mhm HMM A S S O C I A T E S , I N C . LETTER OF TRAf

[SdlNirRS FNVIRONMFNIAI ( ()NSl 'I IAN I S <\ I'l \NNI RS

DATE: June 5, 1990

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

RE: Savage Well Site

SUBJECT: Draft FS Section 2.0

For Your InformationPer Youi Request

FROM: Maik HeubergerHMM Associates, Inc.196 Baker AvenueConcord, MA 01742

JOB NO.: 2176-160

X For Your Review/CommentsFor Your Authorization

REMARKS:

Enclosed is Section 2.0, Identification and Screening of Technologies, of the Draft FeasibilityStudy for the Savage Well Site. The Section is organized as follows:

2.1 Introduction2.2 Remedial Action Objectives2.3 General Response Actions2.4 Identification and Screening of Technology Types and Process Options

Signature

COMMENTS:

Date

Signature Date

2176-160/HAZ/3701 - 6/5/90

1% Baker Avenue • Concord • Mnssachusctls • (IT 742 • (-508) J71-4000 • FAX: (508) 371-2468lime Fxccnl ivo l',nk Drive • Bedford • Neu I Unpshiir • O i l 02 • (601) 647 1010 • TAX (60 i) 6^6

2.0 IDENTIFICATION AND SCREENING OF TECHNOLOGIES

2.1 INTRODUCTION

The purpose of Section 2.0 of the Savage Well Site FS is to identify, screen, and select the

most appropriate remedial technologies which can be subsequently combined into remedial

action alternatives. The selectk process is performed pursuant to current EPA RI/FS guidance,

(Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA -

Interim Final OSWER Directive 9355.3-01, October, 1988), and the National Contingency Plan

as revised and reported in the March 8, 1990 Federal Register.

The development of remedial alternatives consists of six general steps which are discussed

below:

• Develop remedial action objectives specifying the contaminants and media of

interest, exposure pathways, and remediation goals that permit a range of treatment

and containment alternatives to be developed. The objectives developed are based

on contaminant-specific ARARs, when available, and risk related factors.

• Develop general response actions that address the objectives for each medium of

interest.

• Identify volumes or areas of media to which general response actions might be

applied, taking into account the requirements for protectiveness as identified in the

remedial action objectives.

• Identify and screen the technology categories applicable to each general response

action to eliminate those that cannot be implemented technically at the Savage

Well site or would not be effective in treating site contaminants.

Identify and evaluate technology options to select a representative process for each

technology category retained for consideration. Although specific processes are

selected for alternative development and evaluation, these processes are intended

to represent the broader range of process options within a general technology type.

• Assemble the selected representative technologies into alternatives representing a

range of treatment and containment combinations, as appropriate.

2176-160/HAZ-3495 2-1

The selection process emphasizes sorting of technologies to achieve a reliable remedy

which acknowledges the practical limitations of the use of treatment. Furthermore, this process

is undertaken with the flexibility necessary and appropriate to ensure that remedial actions

selected are reliable solutions for the identified site problems.

The following sections of the Feasibility Study follow a site-specific analysis and one that

is biased toward action. This approach is focused on the remedial alternatives that are available

to effectively contain DNAPL sources and the alternatives that are practical given the extent and

nature of the contamination and the unprotected, unconfined nature of the aquifer. In addition,

many identifiable alternatives are inappropriate because the risk assessment has demonstrated

that groundwater is the only medium of concern at the Site. Therefore, the alternatives that are

developed in ensuing sections of the Feasibility Study are those that are appropriate for the

specific conditions of the Site.

The National Contingency Plan provides several other criteria and conditions that

emphasize that a site-specific selection process is warranted. The groundwater at the Site is not

currently used as a drinking water source. In addition, adequate drinking water supplies are

currently available to replace the supply formerly provided by Savage Well. New Hampshire

regulations may proscribe future use of the aquifer as a municipal supply because the current and

foreseeable future use of the land area that is contributory to the aquifer includes incompatible

uses such as industrial, commercial and agricultural. Therefore, remediation of the active

aquifer to the 10 to 10"" human health criteria levels may not be appropriate. The nature and

extent of contamination at the Site and the location of potential receptors indicate that ambient

water quality criteria or criteria based on human ingestion of fish may be the most appropriate

remedial goal. That is, environmental receptors may well determine the extent of groundwater

remediation.

Subsequent evaluations of groundwater treatment options will assess the relative benefit

of pumping and treatment versus natural flushing combined with source containment and/or

management of migration to effect a reasonable restoration time for the aquifer down gradient of

the contained sources. The time frames will be assessed in the context of what the NCP

considers to be rapid restoration, one to five years, and relatively extended restoration periods,

several decades. In addition, the need for a rapid restoration time will be assessed in light of the

existence of an adequate drinking water supply and the implementability of other institutional

controls. For example, replacement of the water supplies, which were drawn from the Site

aquifer, has been for the most part implemented.

2176-160/HAZ-3495 2-2

The benefits of natural flushing will be examined in conjunction with source containment

and protection of environmental receptors. Natural advection, biodegradation, dispersion,

dilution and absorption may effectively reduce the level of contaminants in the portions of the

aquifer outside the source containment areas to concentrations protective of human health and

the environment in a time frame that is sufficiently rapid not to warrant the high cost and

potential environmental impact of high volume pumping and treatment within the plume

downgradient from the contained sources. Institutional controls may be necessary to ensure that

the groundwater is not used for potable purposes during the time period in which the CERCLA

regulated contaminants are naturally attenuated. This recognizes that the presence of

non-CERCLA regulated contaminants and the New Hampshire regulations for siting municipal

water supply wells may preclude use of the groundwater at the Site.

Phased implementation of pumping and treatment will be analyzed to determine if there is

a benefit to first containing the source and/or minimizing migration toward receptors and then

examining further the fate of the plume to afford better planning of any appropriate additional

groundwater extraction.

Clearly in the case of the DNAPL source, restoration of the groundwater is unpractical in

a rapid time frame. The Feasibility Study will consider containment options only for the

DNAPL source.

Based on the existing information regarding the nature and extent of contamination, and

the risks posed to public health and the environment, two general response categories have been

developed for the Savage Well site: 1) Source Control; and 2) Management of Migration.

These categories are identified and explained in Section 2.2, Remedial Action Objectives.

2.2 REMEDIAL ACTION OBJECTIVES

This Feasibility Study develops and evaluates remedial alternatives for Source Control

and Management of Migration measures. The Source Control alternatives focus on mitigating

contaminant migration from source areas including O.K. Tool, Hitchiner Manufacturing and

other potential industrial, commercial and private sources located in the western portion of the

site (i.e., between OK Tool and the Drive-In access road).

These source areas are likely to result in continued long-term release and contamination of

downgradient groundwater. Based on recent research and experience at other sites, the

concentration of VOCs detected downgradient of OK Tool indicate that it is likely that VOCs

exist in the aquifer beneath OK Tool as dense non-aqueous phase liquid (DNAPL). Remedial

alternatives should place strong emphasis on controlling contaminant migration from the source

2176-160/HAZ-3495 2-3

areas. 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

presistent long-tem source of solvents. It may be feasible to confine contaminants to immediate

areas of DNAPL residuals, but 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. However, removing or containing

volumes or masses of contaminants at the source areas will reduce the overall extent of

contamination and the time frame required to return the balance of the aquifer to its beneficial

use.

The Management of Migration alternative focuses on remediating contaminated off-site

groundwater east of the trailer park and preventing further migration of contaminated

groundwater to downgradient receptors including fish hatcheries, the Souhegan River and other

potential water users. There currently exists a discharge of contaminated groundwater from the

aquifer to the Souhegan River. There is also evidence that there is limited migration of

contaminated groundwater to the north of the Souhegan River including migration to production

wells used by a private fish hatchery (Souhegan Valley Aquaculture). Remedial alternatives

should be developed and evaluated as to the feasibility of mitigating any environmental or health

impact posed by this migration of contaminated groundwater.

Due to the potential future demands for groundwater and surface water resources in the

Milford area, remedial action objectives should include consideration of returning the aquifer to

a level of water quality which is consistent with its most beneficial use in the future. Although

the majority of the land area overlying the contaminated portion of the aquifer is currently and

for the foreseeable future zoned for industrial use, only a portion of it has been developed as

such. Depending upon subsequent growth and municipal needs, portions of the industrially

zoned portion of the aquifer may at some point be reclassified as commercial.

Some portion of the contaminated aquifer may be excluded from full remediation due to

technical feasibility and cost considerations. However, remedial alternatives should be

developed and evaluated which would over some time frame restore a portion of the aquifer to

some practical level of beneficial usefulness.

2.2.1 Contaminants of Interest

Contaminants have been detected at the Savage Well Site in groundwater, surface water,

sediments, soil, and air. The overall objectives of remediating the site are to reduce the risks to

public health and welfare and to the environment. Specific remedial response objectives for the

Savage Well Site are based on the exposure levels and associated risks posed by the nature and

2176-160/HAZ-3495 2-4

extent of contaminants. These exposure levels, risks and supporting documentation are

identified in the Remedial Investigation (RI), in the baseline risk assessment, and in the

Applicable or Relevant and Appropriate Requirements (ARARs) for remedial alternatives.

Groundwater

The primary remedial action objectives for the site focus on groundwater. The specific

objectives are to return the groundwater to some level of beneficial uses in a reasonable time

frame consistent with the current land-use of the site; the nature and distribution of

contaminants; the physical/technological constraints to removing contaminants; and the sources

of the on-site contamination.

Contaminants of interest in developing remedial action objectives for groundwater were

determined based on the results of the RI, the baseline risk assessment, and the chemical specific

ARARs as identified in Section 2.2.6. The remedial response objective for groundwater to

protect human health is to prevent future ingestion or household use of groundwater having the

compounds of interest at levels which exceed Maximum Contaminant Levels (MCLs); exceed a

total excess lifetime cancer risk of 10 to 10"" (based on the risk assessed); and/or exceed

reference doses. Exposure scenarios for potential future use of groundwater as drinking water or

for household use produced cancer risks or hazard indices above typically acceptable

remediation target ranges for the following compounds:

tetrachloroethylene (PCE)

trichloroethylene (TCE)

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

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

An additional contaminant of interest is 1,1,1-trichloroethane (TCA) since it occurs at

concentrations above the MCL. However, TCA was detected during the RI at concentrations

above the MCL only at MI-30, adjacent to the Hitchiner plant.

Groundwater at the site is not currently used for drinking water or for other household

uses. Thus, it is not a current exposure problem but only a potential for future exposure that

should be considered.

The remedial objectives for groundwater may be achieved by: 1) reducing the levels of

contaminants in groundwater; 2) preventing ingestion or household use of groundwater within

the site area through the use of institutional controls (i.e., eliminating the potential

2176-160/HAZ-3495 2-5

for exposure route; 3) preventing the migration of groundwater contaminants off-site toward a

potential receptor; or 4) some combination of the above. This objective has been partially

achieved by the installation of a drinking water supply line to the site area.

An additional remedial objective for groundwater is to prevent or mitigate migration of

contaminants beyond their current extent. Areas with distinctly higher levels of contaminated

groundwater have been identified at the site and may serve as source areas for continued

migration of contaminants through groundwater. The objective of minimizing further migration

of contaminants may be achieved by controlling migration from such source areas. This action

is considered source control in nature.

In general, remedial objectives for groundwater are also designed to protect the

environment. While the results from the RI for the Savage Well Site indicate that groundwater

in the area of the leading edge of the contaminant plume discharges to the Souhegan River, the

analytical results of the surface water and sediments sampled in the river do not indicate that

groundwater contaminants are adversely impacting the river.

Therefore, Ambient Water Quality Criteria (AWQC) may be more appropriate as

regulatory levels and remedial target levels than the Maximum Contaminant Levels (MCLs).

The Ambient Water Quality Criteria (AWQC) levels for aquatic life are significantly higher than

MCLs (i.e., 840 ug/1 for PCE). Because fish in the river may be consumed, and because of the

existance of fish hatcheries to the north of the river, the Ambient Water Quality Critieria

(AWQC) standards for waters supporting fish used for human consumption as stipulated in the

Clean Water Act are appropriate as remedial action objectives for these areas. AWQC levels for

human ingestion of fish are set at 8.85 ug/1 for tetrachloroethylene and 80.7 ug/1 for

trichloroethylene. (See Table 2-4)

As stated at the beginning of this section, the overall remedial action objective for

groundwater is to return the aquifer to appropriate beneficial uses in a reasonable time frame

given the current land-use and potential future land-use of the site and the nature and extent of

contamination. The site is characterized by a large, high-yield sand and gravel aquifer situated

in a river valley which, along its southern border, is also the site of numerous industries and

commercial operations which use and store some amounts of hazardous materials and wastes.

Groundwater at the site is not currently used for drinking water and, given ARARs such as New

Hampshire Public Water Supply Regulations for siting of public water supplies, it is anticipated

that it will not be possible for the entire aquifer at the Savage Well Site to be used as a public

drinking water supply in the future, and the beneficial uses to which the aquifer should be

returned may be limited to industrial process water, irrigation, and other

2176-160/HAZ-3495 2-6

non-drinking uses. Therefore, MCLs do not seem to be appropriate remediation goals for the

entire aquifer. Current New Hampshire Water Supply Regulations Section WS 309.05,

"Protective Radius - Chemicals", states that no new water supply may be located in an aquifer

which has, at any tributary point to it, a facility which uses, stores or disposes of significant

amounts of hazardous waste. This regulation has evidently been uniformly interpreted and

applied by the State to proliibit the siting of a public water supply at locations similar to the

Savage Well, having potential hazardous waste sources at points tributary to them.

The State of New Hampshire currently is drafting a wellhead protection program as

required by Section 1428 of the 1986 Safe Drinking Water Acts Amendments (SDWA). The

provisions of this draft program confirm the increasing stringency being applied by State

regulators to the siting of public water supplies.

These draft regulations would provide for groundwater classifications.

The Savage Well Site would likely be currently classified as "GC", but no higher than

"GB". The State policy with respect to GC classified sites would be to prohibit public water

supplies in the area and contain contamination, including protection from exposure by

institutional controls.

Thus, the most likely future beneficial use of the groundwater is industrial process water,

irrigation and other non-drinking water uses.

Soils

The risk assessment for exposure to soil contaminants via ingestion or dermal absorption

resulted in risk estimates within the target range for performance goals and hazard indices

below unity, i.e., reference doses were not exceeded. There are no Federal or New Hampshire

ARARs that specify soil concentration limits. Therefore, no compounds of interest are

identified and no remedial action objectives are developed for the protection of human health.

However, in general, it is also necessary to consider remedial action objectives for source

control and protection of the environment, i.e., to prevent or mitigate the migration of VOC

contaminants from soil into groundwater that would result in contamination in excess of

groundwater remediation objectives, or would unreasonably lengthen the time to achieve

groundwater remedial goals. The data for this site indicate that the original sources of

contaminants at OK Tool have been remediated and that remaining residual contaminants in

soils are below the current concentrations of contaminants in the groundwater. Therefore,

further remediation of soils below the building's concrete floor slab is not warranted. However,

2176-160/HAZ-3495 2-7

due to the high concentration of contamination in the saturated zone beneath the building and the

potential existence of Dense Non-Aqueous Phase Liquids (DNAPLs), the control of further

release of contaminants to the aquifer from source areas in the saturated zone will be considered

as an objective of the groundwater response actions.

As a result of alternatives developed in Section 3.0, soil column flushing studies were

performed to estimate soil flushing rates and residual soil concentrations. A discussion of these

results and their relevance to remedial alternatives for groundwater are included in Section 4.0,

Detailed Evaluation of Alternatives.

Surface Water

The risk assessment for surface water exposure scenarios produced risk levels and hazard

indices below the target ranges. Because there is a low potential for use of surface waters as a

drinking water supply, MCLs are not applicable in developing remedial action objectives for

human health protection. There are, however, several contaminants which were detected in

surface waters at levels which exceed the Federal and New Hampshire Ambient Water Quality

Criteria for protection of aquatic life, which are applicable ARARs. These include toluene

(SW-19), acrolein (SW-19), copper (SW-4 through SW-9), lead (SW-5), nickel and chromium

(SW-5).

The locations of the elevated levels of toluene, acrolein, lead, and chromium are all in the

process water discharge stream, at or immediately adjacent to the permitted industrial outfall

from the Hitchiner facility, and are within the limits established by the NPDES permit. Copper

levels were found to exceed AWQC levels at five points (SW-5 through SW-9) along the length

of the discharge stream, but were below the permitted discharge levels. Copper levels drop

significantly along the length of the discharge stream and are below detection limits (and below

ARAR levels) in the Souhegan River, indicating that the river is not being impacted by copper in

the discharge stream.

VOCs occur in the discharge stream in part as the result of process water pumping wells

intersecting the outer fringes of the plume on the south side of Route 101. The concentrations in

the discharge stream are significantly lower than those in the aquifer to which it discharges.

Discharge of low levels of contamination to the area of the aquifer that is already affected by

high levels of contaminants would not increase the overall contaminant level or the time frame

requked to reach remedial goals. Therefore, remediation of discharge stream waters is not

appropriate in protecting groundwater quality or in achieving groundwater remediation

objectives.

2176-160/HAZ-3495 2-8

For the reasons discussed above, no compounds of concern have been identified and no

remedial action objectives need to be developed for surface water for protection of either human

health or the environment.

Sediments

The baseline risk assessment for exposures via ingestion or dermal absorption of

contaminants in sediments produced risk estimates within the target range for performance goals

and hazard indices below unity, i.e., references doses were not exceeded. There are no Federal

or New Hampshire ARARs that specify sediment concentration limits for protection of human

health. Therefore, no compounds of interest are identified and no remedial action objectives

need to be developed for the protection of human health.

Remedial action objectives for the protection of the environment should be to prevent or

mitigate releases from sediments which would result in surface water contaminant levels in

excess of AWQC. The only contaminants for which concentrations detected in sediments are

significantly higher than AWQC levels in surface water are metals in sediments immediately

adjacent to the NPDES-permitted industrial outfalls at the Hitchiner Facility (SW-4, SW-5, and

SW-6), at the extreme upstream end of the discharge stream. As discussed in the surface water

section, there is no indication of elevated levels of any metals in the waters of the discharge

stream except copper and there is no indication of an impact to the Souhegan River from metals

in the discharge stream. The chemistry of the soils, metal and water suggest that these metals

are relatively immobile in their present location. For these reasons, no remedial action

objectives need to be developed for sediments for protection of the environment.

Ak

Contaminants detected in air consist of acetone, methylene chloride, tetrachloroethylene,

and 1,1,1 trichloroethane. All detected concentrations were below the proposed New Hampshire

Ambient Air Level (AAL) guidelines and the Risk Assessment did not identify any unacceptable

risks from inhalation exposures. Therefore, no remedial action objectives are developed for air.

2.2.2 Allowable Exposure Based on Risk Assessment (including ARARs)

In terms of health risks, remediation goals and acceptable contaminant target action levels

are established for carcinogenic compounds by EPA target ranges for acceptable excess lifetime

cancer risks (1 x 10"4 to 1 x 10""), and for non-carcinogenic compounds by reference doses

established for individual contaminants. Additionally, remediation standards and target levels

2176-160/HAZ-3495 2-9

for remediation are based on institutional requirements provided by The Comprehensive

Environmental Response, Compensation, and Liability Act (CERCLA) as amended by The

Superfund Amendments and Reauthorization Act (SARA). The National Contingency Plan

(NCP) includes a summary of Federal and State statutes, regulations, etc. that are potentially

applicable or relevant and appropriate requirements (ARARs) for remedial alternatives.

Applicable Requirements are Federal and State public health and environmental

requirements which would be legally applicable to the response or remedial action if that action

was not undertaken pursuant to CERCLA (Federal, State, and local permits are not required for

fund-financed remedial actions or remedial actions taken pursuant to Federal action under

Section 106 of CERCLA).

Relevant and Appropriate Requirements are Federal public health and environmental

requirements that apply to circumstances sufficiently similar to those encountered at CERCLA

sites such that their application would be appropriate although not legally requked.

Section 121(d)(2)(A)(ii) of SARA now requires compliance with State environmental or

facility siting laws that are more stringent than Federal requirements. As a result, these statutes

and regulations are to be considered as potentially applicable or relevant and appropriate to the

remediation of CERCLA sites. These requirements include ARARs as follows:

1. Chemical-specific ARARs govern the extent of site clean-up in terms of actual

clean-up levels and are used in the development of remedial action objectives, as

discussed below, in the screening of technologies and in the development of

remedial alternatives.

2. Location-specific ARARs govern natural site features such as wetland and

floodplains and manmade features such as existing landfill and disposal areas.

3. Action-specific ARARs are technology-based requirements that set restrictions on

particular kinds of activities related to managing hazardous wastes.

Potential chemical-specific, location-specific, and action-specific ARARs are presented in

Tables 2-1 through 2-4 respectively.

2.2.3 Development of Remediation Goals

Based on the previous analysis, the two primary objectives which form the site-specific

remediation goals are source control objectives and management of migration objectives for

contaminated groundwater. Each of these are discussed on the following herein.

2176-160/HAZ-3495 2-10

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Source Control Objectives

The remedial response objectives for source control measures include:

1. Contain the hazardous substances, pollutants, and contaminants (VOCs) thereby

reducing migration to downgradient groundwaters (i.e., northward and eastward of

the Savage Well) and surface waters including the Souhegan River.

2. Treat/destroy to reduce or eliminate mobility, toxicity, or volume of hazardous

substances, pollutants, or contaminants (VOCs).

Management of Migration Objectives

The remedial response objectives for management of migration measures include:

1. Preventing or mitigating further migration of contaminants beyond their current

extent, including migration beyond the Souhegan River.

2. Eliminating or minimizing any threat which may be posed to public health, welfare

and the environment from the current extent of contaminant migration.

Specific action (target) levels for the source areas and the downgradient aquifer should be

developed separately. Source areas may contain DNAPLs. Because of the chemical behavior of

DNAPLs, even with costly, extensive long-term pumping, remedial actions may not achieve

action levels appropriate for drinking water (MCLs). Final downgradient aquifer action levels

may not necessarily correlate with MCLs either, and alternate concentration levels (ACLs) may

be developed based on reasonably foreseeable exposure scenarios and practical beneficial uses

of the aquifer.

2.2.4 Areas and Volumes of Concern

The Savage Well site may be described as three zones, each characterized by different

contaminant levels and distributions. Two of the three zones are considered source areas

(Source Area Zones 1 and 2) and the third is considered herein as the Management of Migration

Zone. These areas are depicted on Figure 2-1. Each of these three areas have somewhat

different contaminant levels and objectives of remediation.

2176-160/HAZ-3495 2-20

The first zone is a source area of relatively high contamination from on site releases of

chlorinated solvents, primarily tetrachloroethylene (PCE), in the immediate proximity of the

O.K. Tool facility. Saturated unconsolidated materials, and possibly bedrock, in this area are

likely to contain pockets or "stringers" of solvent contaminants which likely exist as dense,

non-aqueous phase liquid (DNAPL). Concentrations detected in this Source Area Zone 1 ranged

up to approximately 22 ppm (MI-24), and higher concentrations are likely to exist since the

screened interval at MI-24 is 80 feet, which could have resulted in significant dilution of

samples.

The estimated volume of the contaminated aquifer in Source Area Zone 1 is

approximately 400 feet wide by 400 feet long by 80 feet deep. Assuming an overall porosity of

30 percent, the liquid volume is estimated to be approximately 29 million gallons. It should be

noted, however, that the volume of groundwater to be treated may be substantially greater due to

the possible presence of DNAPLs and to solvents being slowly solubilized from pools and lenses

into clean inflowing groundwater. Because of the presence of this persistent contaminant

source, and because of the low miscibility of PCE and other chlorinated solvents, this source

area should be handled with a long term containment action where the objective for groundwater

remediation should be to prevent further release of contamination into Source Area Zone 2 or

into the Management of Migration zone.

Source Area Zone 2 is located to the east and downgradient of Source Zone 1 and consists

of contaminated groundwater with concentrations generally ranging from approximately several

hundred parts per billion (ppb) to several ppm. These values were considered to be more

representative of actual contaminant levels since the screened intervals of most of the

monitoring wells in this area are limited to ten feet and are located so as to characterize discrete

vertical zones and geologic boundaries. This source area may consist of several individual

contaminant sources. First, 1,1,1 trichloroethane (TCA) appears to have a principal source in the

immediate vicinity of Hitchiner Manufacturing. Secondly, there are a number of potential

additional sources in this area and the distribution of VOCs in groundwater indicate an apparent

anomaly of relatively elevated VOC levels in the vicinity of the Drive-In road (i.e., between well

MW-17 and MW-20). Thirdly, the Hitchiner-Hendrix discharge stream recharges the aquifer in

this vicinity. Contaminants released at O.K. Tool, Hitchiner and possibly at other operations

located south and/or west of the trailer park area may have settled into the bedrock depression in

this area after migrating eastward and downward. However, the concentrations in this zone are

significantly lower than Source Area Zone 1 and are probably not the result of nearby DNAPL.

The estimated volume of the contaminated aquifer in this area is approximately 1400 feet long,

600 feet wide and 60 feet deep. Assuming an average porosity of 30 percent, this amounts to

approximately 113 million gallons of contaminated groundwater. The volumes of groundwater

requiring pumping to remediate Zone 2 will be significandy greater than the volumes required to

contain the sources in Zone 1.

2176-160/HAZ-3495 2-22

The third zone of contamination is much more extensive than Zones 1 and 2 and is

considered herein as a Management of Migration Zone. Contamination levels in this area range

from 10 ppb to a high of 1 to 2 ppm. The volume of contaminated groundwater is much more

difficult to quantify since some low levels exist adjacent to the source area zones and

contamination may be non-existent in the area north of the trailer park and south of the

Souhegan River. An approximate estimate of volume is 1000 feet wide by 2,500 feet long by 60

feet deep. Again using an estimated porosity of 30 percent, the volume of contaminated

groundwater is approximately 337 million gallons. Site-specific characteristics defined by the

RI and treatability studies (i.e., air stripper and carbon modeling, on-site pump test, and soil

column flushing studies) which are relevant to consideration of remedial action include: 1) the

low contaminant concentration, 2) coarse-grained highly permeable soils, 3) low organic carbon

content, 4) relatively high groundwater transport velocities. This area may potentially be

remediated to some useful water supply purpose. The remediation objective would be to

intersect the principal mass of the contaminant plume before it crosses the river such that future

concentrations of contaminants in groundwater pumped by the fish hatchery do not exceed the

current AWQC standards for human consumption of fish. The development of this objective

will be in part dependent on the ongoing definition of the steady-state nature of the plume, i.e.,

whether the plume is migrating and whether concentrations at the end of the plume are likely to

increase.

2.3 GENERAL RESPONSE ACTIONS

General response actions describes those actions that will satisfy the remedial action

objectives outlined in Section 2.2. Based upon evaluation of Remedial Investigation data, the

remedial responses considered to be appropriate for groundwater at the Savage Well Site include:

• No Action

• Institutional Controls

• Collection/Discharge

• Diversion/Containment

• Collection/Treatment/Discharge

General information on remedial response actions is presented in the following sections,

including a definition of the response, a description of what it entails and what it accomplishes,

and when the response is generally preferable. Information also is provided on compatible

source control responses, and technologies available to enact this response. Table 2-5

summarizes the general response actions and technology types which are applicable to the

Savage Well Site.

2176-160/HAZ-3495 2-23

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No Action

The NCP 300.68(f) states that to the extent it is both possible and appropriate the "No

Action" alternative shall be developed as part of the feasibility study. The no action alternative

allows migration of contaminants to continue (i.e., via contaminated groundwater). There is no

treatment or disposal involved with the no action response. The current condition and the

projected environmental fate are to be evaluated. Under natural conditions, the contamination in

the groundwater is expected to diminish over time due to dilution, dispersion, and to some

extent, degradation and attenuation. The no action response would consist primarily of

environmental monitoring of the off-site migration of contaminants. This response evaluates

whether there would be any threat to public health, welfare or the environment, if no action is

taken. It provides the baseline risk against which all other responses can be compared. This

response may be selected for management of migration problems where natural environmental

mechanisms will result in degradation or immobilization of the contamination concentration

within a reasonable period of time or if risks shown are acceptable by EPA standards.

A comprehensive program would be developed and conducted to monitor changes in both

groundwater and surface water qualities. The monitoring program for groundwater includes

both on-site and off-site monitoring wells and the program for surface water includes sampling

of Souhegan River. The current level of contamination in the groundwater will preclude its use

as a drinking water source for a period of time.

The following technology could be used to enact this response:

• Long Term Environmental Monitoring

The no action response was retained for further consideration.

Institutional Controls

This is a response which allows the Federal, State and local governing bodies to mitigate

management of migration problems through institutional controls. This response employs the

restriction of access and/or use of contaminated groundwater and surface water to sensitive

receptors. It is important to recognize that alternate drinking water supplies have been provided

to the town and users by completed remedial action.

2176-160/HAZ-3495 2-25

The following controls could be used to enact an institutional action response:

• Site Security

• Additional Alternate Water Supplies

• Industrial Water Supply

• Purchase of Water Rights

• Land Use Controls

• Deed Restrictions

The institutional action response was retained for further consideration.

Collection/Discharge

This response allows the groundwater that is extracted to be discharged either on or off the

site. On-site disposal entails groundwater extraction or removal and discharge. On-site disposal

may include discharge to a surface water body or recharge to the aquifer by spraying, trenching,

seepage ditches, or reinjection wells. Discharge to surface waters or groundwater normally

involves the National Pollution Discharge Elimination System (NPDES) program which defines

the contaminant levels to which the water must be treated prior to discharge. The on-site

disposal response enables the groundwater to be handled on-site without extensive storage and

off-site transportation requirements and is therefore preferable to off-site disposal when feasible.

In addition to considering indirect containment and collection of dissolved chlorinated

solvents, the FS will consider application of enhanced DNAPL recovery techniques that are

currently under research. These methods would produce an effluent that would be predominatly

product, which would require handling and management pursuant to applicable waste

management regulations.

Off-site disposal may entail either piping the collected groundwater to local POTW or

river. Discharge to surface water must fall within NPDES permit standards stipulated for that

discharge. Groundwater discharged to POTW must meet pretreatment standards stipulated for

that facility. The function of this response is to reduce the level of contamination by dilution,

transfer to another media or assist in hydrodynamic control of the contaminant plume.

The following technologies could be used to enact this type of response:

Groundwater Extraction Wells

Interceptor Trenches

2176-160/HAZ-3495 2-26

• Discharge to Hitchiner-Hendrix Stream

Discharge to POTW

• Discharge to River

• Enhanced DNAPL Recovery

The Collection/Discharge response was retained for further consideration.

Containment/Diversion

Containment - Containment of contamination is more difficult to achieve in terms of a

management of migration response. Containing a migrating plume usually requires a greater

expenditure of resources than containing a source due to the larger areas and volumes of water.

Additionally, an impervious cover is constructed to minimize development of a hydraulic head

in the contained area. Generally speaking, containment may also be employed by capping

contaminated soils to minimize contaminant migration. Hydrodynamic control can also be used

to contain a plume.

Diversion - Diversion is a response which allows management of migration problems (i.e.,

contaminated groundwater and surface water), to be controlled. This response includes the use

of diversion structures, selective pumping, or conduits of high permeabilities to redirect flow or

migration patterns across a site. This response allows contaminated groundwater or surface

water to be diverted away from sensitive areas or sensitive receptors, such as drinking water

wellfields downgradient of source areas. Another objective is to divert groundwater upgradient

of source areas and reroute surface water to prevent it from flowing through the contamination

thereby reducing the migration of contaminants from source areas. Diversion of groundwater

flow is preferable when the horizontal component of groundwater flow through the overburden

is significant and easily controlled.

The following technologies could be used to enact a containment/diversion response:

• Impermeable cap

• Permeable cap

• Grout Curtain

Slurry Walls

Sheet Piling

• Bottom seal grouting

• Groundwater Interceptor Trench

• Cofferdams

2176-160/HAZ-3495 2-27

• Capping Barriers

• Wellpoint System

• Subsurface Drains

• Infiltration/Recharge Basin

• Surface Controls

The diversion/containment response was retained for further consideration.

Collection/On-site Treatment/Discharge

To the extent that the collection and treatment are effective this treatment response

eliminates the potential of further migration of contaminants and exposure to receptors. Many

treatment processes create their own contaminant releases (sidestreams and/or residuals) and

these must be controlled. Treatment does, however, allow the groundwater to be discharged

locally, either via recharge to the groundwater or discharge to the surface water at a higher level

of quality.

Pretreating the groundwater followed by pumping to a local off-site facility is also an

option. Unless hookup to a sewer line is feasible, however, off-site treatment can require a

considerable transportation effort because of the large volumes typically associated with

groundwater pumping. Such large volumes are usually more appropriate for on-site treatment of

groundwater. On-site treatment of groundwater is generally preferred over containment or

diversion because it provides a more permanent, long-term solution to the groundwatercontamination problem.

The following collection/on-site treatment/discharge technologies (biological, chemical,

and physical) are consistent with 300.70 of the NCP and could be used to enact this type of

remedial response:

Collection

High yield recovery well system

Wellpoint recovery system

Interceptor trench

• Chemical Treatment

Soil Flushing

Solvent Extraction

Coagulation/Flocculation

Sequestering

Ion Exchange

2176-160/HAZ-3495 2-28

Electrolysis

Steam Stripping

Air Stripping

Oxidation/reduction

Wet Air Oxidation

Neutralization

In-situ Chemical Treatment

Surfactant Mobilization of DNAPL

• Physical Treatment

Sedimentation

Filtration

Carbon Adsorption

Solvent Separation/Recovery

Reverse Osmosis

Ultra Filtration

Dissolved Air Flotation

Distillation

Evaporation

Steam Injection and Heat Application

• Biological Treatment

Rotating Biological Contactors

Lagoons (Aerated-Aerobic)

Lagoons (Anaerobic)

Trickling Filters

In-situ Biodegradation

Packed Bed Reactor

Enzymatic Degradation

Discharge

POTW

RCRA Facility

Hitchiner-Hendrix Discharge Stream

Recharge Well

Leachfield

Pipeline to River

The treatment response was retained for further consideration.

2176-160/HAZ-3495 2-29

2.4 IDENTIFICATION AND SCREENING OF TECHNOLOGY TYPES AND PROCESS

OPTIONS

Prior to the development of alternatives, an evaluation of general response actions and

technology screening for inclusion in potential remedies applicable to the Savage Well Site was

performed. General response actions to reduce contaminant levels and/or reduce exposure to

contaminants were previously identified. Technology types and process options for each general

response action were identified and screened with specific attention given to the type of

contamination media and general physical setting. The universe of potentially applicable

technologies consists of source control and management of migration technologies. The

evaluated source control technologies are identified in Figure 2-3. The evaluated management

of migration technologies are identified in Figures 2-4.

Both general response actions and remedial technologies were evaluated with respect to

source control and management of migration measures. During this step, process options and

entire technology types may be eliminated on the basis of technical implementability. This

process considers waste limiting factors (waste characteristics that limit the effectiveness or

feasibility of a technology) and site-limiting factors (site characteristics that preclude the use of

a technology) unique to the site, and the level of technical development for each technology.

The remedial technology types were first evaluated in accordance with EPA Guidance

Documents in terms of their technical implementability on a site specific basis. Once the

technology types were evaluated, it was found that no item under this category could be screened

out from further consideration of feasibility.

The remedial technologies and associated process options were then screened for both

source control and management of migration primarily for site specific implementability in

Section 2.4.1. The technology types and associated process options remaining were evaluated

further after initial screening according to three criteria - effectiveness, implementability and

cost in Section 2.4.2.

2.4.1 Identification and Screening of Process Options

Further evaluation and screening of process options within each remedial technology

category was performed.

Figure 2-3 summarizes the results of the source control technology screening and Figure

2-4 summarizes the results of the management of migration technology screening. The

discussion to follow will further expand on the reasons why certain process options are retained

or eliminated from further consideration.

2176-160/HAZ-3495 2-30

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• No Action:

No action is retained for comparison against other alternatives.

Alternate Water Supply:

Providing an alternate water supply for residences at by the Savage Well Site has already

been completed. Further remedial actions of this type could be undertaken if necessary.

Alternate water supply is retained because this action provides a potable water supply while

eliminating or restricting the use of the contaminated water supply.

• Industrial Water Supply:

Industrial Water Supply is retained because this action provides a beneficial use of

groundwater which may be too contaminated to supply potable water.

• Vertical Barriers:

Grout Curtain - this is a barrier wall created by drilling a series of adjacent, overlapping

bore holes and filling them with a relatively impermeable material, usually a fluid which sets

and hardens. These walls are usually placed at least two or three rows deep. Grout curtains

were considered as a possible method for containing contamination migration in the vicinity of

OK Tool, but were eliminated due to the difficulty in implementation given site geology

(boulder zones) and depths to bedrock.

Slurry Wall - Slurry walls are subsurface barriers designed to reduce groundwater flow in

unconsolidated earth materials. The term slurry wall can be applied to a variety of barriers all

having one thing in common: they are all constructed in a vertical trench that is excavated under

a slurry. This slurry, usually is a mixture of bentonite and water, acts essentially like a drilling

fluid. It hydraulically shores the trench to prevent collapse, and, at the same time, forms a filter

cake on the trench walls to prevent high fluid losses into the surrounding ground. Slurry wall

types are differentiated by the materials used to backfill the slurry trench. Most commonly, an

engineered soil mixture is blended with the bentonite slurry and placed in the trench to form a

soil-bentonite slurry wall. In some cases, the trench is excavated under a slurry of portland

cement, bentonite, and water, and this mixture is left in the trench to harden into a

cement-bentonite slurry wall. In the rare case where great strength is required of a subsurface

barrier, pre-cast or cast-in-place concrete panels are constructed in the trench to form a

diaphragm wall. Slurry wall is eliminated for the same reasons as grout curtain.

2176-160/HAZ-3495 2-44

Sheet Piling - Sheet piling is a horizontal groundwater barrier technique whereby sheets of

material are driven vertically into the ground surface. Sheet piles can be made of wood, pre-cast

concrete, or steel. Sheet piling is eliminated for the same reasons as grout curtains and slurry

walls.

Bottom Seal Grouting - is eliminated because this technology is not well developed and is

difficult to employ.

• Sediment Control Barriers:

Cofferdams - Cofferdams is a construction technique to divert stream flow. Cofferdams

may be constructed of many materials, such as soil, sheet piling, and earth-filled sheet pile cells.

Cofferdams is eliminated because this technology will not be needed due to site conditions.

Capping Barriers - Capping barriers are eliminated because this technology will not be

needed to address site contaminants. Geomembrane, geotextiles and rip rap may be used to

prevent contaminant migration.

• Groundwater Control Barriers:

Well-Field Systems - Well-field systems are best suited to relatively high yield aquifers.

The relative yield of the overburden aquifer at the Savage Well Site is high, therefore, well-point

systems are retained as a method of partial groundwater control.

Groundwater Interceptor Trenches - Groundwater interceptor trenches are subsurface

drains which include any type of buried conduit used to convey and collect aqueous discharges

by gravity flow. Interceptor trenches essentially function like an infinite line of extraction

wells. They create a continuous zone of influence in which groundwater within this zone flows

towards the drain. Groundwater interceptor trenches are also retained as a method of partial

groundwater control.

Infiltration/Recharge Basin - is retained because this technology is used for discharge of

clean surface water/groundwater flush contaminated groundwater, or to form a hydraulic barrier.

2176-160/HAZ-3495 2-45

Surface Controls:

Levees - Levees are earthen embankments that function as flood protection structures in

areas subject to inundation from tidal flow or riverine flooding. Levees create a barrier to

confine floodwaters to a floodway and to protect structures behind the barrier. The aquifer upon

which treatment systems may be constructed is within a 100 year floodplain. Therefore, levees

are retained for further evaluation.

Dikes and Berms - Dikes and berms are well-compacted earthen ridges or ledges

constructed immediately upslope from or along the perimeter of disturbed areas (e.g., disposal

sites). These structures are generally designed to provide short-term protection of critical areas

by intercepting storm run-off and diverting the flow to natural or manmade drainage ways, to

stabilized outlets, or to sediment traps. The two terms, dikes and benns, are generally used

interchangeably; however, dikes may also have applications as flood containment levees.

Therefore, dikes and berms are retained for further evaluations.

• Chemical:

Soil Flushing - Soil flushing is the in situ extraction of inorganic or organic compounds

from soil by passing appropriate extractant solutions through the soils to dissolve or solubilize

contaminants. The area to be treated must be isolated by vertical and horizontal groundwater

containment barriers. Water or an aqueous solution is flooded or injected into the area of

contamination, and the contaminated elutriate is collected to the surface for removal,

recirculation, on-site treatment or reinjection. During elutriation, sorbed contaminants are

mobilized into solution by reason of solubility, formation of an emulsion, or by chemical

reaction with flushing solution. These solutions may include water, surfactants, acids or bases,

chelating agents, oxidizing and reducing agents. Soil flushing is retained because this

technology is applicable to the contaminants found at the Savage Well Site.

Solvent Extraction - is eliminated because the solvent solution itself may prove to be more

toxic than the contaminants that are being extracted.

2176-160/HAZ-3495 2-46

Coagulation/Flocculation/Precipitation - Coagulation/Flocculation/Precipitation is a series

of physical treatment processes which are used to enhance sedimentation or clarification and

could be used as a pretreatment technology for removal of metals in groundwater. The waste

stream is mixed while a coagulant is added. Coagulants adhere readily to suspended solids and

with each other (agglomerate) so that the resultant particles are too large to remain in

suspension. Flocculation is primarily used to enhance precipitation of inorganics such as

metals. Slow mixing is provided by a mixing paddle. Coagulation/Flocculation/Precipitation

technologies are retained for further evaluation as a pretreatment process for removing metals

and solids including iron and manganese.

Sequestering - Sequestering is a process whereby chemicals are added to bind up certain

constituents by forming complexes. Typically this process is targeted to soluble iron and

manganese at low to moderate levels and therefore is retained for further evaluation as a

pretreatment technology.

Ion Exchange - Ion exchange is a process whereby selected contaminant ions are removed

from the aqueous phase and replaced by less toxic ions held by ion exchange resins. Ion

exchange resins are primarily synthetic organic materials containing ionic functional groups.

Resins with negatively charged sites are cation exchangers because they absorb positively

charged ions. Anion exchangers contain positively charged sites and, consequently, take up

negative ions. Ion exchange is retained because this technology is applicable to removing iron

and manganese which may foul other operational units.

Electrolysis - In this process cathodes and anodes are immersed in a tank containing a

waste to be oxidized, and a direct electrical current is imposed on the system in order to

decompose the contaminant material. During the decomposition, metals present are plated out

on the cathodes. Electrolysis is used to treat high concentrations (up to 10 percent) of cyanide

and to separate metals to allow their potential recovery. This process needs a separate

arrangement for each metal.

Limitations on this process include the physical form of feed (solids must be dissolved),

nonselective competition with other species and long process times. This technology is not

applicable for the contaminants present in dilute form in groundwater at the site and is therefore

eliminated from further evaluation due to technical feasibility concerns.

2176-160/HAZ-3495 2-47

Steam Stripping - Steam stripping is a physical treatment which uses steam to evaporate

volatile organics from aqueous wastes. Steam stripping is essentially a continuous fractional

distillation process carried out in a packed bed or tray tower. Steam provides direct heat to the

column in which gas flows from the bottom to the top of the tower. The resulting residuals are

contaminated steam condensate, recovered solvent and treated effluent. The organic vapors are

sent through a condenser in preparation for further treatment. The bottoms require further

treatment such as incineration, carbon adsorption or land disposal.

Steam stripping will treat less volatile and more soluble wastes than air stripping will and

can handle a wide concentration range (e.g., from less than 100 ppm to about 10 percent

organics). The steam stripping process may require air pollution controls to eliminate toxic

emissions. The contaminants present in Savage Well site groundwater are air strippable. Steam

stripping is normally used when the organic contaminants present in groundwater are not

removable by conventional air stripping. Steam stripping is costly but may be needed for

treatment of the VOCs present in Source Zone 1 site groundwater. It is retained for further

evaluation.

Air Stripping - Air stripping is a mass transfer process in which volatile organic

contaminants in groundwater are transferred to the gaseous (vapor) phase. Factors affecting the

removal of specific organics from groundwater include temperature, pressure, air to water ratio

and surface area available for mass transfer. Air to water volumetric ratios may range from 10:1

to 300:1, and are typically 50:1. A packed column or tower with an air blower with

countercurrent flow of air to water is commonly used. The products are die effluent and the

contaminated off gas or vapor phase.

Air stripping is retained because this technology is used to treat aqueous organic wastes

with relatively high volatility, low water solubility and aromatics. The volatilized hazardous

material may require subsequent treatment (carbon adsorption, for example).

Oxidation/Reduction - Oxidation and reduction are processes which are utilized to change

the chemical form of a hazardous material in order to render it less toxic or to change its

solubility, stability, separability or otherwise change it for handling or disposal purposes. In any

oxidation or reduction reaction the oxidation state of one compound is raised ( i e . oxidized)

while the oxidation state of another compound is lowered (i.e , reduced) The leact ion can be

enhanced by catalysis, electrolysis or irradiation. Common commercially available oxidants

include potassium permanganate, hydrogen peroxide, calcium or sodium hypochlorite and

chlorine gas.

2176-160/HAZ-3495 2-48

This treatment may be applied to chemicals such as hexavalent chromium, mercury and

lead. It is likely that other treatment processes may be used in conjunction with chemical

reduction. The waste composition must be well known to prevent the inadvertent production of

a more toxic or hazardous end product. This technology is not applicable for the contaminants

present at the site and is therefore eliminated from further evaluation due to technical feasibility

concerns.

Neutralization - Neutralization is used to eliminate or reduce the reactivity and

corrosiveness of contaminated groundwater and/or treated groundwater for final disposal and

could be used as a pretreatment technology for removal of metals in groundwater. Residuals

include a neutral effluent containing dissolved salts and only precipitated salts. pH adjustment is

a partial neutralization process which makes the waste stream either more acidic or more

alkaline to enhance chemical, biochemical reactions, and precipitation. When pH is adjusted by

adding CC>2 the process is called recarbonation. During this process excess calcium present in

the groundwater will precipitate as CaCOg. Groundwater and landfill leachate may require

neutralization prior to discharge. This process would be required as part of chemical

precipitation using excess lime and is therefore retained for further evaluation.

In-situ Chemical Treatment - is eliminated because many techniques to hazardous waste

disposal site reclamation are conceptual or in the developmental stage.

Physical:

Sedimentation - Sedimentation is the separation from water by gravitational settling, of

suspended particles that are heavier than water. This technology must be used in conjunction

with other applicable technologies to be effective. Sedimentation is retained as a separation

process only.

Filtration - Filtration may be a major treatment component to remove precipitated metals

and suspended solids. It can also be used as a polishing step for treated waste effluent. It is

retained for removing suspended solids and dewatering sediments of sludges from other aqueous

waste treatment processes.

Carbon Adsorption - Carbon adsorption is a physical treatment process involving

adsorption of chemical contaminants onto activated carbon. It involves contacting a liquid or

2176-160/HAZ-3495 2-49

vapor waste stream with the carbon, usually by flow through a series of packed bed reactors.

The activated carbon selectively adsorbs hazardous constituents in the aqueous wastes by a

surface attraction phenomenon in which the organic molecules are attracted to the internal

probes of the carbon granules. Adsorption depends on the strength of the molecular attraction

between adsorbent and adsorbate, molecular weight, type and characteristics of adsorbent,

electrokinetic charge, pH, and surface are. Once the micropore surfaces are saturated with

organics, the carbon is "spent" and must either be replaced with fresh carbon or removed,

thermally regenerated, and replaced.

Activated carbon absorption is a well developed technology which is widely used in the

removal of the volatile and semivolatile organics. Carbon adsorption is retained because this

process can be used to treat single-phase aqueous organic wastes with high molecular weight

and boiling point and low solubility and polarity, chlorinated hydrocarbons and aromatics. It can

also be used to capture volatile organics in gaseous mixtures.

Solvent Separation/Recovery - Solvent Separation/Recovery is a physical process

involving the solution of contaminants into solvent. It involves mixing the liquid waste stream

with solvent then by raising the temperature the contaminants preferentially solubilize into the

solvent. Water/solvent mixture is separated into two layers in the separator and the solvent

containing contaminants continues in the process into a heat exchanger. The temperature of the

solvent is decreased to the point where the contaminants are no longer soluble in the mixture

forming two layers. Contaminants are separated from the solvent in a concentrated form, and

drummed for ultimate disposal. The remaining solvent is recycled back through the system.

Solvent Separation/Recovery is eliminated because concentrations of contaminants in the

groundwater are not high enough for this technology.

Reverse Osmosis - Reverse osmosis is a process in which water is separated from

dissolved salts in solution by filtering through a semipermeable membrane at a pressure greater

than the osmotic pressure caused by the dissolved salts in the wastewater. With existing

membranes and equipment, operating pressures vary from atmospheric to 10,000 kN/m^ (1000<-\

Ib/in ). Reverse osmosis is retained because this technology is applicable to organic

components.

Ultrafiltration - Ultrafiltration is a similar process as reverse osmosis except operated at a

much lower pressure and therefore is retained for the same reasons as reverse osmosis.

2176-160/HAZ-3495 2-50

Dissolved Air Flotation - In dissolved-ak flotation systems, air is dissolved in the

wastewater under a pressure of several atmospheres, followed by release of the pressure to the

atmospheric level. In small pressure systems, the entire flow may be pressurized by means of a

pump (40 to 50 Ib/in2 gage) with compressed air added at the pump suction. The entke flow is

held in a retention tank under pressure for several minutes to allow time for the air to dissolve.

It is then admitted through a pressure-reducing valve to the flotation tank where the air comes

out of solution in minute bubbles throughout the entke volume of liquid. Dissolved air flotation

is eliminated because this technology is normally used for emulsified oils or organic liquids,

typically found in municipal waste leachate or petroleum waste not found at the Savage Well

site.

Distillation - Distillation is a physical separation process whereby a liquid is alternately

heated and then cooled to achieve separation. Distillation is eliminated because the

concentration of contaminants present in groundwater at the Savage Well Site, is too low to be

effective.

Evaporation - Evaporation, like distillation, is a physical separation process; however, the

liquid is heated and completely evaporated until only solids remain. Evaporation is eliminated

for the same reason as distillation.

• Biological:

Rotating Biological Contactors - A rotating biological contactor (RBC) consists of a series

of closed spaced circular disks of polystyrene or polyvinyl chloride. The disks are partially

submerged in water to be treated and rotated slowly through it. In operation, biological growths

become attached to the surfaces of the disks and eventually form a slime layer over the entire

wetted surface area of the disks. The rotation of the disks alternately contacts the biomass with

the organic material in the wastewater and then with the atmosphere for adsorption of oxygen.

The disk rotation affects oxygen transfer and maintains the biomass in an aerobic condition. The

rotation also is the mechanism for removing excess solids from the disks by the shearing forces

it creates and maintaining the sloughed solids in suspension so they can be carried from the unit

to a clarifier. Rotating biological contactors is generally used for secondary treatment, and they

can also be operated in the seasonal and continuous-nitrification modes.

RBC is eliminated because the organic concentrations are too low to maintain the biomass

and chlorinated compounds are difficult to biodegrade.

2176-160/HAZ-3495 2-51

Lagoons (Aerated-Aerobic) - Lagoons (Aerated-Aerobic) are essentially the same as the

conventional extended-aeration activated-sludge process, except that an earthen basin is used for

the reactor, and the oxygen required by the process is supplied by surface or different aerators.

Lagoons (Aerated-Aerobic) are eliminatedfor the same reasons as RBC.

Lagoons (Anaerobic) - Anaerobic lagoons are primarily used for the treatment of

high-strength organic wastewater. Typically, an anaerobic lagoon is a deep earthen pond with

appropriate inlet and outlet. Stabilization is brought about by a combination of precipitation and

the anaerobic conversion of organic wastes to CC^, CH^ and other gaseous end products.

Lagoons (Anaerobic) are eliminated for the same reasons as RBC.

Trickling Filters - Trickling filter consists of a contact bed filled widi water to be treated

from the top. The water is allowed to contact the media for a short time. The bed is then

drained and allowed to rest before the cycle was repeated. The trickling filter consists of a bed

of highly permeable media to which microorganisms are attached and through which wastewater

is percolated. Trickling filter is eliminated for the same reasons as RBC.

Activated Sludge - Process activated sludge process is a biological process which reduces

the organic loading in either soluble or colloidal size range particles in aqueous solutions,. The

conventional activated-sludge process consists of an aeration tank, a secondary clarifier, and a

sludge recycle line.

This process is eliminated from further evaluation for the same reason as RBC. However,

blending into the waste at the Milford, New Hampshire WWTF may be feasible.

In-situ Biodegradation - is eliminated because of lack of technology development

pertaining to in-situ biodegradation in the groundwater.

Packed Bed Reactor - Typically, a packed-bed reactor consists of a container that is

packed with a medium to which nitrifying microorganisms can become attached to water to be

treated is introduced from the bottom of the reactor and air or pure oxygen is also introduced

from the bottoms. Packed bed reactor is eliminated for the same reasons as RBC.

Enzymatic Degradation - Enzymatic degradation is a bioremediation process whereby

specific enzymes are introduced to a reactor containing water to be treated. The enzymes

function as catalysts in breaking down the contaminants. Enzymatic degradation is eliminated

because this technology is used primarily for degradation of pesticide diazinon. Pesticide

contamination is not a problem at the Savage Well Site.

2176-160/HAZ-3495 2-52

• Off-site Discharge:

Discharge to POTW - Under this technology, treated groundwater would be piped to a

publicly owned treatment works (POTW). A new piping system would have to be constructed to

transport the treated groundwater. Pretreatment standards must be reached by the discharge

before POTW would accept it. The city of Milford has a secondary wastewater treatment

facility which may accept treated discharge.

This technology is retained for further evaluation.

Discharge to RCRA Facility - Under this technology, treated groundwater would have to

be transported over long distances making this technology unfeasible. Therefore, this

technology is eliminated from further evaluation.

Discharge to River - is retained because of proximity to the Souhegan River. The

Souhegan River is a Class B waterway and currently receives discharges from a number of point

sources. This technology would be combined with pretreatment and treated waste would meet

criteria levels established by the permitting authority. This technology would have to be

designed to meet the requirements of the NPDES program.

• On-site Discharge:

Discharge to Local Stream - Under this technology, treated groundwater would be piped to

an on-site stream. This technology is retained for further evaluation. Discharge would require

an NPDES permit.

Discharge to Recharge Well - A recharge well re-injects treated groundwater back into the

on-site aquifer. This technology is being retained for further evaluation. A groundwater

discharge permit would be required.

Discharge to Leachfield - A leachfield consists of a series of wrapped perforated pipe laid

beneath the surface in highly permeable soil, typically coarse sand or gravel. Treated

groundwater effluent is pumped to the backfield where the water is transmitted back into the

ground through the perforated pipe. This technology is retained for further study. A

groundwater discharge permit might be required.

2176-160/HAZ-3495 2-53

2.4.2 Evaluation of Selected Process Options

The evaluation of process option is the final step of technology screening prior to

alternative development. At this point, the process options remaining after the initial screening

are evaluated according to effectiveness, implementability, and cost.

Effectiveness

The effectiveness of each technology type and process option is analyzed in terms of

protecting human health and the environment relative to the risk assessment and objectives of

the ARARs in Section 2.2.2. The following considerations are the basis of the effectiveness

evaluation:

• the potential for the process option to reach the contaminant reduction goal and/or

reduce exposure levels,

• the potential environmental impact during the construction phase, and

• how proven and reliable the process is with respect to the contaminants and

conditions at the site.

Implementability

Implementability of a technology is analyzed in terms of technical and institutional

feasibility. Those process options which are clearly inapplicable due to site and/or matrix

limitations are eliminated. However, more emphasis is placed upon institutional concerns when

evaluating implementability because many of the technical issues are addressed in the

effectiveness evaluation.

Implementability evaluation focused on the following:

compliance with location - and action-specific ARARs, and

• availability of treatment, storage, and disposal services and capacity.

Finally, cost is evaluated for each technology type and process option. Compared to the

other criteria, relative costs are not emphasized at this stage of the screening process. However,

2176-160/HAZ-3495 2-54

when process options are very similar in terms of effectiveness and implementability, cost

becomes an important factor in the decision-making process.

This evaluation is intended to be rather broad and general with the overall intent of being

better able to choose technologies with which cost-effective remedial alternatives may be

developed. Figure 2-5 presents a summary of the results of the process option evaluation.

The objective of this phase of the study is to provide sufficient information to select one

representative process option, if possible, from each technology type to simplify the subsequent

development and evaluation of alternatives without limiting flexibility during remedial design.

A more detailed evaluation of individual and combined technologies is reserved for the

subsequent sections on Alternative Development and Screening and Detailed Analysis of

Alternatives.

2176-160/HAZ-3495 2-55

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