, TCA and PCE; detected at

maximum concentrations of 300 ug/1, 260 ug/1, and 29 ug/1, respectively.

2176-160/HAZ/3560 1-17

As summarized in the 1985 NHWSPCC Hydrogeological Investigation, data from

sampling performed at Hitchiner outfalls (including the ponded area) in 1983 and 1984, prior to

the RI, indicated the presence of acetone at concentrations up to 2010 ug/1, TCA at

concentrations up to 1800 ug/1, and PCE at concentrations up to 56 ug/1. Other VOC'spreviously detected include 1,1-DCA, 1,1-DCE, 1,2-DCE, TCE, methylethyl ketone, methyl

isobutyl ketone, toluene, and benzene.

Concentrations of individual VOC's were in some instances higher in discharge stream

samples than in the Hitchiner production well, and in some instances lower than in the well.

During the RI, Acetone and TCA have been detected in the upper portion of the discharge

stream (south of Elm Street) and in the lower portion of the discharge stream (stations SW-8 and

SW-9). The source of acetone and TCA detected in surface water appears to be permitted

process water discharges from the Hitchiner facility.

PCE has been detected downstream of the Hendrix outfalls and throughout the length of

the lower discharge stream, but at concentrations less than 20 ug/1. Other VOCs detected in the

Hendrix outfalls included TCA, toluene, benzene, acetone, styrene, acrolein, and MTBE. These

permitted discharges from the Hendrix facility were ceased in March, 1990 when Hendrix

installed a process water recycling system. PCE concentrations detected during the RI in theHendrix production well and in MW-8, located immediately upgradient of the Hendrix well,

were comparable and in some cases higher than the concentrations in the Hendrix outfalls prior

to the cessation of discharges. Data compiled by NHWSPCC prior to the RI also indicates

higher PCE concentrations in the production well than in the Hendrix outfall or in the discharge

stream downstream of Hendrix. Therefore, the PCE which was discharged from the Hendrix

facility prior to March 1990 appears to have been derived from the interception of

PCE-contaminated groundwater south of Elm Street by the Hendrix production well. Other

VOCs were in some instances higher in the outfall and the discharge stream and in some

instances lower.

It should be noted that the Hitchiner NPDES permit allows discharge of total VOCs at

levels up to 600 ug/1 and that the historical Hendrix permit allowed total VOC discharges up to

600 ug/1.

2176-160/HAZ/3560 1-18

1.3.4 Sediment

VOCs were detected in stream sediments primarily at locations adjacent to or immediately

downstream of NPDES-permitted process water outfalls from the Hitchiner facility. Theprincipal VOC contaminants detected in sediments were acetone, TCA, and 1,1-DCA. All arelikely derived from process water discharges from the Hitchiner facility as discussed above in

regard to surface water contaminants. Also detected in sediments near the Hitchiner outfalls

were toluene and chloroethane. Levels of VOCs in sediments drop off rapidly further

downstream from the Hitchiner outfalls. Acetone, PCE, and 1,2-DCE were also detected in low

levels in sediments at the Savage Pond, located approximately 100 feet southwest of the Savage

well. TCE and 1,2-DCE detected at this location are likely derived from groundwater recharge

to the pond.Several ABNs were detected in sediments along the upper portion of the discharge stream,

with elevated levels limited to sediments immediately downstream from the Hitchiner outfalls.

Fluoranthene and bis(2-ethylhexyl)phthalate were the most commonly detected compounds and

appear to be derived from discharges from the Hitchiner facility.

A number of ABNs were also detected in sediments at the upstream end of the SouheganRiver. The source of these contaminants has not been determined, but is clearly located

upstream from the study area.

During the sampling of surface water systems, polychlorinated biphenyls (PCBs) were

detected only in sediments immediately adjacent to the Hitchiner outfalls, at concentrations upto 6.5 mg./kg.

1.3.5 Groundwater

Volatile Organic Compounds

Groundwater is the only medium in the study area requiring remediation for volatile

organic compounds (VOCs).

The four principal VOC contaminants detected in groundwater at the site are:

tetrachloroethylene (PCE)

1,1,1 -trichloroethane (TCA)

trichloroethylene (TCE)1,2-dichloroethylene (1,2-DCE)

2176-160/HAZ/3560 1-19

Detected less frequently and at lower concentrations in groundwater are the following

VOCs:

1,1 -dichloroethylene (1,1 -DCE)

1,1 -dichloroethane (1,1 -DCA)

methyl-t-butyl ether (MTBE)

Several other VOCs have been detected in groundwater at the site either by HMM or

NHDES sampling during the RI. The following VOCs were detected in the following ranges of

concentrations:

Concentrations fug/1)

1, 1,2, 2-Tetrachloroethane traceToluene 9Methylene Chloride 7-10Ethylbenzene traceTotal Xylenes 62Carbon Tetrachloride 54-Methyl-2-Pentanone 72-Hexanone 9

These compounds are not considered important to an evaluation of the nature and extent of

site contamination for one or more of the following reasons: (1) the compounds are considered

to be the result of laboratory induced contamination; (2) they occur at concentrations below

existing regulatory levels (MCLs); or (3) they occur at only one sampling location.

VOC Contamination in the Unconsolidated Aquifer

Figure 1-4 shows the inferred distribution of total volatile organic compounds from data

collected during the period of January 1989 to January 1990. This map and the following

contour maps were developed based on an analytical data obtained during three rounds of

sampling by HMM and data obtained by NHDES for 8 residential drinking water supply wells

(RW-1 through RW-8) located north of the Souhegan River along North River Road, 19

observation, production, and test wells (FH-9 through FH-30) located on the MiJford Fish

Hatchery and Souhegan Valley Aquaculture properties to the north of the Souhegan River, and

four groundwater monitoring wells (RFW-1 through RFW-4) at the former AMP Technology

Facility.

2176-160/HAZ/3560 1-20

The observed distribution of volatile organic compounds is approximately 5750 feet long

and approximately 2500 feet wide, extending from the vicinity of OK Tool and Hitchiner

(MI-20, MI-24, MI-26, MI-27 and MI-30) Manufacturing in the west to the Souhegan River in

the east and from Old Wilton Road in the south to the Souhegan River in the north. The highest

concentration of VOCs (22,100 ug/1) was detected in MI-24, immediately to the east of OK

Tool, which is screened from 5 to 85 feet in the overburden (see Figure 1-4). Concentrations

greater than 1000 ug/1 of total volatile organics were detected at all depths sampled in

overburden wells MW-9, MW-10, MI-7, MI-26, MI-30, MI-32, MW-14, and MW-20.

Concentrations of greater than 1000 ug/1 were detected in MW-16 from 40 to 83 feet below

ground and in MW-17 from 50 to 95 feet below ground.

It should be noted when examining Figure 1-4 and subsequent VOC contour maps that

several wells adjacent to OK Tool and Hitchiner have long screened intervals (i.e., 30 to 80 feet)

as compared to the typical 10 foot well screens at the MW wells and the 5 to 15 foot screens at

most other MI wells.

Tetrachloroethylene (PCE) is the most widespread and most highly concentrated VOC

contaminant detected in groundwater and mimics the distribution and extent of total volatile

organic compounds (see Figure 1-5). The highest detected concentration of PCE was 18,000

ug/1 at MI-24. Concentrations greater than 1,000 ug/1 occur as far downgradient as MW-14,

approximately 4,000 feet east of OK Tool.

The data indicates that the VOC contamination in the overburden is limited to the area

south of the Souhegan River with the exception of MI-67 and MI-68, located on the Milford Fish

Hatchery property, and the private fish hatchery pumping wells (FH-28, 29, and 30). Total VOC

concentrations of 582 ug/1 were detected at MI-68, located approximately 50 feet north of the

river and at 17 ug/1 at MI-67, located approximately 250 feet north of the River. Additionally,

November, 1989 results from NHDES sampling of pumping wells at the private fish hatchery

indicated 1 to 2 ug/1 of PCE in 3 of 5 sampled wells (FH-28, 29, and 30). Sampling performed

by HMM in April, 1990 confirmed these results.

2176-160/HAZ/3560 1-22

Sources of VOC Groundwater Contamination

Based on the distribution of PCE contamination in groundwater at the site (see Figure

1-5), the occurrence of significantly higher levels (>15,000 ug/1) of PCE in groundwater

immediately downgradient of the OK Tool Facility, and the historical occurrence of high levels

in soils adjacent to the OK Tool building (up to 1,150,000 ug/kg) and in a floor drain inside the

building (up to 300,000 ug/1), it is apparent that the principal source of PCE contamination in

groundwater at the site was associated with the OK Tool facility. Specific sources and potential

sources include a floor drain, an underground tank, and a vapor degreasing tank formerly located

inside the building, an above ground PCE tank located outside the building, and areas outside the

building which were apparently used for the disposal of oily wastes and metallic wastes. The

distribution of PCE in groundwater indicates that there may be additional sources at the site, as

further discussed later in this section.

TCE, 1,2-DCE, and 1,1-DCE exhibit distributions throughout the site that are generally

similar to that of PCE, although these compounds are somewhat less widespread in occurrence,

are less continuously detected throughout the aquifer, and occur at concentrations which are

generally at least an order of magnitude lower than those of PCE. TCE readily forms as a

degradation product of PCE, while 1,2-DCE and 1,1-DCE form as degradation products of both

PCE and TCE. The results of the RI do not indicate any separate primary source areas for TCE,

1,2-DCE, or 1,1-DCE contamination in groundwater, and it appears that TCE, 1,2-DCE, and

1,1-DCE contaminants in groundwater at the site are derived primarily from degradation of PCE

or are impurities in the raw PCE source material, and thus are derived from a common principal

source(s).

Given the known and potential use of PCE-based solvents at other industries and

commercial operations within the site area, it is likely that additional sources within the site area

contributed to the PCE and related groundwater contamination. Other potential sources are

discussed in more detail at the end of this section.

The sampling results for the soils beneath OK Tool, as previously discussed in the soils

section, do not suggest a contaminant source area which warrants source control remedial action

specific to the soils. There are, however, high levels of PCE contamination in groundwater

downgradient from the OK Tool facility, which imply the existence of source(s) at depths within

the aquifer, beneath the OK Tool building, therefore source control of the groundwater may be

appropriate.

2176-160/HAZ/3560 1-23

Because PCE is a denser-than-water contaminant (1.63 g/cm^) and is only partially

soluble in water, it tends to sink within the aquifer. Given the levels of PCE detected

downgradient of OK Tool (>20,000 ug/1), it is likely that PCE exists in the aquifer below OKTool as a dense non-aqueous phase liquid (DNAPL). It is also possible that DNAPL sources

exist elsewhere within the area where high VOC concentrations have been defined. Potential

additional source areas are further discussed below. Current research and experience at other

sites indicates that DNAPLs typically exist as discontinuous accumulations both within the

unconsolidated aquifer and within fractured bedrock below. It is difficult to prove directly the

existence of DNAPLs, and impractical to delineate the location and extent of individual DNAPL

accumulations due to the difficulty in intercepting and sampling these accumulations.

Regardless of the existence of DNAPLs, the high levels of groundwater contaminants adjacent

to OK Tool indicate that this location is a source for continued long-term migration of

contaminants into downgradient portions of the aquifer. Source control of the groundwater in

this area will be evaluated as an integral component of the remedial alternatives for the site.

Ensuing sections of the FS examine the feasibility of source control alternatives.

TCA contamination exhibits some significantly different characteristics of occurrence and

distribution from PCE and the related compounds discussed above (see Figure 1-6). The highest

detected concentration of TCA was 1,300 ug/1 at monitoring well MI-30, located downgradient

from the Hitchiner Facility. TCA was detected most frequently in wells on the south side of Elm

Street, adjacent to and downgradient from the Hitchiner Facility. TCA was detected less

frequently, but in concentrations up to 300 ug/1, in wells immediately downgradient from the OK

Tool Facility. TCA has been historically used at Hitchiner and is still currently being used.

TCA is also used by Hendrix Wire and Cable and was formerly used by New England Steel

Fabricators, as documented in the 1985 NHWSPCC report, and low levels of TCA have been

detected in groundwater samples collected at NESFAB prior to the RI. It should be noted,

however, that TCA was detected in two wells at NESFAB in a 1983 sampling round but was not

detected in a 1984 sampling round of the same wells. Furthermore, the results of groundwater

sampling completed during the RI does not indicate sources of TCA contamination in the

vicinity of the Hendrix or NESFAB facilities. TCA has been detected consistently in water and

sediment samples from permitted process water outfalls at the Hitchiner facility and in the

Hitchiner-Hendrix discharge stream immediately downgradient from the Hitchiner facility. For

these reasons, it appears that a principal source of TCA contamination in groundwater

2176-160/HAZ/3560 1-25

was located at the Hitchiner Facility. Specific potential sources within the Hitchiner Facility

include the process water discharge system and the dry well formerly located in a photographic

lab within the building. Historical and current sampling data also suggest a TCA source at OK

Tool, possibly related to the PCE source(s) previously discussed. Both 1,1-DCE ancj ij-DCA,

also detected at the site, may form as degradation products of 1,1,1 TCA and are likely derived

from a common source.

Given the varied industrial and commercial history of the site area and the highly

permeable nature of the aquifer underlying the site area, it is likely that additional source areas

contribute or have previously contributed to the VOC groundwater contamination at the site.

The RI data have not delineated specific additional sources for the VOCs of concern, and it may

be impossible to do so given the nature of the aquifer and the contaminant plume. However, a

number of potential additional source areas exist in the site area and it is possible that other

DNAPL sources exist in these areas. The distribution of PCE in groundwater indicates an

apparent anomaly of relatively elevated levels within the plume in the vicinity of the Drive-In

access road (i.e., between wells MW-17 and MW-20), which potentially indicates an additional

source(s) located between OK Tool and the Drive-In road. Past and present operations in this

area include the Hendrix facility, Body Magic Autobody (formerly Talarico Pontiac), the trailer

park and leach field, and a former paving company operation. Additionally, the

Hitchiner-Hendrix discharge stream exits from a culverted section just west of the Drive-In road

prior to crossing under the road and flowing eastward.

A number of other potential source areas for VOC groundwater contamination were

identified during the RI based on past and current site operations. Figure 1-7 indicates the

locations of nineteen such locations within the study area.

As a secondary issue, several source areas have been indicated for contaminants other than

the principal VOCs of concern.

First, the distribution of MTBE detected in groundwater at the site suggests that it is

derived from a source located upgradient of the Hitchiner facility (i.e., further west along Elm

Street). MTBE is a common additive in unleaded gasoline and is typically found as a

contaminant in groundwater as the result of gasoline spills or leaking underground storage tanks.

Secondly, a number of ABNs were also detected in sediments at the upstream end of the

Souhegan River. The source of these contaminants has not been determined, but is clearly

located upstream from the study area.

2176-160/HAZ/3560 1-27

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Thirdly, accumulations of metallic wastes exist along the south bank of the Souhegan

River on the OK Tool Property and on the adjacent state-owned lot. Elevated levels of metals

and ABNs have been detected in soils associated with this waste material.

Lastly, petroleum product (fuel oil or waste oil) has been observed in well MW-21 located

adjacent to Medlyn Motors.

VOC Contamination - Bedrock

VOCs were also detected in some wells screened in bedrock, (MW-19B, MI-19, MI-22,

and MI-25). However, all of these wells are screened within the upper 10 to 20 feet of bedrock,

which is typically weathered and fractured and may be viewed as hydraulically connected to the

unconsolidated aquifer.

Wells MW-2R, 4R, 11R, and 14R are open bedrock wells which are cased off from the

uppermost weathered bedrock zone. The results of Phase I and Phase EL groundwater sampling

indicated the presence of VOCs in samples collected from deep bedrock wells MW-2R,

MW-11R, and MW-14R, but no detection at MW-4R. However, observations of bedrock core

samples indicate that the rock at MW-11 and MW-14 is not fractured and bedrock permeability

testing performed at all three wells indicates that the bedrock is not transmissive. Moreover,

field measurement of pH in groundwater samples from these wells indicate anomalously high

pH values of between 9.75 and 12.48, potentially indicative of water leaking past the

cement-bentonite grout seal from the unconsolidated aquifer (i.e., water that has been in contact

with the grout will contain some dissolved grout and will thus tend to have a high pH).

Three additional bedrock wells were installed and sampled using discrete interval packer

sampling techniques in order to more clearly define whether transmissive zones exist in the

bedrock and whether contaminants could be migrating off-site via transmissive bedrock zones.

The results of this bedrock well sampling program indicate that VOC contamination exists

in the bedrock at MW-16R (up to 3500 ug/1), located within the bedrock channel directly east of

OK Tool and underlying the most-highly contaminated portion of the overburden aquifer.

The concentrations of VOCs in the bedrock are significantly lower than those detected in

the overlying overburden aquifer. For example, VOC concentrations greater than 6400 ug/1 have

been detected at MW-16C, the overburden well which is located immediately adjacent to

MW-16R (<3500 ug/1) and screened immediately above the bedrock surface. As an additional

example, VOC concentrations of 220 ug/1 were detected in the shallow bedrock well at MW-25

in comparison to 1800 ug/1 in the adjacent overburden well MW-26.

2176-160/HAZ/3560 1-29

Sampling of bedrock wells at MW-30 and MW-31 provided additional information on the

potential for migration of contaminants off-site through transmissive bedrock fracture zones.

The results of the program indicate that at MW-31, located at the downgradient leading edge of

the overburden aquifer contaminant plume, a highly transmissive fracture zone exists at depth in

the bedrock. Analytical results for six groundwater samples, two each from three test intervals,

indicate no detectable VOCs in five of the samples and 13 ug/1 of TCE in the sixth.

Drilling results and yield testing at MW-30, located approximately 900 feet northeast of

OK Tool and to the north of the Souhegan River, did not indicate the presence of a productive

zone (i.e., greater than 1 gallon per minute) within 300 feet of the ground surface. Nonetheless,

sampling of the entire open bedrock interval was performed. Analytical results indicated the

presence of PCE at concentrations ranging from 80 ug/1 to 26 ug/1.

Several residences located along North River Road use bedrock wells for drinking water

supply. Bedrock elevations in the vicinity of the residential wells range from 170 to 210 feet.

These residential wells are thus located topographically upgradient from MW-30 in terms of

both ground surface and bedrock surface and are likely to be hydraulically upgradient. Sampling

of eight residential wells (RW-1 through RW-8), including six bedrock wells, has identified no

detectable concentrations of VOC contaminants (see Figure 1-2 and Plate I).

Other Groundwater Contaminants

Acid and base/neutral extractable organic compounds were not detected in groundwater,

except as the result of apparent laboratory contamination of groundwater samples, as determined

during data validation procedures. Metals were detected in groundwater at levels slightly above

MCLs at only three monitoring wells (MW-6A, MW-8A, MW-25). However, the occurrence of

elevated levels of iron and manganese will need to be considered in terms of the evaluation of

technology options and remedial alternatives in Sections 3.0 and 4.0.

Other non-CERCLA regulated contaminants (in addition to petroleum-derived compounds

which are known to exist) may be present, but have not been analyzed for. These include

pesticide residues and metabolites associated with agricultural application, nitrate from

fertilizers and septic systems, and road salt.

2176-160/HAZ/3560 1-30

1.5 RISK ASSESSMENT

The Baseline Health Risk Assessment portion of the RI was prepared by Environmental

Science & Engineering (formerly Buonicore-Cashman Associates) and submitted to EPA as a

separate document on October 31, 1989. The objective of the Risk Assessment was to determine

the extent to which the site conditions, as delineated by the Remedial Investigation, may impact

human health, welfare, or the environment. It should be noted that groundwater in the affected

areas of the aquifer is not being used for potable supply. The potential impacts were determined

based on existing exposures or, in the absence of existing exposures, on hypothetical exposures

(e.g., for groundwater exposures). The Risk Assessment consisted of the following general

components.

• Hazard identification and selection of constituents of concern

• Toxicity (dose-response) assessment

Exposure assessment

Risk characterization

Constituents of concern were selected for the various media (groundwater, surface water,

soil and sediment, and air) based on toxicity, mobility, persistence in the environment,

concentration, and frequency of detection. For groundwater, the following constituents were

selected.

Tetrachloroethylene (PCE)

Trichloroethylene (TCE)

1,2-Dichloroethylene (1,2-DCE)

1,1,1 -Trichloroethane (TCA)

1,1 -Dichloroethylene (1,1 -DCE)

1,1 -Dichloroethane (1,1 -DCA)

For surface water, the selected constituents of concern were:

• Acetone

1,1,1 -Trichloroethane (TCA)

Tetrachloroethylene (PCE)

• Benzene

• Styrene

2176-160/HAZ/3560 1-31

For soils and sediments, the following compounds were selected:

• Acetone

• Carbon tetrachloride

• Methylene chloride

Tetrachloroethylene (PCE)

• Toluene

Arsenic

• Cadmium

• Chromium

• Lead

• Mercury

• Nickel

PCBs

Contaminant concentrations detected during air samples were below proposed New

Hampshire Ambient Air Level (AAL) guidelines. However, the N.H. Division of Public Health

maintains that the AALs are not appropriate for evaluating the potential for risk from exposure

to airborne chemicals, therefore, a risk assessment was conducted for all chemicals detected:

• Acetone

• Methylene Chloride

Tetrachloroethylene (PCE)

1,1,1 -Trichloroethane (TCA)

Exposure scenarios were considered for "worst case" situations in order to estimate

exposure point concentrations and to characterize risk in terms of carcinogenic and

non-carcinogenic risk.

The following exposure scenarios were considered:

Theoretical "worst case" scenarios in which groundwater is used by an individual

household for drinking water and bathing.

• Exposure to children playing or wading in surface waters in the Hitchiner-Hendrix

discharge stream.

Exposure through ingestion or dermal absorption of chemicals in soils.

2176-160/HAZ/3560 1-32

In summary, total cancer risks were estimated by exposure pathway under the assumption

that the carcinogenicity of mixtures of compounds is additive. The only exposure scenario

estimated to produce risks above the typical range used by EPA for performance goals (10~4 to

10"" excess lifetime cancer risk) are the theoretical drinking water scenario and the theoretical

household groundwater use scenarios. The soil contact scenario produces risk estimates within

the range, while all estimates of risk for surface water are below the range.

For theoretical drinking water scenario risks calculated using maximum groundwater

concentrations, PCE contributes a large majority of the risk, while at the mean concentration risk

contribution is shared between 1,1-DCE and PCE. The risk level determined for the maximumi~\

concentration of PCE detected in groundwater (18,000 ug/1) was 3 x 10 and the risk level

determined for the mean concentration detected in groundwater at the site (41 ug/1) was 6 x 10"^.

For theoretical household water use (e.g., showering, sink, toilet), PCE contributes therj

majority of the risk for the maximum case (1 x 10" ) while 1,1-DCE is the greatest contributor

to risk at the average value (3 x 10 ).

The Hazard Indices for VOCs were summed under the assumption of additivity of toxic

effects. However, the additive Hazard Index for metals were not calculated because each metal

exhibits a different toxic endpoint. The theoretical exposure to groundwater presents the only

pathway where reference doses were exceeded. The Hazard indices calculated for other

exposure routes were found to be substantially below unity (1.0), even when the values were

added, suggesting that health impact is improbable. Individually, PCE and DCE are the only

compounds to exceed the minimum reference dose requirements (trans-1,2-dichloroethylene

does not exceed the Reference Dose in the average exposure case). If the Hazard Indices for all

VOCs are treated in an additive fashion (i.e., it is assumed that all will have a similar toxic

effect), PCE still contributes the large majority of the noncarcinogenic impact.

In summary, the only exposure scenarios at the site which produced risks above the target

range were theoretical future exposures to groundwater. There were no current exposure

pathways identified which pose an unacceptable risk to human health.

The results of the risk assessment and the results of the characterization of the nature and

extent of contamination, as discussed in the preceding summary, form a basis for the

development of remedial response objectives in Section 2.0 and for the development and

evaluation of remedial alternatives in Section 3.0 and 4.0.

2176-160/HAZ/3560 1-33

1.6 REMEDIATION GOALS

The newly revised NCP stresses the development of remediation goals based on

groundwater classification. The Site does not fit clearly into the EPA classification system.

Sources for groundwater contamination likely exist in the form of dense non-aqueous

phase liquids (DNAPLs). Because of the typical occurrence of DNAPLs in discontinuous lenses

and pools, and because of the low miscibility of PCE and other chlorinated solvents, the

DNAPLs present a persistent long-term source of solvents. It may be feasible to confine

contaminants to immediate areas of DNAPL residuals, but it may not be technically feasible to

recover the DNAPL sources, and concentrations in the immediate vicinity of DNAPLs may

remain elevated due to the difficulty in effectively remediating DNAPL sources.

The practically achievable remediation goals for the site appear to be: 1) confine

contamination to immediate vicinity of DNAPL sources, 2) minimize migration toward potential

receptors, and 3) render balance of aquifer available for such beneficial uses as land use and

regulations may permit, within a timeframe that is reasonable given the nature of the site, the

contaminants, and the contaminant sources.

The remedial alternatives to be evaluated in ensuing sections of the FS will include plume

containment, groundwater pumping and treatment, and institutional controls.

2176-160/HAZ/3560 1-34