hmm associates, inc. letter
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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