PB97-963106
EPA/541/R-97/008
November 1997
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Savage Municipal Water Supply,
(OK Tool Source Area) (Operable Unit 1)
Milford, NH
12/19/1996
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DECLARATION FOR THE EXPLANATION
OF SIGNIFICANT DIFFERENCES
SAVAGE MUNICIPAL WATER SUPPLY WELL SUPERFUND SITE << ,
December 19,1996 ^
Site Name and Location
Savage Municipal Water Supply Well Superfund Site
OK Tool Source Area, Operable Unit 1
Milford, New Hampshire
Identification of Lead and Support Agencies
Lead Agency: US Environmental Protection Agency
Support Agency: NH Department of Environmental Services
(Lead Agency for Design designated in Cooperative
Agreement dated September 26,1994)
Statement of Purpose
This decision document sets forth the basis for the determination to issue the attached
Explanation of Significant Differences (ESD) for the Savage Municipal Water Supply
Well Superfund Site (OK Tool Source Area portion) in Milford, New Hampshire.
Statutory Basis for Issuance of the ESD
Under Section 117(c) of the Comprehensive Environmental Response, Compensation
and Liability Act (CERCLA)1 if the US Environmental Protection Agency (EPA)
determines that the remedial action being undertaken at a site differs significantly from
the Record of Decision (ROD) for that site, EPA shall publish an explanation of the
significant differences between the remedial action being undertaken and the remedial
action set forth in the ROD and the reasons such changes are being made. EPA policy
and regulations2 indicate that an ESD, rather than a ROD amendment, is appropriate
where the changes being made to the remedy are significant but do not fundamentally
alter the overall remedy with respect to scope, performance, or cost. After review of the
proposed changes to the remedy, EPA has determined that the adjustments to the ROD
provided in the ESD are significant but do not fundamentally alter the overall remedy
for the Site with respect to scope, performance, or cost. Therefore, this ESD is being
issued properly.
In accordance with Section 300.435(c) of the NCP, this ESD and supporting
documentation will become part of the Administrative Record which is available for
public review at both the EPA Region I Records Center in Boston, Massachusetts, and
the Wadleigh Memorial Library in Milford, New Hampshire.
l42U.S.C.§9617(c).
2See 40 CFR 300.435(c) (National Contingency Plan, § 300.435(c)); EPA Office of Solid Waste
and Emergency Response Directive 9355.3-02.
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Savage Municipal Water Supply Well Superfund Site Page 2
OK Too< Source Area-Exptanatton of Stanfflcant Differences
Background
On September 27,1991, EPA issued a Record of Decision (ROD) selecting a remedy
for the cleanup of the Savage Municipal Water Supply Well Superfund Site. The ROD
identified two portions of the contaminated plume that needed to be remediated; the
two portions were referred to as the concentrated plume and the extended plume.
Since issuance of the ROD, the remedy has been divided into two operable units based
upon the portions of the plume ident'rfed in 1991. The portion of the plume where the
levels of groundwater contamination are the highest is now Operable Unit 1 (OU 1),
the OK Tool Source Area (OKTSA). The OKTSA, defined in detail in the Consent
Decree, includes all of the OK Tool property and additional properties to the east, north
and west of the OK Tool Property. Operable Unit 2 (OU 2) is the Extended Plume. It
includes both the remaining portion of the concentrated plume and the dissolved
plume; it extends eastward approximately one mile in length and is about 2500 feet in
width.
The current document only addresses remediation of the fund lead portion of the site
which is the OK Tool Source Area. New information obtained during the design
studies, a better understanding of the nature of the contamination, and site restrictions
revealed during the design studies all support the need to address changed conditions.
However, the original goal of remediating the aquifer has not changed.
Remedy selected in 1991 ROD
The 1991 ROD remedy encompassed the entire site and included six extraction wells
(pumping a total of 1100 gpm) and three treatment plants utilizing two treatment
technologies. The two treatment technologies were ultraviolet oxidation (UV/ oxidation)
and air stripping with carbon adsorption. The ROD made provision for decisions to be
made during design for discharge of treated groundwater and for studies to determine
the best method to control the concentrated plume.
More specifically, the 1991 ROD described the remedy for the area now known as the
OKTSA to be one extraction well pumping at an estimated rate of 250 gpm;
groundwater treatment using UV/oxidation; and discharge to either surface water or
groundwater to be decided during design. The 1991 ROD considered the placement of
a barrier wall to control the volume of water to be pumped.
Changes to the 1991 remedy
The changes to the remedy described in this document apply only to the remediation of
the OKTSA. The changes include the acquisition of property upon which the treatment
plant will be built; the addition of a slurry wall; the addition of three extraction wells
(bringing the total to four); the reduction of the pumping rate to 70 gpm; the
construction of a soil vapor extraction system with air sparging; and the treatment of
groundwater by air stripping with carbon adsorption. Treated groundwater will be
discharged to the ground using two injection wells and a recharge pit.
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Savage Municipal Water Supply WeU Superfund Site Page 3
OK Tool Source Area- Explanation of Significant Differences
Overview of the ESD
Evaluations using data developed during pre-design indicate that tetrachloroethylene is
present in the subsurface as a dense, non-aqueous phase liquid (DNAPL). The
presence of DNAPL makes the extraction of groundwater contamination more complex
than does the presence of dissolved phase contaminants alone. DNAPLs are not
readily removed by the pump and treat methods called for in the ROD. While
hydrodynamic capture could prohibit further migration of contamination from the source
area, it would not effectively remove DNAPL mass or dissolved contaminant
concentrations in a reasonable time frame.
Therefore EPA and the NHDES have concluded that a physical barrier (the proposed
slurry wall) in combination with more aggressive contaminant removal technologies is
the preferred technical solution as well as being a more cost effective method of
managing the plume. The slurry wall will enclose the area containing the DNAPL and
the highest dissolved phase contaminant concentration area thereby prohibiting
continued contaminant migration to the downgradient extended plume area. In addition
the slurry wall will reduce the total volume of groundwater needing treatment over time.
Soil Vapor Extraction with air sparging has been chosen to remove the near surface
contamination sources within the slurry wall. In the 1991 ROD, the treatment
technology for the groundwater pumped from the OK Tool area was UV/oxidation. This
technology has been changed to air stripping with carbon adsorption. This changed
treatment scenario will combine the air streams from two types of contaminant removal
technologies - air stripping of groundwater and SVE of soil - to one type of treatment
technology — carbon adsorption.
Predesign evaluations indicate that the OK Tool property is not suitable for the location
of the treatment plant called for in the ROD. The OK Tool property is almost entirely
within the 100-year floodplain. Furthermore, the proposed remedial action (including
construction of the slurry wall, soil vapor extraction system, and groundwater extraction
and injection wells) will occupy nearly all the OK Tool property. As a result, there will
not be sufficient space for the location of the treatment plant on that same property.
Therefore, the remedy is being modified due to the physical limitations posed by site
conditions to include the acquisition of an adjacent 0.78 acre property upon which the
treatment facility will be located.
The Conceptual Remediation Design Report3 compared several pump and treat
alternatives with several slurry wall/pump and treat alternatives. All of the different
alternatives used air stripping with carbon adsorption. The estimated cost (present
worth analysis over a 30 year period of operation) of the slurry wall/SVEteir stripping
alternative is $ 8.2 million. The estimated cost of a pump and treat/SVE/ air stripping
alternative without a slurry wall is $ 9.7 million. The changes proposed here result in a
cost effective remedy with greater certainty of meeting the clean up goals established
3CDM Inc., March. 1996, revised June, 1996.
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Savage Municipal Water Supply Well Superfund Site Page 4
OK Tool Sooroe Area-Explanation of Significant Differences
in the ROD and the requirements defined in the Consent Decree governing the mixed
work site.
Declaration
For the foregoing reasons, by my signature below, I approve the issuance of an
Explanation of Significant Differences for the Savage Municipal Water Supply Well
Superfund Site.in Milford, New Hampshire, and the changes stated therein.
*y^
Date Unda M. Murphy, Director
Office of Site Remediation & Restoration
USEPA, Region I
Date Robert W. Vamey, Commissioner
Department of Environmental Services
State of New Hampshire
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EXPLANATION OF SIGNIFICANT DIFFERENCES
SAVAGE MUNICIPAL WATER SUPPLY WELL SUPERFUND SITE
Introduction
A. Site Name and Location
Site Name: Savage Municipal Water Supply Well
OK Tool Source Area
Site Location: Town of Milford, New Hampshire
B. Lead and Support Agencies
Lead Agency: US Environmental Protection Agency
Support Agency: NH Department of Environmental Services
(Lead Agency for Design designated in Cooperative
Agreement dated September 26,1994)
C. Legal Authority
Under Section 117(c) of the Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA),1 Section 300.435(c) of the National
Contingency Plan (NCR),2 and U.S. Environmental Protection Agency (EPA)
guidance,3 if EPA determines that differences in the remedial action significantly
change but do not fundamentally alter the remedy selected in the Record of
Decision (ROD) with regard to scope, performance, or cost, EPA shall publish an
explanation of the significant differences (ESD) between the remedial action
being undertaken and the remedial action set forth in the ROD as well as the
reasons such changes are being made.
D. Summary of Circumstances Necessitating this Explanation of Significant
Differences
The Consent Decree4 governing the performance of remedial work at the Site
resulted in a division of work between the government agencies (EPA and New
Hampshire Department of Environmental Services, NHDES) and the Performing
Parties (Hitchiner Manufacturing Company and Hendrix Wire and Cable
142 U.S.C. Section 9617(c).
240 C.F.R. 300.435(c).
3Office of Solid Waste and Emergency Response {OSWER} Directive 9355.3-02.
4United States of America and State of New Hampshire v. Conduction Corporation d/b/a Hendrix
Wire &Cable. et al.. Civil Action No. 94-174-JD, June 27.1994 (New Hampshire District Court).
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Savage MunWpal Water Supply Wed Superfund Site Page 2
OK Tool Source Area -Explanation of Significant Differences December 19.1996
Company). The terms of the Consent Decree did not change the original goal of
restoring the aquifer to drinking water quality. The agreed upon division of work
is shown on the attached map (See Figure 1) which delineates the OK Tool
Source Area (OKTSA) and the Extended Plume. The remedial work in the
OKTSA is being funded by the federal and state governments in accordance
with the Hazardous Waste Superfund Program. The remedial work in the
Extended Plume is being funded by the Performing Parties. The Consent
Decree arid the attached Statement of Work (SOW) created a mixed work site
where long-term successful remediation in the Extended Plume Area is
dependent upon successful remediation efforts in the OKTSA. The SOW allows
the Performing Parties to stop remediation efforts after 30 years if contamination
from the OKTSA is the reason that the Performing Parties are unable to attain
the ROD cleanup goals.
The presence of dense, non-aqueous phase liquid (DNAPL) at the OKTSA
changes assumptions about the duration of remediation and the ability of current
technology to achieve cleanup levels in that area. DNAPL has proven to be
difficult to remediate and experience has shown that timeframes for cleanups
may be very long or impossible to predict with any certainty. The presence of
DNAPL in the subsurface was contemplated during the development of the ROD.
Predesign studies evaluated that possibility and clearly have indicated that
DNAPL is present at several locations in the subsurface. The ROD also
provided for the consideration of structural or hydrogeologic barriers to speed or
to redirect the contaminant movement and thus speed the cleanup.
Groundwater modeling shows that significant volumes of clean water enter the
OKTSA from the Souhegan River. Therefore the ESD proposes the addition of a
barrier wall which will significantly reduce the mobility of contaminants, is
permanent, reduces the volume of groundwater to be pumped and improves the
long-term effectiveness of the remedial action.
Ultraviolet oxidation (UV/oxidation) and air stripping with carbon adsorption had
been selected in the 1991 remedy for groundwater treatment. The treatment for
the OK Tool portion of the Site was UV/oxidation. As a result of finding DNAPL
at several locations and depths under and near the OK Tool building during the
design investigations, soil vapor extraction (SVE) with air sparging and carbon
adsorption has been chosen as the best technology for removing those source
contaminants. Because it is not efficient to use two different treatment
technologies, it has also been decided that air stripping and carbon adsorption
will replace UV/oxidation as the technology for remediating the groundwater. As
a result of that decision, the contaminated air streams from the air stripping unit
and the SVE system can be combined and treated by a single carbon adsorption
unit.
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Savage Municipal Water Supply Wed Superfund Site Page3
OK Tool Source Area - Explanation of Stanfflcai* Difference* December 19.1996
Predesign evaluations indicate that the property owned by the OK Tool
Company is not suitable for the location of the treatment plant called for in the
ROD. The OK Tool property is almost entirely within the 100-year floodplain.
Furthermore, the proposed remedial action (including construction of the slurry
wall, soil vapor extraction system, and groundwater extraction and injection
wells) will be located on the OK Tool property. As a result, there will not be
sufficient space for the location of the treatment plant on that same property.
Therefore, as a result of site limitations, the remedy is being modified to include
the acquisition of an adjacent 0.78 acre property upon which the treatment
facility will be located. The parcel to be acquired is outside the 100-year flood
plain and adjacent to Route 101A which will provide additional access during the
remedial action.
E. Availability of Documents
This Explanation of Significant Differences (ESD) and supporting documentation
shall become part of the Administrative Record for the Site. The ESD,
supporting documentation for the ESD, and the Administrative Record are
available to the public at the EPA Records Center on weekdays from 10:00 a.m.
to 1:00 p.m. and from 2:00 p.m. to 5:00 p.m. and at Wadleigh Memorial Library.
US Environmental Protection Agency
Records Center
90 Canal Street
Boston, MA 02114
(617)573-5729
Wadleigh Memorial Library Please call for hours at the library
49 Nashua Street
Milford, NH 03055
(603) 673-2408
II. Summary of Site History, Contamination Problems, and Selected Remedy
A. Site History and Contamination Problems
The Site is in the western portion of the Town of Milford, New Hampshire near
the intersection of Route 101 and Elm Street (Route 101 A). The Site extends
over a mile to the east of this intersection. Much of the Site lies between the
Souhegan River to the north, and Elm Street to the south. The contamination
impacts a 6000-foot long by 2500-foot wide area of a major aquifer named the
Milford-Souhegan Aquifer. Discovery of the contamination and evaluation of the
site began in 1983.
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Savage Municipal Waiter Supply Wett Superfund Site Page 4
OK T(»l Source ATM-Exptonatkxi of StonmcantDtffefBnces December 18.1996
In February, 1983, NHDES detected five volatile organic compounds (VOCs) in
the Savage Municipal Water Supply Well. Because of the risk to the community
drinking the well water, the well was closed. The Site was placed on the
National Priority List (NPL) on September 1,1984.
Remedial Investigation and Feasibility Study reports were completed in June, .
1991. Two groundwater plumes were defined and their sources identified. One
plume was mainly contaminated with tetrachloroethylene (PCE) and its
degradation products, while the second was mainly contaminated with 111,
trichloroethane (TCA) and its degradation products. The PCE plume emanated
from the OK Tool facility while the TCA plume came from the Hitchiner and
Hendrix facilities. The two plumes came together downgradient of the sources.
The source of contaminants was determined to be the handling and disposal of
hazardous materials and hazardous waste at the OK Tool, Hitchiner, and
Hendrix manufacturing facilities.
The Record of Decision (ROD) was signed on September 27,1991. The ROD
remedy selected for the OKTSA (identified in the ROD as part of the
Concentrated Plume Area) was to contain and treat the contaminated
groundwater and, if present, the DNAPL source area. The remedy specified for
the Concentrated Plume Area used multiple extraction wells pumping at an
estimated 400 gallons per minute (gpm) and two treatment technologies,
UV/oxidation and air stripping and carbon adsorption. The remedy for the
remainder of the site, now identified as the Extended Plume Area or Operable
Unit 2, specified multiple extraction wells pumping at 700 gpm and groundwater
treatment consisting of metals removal and UV/oxidation.
Negotiations after the ROD was issued resulted in two consent decrees. The
first was entered on June 27,1994, and required the Performing Parties to
perform the work in the Extended Plume Area. The Extended Plume is all areas
of the Savage Site other than the OKTSA. The second consent decree was
entered on December 8,1994, and was a cash out for the parties connected to
the OK Tool Company. As a result of the cash out, the remediation in the
OKTSA is being funded by the federal and state governments. The Site is now
designated as a mixed work site.
Through the terms of a Cooperative Agreement with EPA in 1994, the State of
New Hampshire accepted the lead for the Remedial Design and Remedial Action
at the OK Tool Source Area. Vertical profiling was conducted by EPA and
identified areas of DNAPL accumulation. Meanwhile, NHDES procured the
services of a design engineer under a contract.
Predesign studies developed several scenarios for site remediation including
pumping at different rates, a partially-encircling barrier wall, and a completely-
encircling barrier wall. Groundwater modeling indicated that hydraulic
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Savage Municipal Water Supply Wei Superfund Sfte Page 5
OK Toot Source Area-Exptanatton of StanlflcantDtffefences December 18.1996
containment of contamination in the OKTSA required a minimum pumping of 150
gallons per minute. However, actual design of a system would be for 250 gpm
due to uncertainty of the modeling and a conservative approach to increase the
probability of success. Much of the groundwater pumped would be groundwater
recharge coming from the Souhegan River. By comparison, using a completely-
encircling barrier wall the pumping rate will be reduced to 20 gallons per minute
within the wall (the rate is dependent on the contribution from bedrock
groundwater) while successfully containing the contamination. Based on the
performance requirements of the CD, groundwater modeling suggested that the
location of additional extraction wells to remove dissolved contamination outside
the barrier wall would be appropriate to meet the remediation goals of the
OKTSA. Such additional extraction wells will prevent significant offsite migration
of contaminants from the OKTSA to the Extended Plume Area and will help
achieve remediation at this mixed work site.
B. Summary of the Selected Remedy
The selected 1991 ROD remedy is intended to restore the groundwater in the
aquifer to drinking water quality. The remedy has the following five components:
extraction and treatment of the groundwater in the concentrated plume;
extraction and treatment of groundwater in a portion of the extended plume;
natural attenuation; environmental monitoring; and institutional controls. The
1991 ROD also contemplated containment and the removal of DNAPL if present.
This ESD only affects the remedy in the OK Tool portion of the concentrated
plume area. The following quotations from the ROD provide the salient
information concerning the extraction and treatment of the concentrated plume:
A groundwater extraction and treatment system will be installed
near the OK Tool and Hitchiner plants to capture and treat the
groundwater from the concentrated plume. The wells will be
located to extract an estimated 400 gallons per minute of the
heavily contaminated groundwater to prevent movement of those
contaminants into remaining portions of the aquifer. The
groundwater will be treated by two separate treatment processes.
Ultraviolet oxidation will be used to treat water from the OK Tool
well. Air stripping will be used to treat water from the Hitchiner
weil.
The removal of metals from the groundwater is dependent upon
both the determination of discharge limitations and the treatment
process design requirements. If the discharged treated water is
used for groundwater recharge (which may include recharge to the
Hitchiner-Hendrix discharge stream because the stream recharges
the aquifer), MCLs will be the proper ARAR to be met and
discharge limitations will be set appropriately.
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Swage Municipal Water Supply Wen Superfund Stte Page 6
OK Tool Source Aree-Exp>anatk>n of StgnfficantDtfferences December 19.1996
If the water is discharged to a surface water body which does not
recharge the groundwater, the discharge must meet the NPDES
discharge requirements (which may be based on Ambient Water
Quality Criteria if aquatic life is affected) and the appropriately set
discharge limitations. If the treatment processes require metals to
be removed for treatment efficiency, the discharge limitations
described above still apply. The two treatment trains are
necessary due to the relative locations of the wells and the-nature
of the contaminants identified at each location.
The well locations and pumping rates for all extraction points are
subject to change during design studies. Additional changes may
also be needed in the remediation phase based on field data
obtained during system operation.
Ultraviolet (UV) oxidation is a technology that has proven to be
effective in destroying chlorinated solvent contaminants of the kind
found to be predominant within the plume, e.g. PCE. Volatile
organic contaminants dissolved in groundwater are brought into
contact with a proportional amount of hydrogen peroxide solution in
the presence of ultraviolet radiation. The ultraviolet radiation
breaks the hydrogen peroxide solution into hydroxyl radicals while
simultaneously exciting the bond structure of the organics so that
they become susceptible to oxidation. The end products of the
reaction are carbon dioxide, water and a chloride ion.
Air stripping with metals pretreatment coupled with vapor phase
carbon treatment is the treatment process for the contamination at
Hitchiner due to the presence of 1,1,1 -TCA. Air stripping is more
efficient and thus more cost effective than ultraviolet oxidation in
treating saturated organics such as 1,1,1-TCA which is located at
the Hitchiner facility. In this process, contaminated groundwater is
passed through a packed column countercurrent to an air flow
which volatilizes the compounds from the liquid stream. The
contaminant laden air stream is then treated using carbon to
remove the contaminants. The carbon is regenerated off site and
the contaminant is destroyed during that process.
The investigation of the concentrated plume suggests the presence
of DNAPLs. Even if DNAPLs are determined to be present, this
remedy will initially contain that portion of the plume where
DNAPLs are found so that the remainder of the contaminated
aquifer can be restored to beneficial use. EPA will periodically
review advances in groundwater cleanup technology to determine
if new techniques have been developed to effectively remediate
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Savage Municipal Water Supply Weasuperfund Site Page?
OK Tool Source Area- Explanation of Significant Differences December 19.1996
DNAPL conditions. Consistent with CERCLA and the NCR, EPA
will determine whether any modifications to the remedy are
appropriate,5
In addition, studies will be conducted to determine whether the remedy
will result in a lowering of the water table at the Site. A lowered water
table could have a negative effect on agricultural land use or on
environmentally-sensitive areas within the Site. Similarly, both the specific
location for the discharge of treated water and the method of discharge
for the treated water will be examined during the design phase for other
possible negative impacts on either wetlands or areas currently being
used for agriculture. If the design studies indicate that negative impacts
may occur in those areas or if negative impacts do occur in those areas
after the cleanup has begun, appropriate mitigation efforts will be made.
The use of groundwater recharge or structural or hydrogeologic barriers
may also be considered to speed or to redirect the contaminant
movement and thus to speed the clean-up.
Chemical data from the concentrated plume area suggest that
DNAPLs may be present in the overburden aquifer. Studies to
further investigate that possibility will be undertaken in the
remedial design stage. If DNAPLs are determined to be present,
the remedy initially would be to contain that portion of the plume
so that the remainder of the contaminated aquifer can be restored
to beneficial use.6
In summary the ROD contemplated that several decisions concerning the
remedy would be delayed until the design provided better information. The ROD
did not anticipate the establishment of a mixed work site where the governments
assume responsibility for performing part of the remedy.
III. Description of Significant Differences
The remedy at the Site has been divided into two operable units (OU) since the signing
of the 1991 ROD. This document addresses only OU 1, the OK Tool Source Area.
The OKTSA is part of the concentrated plume. The remaining part of the concentrated
plume and the extended plume is OU 2; the work in OU 2 is the responsibility of the
performing parties. As a result of the mixed work settlement, the governments will be
performing the remedy in the OKTSA. In addition the physical limitations posed by site
conditions and the nature of the contamination support the need to alter the remedy.
5Record of Decision, Savage Municipal Water Supply Well Superfund Site, September 27,1991, p.
53.
6lbid.. p. 56.
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Savage Municipal Water Supply Wei Superfund Site Page 8
OK Tool S
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Savage Munteipal Water Supply WeBSuperfund Site Page 9
OK Tool Source Area -ExrianaUon of Significant Differences December 19.1996 ._
located outside the slurry wall to capture dissolved contamination that is between the
slurry wall and the boundary of the OKTSA. The wells outside the wall will pump at a
removal rate of 50 gpm. The contaminated groundwater from all four wells will be
treated using air stripping and the resulting contaminated air will be treated using
activated carbon. The clean air will be discharged to the atmosphere. See Figure 2 for
a plan of the components described for the remedy in the OKTSA.
The ROD selected UV/oxidation as the treatment technology for the groundwater to be
pumped from the OK Tool portion of the concentrated plume, now delineated as the
OKTSA. This selection was made because that technology was more cost effective
than air stripping. At the time it was believed that metals pretreatment was necessary
for air stripping to work. However, experience at other similar Superfund Sites in New
Hampshire and sampling data during the design phase indicate that pretreatment for
metals will not be necessary. Since the ROD called for UV/oxidation, keeping that
treatment technology would mean that two types of technology would be used for
treating contamination on site: SVE with carbon for the soils and UV/oxidation for the
groundwater. A common sense decision was made to change the groundwater
treatment to air stripping so that the air stream from both the soils and groundwater
could be treated by a single treatment technology, carbon adsorption.
The carbon contaminated from treating air from both removal technologies will be
regenerated on site using low pressure steam stripping to remove the contamination
from the carbon and concentrate it in a liquid form. The concentrated contamination in
liquid form will be shipped offsite to an approved facility for treatment, destruction or
recycling.
The ROD did not anticipate the need to acquire any property to perform the remedy.
The proposed remedy calls for the acquisition of a 0.78 acre parcel adjacent to the OK
Tool Company property. The treatment facility will be built upon that newly acquired
parcel. Design studies have indicated that the OK Tool property is no longer the best
site for the location of a treatment facility. First of all, most of the OK Tool property is in
the 100-year floodplain which increases the cost of construction. Secondly, the
proposed remedial action (including construction of the slurry wall, soil vapor extraction
system, and groundwater extraction and injection wells) will be located on the OK Tool
property. As a result, there will not be sufficient space for the location of the treatment
facility on that same property. This modification is due to physical limitations posed by
site conditions.
The ESD describes technology changes that will better enable the selected remedy to
control the OKTSA portion of the concentrated plume and allow the cleanup of the
extended plume. Containment of the concentrated plume was one of the goals of the
1991 ROD. The proposed changes were prompted by new information including site
limitations which were revealed during the pre-design and design studies. The
following paragraphs address how those proposed changes affect statutory and
regulatory evaluations made in the ROD upon which the choice of remedy was based.
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Savage Municipal Water Supply WeN Superfund Ske Page 10
OK Tool Source Area -ExptenaUon of Significant Differences December 19.1996
The NCP articulates nine criteria to be used in evaluating different remedy alternatives.
The 1991 ROD includes a detailed analysis based on those nine criteria of several
different alternatives as well as the reasons why the chosen remedy was selected. As
the following analysis indicates, the proposed technology change has no significant
impact on the evaluation of the chosen remedy using the nine criteria.
Overall Protection of Human Health and the Environment
The remedy continues to provide protectiveness through capture and treatment of the
contaminated groundwater and institutional controls restricting the use of contaminated
groundwater. The slurry wall will reduce the volume of groundwater to be extracted
and treated and will provide more certainty of remediation when used with groundwater
extraction and treatment.
Compliance with ARARs
The remedy continues to meet ARARs, including chemical-specific, action-specific, and
location-specific ARARs. The technology change to air stripping and an SVE system
with carbon adsorption for the treatment of both air streams will meet ARARs for
discharge to the atmosphere. The technology change will not affect the ability of the
remedy to meet the cleanup standards proposed in the ROD. In addition, the
technology change will also meet the performance requirements for the OK Tool
Source Area placed on the government by the Consent Decree.
The estimated timeframe for cleanup established in the ROD was 15 to 85 years. The
remedy is expected to meet ARARs outside the slurry wall within 10 years. The slurry
wall will control the subsurface sources and allow long-term management of potential
migration into the Extended Plume. Due to DNAPL being present within the slurry wall,
no accurate prediction can be made regarding cleanup time for sources within the
slurry wall. As specified in the 1991 ROD, the governments will continue to explore
different technologies which may be appropriate for use in remediating the OKTSA.
Long Term Effectiveness and Permanence
The technology change will not affect the ability of the remedy to provide for capture
and treatment of the OKTSA portion of the concentrated plume. The slurry wall
provides more certainty that a reduction in the mobility of contamination will occur. The
use of SVE with air sparging is a proven technology that will permanently remove the
contamination from the soil. SVE is a proven technology and is recommended as a
presumptive remedy for removal of VOCs in soil. The air sparging is an SVE
enhancement which is consistent with the ROD to apply technologies which will
improve the remedy or reduce cost or time of cleanup.
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OK Tod Source Area- Explanation of Significant Differences December 19.1996
Reduction of toxicity, mobility, or volume through treatment
The slurry wall will improve the certainty of a reduction in mobility of contamination to
the remaining aquifer. The use of air stripping and SVE with carbon regenerated on-
site rather than UV/oxidation will mean that the contamination will be concentrated on-
site and shipped to an approved facility for treatment, destruction or recycling. The
capture of contaminated groundwater outside the slurry wall will continue to reduce the
mobility and volume of contamination moving to the extended plume.
Short Term Effectiveness
There will be a change in the short term effectiveness of the remedy. There will be
greater chance for the creation of dust during the demolition of the buildings. The
asbestos within the buildings has been identified in the design and will be removed in
accordance with Federal and State regulations governing asbestos removal and will be
disposed of in an approved facility. The increase in dust from the demolition will be
lessened by construction techniques. The demolition of the buildings is expected to be
done in less than two months. The Site Health and Safety Plan will address the
monitoring and worker procedures to be followed for the demolition of the buildings.
The change to a slurry wall means that different construction techniques will be used.
he construction will remove contaminated soil from the aquifer that will be handled in an
appropriate manner. Some of the material will be used to make the slurry wall material.
Some of the contamination will volatilize from the soils when exposed to the
atmosphere, however this is expected to be a minimal amount. Construction
procedures such as covering the soils or misting with water will minimize, the creation of
dust from any stockpiled soil. The potential exposure from these operations is
expected to be low. The Site Health and Safety Plan will address the monitoring
requirements and worker safety procedures to be followed during this phase of the
construction. The construction of the slurry wall is expected to be done in
approximately five months.
There are no adverse impacts expected to any of the agricultural or wetland areas of
the site by the remedy in the OKTSA.
Implementability
The proposed technology changes have no effect on the implementability of the
remedy.
Cost
The mixed work settlement prompted a need to reexamine the design concept of the
ROD. The technology identified in the ROD has changed as a result of both new
information about the nature of the contamination gathered during the design and the
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Savage Municipal Water Supply WeUSuperfund Site Page 12
OK Tool Source Area- Explanation of Significant Differences December 19.1996
division of work based on the Consent Decree. The basic design concept of controlling
the contamination so as to facilitate the cleanup of the aquifer did not change.
A Conceptual Design Report prepared for the NHDES in 1996 compared several
alternatives. A comparison of costs is difficult because the ROD does not include the
SVE technology to remove the newly found contamination in the shallow depth of the
OKTSA. The alternative developed in the Conceptual Design Report most similar to
the ROD remedy is pump and treat with air stripping of the groundwater, SVE/air
sparging, and combining the two air streams for treatment with carbon; the alternative
does not include a slurry wall. The estimated 30 year present worth cost for that
alternative is $9.7 million. The estimated 30 year present worth cost of the proposed
remedy as described above but with a slurry wall and reduced groundwater pumping is
$8.2 million. The slurry wall will reduce the volume of water to be pumped which lowers
the long term operation and maintenance costs associated with the continued
remediation of the groundwater contamination. The estimated annual operation and
maintenance cost savings due to installment of a slurry wall is $150,000.
State Acceptance
The NH Department of Environmental Services has determined that the ESD and
proposed changes are acceptable.
Community Acceptance
The NHDES held a public meeting on November 19,1996 at the Milford Town Hall.
There were 22 people in attendance. A site history was given and the final design was
described in detail. Several questions were asked about the construction techniques to
be used, the schedule of construction, the technologies to be used for treating the
water and the cost of the remedy. All questions were answered satisfactorily. The
community appears to be satisfied with the design and is supportive of the remedial
action.
In summary, it is apparent from reviewing the above mentioned criteria that the
proposed changes described in this ESD will protect human health and the
environment, will comply with all applicable or relevant and appropriate Federal and
State requirements, and will provide for a long-term and permanent remedy for the Site
to a similar or greater degree than the remedy for the OK Tool Source Area outlined in
the 1991 ROD. It will pose somewhat greater short-term construction-related risks than
the remedy contained in the ROD, which will be addressed in the Remedial Action
Health and Safety Plan. The proposed changes to the remedy will increase
construction costs, but will reduce Operation and Maintenance costs, especially if
operations continue beyond 30 years.
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Savage Municipal Water Supply Wei Superfund Site Page 13
<>C Tool Source Area-Exptanrtfcxi of Significant Differences December 19.1996
IV. State Agency Comments
Under a Cooperative Agreement with EPA, the State of New Hampshire Department of
Environmental Services has become the lead agency for the design of the remedy for
the OKTSA. The NHDES has generated the information and developed the
modifications to the design that are described here and that support the changes to the
1991 ROD remedy.
V. Statutory Determination
Considering the new information that has been developed and the changes that have
been made to the selected remedy, EPA and NHDES believe that the remedy remains
protective of human health and the environment, complies with Federal and State
requirements that are applicable or relevant and appropriate to this remedial action,
and is cost-effective. In addition, the revised remedy utilizes a permanent solution to
the maximum extent practicable for this site.
VI. Public Information
This ESD and its accompanying supporting information is available for public review at
the locations and times listed in Section I above.
The NH Department of Environmental Services held a public meeting to provide
information and answer any questions on the final design in the Auditorium of the
Milford, NH Town Hall on November 19,1996. Comments received are discussed in
the Community Acceptance paragraph above.
C:\WP\DATAVSAVRA\FINALESD.D19
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OK Tool Source Area
(OKTSA)
Savage Well Site
Orpnic Conpoadt in (kooadmte
THE EXTENDED PLUME AREA INCLUDES
ALL CONTAMINATED OKOUNDWATER AREAS
OUTSIDEOr THE OKTSA
Figure 1: October 1996
SCAUHNFEET
0 SOD 1000
100> MinifliJiHliiiii if^'frff rtputf per bdfioc
bated on 1990 lampfat event
Adapted ftum HMM. Inc. 'i RI/FS docummtf of June 1991
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TREATED GROUNDWATER
RE INJECTION
WELLS II OF 3)
OK TOOL SOURCE AREA/SAVAGE MUNICIPAL WELL SUPERFUND SITE
MLFORD. NEW HAMPSHIRE
NOVEMBER. 1996
LEGEND
- GftOUNDWATER EXTRACTION
* WELLS
O TREATED OROUNDWATER
REMJECTON WELLS
n Aft SPAROIM
U WELLS
- VAPOR EXTRACTION
" WELLS
APPROXIMATE WO YEAR
^^ FLOOD BOUNDARY (EL. 26«t)
•rr, BOUNDARY OF OK TOOL
^ BULOtMS TO BE DEMOLISHED
EDGE OF PAVEMENT
• SLURRY WALL
PROPERTY LWE
Figure 2
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