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8205 SDMS DocID

New Hampshire Department of Environmental Services

OK Tool Source Area Savage Municipal Water Supply

Superfund Site - 0U1

Remediation Systems Alternatives Evaluation

December 1995

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Prepared for: State of New Hampshire Department of Environmental Services Waste Management Division

Prepareci by: Camp Dresser & McKee Inc. Cambridge, Massachusetts I

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environmental services

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Camp Dresser & McKee Inc. Ten Cambridge Center Cambridge, Massachusetts 02142 Tel: 617 252-8000 Fax:617 621-2565

December 15, 1995

Mr. Gary S. Lynn State of New Hampshire Department of Environmental Services 6 Hazen Drive Concord, New Hampshire 03301

Re: Remedial Design - OK Tool Source Area Savage Municipal Well Superfund Site Milford, NH

Dear Gary:

Camp Dresser & McKee Inc. (CDM) submits herewith three copies of the Aitematives Evaluation Report for the referenced project. This report has been finalized to incorporate the Department's review comments provided to us at the November 8, 1995 progress meeting in Concord. Five altemative approaches to the remedial design for the OK Tool Source Area are presented in this report. The alternatives include hydraulic containment of the source area and both full and partial physical containment of the source area utilizing slurry wall technologies. Our subcontractor Aries Engineering, Inc. has developed preliminary model mns of groundwater capture zones at varied pumping rates using the currently available USGS model for the hydraulic and both full and partial physical containment source area containment.

We have developed preliminary conceptual construction and operations and maintenance cost estimates for each altemative in order to develop present worth cost comparisons between the aitematives. We have also evaluated each altemative qualitatively for factors such as compliance with ARARs, long term effectiveness, reduction of toxicity volume and mobility.

At this time, full physical containment of the source area coupled with reduced pumping rates outside of the containment area and full physical containment with enhanced DNAPL removal appear to be the most favorable aitematives to further develop for implementation at the OK Tool Source Area during the conceptual design phase. Additional investigative work presently being completed at the site will provide additional information for use in the conceptual design.

Yours very tmly,

CAMP DRESSER & McKEE INC. / Approved:

Peter J. p^ovAm, f 2 ^ P £ X ' ^ r ^ ' David C. Noonan, P.E. Project Director Associate

cc: C. Wayne Ives - NHDES William Glynn - CDM Peter McGlew - Aries

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OK TOOL SOURCE AREA - SAVAGE WELL SUPERFUND SITE MILFORD, NEW HAMPSHIRE

REMEDIAL SYSTEMS ALTERNATIVES EVALUATION

1.0 PROJECT DESCRIPTION

1.1 Introduction

The Savage Municipal Water Supply WeU Superfund Site has been divided into two operable units (OU), a Fund lead OU and a potentially responsible party (PRP) lead OU. The Fund lead OU (OU 1) is known as the OK Tool Source Area OU. The PRP lead OU (OU 2) is known as the Extended Plume OU. This work effort is associated with the Fund lead OU 1. The approximate boundaries of the OK Tool Source Area (OU 1) are:

• to the north by North Purgatory Road;

• to the east by a tree line and stone waU in the vicinity of monitoring weUs HM-46, MI-63, MW-16, and MI-31;

• to the south by Ehn Street;

• to the west by the access road/driveway (adjacent to MW-28) for the OK Tool Company buUding.

1.1.1 Site Location

The Savage Municipal Water Supply WeU Superfund Site (Savage WeU Site or Site) is located in the Town of Milford, New Hampshire about two mUes west of the center of town. The site location is depicted on Figure 1-1, Site Locus Plan. The area around the site includes residential, agricultural, conrunercial, and industrial uses.

1.1.2 Site Description

The Site includes a groundwater plume that extends from the intersection of Route 101 and Elm Street eastward approximately 6,000 feet (see Figure 1-2, adapted from Remedial Investigation, Savage Municipal Water Supply Site, HMM Associates, June 1991). It is roughly bounded on the north and east by the Souhegan River and on the south by Elm Street and Tucker Brook. The Savage WeU Site lies within the floodplain of the Souhegan River. The floodplain is a relatively flat land surface extending through most of the area of the Site. The Souhegan River flows from west to east for the length of the Site area. At the eastem edge of the Site, the Souhegan River takes a pronounced southward bend before resuming its generaUy west to east orientation. DetaU of the Savage WeU Site OUl is depicted on Figure 1-3 adapted from an EPA GIS map of the study area.

SCALE IN FEET

OK TOOL SOURCE AREA FIGURE 1-1 SAVAGE WELL SUPERFUND SITE

MILFORD, NEW HAMSHIRE CDM SITE LOCUS PLAN

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SAVAGE WELL SITE TOTAL VOC PLUME CDM (adapted from Figure 4 - 1 , Remedial Investigation,

Savage Municipal Water Supply Site, HMM Associates, June 1991) FIGURE 1-2 pfanntfs, Sc manag^m^nt consultont$

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I SAVAGE WELL SITE OU-1 FIGURE 1-3 SITE PLAN DETAIL

(adapted from EPA GIS map of the study area) I CDM enyirvnmental anglneera, t e l t i t b t s , Not to Scale plonnara, A mancgemmt conaultants

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1.1.3 Site History

Four major industrial plants are situated upgradient and to the west of the Savage WeU: Hendrix Wire and Cable Corporation; Hitchiner Manufacturing Company, Inc.; OK Tool Company, Inc.; and New England Steel Fabricators, hie. (NESFAB). From the 1940s untU the 1980s, process waters and wastes from these plants were released untreated onto the ground or into the Hitchiner/Hendrix discharge stream which flows into the Souhegan River.

In 1983, a New Hampshire Department of Environmental Services (NHDES) inspection of the OK Tool Company plant found that a degreasing tank had been directly connected to a drain in the plant floor and that the area located north of the plant showed signs that oUy wastes and other materials had been disposed of onto the ground. NHDES ordered OK Tool Company to cease the discharge of any waste and to begin an investigation to determine the extent of the contamination.

In 1983, as part of a routine sampUng of New Hampshire pubUc water suppUes, the New Hampshire Water Supply and PoUution Control Commission analyzed water from the Savage Municipal Water Supply WeU and found several volatile organic compounds (VOCs) above drinking water standards. The VOCs found were: 1,1,1-tridiloroethane (TCA), trichloroethylene (TCE), trans-l,2-dichloroethylene (trans-l,2-DCE), tetrachloroethylene (PCE), and 1,1-dichloroethane (DCA). VOCs (trans-l,2-DCE and PCE) were also found in the water from the weU supplying the nearby mobUe home park. As a result, the Savage WeU and the traUer park weU were shut down. The 75 residents of the mobUe home park were connected to the town's water supply using EPA Superfund emergency funding.

In 1984 the Savage WeU Site was placed on EPA's National Priorities List (NPL) of hazardous waste sites under the Superfund program.

In 1985, EPA notified OK Tool Company, Hitchiner Manufacturing Company, Inc., Hendrix Wire and Cable Corporation, and NESFAB that they might have contributed to the site contamination and were considered PRPs. In 1987, these four PRPs signed a legal settlement in which they agreed to perform the remedial investigation (RI) and feasibiUty study (FS) for the Site under EPA supervision. The studies began in 1988 and were completed in 1991.

A Record of Decision (ROD) was signed in 1991 to address the groundwater contamination. A description of the selected remedy for Savage Municipal Water Supply site as stipulated in the ROD includes:

• InstaUation of a groundwater extraction and treatment system at the concentrated plume area. The system wUl contain and remove highly contaminated groundwater for treatment using air stripping and ultraviolet oxidation.

• InstaUation of a groundwater and treatment system within the extended plume area. The system wUl remove contaminated groundwater from two locations near the middle of the plume and two locations near the end of the plume for treatment using ultraviolet oxidation.

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• Reliance on natural attenuation of contaminated groundwater to lower contaminant concentrations through physical, chemical and biological processes untU groundwater cleanup levels are met.

• UtUization of institutional controls to reduce the risk to public health from consumption of the groundwater. Institutional controls may include deed restrictions and zoning ordinances to restrict the use of contaminated groundwater. Institutional controls shaU be imposed in the area where the risk to pubUc health is outside of EPA's acceptable risk range.

• Implementation of an environmental monitoring program, initiated during remedial design and continuing for three years after attaining groundwater cleanup levels, to assess the effectiveness of remediation, and to confirm that contaminant concentrations in the groundwater have attained cleanup levels. The program wiU include monitoring of groundwater, surface water, sediments, and existing households obtaining drinking water from the aquifer.

The ROD stipulated that the instaUation of groundwater extraction and treatment would be required for both the concentrated plume area and the extended plume area.

In April 1995, EPA completed discrete interval vertical groundwater sampling and field screening chemical analysis of groundwater at the site to determine the vertical and horizontal distribution of the groundwater contaminant mass (concentrations) and estabUsh vertical and horizontal concentration gradients. A discussion of the results of the July 1995 report titled Vertical Contaminant Profiling is included in Section 1.1.5.4.

1.1.4 Facility Processes

The OK Tool Company has been located on Elm Street in Milford, New Hampshire, since the late 1940s. From that time untU 1987, OK Tool Company was a metal product manufacturer. Processes used to produce the metal cutting tools and tool hardware included machining, grinding, oxidizing, and heat treating. Those processes required the use of cutting fluids, lubricants, and cleaning solvents. The primary cleaning solvent used by OK Tool Company was PCE. Waste from the manufacturing process included metal shavings, spent solvent, and sludge. In addition to metal products, Williams & Hussey, a division of the OK Tool Company, manufactured woodworking tools. These manufacturing process required the machining, painting, and assembling of cast iron and steel components. The predominant Uquid wastes were spent lubricating fluid and lacquer thinner.

There are no manufacturing operations at OK Tool Company at the present time.

1.1.5 Nature and Extent of Contamination

The foUowing description of contaminant assessment focuses primarUy on those compounds detected in OU 1 media during the Rl completed by HMM Associates in June 1991 and the vertical profiling survey completed by EPA in 1995.

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1.1.5.1 Air

Ambient air monitoring conducted during the Rl detected low levels of acetone, TCA, methylene chloride, and PCE at the Site. The highest concentrations detected for each of the compounds were below the proposed New Hampshire Ambient Air Level Guidelines.

The CDM team conducted a soil gas survey at the site in August, 1995. The survey was proposed to delineate potential soU VOC source areas.

The results indicate the presence of the VOCs: PCE, TCE, trans 1,2-DCE and 1,1-DCE in site soU gas. PCE was detected in 72 soU gas samples at concentrations ranging from 1 part per million (ppm) to 1,218 ppm. TCE was detected in 33 soU gas samples at concentrations ranging from 1 ppm to 118 ppm. Trans-1,2-DCE was detected in 7 soU gas samples at concentrations from 1 ppm to 20.55 ppm,whUe 1,1-DCE was detected in soU gas sample SG-43 at a concentration of 38.59 ppm.

The soU gas survey data indicate elevated VOC concentrations consisting predominantly of PCE in the vicinity of the site septic system leach field, the catch basin located on the northeast side of the buUding below the site buUding loading dock area, and to a lesser extent, beneath the site building in the vicinity of the site septic tank.

1.1.5.2 SoU

VOC contamination was found in soU and soU gas samples throughout OU 1. The highest concentrations of contamination were found between the OK Tool Company building and the Souhegan River.

Previous investigation by HMM Associates (HMM) and Normandeau Associates Inc. (NAI) focused predominantly on the area to the north of the faciUty to address locations where: 1) areas of staining were observed by HMM and reported in previous reports by NAI; 2) previous investigations by NAI identified buried waste materials and VOC contamination in soU; and 3) the results of a magnetic survey indicated magnetic anomaUes.

HMM's program, which included the completion of nine soU borings, eight test pits, and two grab samples of stained surficial soils, encountered waste materials and/or stained soUs at a number of locations, and metal shavings and other metal debris located to the northwest of the OK Tool Company buUding (approximately halfway between the buUding and the Souhegan River).

Laboratory analyses indicated the detection of VOCs at 15 of the 19 soU sampling locations. PCE was the most consistently detected compound, with concentrations ranging from 9 ppb (surficial sample) to 440 ppb (2.5-5 ft below ground surface). Other maximum concentrations of VOCs detected were TCE - 6 ppb, trichlorofluoromethane -10 ppb, carbon tetrachloride - 61 ppb (three locations), acetone - 310 ppb (seven locations), trans-l,2-DCE - 6 ppb, and toluene ­20 ppb (four locations).

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Work done at the OK Tool Company facility by NAI included; 1) sampling and remediation of soUs in and around a floor drain inside the building, 2) sampling of soUs to the north of the buUding which resulted in the identification of four potential source areas, and 3) sampling of soUs in the vicinity of an outdoor PCE tank.

One portion of NAl's work was designed to address contaminants in and around the floor drain located adjacent to a discharge pipe from a degreasing tank. Several rounds of sampling indicated concentrations of PCE in soils of up to 300,000 ug/kg under the floor drain, up to 28,000 ug/kg in soUs under the subfloor 9 feet to the northeast of the drain, and up to 4,200 ug/kg in soUs 25 feet to the northeast of the drain. NAI subsequently implemented a remedial action which included the removal of approximately 25 cubic yards of soU from the vicinity of the floor drain. The excavation was limited to approximately 9 feet by 9 feet in area and 10 feet in depth.

NAI also delineated four potential contaminant source areas north of the OK Tool Company buUding, and this delineation was used to focus HMM's soUs investigation of OU 1. The results of this investigation indicated levels of VOCs much lower than those previously reported by NAI. The highest level of PCE detected in soUs in HMM's investigation was 440 ppb.

It is possible that the lower levels of VOCs detected in HMM's investigation indicate that the VOCs have been flushed or volatUized from the source areas during the more than 5 years since the 1984 NAI study.

SoU sampling, classification, and laboratory testing completed to date indicate that the near-surface soUs underlying the OK Tool Company property are generaUy noncohesive sands and gravels with a low percentage of fine materials. These type soUs typicaUy have a low sorption capacity and do not likely retain significant concentrations of VOCs so as to act as a contaminant source material.

Additional soU sampling work was completed by HMM subsequent to submission of the Draft RI to determine whether source areas existed undemeath the OK Tool Company buUding. The results of the additional soUs investigation identified higher levels of PCE beneath the OK Tool Company buUding than had been previously identified in soils sampled elsewhere at the site during the RI.

Eight samples coUected by HMM beneath the OK Tool Company buUding in the vadose zone had PCE levels ranging from 83 ug/kg to 2,400 ug/kg. The highest levels, 2,400 ug/kg in SL-1 and 1,300 ug/kg in SL-2, were detected in soUs located inm\ediately adjacent to the excavation of a former floor drain. Sample SL-8, located approximately 70 feet from the excavation at the eastem most edge of the buUding, had PCE at a level of 900 ug/kg. The highest concentration of PCE detected in soUs outside the buUding was 400 ug/kg. TCE was detected in soU sample SL-8 only, at 19 ug/kg. The presence of methylene chloride, identified in five of the samples, was determined to be the result of laboratory contamination.

Two of the soU samples coUected by HMM from the stockpUes located north of the OK Tool Company buUding were found to contain PCE at levels below the detection Umit (5 ug/kg) whUe the third contained PCE at 44 ug/kg. A sample coUected from the storm drain contained PCE at 840 ug/kg, TCE at 160 ug/kg, and trans-l,2-DCE at 320 ug/kg.

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One sample from the subfloor area of the OK Tool Company was also analyzed for the complete Hazardous Substance List parameters, including add and base/neutral extractable organic compounds (ABNs), polychlorinated biphenyls (PCBs), pesticides, and metals. Analysis of soU samples for ABNs and pesticides detected no contaminants above trace levels.

Metal debris is present in soUs at depths of 1 to 5 feet below the ground surface throughout an area measuring approximately 100 feet by 50 feet between the northwest comer of the OK Tool Company buUding and the Souhegan River. Analysis of soUs samples coUected from this area during prior investigations indicate elevated levels of a number of metals: arsenic, 204 ppm; total chromiiun, 15,100 ppm; and lead, 610 ppm. Laboratory analysis of soU samples from the area of metal debris also indicates comparatively elevated levels of barium, copper, iron, manganese, nickel, and vanadium. CDM wUl utilize historical information and results of the electromagnetic survey to prepare specifications for in-situ sampling of this area. The specifications wUl include required sampling protocols and analytical requirements for characterizing the soUs from this area. The specifications wUl also include requirements for appropriately disposing of the metal contaminated soils, conducting post-excavation confirmatory sampling and backfilling the excavation.

During HMM's site investigation, PCBs were detected near the OK Tool Company buUding (within the area of elevated metals discussed above) in two samples at levels of 0.633 and 3.48 ppm.

1.1.5.3 Siufece Water/ Sediment

No locations for surface water or sediment sample coUection were identified for OKTSA.

1.1.5.4 Groimdwater

The observed VOC plume is approximately 6,000 feet long and 2,500 feet wide. The plume extends from the vicinity of OK Tool Company and Hitchiner Manufacturing Company, Inc. in the west to the Souhegan River in the east, and from Old WUton Road in the south to just north of the Souhegan River in the north. PCE is the most widespread contaminant and has the highest concentrations of any of the VOCs detected in groundwater. Contamination has also been detected at several locations in the bedrock aquifer.

HMM detected only one ABN compound, di-n-butylphthalate, in the monitoring weUs sampled during the RI. This compound was detected in half the weUs sampled, at concentrations ranging from trace to 72 ppb. HMM deduced that the detection of di-n-butylphthalate was the result of laboratory induced contamination. The detection of di-n-butylphthalate was assumed to be the result of laboratory induced contamination for the foUowing reasons: 1) the lack of spatial conformity of the occurrence of this compound with any potential sources or previously identified contaminant plumes; 2) the low and generaUy uniform range of concentrations reported; and 3) the detection of the compound at similar concentrations in samples from upgradient weUs, which have not been found to contain any other contaminants, as weU as monitoring weUs located in the center of the contaminant plume; and 4) this compound was not detected in the Phase 1 surface water sampling program.

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Two metals were detected by HMM during the RI at total concentrations above the Maximum Contaminant Levels (MCLs) in samples from one weU at the OK Tool Company area: 1) chromium was detected at 0.088 mg/l in monitoring weU Ml-25, compared to the MCL of 0.05 mg/l; and 2) lead was detected at 0.16 mg/l in monitoring weU MI-25 compared to the MCL of 0.05 mg/l. Monitoring weU Ml-25 is located approximately 50 feet east of the OK Tool Company facility. Groundwater sampUng analyses coUected in December 1993 show a decrease in metals concentrations as compared to RI data. Elevated metal concentrations in groundwater in the vicinity of the metal debris area is evident.

CDM Federal conducted vertical contaminant profiling in the OK Tool Source Area south of the Souhegan River at the Savage WeU Superfund Site in MUford, New Hampshire on behalf of the U.S. Environmental Protection Agency (EPA) between March 13 and April 19,1995. The work was conducted in cooperation with other govemment agencies including the New Hampshire Department of Environmental Services (NHDES) and the U.S. Geological Survey (USGS).

The primary objective of the vertical profiling work was to determine the vertical and horizontal distribution of volatUe organic compounds, particularly PCE, in the OK Tool Source Area. Additional objectives included identifying specific source areas and obtaining information on factors that may affect contaminant fate and transport. These objectives were met by using a sampling and analysis method which aUowed the coUection of high quaUty real­time groundwater data from discrete depth intervals.

A total of 33 vertical profiling locations were completed using a continuous point groundwater sampUng device referred to as the "Waterloo Profiler" (patent pending). The Waterloo Profiler is a tool developed at the University of Waterloo that is designed specificaUy for determining of the vertical distribution of solutes at sites contaminated with chlorinated solvents. The Profiler is constructed entirely of stainless steel and is driven into unconsoUdated deposits so that samples may be coUected at multiple depths in the same hole to develop a vertical profile of groundwater quaUty. Minimum volume samples were coUected across a very small-screened opening at selected depths in a given hole without withdrawing, decontaminating, and redriving the tool.

The Profiler was advanced using a pneumatic tool driven by an air compressor (air hammer). During driving, a peristaltic purging and sampling pump was run in reverse (i.e., analyte-free water was injected down the sampling tubing and out the sampling ports) to purge the Profiler of formation water from the previous sampling interval and keep the sampling ports unobstructed. As the Profiler approached the desired sampling depth, the pump was run forward to begin pumping formation water to the surface.

Groundwater samples were coUected at 5-foot intervals of depth and analyzed at the on-site laboratory for PCE and five other volatUe organic compounds as weU as pH, conductivity, temperature, and color. Of the 294 total groundwater samples, 31 were coUected as spUts for analysis by both the NHDES laboratory in Concord, New Hampshire and the on-site laboratory.

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I il Concentrations of PCE in groundwater ranged from non-detect to 117,343 ppb, with

concentrations of the remaining VOCs relatively smaU by comparison. PCE concentration data at shaUow depth within the aquifer, corresponding to an elevation of 240-250 feet (NGVD) or 20-30 feet below the average land surface of 270 feet NGVD, indicated 3 principal source areas:

• The first source was detected by VP-1008, which showed the maximum PCE concentration for the site (117343 ppb). This vertical profile was located near a floor drain and former degreasing tank which was documented and accurately located on the basis of previous reports and buUding plans.

• The second source was detected by VP-1005 located just north of the buUding about 70 feet from the northwest comer. This location corresponds to an elbow in a 6-inch diameter pipe leading away from the former decreasing tank, as indicated on buUding plans.

• The third source was detected by VP-1007, located about 110 feet north of the buUding. This location corresponds to a septic system leaching field, which was indicated by site plans as extending 85-125 feet north of the buUding in this area.

PCE concentration data from the bottom 20 feet of the vertical profiling indicate that most of the contamination has migrated downgradient in plan view as weU as deeper within the aquifer. The deeper concentration data indicate that the PCE tends to be concentrated just above the upper tUl surface. The exception to this tendency is the vicinity of the former floor drain and VP-1008. At this location the very high concentration (in excess of 100,000 ppb) appears to be perched within the sand and gravel aquifer, as if resting above an impermeable layer of Umited extent which was not detected in previous deep borings at the site.

1.2 Objective and Scope of Preliminary Remedial Systems Aitematives Evaluation

The objective of this task is to identify, evaluate and screen promising remedial aitematives for the OKTSA site early in the preliminary stages of the design process. The promising remedial aitematives wUl include, at a minimum, an evaluation of hydrodynamic controls, physical containment barriers, groundwater treatment technologies and enhanced DNAPL extraction/treatment technologies. The criteria for screening wUl include technical effectiveness, both short-term and long-term feasibiUty, flexibUity to handle changing conditions, reduction of toxicity, mobiUty and volume, overaU protection of human health and the environment, compliance with ARARs, implementation factors, and the total Ufe cycle cost of the remediation program.

The key design criteria for the OKTSA are:

• Reduce and/or eliminate the migration of DNAPL and concentrated VOC-contaminated groundwaters from the OKTSA;

• Improve and/or reduce the extent of contamination within the OKTSA;

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I il • Develop technical approaches that have proven track records and can meet the technical

chaUenges of "tempered innovation"; and

• Develop effective remedial approaches that reduce O&M costs

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SS&tion Two

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2.0 PHYSICAL CONTAINMENT

2.1 Introduction

In this section, CDM provides an evaluation of physical barrier waU aitematives for containment of the OKTSA site. This evaluation is based on the site information avaUable prior to the field explorations currently being conducted by CDM for this project. Additional evaluations wUl be conducted during conceptual design based on the results of the on-site explorations.

The physical barrier is formed by constructing a low permeabiUty waU to restrict the movement of groundwater. Subsurface barrier waUs can be constmcted either by slurry trench technology, by installing waU components in open cut excavations, by driving waU components (sheet pUes) into the ground or by injecting grout mixtures into the ground.

The Record of Decision did not include a barrier waU for the OKTSA site. However, significant cost savings and other potential benefits may be realized by incorporating a barrier waU into the groundwater coUection/treatment system. The barrier waU, as currently envisioned, may either fuUy or partiaUy encircle the DNAPL source area. The barrier also may be designed as either a "hanging" waU or a fuUy penetrating waU. The combination of these aitematives wUl be evaluated based on relative effectiveness and both short-term and long-term costs.

The barrier waU wUl reduce the subsurface groundwater infiltration from the Souhegan River through the DNAPL source area. In essence, the flow from the Souhegan River wUl be diverted around this subsurface barrier and wUl keep clean upgradient groundwater from coming into contact with the DNAPL source area and becoming contaminated. This wiU reduce the volume of groundwater that wiU need to be removed and treated. This should result in a significant reduction of the groundwater pumping and treatment costs.

To demonstrate the effectiveness of a barrier waU on reducing the volume of water that may need to be treated, CDM made some preliminary calculations based on Darcy's equation: Assuming hydrauUc conductivities of the soUs in the saturation zone (assumed to be above the lower glacial tUl layer) in the range of 50 to 250 ft/day, a 400 foot long projection of the proposed barrier waU perpendicular to groundwater flow, saturated thickness ranging from 45 to 75 ft. across the wall projection and a horizontal gradient across the site of 0.003, CDM calculated a volume of water entering into the DNAPL source area of between 30,000 to 160,000 gal/day. After a barrier waU is constructed, and assuming the barrier would have a permeabUity of 2.834 X 10' ft/day (1 X 10' cm/sec), the estimated volume over the entire barrier waU surface would drop to between 185 and 2400 gal/day (assuming gradients across the waU of between 1 and 10). At the lower estimated flow volume (30,000 gal/day) and assuming a treatment cost of $0.002/gal, this would result in a potential operating cost savings of approximately $20,000 per year. At the higher estimated existing flow volume, the estimated operating cost savings could be on the order of $100,000 per year for comparison to the potential groundwater treatment costs. The cost savings over the extended period of groundwater pump and treat may exceed several miUion doUars.

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CDM calculated the estimated cost of the barrier waU. Assuming the barrier waU constmction costs may range from a low of $6/ft^ of waU face (soU-bentonite constmction under good conditions) to a high of $30/ft^ of waU face (deep soU mixing or jet grouted waU construction in difficult ground conditions) and assuming the average depth of the barrier waU to be 85 feet deep (fuUy penetrating) and the total length of the waU between 1250 and 1600 linear feet (fuUy encircling waU), the estimated barrier waU constmction ranges between $640,000 and $4,000,000. Based on these simple calculations, the barrier waU would pay for itself over the life of the operating system.

The foUowing subsections provide a brief summary of barrier waU aitematives and an evaluation of the aitematives relative to constructabUity at the OKTSA site, long-term and short-term effectiveness and relative cost for a proposed waU configuration. The final waU configuration wUl be based on the results from the ongoing investigation including test pit excavations, soU borings, and the results of groundwater modeling conducted to evaluate the effectiveness of fuUy versus partiaUy encircling waUs on pumping rates for groundwater extraction.

2.2 Wall lype Selection Criteria

The criteria that wUl be used to select the barrier waU type for the OKTSA site include:

• effectiveness, • implementabihty and • cost

2.2.1 Effectiveness

Each barrier waU type wUl be evaluated for its long-term and short-term effectiveness in providing physical containment of the DNAPL source area. Long-term effectiveness wUl include consideration of the barrier's performance over time. Chemical compatibUity of the barrier waU material with the on-site contaminants of concem as weU as the groundwater and soU chemistry, wiU be evaluated. Short-term effectiveness evaluation wiU include consideration of the impacts from the various aitematives on worker health and safety including consideration of contaminated material excavation, handling, and disposal.

2.2.2 Implementability

Implementabihty considerations for each of the barrier waU aitematives considered wUl be based on both the technical and administrative feasibiUty of constmcting the barrier. For this site, the potential depth of the waU and the excavation through the boulder and cobble layers need to be assessed. Administrative feasibUity issues included consideration for the disposal of excess excavated materials and potentiaUy contaminated slurries.

2.2.3 Cost

Cost estimates wiU be developed for each barrier waU technology based on the findings from the ongoing investigations. To the extent possible, direct costs for constmction wUl be based on contractor estimates. A significant consideration in these estimates wiU be the same issues

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presented above, under implementabihty, i.e., depth of the waU and difficulty of excavation through the cobble and boulder layer and into the tUl (if necessary).

2.3 Barrier WaU Design Considerations

The barrier waU design depends to a large extent on the barrier waU type or types selected and the results of the analysis of the aitematives, i.e., whether or not the waU is partiaUy or fuUy encircUng, or fuUy or partiaUy penetrating. This section describes some of the design considerations for the most commonly used and potentiaUy appUcable barrier waU types.

A maximum permeabUity of 1x10" cm/sec is generaUy used as the design criteria for hazardous waste landfiU cap and liner systems as weU as barrier waUs. This permeabiUty is considered to be reaUsticaUy achievable and is considered to be the target permeabUity for the OKTSA barrier waU. It is possible that future groundwater modeling may indicate that a higher permeabUity is acceptable. However, waU technologies have been screened based on this permeabiUty criterion for this report.

The preliminary waU location and configuration was based on the vertical groundwater profUe data of contaminants and the results of initial groundwater modeling. Design efforts will be conducted to avoid physical contact with pure phase chlorinated solvents to limit the risk of waU degradation over time. Chemical compatibUity tests may need to be conducted to adequately assess long-term effectiveness of some of the waU types. Predicted groundwater flow pattems wiU be used to evaluate the final waU configurations and penetration depths. Physical constraints of the site, such as the proximity of the barrier waU to the existing buildings, the Souhegan River, and the adjacent Ehn Street, also need to be considered.

For purposes of planning the explorations for barrier waU design, CDM has assumed that the proposed waU wUl completely encircle the area of suspected DNAPL presence. The delineation of PCE isoconcentrations presented in the Vertical Contaminant Profiling Report prepared by CDM Federal for EPA forms the basis for selection of a probable waU aUgnment zone. The preliminary waU aUgnment zone is indicated on Figure 2-1.

The "Probable Zone of Barrier WaU AUgnment" shown on Figure 2-1 was selected considering possible site constraints as weU as the suspected locations of DNAPL contamination. The aUgnment zone is relatively narrow on the north and east sides where the site constraints are limited and wider on the west and south sides to account for the possibUity of having to encircle the existing buUdings on the site. The preferred waU aUgnment is the inner ring of the zone. DemoUtion of the existing buUdings would be required to accommodate this aUgnment. The length of a barrier waU within the probable zone would vary from about 1250 linear feet to about 1600 linear feet.

During the design phase of the project, CDM wiU consider, separately, altemative barrier waU types adjacent to Elm Street. It may be possible to use (if necessary) a different waU type in this location, e.g., a cement-bentonite waU versus a soU-bentonite waU.

CDM wiU evaluate the possibiUty that the existing buUdings wiU not be demoUshed and the waU wUl need to pass around the buUdings. The preferred waU aUgnment would be nearer the inner edge of the zone to Umit cost of the waU and maximize the distance between the waU and

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Elm Street. However, this would require buUding demoUtion.

The barrier waU may need to penetrate into a low permeabUity soU layer in order to reduce groundwater flowing beneath the waU. The waU could be constmcted to a lesser depth provided that sufficient control of groundwater flowing undemeath the waU is maintained. The lower tUl underlying the site consists mainly of very dense sUt and clay and is likely to provide an adequate barrier to vertical migration of groundwater and contaminants. The waU wUl Ukely extend from the top of the aquifer, through the outwash deposits (including the cobble/boulder layer), the upper tUl layer and terminate at least three feet into the lower tUl. Based on avaUable data, the waU wUl likely need to extend from 55 to as deep as 95 feet below ground surface to adequately key into the lower tUl. Additional data wUl be coUected on the depth to the lower tUl during the ongoing exploration program.

2.4 Preliminary Barrier WaU Altemative Screening

UntU the on-site explorations and groundwater modeling studies are completed and the new data reviewed, insufficient data are presently avaUable to select a barrier waU type. However, the various waU technologies are reviewed below. Technologies that are clearly not implementable, or are not as effective as another technology with a lower cost, are eliminated from further consideration.

SoU-Bentonite Slurry WaU

The soU-bentonite (SB) slurry waU technique has been approved by the U.S. Environmental Protection Agency (US EPA) for hazardous waste containment and has been used extensively throughout the United States and Europe. This type of slurry waU is named for the blended mixture of soU and bentonite used to backfiU an excavated slurry trench. It is a relatively simple and proven technology which is offered at competitive prices by many contractors.

The slurry waU is constmcted by excavating a trench with a backhoe, excavator, or clamsheU bucket. The trench is advanced in depth untU a low permeabUity layer is encountered or untU the hydrauUc gradient beneath the slurry waU is sufficiently low. As the trench is excavated, a mixture of bentonite slurry is pumped into the trench to maintain open and stable sides of the excavation. As indicated earUer, trench depths may need to be from 55 to as deep as 95 feet below ground surface at the OKTSA. A clam sheU bucket would likely be required for trench excavation depths at the higher end of this range (below a depth of 75 feet).

Typical widths of slurry walls are from 2 to 4 feet, and are dependent on the depth of the waU, soil conditions, and degree of containment required. Wider frenches may be necessary for removing boulders or other subsurface obstructions. WaU trench excavations for the OKTSA site are anticipated to be at least three feet wide to accommodate boulder removal. In addition, if there are enough voids in the "boulder zone" to produce significant slurry losses, it may be necessary to add a slurry loss control agent such as intermediate sized particles (sUt or sand), starch, potassium aluminate, aluminum chloride, or sodium carboxymethyl ceUulose (CMC) to the initial slurry. The use of slurry loss control agents in a suitable slurry faciUtates the effective filUng of soU pores and closing of fissures. If slurry loss cannot be controUed through the use of an additive, a cement-bentonite mixture or cement plug may be necessary.

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After excavating to the proper depth, the trench is backfilled with a designed mixture of bentonite and excavated soU. SoU not suitable for backfiU would need to be disposed of, possibly offsite. The mixture is typicaUy designed to provide a permeabUity on the order of 1x10' cm/sec. Once backfiUed, the SB waU is a relatively plastic waU which can tolerate movements without damaging the integrity of the waU. However, the strength of the waU backfiU is relatively low compared to the surrounding soUs. GeneraUy, near surface detaUs are designed to provide sufficient strength and protection for planned post construction use of the site.

The primary contaminants of concem at the site are chlorinated solvents, specificaUy, DNAPL. Long-term effectiveness of SB waUs relative to maintaining low permeabUity requires verification by compatibiUty testing. However, pubUshed Uterature suggests that long-term degradation of the waU is not significant if the SB waU contacts only dissolved chlorinated solvents. However, direct contact of the waU with pure phase chlorinated solvents such as TCE can cause significant detrimental changes to waU permeabUity. As indicated previously, the waU aUgnment wUl be selected to avoid zones of suspected pure phase contamination.

The SB waU is retained for further consideration for the project. The permeabUity criterion can be met with this technology. In addition, trench excavation methods are avaUable to reach the required depth of waU penetration. However, trenching through the boulder layer requires investigation. Near surface trench coUapse is a significant issue if the waU aUgnment passes close to Ekn Street. The abUity to excavate through the boulders are the focus of the test pits included in the exploration program.

Cement-Bentonite Slurry WaU

Cement-bentonite (CB) waUs are constmcted in the same manner as SB waUs except that the slurry used for temporary trench support is a blend of bentonite and ordinary Portland cement. The cement-bentonite slurry wUl set-up without backfilling of soUs, therefore soU excavated from the trench requires disposal. CB waUs can be a favorable altemative compared to SB waUs where higher waU strength is required. However, permeabiUty of CB waUs may be one to two orders of magnitude higher than for a SB waU and thus would probably not meet the permeabUity criterion for the project. In addition, the cost of constmction can be higher when compared to a soU-bentonite slurry waU due to the higher material costs of cement in the slurry and costs related to excavated soU disposal.

At this time, CB waU technology would not be proposed as an acceptable altemative for the project because the permeabUity criterion probably cannot be met with this type of waU and the cost of construction relative to SB waUs is Ukely to be higher. However, CB waU technology may need to be considered later if the existing OK Tool buUding is not demoUshed and strength of the waU becomes a more important factor in maintaining stabUity of the trench adjacent to the buUding. This may be the case the waU aUgnment must pass in the limited area between the existing buUding and Elm Street.

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Geomembrane Cut-off WaU

This altemative is a variation of SB and CB technology. A slurry trench is constmcted as described above. Then, a high density polyethylene (HDPE) geomembrane is placed verticaUy within the slurry trench. The placement of the geomembrane provides an additional barrier to groundwater or leachate flow through either the SB or CB wall. HDPE sections are typicaUy 80 mU thick to provide resistance to mechanical rupture and long-term resistance to chemical degradation. However, HDPE is not very resistant to chlorinated solvents. PermeabUities on the order of 1x10' cm/sec can be attained with geomembrane waUs.

WhUe lower permeabUities and improved resistance to long-term waU degradation are usuaUy attainable, the additional cost of geomembrane instaUation are not considered warranted relative to the cost and effectiveness of an SB waU. Accordingly, geomembrane waU technology has been eliminated from further consideration for this project.

Vibrating Beam Cut-off Wall

Vibrating beam waU constmction is a method of slurry waU construction where the waU is constmcted in panels. Both SB and CB slurry waUs can be constmcted by this technique.

A heavy steel I-beam is driven into the ground and withdrav/n with a vibratory hammer. A bentonite slurry and/or grout mixture is pumped into the ground through nozzles at the base of the steel section during driving and withdrawal to form a soU/bentonite or cement/bentonite slurry "panel". Subsequent panel sections are completed so as to overlap with previous panels to form a continuous slurry waU. This becomes increasingly more difficult with depth. Any breaches in the panel overlaps increases the effective permeabiUty of the waU.

The thickness of the vibrating beam slurry waU is generaUy on the order of 6-inches (150 mm). The positive aspects of this instaUation technique is the limited disturbance to the surface environment and reduced worker exposure to excavated soU or recirculated slurry that may be contaminated.

PermeabUities as low as 1x10' cm/sec are achievable provided that panel aUgnment can be maintained. Subsurface obstmctions such as the boulder layer wiU cause difficulty maintaining aUgnment. Excavation through the boulder field would probably be required prior to instaUing the panels. However, verifying proper waU aUgnment for walls deeper than 20 or 30 feet is difficult even in favorable soU conditions. Accordingly, vibrating beam waU technology is not recommended for this site and has been eliminated from further consideration.

Steel Sheet Pile Cut-off WaU

A steel sheet pUe waU is constructed by driving (with an impact or vibratory hammer) individual sections of steel "Z" sections which are connected to each other with a groove and baU socket system that forms an interlock between panels and helps maintain integrity along the sidewaUs of the steel sections. The steel section thicknesses can vary from about 1/8 to 1/2 inch in thickness.

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The advantage of this waU system is that much of the soUs are displaced rather than excavated, reducing worker exposure and disposal requirements. However, steel sheet pUe waUs are not considered low permeabUity due to the potential for leakage along the interlocks between panels. Grouting or seals in the interlocks can be used to decrease the waU permeabUity at additional cost.

Subsurface obstmctions such as the boulder layer wiU cause difficulty maintaining sheet pUe aUgnment. Excavation through the boulder field would be required prior to instaUing the sheet pUes. Also, waU seal degradation in the presence of dissolved chlorinated solvents would need to be analyzed.

Steel sheet pUe walls are not considered appropriate for the site due to permeabiUty and difficulties with instaUation. However, steel sheeting may be useful as a secondary barrier during SB waU construction along the river to minimize slurry loss if high groundwater velocities are determined to be a significant problem.

Deep SoU Mixing Cut-off Wall

Deep soU mixing cut-off waUs combine in-situ soUs with a cement grout or cement-bentonite grout to form a physical barrier to hydrauUc flow. The diameter of the augers are typicaUy 24 to 30 inches, which is also the approximate width of the completed waU. An auger system is advanced to the required waU depth. Grout is injected during auger advancement whUe the augers mix the grout with the soUs. The continuity of this waU system is achieved by overlapping the "panels" formed by the augers.

SimUarly to vibrating beam waUs and sheet pUe waUs, the presence of boulders and cobbles at the site may inhibit auger advancement or may cause misaUgnment of mixed soU panels aUowing gaps to be formed between panels. WhUe the cement grout produces a relatively high strength waU, the cement may be subject to long-term degradation from chemical attack. In addition, the hydrauUc conductivity of this type of system is higher than for SB waUs, chiefly because of the use of in-situ soUs and cement and the possibUity of ungrouted zones between adjacent panels. FinaUy, the anticipated depth of this waU makes the use of augers more difficult. Accordingly, deep soU mix waUs are not considered appropriate for the site and have been eliminated from further consideration.

let Grouted Slurry WaU

Jet grouting is accompUshed by advancing a grout pipe (typicaUy 4 to 6 inches in diameter) into the ground. The grout pipe has smaU diameter jets at the tip capable of injecting water and/or grout at very high pressures. Water is jetted at high pressure to loosen the soU at the tip of the pipe, aUowing the pipe to be advanced into the ground. The pipe is rotated whUe being withdrav^m and grout is jetted into the soU to form grouted colunms. The jetting force is great enough to displace the soU, thereby mixing it v^th the grout to form the soU/grout coluirm. The column diameter is a function of the type and density of soU and the jet pressure. Columns typicaUy range from 1.5 feet to 9 feet in diameter depending on soU conditions and whether single, double, or triple fluid systems are used. The soU/grout colunms are spaced so that they overlap, forming a continuous waU of cemented soU.

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The boulder layer at the OKTSA site wiU inhibit grout pipe advancement though this technique would probably not require pre-excavation of boulders. As with other techniques using panels or single vertical elements, gaps between the grouted columns wiU increase the waU permeabUity.

As with other cement-based waUs, higher permeabUity and the potential for chemical attack make this waU type undesirable for use at the site. In general, jet grouting is significantly more expensive than otiier aitematives. Based on a high cost and concem with adequate overlapping between columns, this altemative has been eliminated from further consideration for this project.

Reaction Gate Walls

A reactive gate, in combination with two barrier waUs, is another potential technology appUcable to the OKTSA site. The two barrier waUs would be constructed subparaUel to the direction of groundwater flow with the contaminated zone between them. These waUs would act as a "funnel" capturing contaminated groundwater and directing it toward the reactive gate. The gate contains a reactive medium and has a high hydrauUc conductivity which aUows water to easUy pass through the reactive media. The reactive media consists of metal (iron) filings. This technology has been studied and pUot tested by the Waterloo Center for Groundwater Research at the University of Waterloo, Waterloo, Ontario. The proprietary technology has been Ucensed to vendors in the U.S.

It has been shown that TCE and other halogenated aUphatic compounds in solution are rapidly degraded when the solution comes in contact with certain metals. GUlham and O'Hannesin (1992) observed this phenomena in a series of tests using TCE and metal fiUngs. CDM has recently investigated the feasibiUty of the technology to treat a TCE and TC-99 plume for the Department of Energy (DOE). For this site, the TCE concentration in the influent plume was assumed to be at 10 mg/L. For a gate length of 150 feet, a saturated depth of 40 feet, and an estimated flow of 7,200 ftVday, CDM calculated that the design retention time for the water flowing through the gate, with an adequate factor of safety, was 40 hours. This required a 6.7 foot length-of-flow.

Permeable reaction waU technology is a relatively new unproven technology. The treatment of the groundwater using the reactive gate would eliminate the need for groundwater pumping and treatment in the source area. However, the suitabUity of this remedial technique for DNAPL source areas and in this high permeabUity aquifer is questionable. Extensive on-site pUot testing would be required to determine the system's feasibiUty. This technology has therefore been eliminated from further consideration.

Summary

As indicated by the preceding discussions, the most favorable barrier waU altemative for the OKTSA site is the soU-bentonite waU. As the project progresses and additional information becomes avaUable, other waU construction aitematives may become desirable for use, either alone or in combination with soU-bentonite waU technology. The final aUgnment, extent and depth of the central waU wiU be determined during the design phase of the project.

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I ll 2.5.5 Data Needs

Based on the discussions presented in Section 3.4, the foUowing issues require investigation during subsequent phases of the project:

• the thickness and composition of cobble/boulder layer and trench "excavatabUity" through the cobble/boulder layer;

• the depth to lower tiU along the anticipated waU aUgnment;

• the relationship of groundwater flow to stratum to assess the required depth of the barrier waU;

• the future use of site and disposition of existing stmctures (this wUl affect selection of waU aUgnment and the stmctural requirements of the waU);

• results of groundwater modeling for fuUy or partiaUy encircling waU aUgnments; and

• anticipated hydrauUc gradients across the waU aUgnment.

These issues are the subject of the ongoing site investigations and proposed engineering analyses. Clarification of these issues wUl aid in evaluating whether or not a barrier waU is feasible for the site and, if so, what waU constmction technology would be most appropriate.

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3.0 HYDRAULIC CONTAINMENT/ GROUNDWATER MODELING

3.1 Infroduction

As part of the O.K. Tool Source Area (OKTSA) pre-design study, the CDM team modeled selected hydrauUc containment scenarios. The hydrauUc containment scenarios ranged from a slurry wall surrounding Ukely source areas, to hydrauUc containment through groundwater extraction and treatment. Preliminary groundwater modeUng was used to assess the hydrauUc containment scenarios.

The site groundwater modeling objective was to assess plausible hydrauUc containment scenarios and provide groundwater extraction/treatment system design information. The groundwater model provides: groundwater extraction rate estimates; extraction weU locations and capture zone estimates; and containment waU locations and resulting capture analysis.

3.2 General Groundwater Model Area Geologic Description

FoUowing is a site geologic description based on avaUable information. The Savage WeU Superfund site (site) is located in the Town of MUford New Hampshire which is situated in south-central New Hampshire. The site is approximately two mUes west of MUford center on Route lOlA. The site area borders the easterly flowing Souhegan River flood plain. The study area is located in the westem region of the Massabesic-Merrimack Rye terrain which consist of Precambrian to Ordovician plutonic rocks, and SUurian to Devonian metasediments. Granite and gneiss underUe the site and immediate surrounding areas. The CampbeU HiU Fault is located approximately 1,000 feet west of the site.

The site aquifer consists of unconsoUdated Pleistocene glacial sediments deposited within a pre-Pleistocene vaUey. The glacial deposits generaUy consist of weU sorted stratified drift predominantly sands and gravels with some sUt. The stratified drift is extremely variable both lateraUy and verticaUy. However, the stratified drift generaUy is coarser in the westem site areas near OKTSA. A nested boulder field has been observed approximately 20 feet below ground surface at the OKTSA. A discontinuous layer of tUl underUes the stratified drift deposits. The tiU consists of two distinct units: an upper tiU consisting of a sandy gray deposit, and a dense brown lower tiU. The site stratigraphy is based on a Umited number of widely spaced test borings and preliminary information coUected during this project where interpretations have been made by the CDM team and others to develop the preceding geologic description. The geologic information wUl be updated as additional site subsurface work is completed and field data is analyzed for the conceptual design report.

Based on our preliminary findings, the depth to bedrock ranges from approximately 58 feet below ground surface (bgs) to approximately 106 feet bgs. Recent geologic information is generaUy consistent with previous test borings except that thinner sequences of upper and lower tiU and locations where outwash directly overUes bedrock were observed.

Site aquifer groundwater originates from precipitation infiltrating the glacial deposits, infiltrating runoff from upland areas, and stream flow seepage. Site groundwater is largely unconfined and may be semi-confined at some locations. USGS estimated the site sand and gravel horizontal hydrauUc conductivities for the model to be in the range of 45 feet per day

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(ft/day) to 210 ft/day. Glacial tiU deposits have estimated hydrauUc conductivities of about 5 ft/day for the sandy tUl, and 1 ft/day for the clayey tUl. The USGS conducted a pumping test at the Keyes weU east of the site and calculated a vertical hydrauUc conductivity of .15 to 2.5 ft/day which was one tenth of the horizontal hydrauUc conductivity measured in the Keyes WeU sand and gravel deposits. This ratio may not represent the OKTSA horizontal/vertical hydrauUc conductivity ratio. Pre-design in-situ permeabUity testing wUl be used to assess the site horizontal hydrauUc/vertical hydrauUc conductivity ratio.

OKTSA groundwater flow is easterly. The Souhegan River at the upgradient westem portion of the OKTSA discharges from a low permeabUity tUl and steep bedrock hiU to a flat river vaUey consisting of high permeabUity sand and gravel. The OKTSA area has many areas where cobbles and boulders were observed in the upper 20 feet. To the east towards the more distal portions of the ice margin deposits, observed materials range from fine to coarse sands with few cobbles and traces of sUt. The stratified deposits are relatively thick, approximately 70 feet, in the OKTSA buUding area. The Souhegan River is a losing stream in the OKTSA. The estimated average model linear groundwater flow velocity in the OKTSA ranges from 1.5 ft/day to 2.5 feet per day. The preceding paragraph is a generalized description of the OKTSA hydrogeologic characteristics which is based on an interpretation from a Umited number of test borings, surface water and groundwater elevation measurements.

3.3 Groundwater Modeling Code

The MODFLOW (McDonald and Harbaugh, 1988) groundwater modeUng computer code developed by the United States Geologic Survey (USGS) was used to perform the ground water flow simulations. MODFLOW reUes on a block-centered, finite-difference approach to simulate groundwater flow in three dimensions. MODFLOW simulated groundwater flow was horizontal within layers and vertical between layers. Vertical flow within layers is not simulated. Leakage between layers is simulated. CDM's team consultant Aries Engineering, Inc. (Aries) used the December 1994 Maximal Engineering, Inc. PC compUed version of MODFLOW including ceU re-wetting capabUity, PCG2 numerical solver and horizontal flow barrier options.

The USGS particle-tracking model, MODPATH (D.W. PoUock, 1994), was used to conduct pathUne analyses as a post-processor to MODFLOW simulations. Aries used the November 1994 Maximal Engineering, hic. PC compUed version of MODPATH. SURFER (Golden Software, Inc., 1988) was used to contour and view the model output. The MODFLOW or MODPATH modeUng codes used in the site simulations were not modified.

The site 3-D 5-layer groundwater flow model was developed by the USGS under contract to the EPA. Aries received the updated USGS site model data files in June 1995. The model files were dated AprU 1995. Aries did not modify the input data arrays.

3.4 Groundwater Model Framework and Input Data

A discussion of the site conceptual groundwater model (model) and input data for the model foUows.

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3.4.1 Conceptual Model

Site groundwater occurs under water table conditions in the uppermost saturated deposits whUe semi-confined conditions may occur in the glacial tiU, site bedrock or sUt layers within the stratified drift deposits. Site area groundwater originates as infiltrating precipitation on the uppermost geologic deposits and from Souhegan River water infiltrating to the aquifer. Site groundwater flows mainly through the more permeable outwash strata generaUy east from the Souhegan River which is a losing stream in the OKTSA area. Further to the east, near the MUford Drive-In Theater, the Souhegan River becomes a gaining stream and area groundwater flows eastward and discharges into the river.

The bedrock surface is shaUowest in the site westem area and slopes downward to the east and northeast across the OKTSA site. The glacial tUl interfaces also generaUy foUow this topography. The greater thicknesses of more highly permeable outwash deposits are along the eastem end of the site buUding and intersect the Souhegan River north of the buUding. Therefore, significant volumes of groundwater are able to flow from the river across the northem and eastem site areas.

Site groundwater hydrauUc gradients are shaUow. This is due to the highly permeable outwash saturated thicknesses between approximately 20 and 80 feet and a broad outwash vaUey aquifer extending downgradient over 1.5 mUes to the east.

Because the Souhegan River water infiltrates into the aquifer at the OKTSA site, site ground water extraction would tend to induce additional river water infiltration to the aquifer. Capture zones of extraction weUs would tend to propagate upgradient to the Souhegan River and induce infiltration rather than spread laterally to reach equUibrium conditions.

Because the Souhegan River is a major source of aquifer recharge in the OKTSA and Hitchiner area, the Hitchiner water supply production weU, Ml-33, may compete with OKTSA site groundwater extraction weUs for aquifer water induced from the Souhegan River. This may increase the pumping rates needed to maintain a given capture zone at the OKTSA site.

3.4.2 Model Grid System

The modeled area was 10,320 feet long by 8,290 feet wide. A variable grid spacing layout was used to provide good spatial resolution in the OKTSA area and other areas of interest throughout the site. The OKTSA had a grid spacing of 25 feet by 50 feet. The model edges were far enough away to reduce potential effects of the model boundaries on groundwater simulation in the OKTSA.

The model grid has 175 rows and 189 colunms, with a minimum grid spacing of 25 feet by 50 feet in the OKTSA and Savage WeU area. The smaUer grid spacing provides increased spatial resolution where input data density is higher and higher simulation resolution is needed. The smaUer grid spacing provides more detaUed simulation of groundwater elevations and flow directions in the anticipated extraction weU areas. The row and column grid spacing expands outward from the middle of the site to larger spacing of 200 feet by 100 feet near the site boundaries where the stratified drift deposits pinch out.

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3.4.3 Model Layers

In general, the model was verticaUy discretized into up to 5 layers each about 20 feet thick to simulate vertical flow in stratified drift deposits. Layer 1 was simulated as type 1, unconfined, whUe layers 2 through 5 were simulated as type 3, convertible to either confined or unconfined. The lower layers were used only for thicker aquifer areas, generaUy at a bedrock low.

3.4.4 Model Botuidary Conditions

HydrauUc boundary conditions specify the interaction of simulated groundwater with hydrologic features such as streams and wetlands, and the inflows or outflows that occur at model edges or boundaries. The foUowing hydrauUc boundary conditions were used in the model.

• No-flow occurs at model edge nodes unless other hydrauUc boundary conditions were specified.

• River leakage boundaries were used to represent streams and wetlands where groundwater may flow into or out of the groundwater flow system. River leakage boundaries account for hydrauUc conductance of the stream bed and head differences between the stream and groundwater .

Groundwater flow near the other model edges was generaUy paraUel to the model edges except where river nodes were located at the grid edge. Because groundwater flow would not cross a groundwater flow Une, flow Unes may be treated as no-flow boundaries. Therefore model edges with paraUel groundwater flow would represent no-flow boundaries. Model edges in the westem and eastem ends with groundwater flow perpendicular to the model edge had a saturated thickness of 10 feet or less with a minimum width at these locations. These areas were also modeled as no flow boundaries because the flow in and out at the east and west end of the model was negUgible.

Tucker Brook, the discharge stream, Souhegan River and its upland tributaries were simulated as river leakage boundaries. The upper model boundary layer was a specified-flux boundary which receives inflow from upland areas outside the model, and precipitation. Bedrock surface was the lower layer model boundary. This boundary underUes aU of layer 5 and other layers which were the bottom most active layers. This boundary was modeled as a no flow boundary because there was Uttle to no quantitative information on the flow within the site bedrock. However, the bedrock contribution to the eventual discharge was accounted for by the recharge to the overburden layers above.

3.4.5 Bottom Elevations of Model Layers

The bottom of layers 5 and 4 generaUy conformed to the interpreted top of bedrock presented in the Remedial Investigation in bedrock lows. As bedrock rose to the north and south the bedrock surface ranged from layers 3 to layer 1.

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3.4.6 HydrauUc Conductivity Values

HydrauUc conductivity values for the groundwater model were based on site slug test and pumping test data provided in Tables 3-3 and 3-5 of the Remedial Investigation (RI). HydrauUc conductivity values for each node throughout the model were based on estimated approximate weighted averages for saturated overburden deposits at that node. AvaUable site test boring logs, hydrauUc conductivity tests, pumping tests and geologic cross-section information were used in estimating model hydrauUc conductivity values. Model average hydrauUc conductivity values for the stratified drift ranged from 45 ft/day to 210 ft/day. HydrauUc conductivity for the tUl ranged from 5 ft/day for the upper tUl to 1 ft/day for the lower tUl. Transmissivity estimates for the Savage WeU ranged from 7,600 ft^/day to 29,400 ft^/day. OKTSA transmissivities are expected to be in the same range as the Savage WeU.

There are 2 horizontal hydrauUc conductivity zones in model layer 1 and 5 zones in layer 2. Model layer 3 has 3 zones of hydrauUc conductivity and model layer 4 has 5 hydrauUc conductivity zones. Layer 5 consists of 2 hydrauUc conductivity zones.

Horizontal to vertical hydrauUc conductivity ratios were generaUy 10:1 for the stratified drift deposits. Horizontal to vertical hydrauUc conductivity ratios would affect the flow of groundwater between model layers. High ratios would impede flow in the model simUar to an aquitard in a hydrogeologic system.

3.4.7 Groundwater Recharge

Recharge to groundwater from infiltrating precipitation was simulated. Recharge was active on the model layer 1. Lateral inflow of water from upland areas was simulated by specifying increased recharge rates to the model edges. The recharge was estimated for each ceU by the approximate drainage area associated with that ceU. The drainage area was multipUed by the drainage discharge factor for this area of .205 cubic feet per second per square mUe. The recharge rate from infUtrating precipitation for layer 1 was 23 in/yr. Note that the site buUding area was considered a recharge area in the model to assess groundwater extraction rates without the existing buUding on the site.

3.4.8 Streams

Tucker Brook, the discharge stream, Souhegan River and its tributaries from upland areas were simulated as river leakage boundaries.

3.5 HydrauUc Containment Modeling Scenarios

The CDM team preUminarUy modeled four site hydrauUc and physical groundwater containment scenarios. The objective of groundwater modeUng was to preUminarUy assess the effectiveness and relative efficiency of proposed groundwater pumping and containment waU aitematives. The primary measure of containment effectiveness would be the abiUty of the containment system to Umit off-site migration of contaminated groundwater from site source areas. The criteria to evaluate relative efficiency of the containment system included rates and duration of groundwater pumping required for containment, and rates of river water leakage to the aquifer induced by the groundwater pumping.

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The hydrauUc containment modeUng assessment included simulating four general hydrauUc containment configurations; some simulations with variations of pumping weU locations and pumping rates. In general, initial pumping weU locations were selected based on ground water flow contours from non-pumping simulations and Rl site observations. Several pumping weU locations and rate configurations were simulated for each containment scenario. Pumping weU locations and rates wiU be reassessed and refined when additional site data from the field exploration program and is analyzed.

The site groundwater model wUl be updated and refined by analyzing and incorporating additional site hydrogeologic and contaminant distribution data from project field activities. After the model is updated and refined, the CDM team wUl complete and refine the assessment of remedial aitematives being considered at that time.

The foUowing describes the preliminary hydrauUc containment modeUng scenarios.

3.5.1 Hydraulic Contaiiunent without Containment WaU with DUute Plume Pumping

The model simulated hydrauUc containment of site groundwater using groundwater pumping without a containment waU. The primary purpose of this hydrauUc containment scenario was to assess potential pumping rates needed to contain site groundwater and assess the amount of river water that would be induced to leak into the aquifer and flow across the site for a particular pumping rate.

Two extraction weUs were simulated. The weU screens were located in layers one and two of the model. Groundwater recovery weU GRW-1 on Figures 3-1 and 3-2 was located downgradient of OKTSA source areas to capture higher concentrations of contaminants, whUe recovery weU GRW-2 was located further downgradient in the dUute plume to primarUy capture areas of dUute contamination. A single recovery weU could be used, but would cause longer travel times of ground water from site contaminant sources and less flexibUity to adapt to changing site hydrauUc conditions such as seasonal infiltration variations or off-site ground water pumping variations. Total groundwater pumping rates simulated were 100 gpm, 150 gpm and 250 gpm. In each simulation the total pumping rate was divided equaUy between the two extraction weUs. The extraction weU locations and weU capture zones are depicted on Figure 3-1 and 3-2.

3.5.2 Partial Contaiiunent Wall with Pumping

A partial containment waU along the westem and northem site boundaries was simulated by placing the model horizontal flow barrier in the configuration shown on Figure 3-3. The purpose of the partial containment waU was to assess the effects of an upgradient groundwater flow barrier to limit the rate of river water induced to flow through the site by extraction weUs. The partial cut-off waU was also modeled to simulate an average five-foot waU thickness with material permeabiUty of 1 x 10' cm/s. The partial cut-off waU extended verticaUy through layers 1, 2, 3 and 4 representing sand and gravel outwash at the site.

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SC-3 PARTIALLY ENCLOSED PHYSICAL BARRIER WITH PLUME CONTROL AT 75 GPM

environmental engineers, scientists, SCALE IN FEET planners, A management consultants FIGURE 3 - 5 CDM

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Two groundwater exfraction weUs were simulated near site source areas, one east of the site buUding and one southeast of the leach field, each pumping at rate of approximately 7.5 gaUons per minute (gpm). The purpose of these extraction weUs was to capture groundwater flowing through observed VOC source areas. The weU screens were located in layers 2 and 3. Two groundwater extraction weUs were located in dUute plume areas east of the containment area. The dUute plume extraction weUs were simulated to capture contaminated groundwater off-site east of site source areas. The dUute plume weU pumping rates were simulated at 25 gpm each, The dUute plume extraction weUs were screened in model layers 1 through 4. The dUute plume extraction weUs could be combined into a single extraction point, however, two weUs aUows the adjustment of pumping rates which moves the pumping center and therefore can be used to adjust the capture zone.

3.5.3 Fully Surrounding Containment Wall with DUute Plume Pimiping

The fuUy surrounding containment waU was simulated by placing the model horizontal flow barrier in the approximate configuration shown on Figure 3-4 and with enhanced DNAPL removal weUs in Figure 3-5. This horizontal barrier configuration approximates the proposed cut-off waU surrounding the OK Tool buUding and property contaminant source areas. The cut-off waU was simulated to represent a waU penetrating the site permeable sand and gravel outwash deposits and keyed into the underlying glacial tiU.

The cut-off waU was modeled to simulate an average five-foot waU thickness with material permeabUity of 1 x 10"'' centimeters per second (cm/s). The simulated containment waU extended verticaUy through model layers 1 and 2 for the waU's circumference. The simulated containment waU extended through model layers 3 and 4 only in the eastem site portions because the upper surface of the glacial tUl was in layer 3 in the westem site area. The waU did not extend into layer 5.

Two groundwater extraction weUs were simulated inside the waU, one east of the site buUding and one southeast of the leach field, each pumping at rate of approximately 4 gaUons per minute (gpm). The purpose of these weUs was to prevent an increase of hydrauUc head inside the containment wall from areal recharge and upgradient side leakage through and under the waU. With hydrauUc heads inside the waU higher than outside of the waU downward vertical gradients would result inside the waU. This may increase the potential for groundwater migration in downgradient waU areas, increasing potential groundwater leakage out of the containment area. The weU screens were located in layers 3 and 4 to capture deeper ground water because of the concem with downward gradients.

Two groundwater extraction weUs were simulated outside the waU in dUute plume areas east of the containment area. The dUute plume extraction weUs were simulated to capture volatUe organic compound (VOC) containing groundwater off-site east of site source areas. The dUute plume weU pumping rates were simulated at 25 gpm each. The dUute plume extraction weUs were screened in model layers 1 through 4. Again, the dUute plume extraction weUs could be combined into a single extraction point, however, two weUs aUows the adjustment of pumping rates which moves the pumping center and therefore can be used to adjust the capture zone.

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3.6 Hydraulic Contaiiunent Modeling Results

HydrauUc Containment without Containment WaU

Figure 3-1 and 3-2 shows hydrauUc containment of site groundwater using groundwater pumping at a total rate of 250 and 150 gpm without a containment waU, respectively. PathUne analysis indicated that site groundwater was captured by the two extraction weUs pumping at a total rate of 150 gpm. The simulated capture zone width at the OKTSA property was approximately 550 feet. PathUne analyses were conducted using the USGS MODPATH particle fracking code. Particles were placed in layers 1, 2 and 3 upgradient of the OKTSA and tracked in a forward direction.

The combined simulated capture zone width of two weUs each pumping at a rate of 50 gpm was approximately 350 feet, which is not sufficiently wide to capture site groundwater. The combined simulated capture zone width of two weUs each pumping at a rate of 125 gpm was approximately 800 feet, which captures site groundwater as well as a large amount of river water.

The effects of seasonal or transient conditions on pumping rates and capture zones were not assessed using the model. However, the need to increase pumping rates seasonaUy would be based on higher ambient groundwater flow through the site aquifer. Because aquifer permeabUity and geometry do not change with time, the only factor affecting groundwater flow volume through the site is hydrauUc gradient. RI 1989 site water level data for upgradient site monitoring weU MI-21 and downgradient site monitoring weU MI-63 indicate that the hydrauUc gradient across the site decreased approximately 2 percent from February to August. Although Febmary is not the typical high groundwater month, it seems Ukely that the April high groundwater would not cause a gradient increase more than 10 times the February increase of 2 percent. This would indicate less than a 20 percent seasonal increase in hydrauUc gradient and therefore less than a 20 percent seasonal increase in ground water flux across the site. Seasonal data should be used in assessing the safety factor in designing final flow rates for pumping weUs in a final design.

Partial Containment WaU with Pumping

Figure 3-3 depicts the results of the partial containment waU simulation. PathUne analysis indicates that groundwater upgradient of the waU flows around and beneath the waU to the downgradient side of the wall. PathUne analysis indicates that source area and dUute plume extraction weUs captured the majority of site groundwater. OKTSA site groundwater flow paths were changed substantiaUy by the containment waU. SUghtly greater pumping rates and different extraction weU locations would likely be needed to effectively capture site groundwater. Moving the southwest dUute plume extraction weU about 50 feet to the north and increasing the pumping rate to 35 gaUons per minute is anticipated to increase capture effectiveness.

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FuUy surrounding containment waU with dilute plume pumping

Figure 3-4 depicts the containment waU and dUute plume extraction weUs capture zone. PathUne analysis indicates that a total dUute plume pumping rate of approximately 50 gpm would be needed to capture groundwater outside of the containment waU downgradient to approximately the poUce station area.

The pathUne analysis also indicates that the 4 gpm pumping rate for each of the extraction weUs inside the containment waU does not completely contain groundwater in the downgradient area of the containment waU. The pathUne analysis shows leakage beneath the waU at the upgradient and downgradient sides. The downgradient leakage is captured by the dUute plume extraction weUs.

The downgradient leakage beneath the containment waU could be reduced by either reducing recharge from infUtrating precipitation by capping unpaved site areas or increasing pumping rates inside the waU. DUute plume groundwater extraction near the downgradient side of the waU lowers hydrauUc head outside the waU and therefore increases the potential for leakage beneath the waU. Aries did not assess leakage from the containnaent waU with a cap or without dUute plume pumping using the model.

River Leakage

An assessment of the amount of leakage induced from the Souhegan River into the aquifer was conducted to determine the contribution to the pumping from extraction weUs in the hydrauUc containment scenarios. The induced river leakage was calculated from the model overaU volumetric budget. Therefore, the leakage factors were based on the whole river. The total leakage from the aquifer was subtracted from the total leakage into the aquifer to obtain the net river node leakage into the aquifer. The net river node leakage from each scenario was compared to that of the model simulation without OK Tool site or dUute plume pumping. The preliminary induced leakage estimates were conservatively high since these values were based on net river leakages and were not limited to the OKTSA only. Because the majority of river leakage node head changes caused by site pumping weUs are in areas within the pumping weU capture zones at the OKTSA, the overaU volumetric budget values are a good representation of the OKTSA induced infiltration. The foUowing Table 3-1 summarizes the preliminary induced river leakage for the hydrauUc containment scenarios.

3.7 Comparbon of HydrauUc Containment Scenarios

A comparison was made between the relative effectiveness and relative efficiency of the modeled hydrauUc containment configurations. The comparison was based on: the abiUty of the containment system to limit off-site migration of VOC containing groundwater from site source areas; the rates and duration of groundwater pumping required for containment; and rates of river water leakage to the aquifer induced by the groundwater pumping. This comparison of modeled hydrauUc containment configurations does not consider potential enhanced source removal effects. Therefore, extraction weUs capturing groundwater flowing through source areas are assumed to have an indefinitely long pumping duration required to contain site VOC containing groundwater. The foUowing Table 3-2 sununarizes the hydrauUc containment comparison.

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Model Run

1) No site pumping

2) FuUy surrounding waU

3) PartiaUy surrounding waU

4) Treatment gate waU

5) Pumping without waU - 100 gpm

6) Pumping without waU -150 gpm

7) Pumping without waU - 250 gpm

New Hampshire Department of Environmental Services

OK Tool Source Area/ Savage WeU Superfund Site Table 3-1 Comparison of River Node Leakage Rates

B D

River River node Net river Net node leakage node leakage

leakage from leakage increase from river aquifer to from river from no-to aquifer river to aquifer pumping

(gpm) (gpm) (gpm) (gpm)

1956 1499 457

1991 1497 494 37

1998 1491 507 50

1995 1497 498 41

2041 1497 544 87

2096 1491 605 148

2167 1492 675 218

Where: [A - B = C] [D2 = C2 - Cl; D3 = C3 - Cl; etc.]

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New Hampshire Department of Environmental Services

OK Tool Soiu-ce Area/ Savage Well Superfund Site

Table 3-2 Comparison of HydrauUc Containment Options

Model Run Containment Total Estimated Amount Effectiveness pumping duration of of induced

(relative rate pumping river ranking) (gpm) (gpm) leakage

source:dUute (gpm)

FuUy surrounding waU High 58 indefinite: 37 10 yrs.

PartiaUy surrounding waU Medium 65 indefinite: 50 indefinite

Treatment gate waU Low 50 indefinite: 41 10 yrs.

P Pumping w/out waU -100 gpm Low 100 indefinite: 87 indefinite

Pumping w/out waU -150 gpm High 150 indefinite: 148 indefinite

Pumping w/out waU - 250 gpm High 250 indefinite: 218 indefinite

Note: The treatment gate waU containment was considered low because simulation showed contaminants exiting the waU in areas other than the treatment gate.

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The most effective hydrauUc containment configurations based on the groundwater modeUng results appear to be the fuUy surrounding waU and the higher pumping rate pimiping without waU scenarios. However, the pumping rates needed to hydraulicaUy contain site groundwater without a cut-off waU are mudi higher than ambient site groundwater flow and are therefore an inefficient aspect of this configuration. The partial containment waU may also be a viable option.

Based on the above criteria, and not considering enhanced source removal techniques, a surrounding containment waU combines containment effectiveness with relatively low pumping rates. Based on studies conducted by the University of Waterloo at Base Bordon in Ontario, Canada and observations at the South Municipal WeU Superfund Site in Peterborough, NH with simUar stratified drift deposits, the dUute plume extraction weUs may be shut down after approximately ten years. Solute transport analyses could be used to refine and check these estimates.

Based on the preliminary groundwater modeUng of site hydrauUc containment options, the foUowing conclusions can be made:

• The hydrogeologic site setting in permeable sand and gravel outwash deposits adjacent to a losing stream is a major factor affecting hydrauUc containment of site VOC containing groundwater. Because ambient groundwater gradients and flow are from the Souhegan River into the site aquifer, site groundwater withdrawals are recharged mainly by additional leakage of water from the Souhegan River.

• Because of the site hydrogeology, a containment waU with source area and dUute plume groundwater extraction appears to be a more efficient hydrauUc containment method.

• HydrauUc containment options not using a cut-off waU may be efficient on a long term basis if enhanced site source removal is conducted so that indefinite groundwater pumping would not have to be emphasized.

3.8 Conclusions

Because the site groundwater model wUl be updated and refined by incorporating additional site hydrogeologic and VOC distribution data from ongoing field activities, the results of the hydrauUc containment modeling may change. After the model is updated and refined, the CDM team wUl complete and refine the assessment of remedial aitematives . The conclusions should be reassessed after additional model refinement and updated simulations are completed.

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I 4.0 GROUNDWATER TREATMENT TECHNOLOGIES

I 4.1 Infroduction

In this section, potentiaUy appUcable groundwater treatment technologies were identified and

I assessed for implementabihty and feasibiUty regarding the OKTSA site conditions. Several groundwater treatment technologies from each of the foUowing categories were considered: metals treatment, volatUe organics treatment, and vapor treatment. A preliminary screening

I was completed to identify options for further consideration.

4.1.1 Groimdwater QuaUty

I During the CDM Federal sampUng round conducted in December 1993, groundwater samples

I were coUected from over 21 monitoring weUs located throughout the site. Based upon a review of the monitoring weUs in the vicinity of the OKTSA site, the CDM team has estimated groundwater quaUty data for the extracted groundwater from the OKTSA site in Table 4-1.

I Tetrachloroethylene is the predominant organic contaminant, however, 1,1,1 trichloroethane concentrations appear to be significantly lower in the vicinity of OKTSA than other areas of the Savage WeU Superfund site. Ketones and ethers also appear to be absent in and around the OKTSA site, although acetone was detected in the soU samples along the north dump area of

I the site. Total metal concentrations in groundwater may exceed water quaUty discharge criteria.

Based upon the chemical constituents found in the groundwater at the OKTSA site, there are

1 treatment options with proven reUabUity. The major constituents identified in the groundwater are VOCs. Elevated levels of iron, manganese and other trace metals (see Table 4-1) may also be present in the groundwater based upon the presence of high background levels.

I Understanding the interactions of these constituents is essential to designing a cost-effective

I treatment system. Concentrations of conventional groundwater parameters that need to be considered whUe designing remedial equipment, including TDS, TSS, chloride, alkalinity and hardness are also reported in Table 4-1.

I Based upon review of avaUable groundwater analytical data and the proposed effluent discharge option, several water quaUty criteria must be addressed when selecting the remedial system. The primary concem is the removal of VOCs from groundwater. Removal of the solvents from groundwater can be accompUshed by UV/oxidation or air stripping as specified

I in the ROD. The selection of the most effective and reduced cost treatment process is in part dependent on effluent disposal options, degree of treatment required, and the proven ability of

I the technology to meet effluent quaUty goals. The selection of the treatment process wiU be based on tedmical feasibiUty, system reUabiUty and capital and O&M costs. A brief discussion of candidate groundwater treatment technologies at the OKTSA site foUows.

I Discharge Options

Because the water treatment system design is based on the guidance discharge criteria presented in Table 4-1, several discharge options are discussed below.

I I -40­

I New Hampshire Department of Environmental Services

OK Tool Source Area/ Savage Well Superfund Site Table 4-1 Maximiun Groimdwater QuaUty

Chemical Name Maximum Guidance Groundwater Qeaiiup Levels Concentration WeU Location Primary/ Secondary MCL

(ppb) (ppb)

Tetrachloroethylene 11,000 MI-24 5

TCE 650 MI-24 5

1,1,1 Trichloroethane 69 MI-32 200

trans 1,2 640 MI-63 100 Dichloroethylene

1,1 Dichloroethane ND MI-24 800

1,1 Dichloroethylene 4 MI-32 7

Toluene 2 MI-32 1,000

Benzene ND 5

Methylene Chloride 950 MI-24 5

Total Xylenes 3 MW-22 10,000

Chlorobenzene ND 100

Ethylbenzene ND 700

„Vinyl Chloride ND 2

„1,1,2 Trichloroethane ND 5•• „

.Acetone 1400 MI-24

Iron 75,500 MI-27 300

Manganese 836 MI-63 50

Arsenic 86 MI-27 50

Antimony <60 3. .

Barium 329 MI-27 1,000

Chromium 127 MI-27 100

Copper 143 MI-27 . 1,000

Lead 42 MI-27 15

Zinc 152 MI-27 5,000

TDS 307,000 MI-16A -

_,TSS 208,000 MI-27

Chloride 150,000 MI-27

Total Alkalinity 112,000 MI-19 •

W Hardness 88,470 MI-27

Notes: 1. Groundwater q uality is based on s ample analyses in December 1993. 2. Acetone has been detected (190 mg/kg) in soils at the OK Tool site. 3. All metal analysis results were based on unfiltered samples. 4. Elevated metal concentrations in groundwater may be related to the metal debris area.

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Surface Water Discharge

Treated groundwater could be transported to the Souhegan River via a smaU diameter, pumped, effluent discharge system. The option is potentiaUy inexpensive and easUy implementable. Implementation of this option would require a NPDES permit for discharge. The effectiveness of the surface water discharge scenario is favorable because of the anticipated quaUty of the treated groundwater, implementation of engineering controls to monitor and shutdown treatment operation if equipment faUure occurs and the dUution factor provided by the significant flow of the Souhegan River. This option has been retained for future consideration.

On-site Reuse

Treated groundwater may be used as backwash water and makeup water for NAPL reduction enhancement processes. Recycling of treated influent is advantageous because a potable water source does not need to be tapped and sufficient volume is readUy avaUable. This is not a treatment altemative, as the recycled water must eventuaUy be discharged, but it is a viable cost saving use of treated groundwater and wiU be retained for future consideration.

Injection System

An injection system may be used to inject treated water back into the aquifer. Injection can be accompUshed using either injection weUs, infiltration gaUeries, or infiltration basins depending on flow rates and the area and depth of injection. In general, infiltration gaUeries can handle higher flows than injection weUs; however they are Umited to shaUow injection depths (up to 40 feet) compared to injection weUs which can be drUled and screened at any depth. Reinjection, regardless of the mechanism, is feasible at the OKTSA site because of the high hydrauUc conductivity of subsurface materials, particularly downgradient of the source area.

One disadvantage of on-site reinjection is the potential for introducing the reinjected water into the capture zone of the groundwater extraction weUs. This would result in treating large volumes of previously treated groundwater and treating large volumes of dUuted groundwater. Strategic placement of the reinjection system could circumvent this potential problem. This altemative wUl be retained for future consideration.

4.2 Identification and Screening of Treatment Technologies

4.2.1 Metak Treatment

Metal concentrations measured in on-site monitoring weUs indicate the potential need for metals removal equipment prior to final discharge. Although the former dump area is suspected to contribute much of the metals contamination in the groundwater, laboratory results from the December 1993 sampling round indicate that the highest metal concentrations were not found in this area. It appears that the background metal concentrations are high enough to require treatment. Reduction of metal concentrations, in particular iron and manganese in the influent groundwater stream, wiU reduce scale buUdup in downstream remediation equipment proposed in one of the design aitematives discussed in Section 6. Other proposed remedial equipment does not require pretreatment to remove metals from the groundwater prior to treatment. In addition to iron and manganese, effluent discharge criteria may require reduced groundwater metal concentrations of arsenic, antimony, chromium and lead before discharge. FoUowing is a description of three appUcable technologies for the removal of metals from the groundwater .

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4.2.1.1 Precipitation/ Flocculation/ Sedimentation

Precipitation/flocculation/sedimentation technology is commonly used to remove soluble metals from groundwater. It is a unit process involving pH adjustment to precipitate the metals, polymer addition to promote coagulation and settling of the precipitates foUowing by gravity sedimentation to coUect the soUds..

Sodium hydroxide is often used to raise the pH of the groundwater and form precipitate metals oxide precipitates. Polymer is added to promote flocculation of metal oxides and suspended soUd agglomerates into more rapidly settling particles. Settling of the agglomerates is accompUshed in a paraUel plate separator consisting of a series of paraUel plates instaUed in a settUng chamber. Settled particles are coUected in a conical-shaped sludge hopper. The sludge could then be discharged to a sludge thickening tank and aUowed to settle for offsite disposal or directed to a filter press for dewatering prior to offsite disposal.

TreatabUity testing is recoirunended to assess operating parameters including chemical addition, optimal pH adjustment, identification of polymer type and dosage, chemical composition and volume estimate of the sludge and disposal requirements for the sludge.

4.2.1.2 Green Sand Filters

Green sand filters reduce metal concentrations in groundwater by first oxidizing the metals with potassium permanganate and then capturing the precipitates with a multimedia (green sand) filter system. As the metal precipitates accumulate in the filter media, the back pressure through the system increases untU a backwash cleaning is necessary. Continuous regeneration of the green sand with potassium permanganate prolongs system operation between backflushing. TypicaUy dual systems are instaUed to aUow back flushing and regeneration of one filter as the other filter continues to operate.

4.2.1.3 Sequestering Agents

Sequestering agents are added to influent groundwater flows to reduce metal precipitate deposits on process equipment. Sequestering agents hold metals in solution and reduce the oxidation rate of the metals.

Polyphosphate based sequestering agents are often used to control metal deposits in process equipment by keeping the metals in solution and preventing precipitation. Sequestering agents are not appUcable for this site because metal concentration reduction may be necessary to meet guidance discharge criteria.

4.2.1.4 Ion Exchange

Ion exchange involves the removal of dissolved ions (metals) from groundwater by capturing ions on synthetic resins. During the process of removing ions from the groundwater, other ions that are bound on the resin are released. This process is reversed during regeneration of the resins. The exchange process aUows the resin to be cleaned (regenerated) using acid or caustic chemicals depending whether anions or cations are being removed from the groundwater, displacing the metal ions captured by the resin, and capturing them in a smaU-volume stream requiring disposal. Offsite regeneration of the resins wUl also be considered.

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A bench scale study conducted by an ion exchange resin manufacturer is recommended to determine the feasibiUty of this technology at the OKTSA site. The vendor wiU identify the proper resin for optimal metals removal. In addition groundwater characteristics including pH, TSS, alkalinity, conductivity and hardness wiU be identified as part of the vendors analytical evaluation.

4.2.2 Volatile Organic Removal

Groundwater at the OKTSA site is contaminated with several volatUe organic compounds. Chlorinated solvents are present in the highest concentrations foUowed by lower concentrations of benzene, toluene, and xylenes. Tetrachloroethylene (PCE) is present in the greatest concentrations in the largest number of weUs. The guidance discharge criteria for PCE is 5 ppb. For these reasons, PCE is the target compound and the VOC removal equipment was assessed by its abUity to remove PCE from the groundwater.

FoUowing is a description of several VOC removal technologies screened for potential use at the OKTSA site.

4.2.2.1 Air Sfripping

Air stripping is a proven physical process commonly used to remove VOCs from groundwater. Groundwater is introduced to the top of an air stripper tower. At the same time, clean air is forced up the tower, countercurrent to the groundwater flow. The water cascades down the tower on to packing material constmcted to maximize surface area and contact time for mass transfer of the organic contaminants from the Uquid to the vapor stream. The vapor stream may require treatment prior to discharge and is discussed in the next section.

The extent of contaminant removal is governed by many factors including contaminant concentration, air and water temperatures, air-to-water ratio and contaminant physical properties. One such physical parameter is the Henry's Law constant. Henry's Law constant is a partition coefficient that describes the relative tendency for a compound to partition between the gas and Uquid phases at equUibrium conditions. The larger the Henry's Law constant, the greater the equUibrium concentration of the contaminant in the vapor phase. High Henry's Law constants indicate compounds that are more easUy stripped from the liquid phase into the vapor phase. Compounds having dimensionless Henry's Law constants greater than 0.1 are generaUy weU-suited for treatment by air stripping. As shown in Table 4-2, many of the compounds present in the groundwater at the OKTSA site, such as PCE, TCE, 1,1,1 TCA, and frans 1,2 DCE have Henry's Law constants greater than 0.1. Removal efficiencies for the VOCs of concem at the OKTSA site wiU Ukely exceed 99% utUizing air sfripper tower technology.

The use of two air stripper towers configured for operation in both paraUel or series would provide the flexibiUty to treat groundwater flow rates of 50 gpm - 250 gpm. The typical units would measure 2-3 feet in diameter, contain packing heights of 20 - 30 feet and operate at an afr-to-water ratio of 20-30:1. Depending on the groundwater extraction method chosen, towers operating in a series configuration could be used to treat the more contaminant concentrated 50 gpm flow drawn from the source area. If the 250 gpm altemative is chosen the towers could operate in a paraUel configuration and effectively treat the more dUute 250 gpm flow. Two tower avaUabUity provides necessary flexibiUty for treating varying flow rates and contaminant concentrations.

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New Hampshire Department of Environmental Services

OK Tool Source Area/ Savage Well Superfund Site

Table 4-2 Heiuy's Law Coiwtants

Air Stripper Tower Design

Compound Henry's Law Constant f^dimensionless)

Tetrachloroethylene 1.08

TCE 0.41

1,1,1 Trichloroethane 0.89

trans 1,2 dichloroethylene 0.29

1,1 Dichloroethylene 1.41

Toluene 0.27

Benzene 0.23

Methylene Chloride 0.08

Xylenes 0.29

Notes:

I.Henry's Law constants were determined experimentaUy by the EPICS Method at 25oC.

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4.2.2.2 Low Profile Air Sfripper

Low profUe air stripper towers or shaUow tray aerators are used for removal of VOCs from groundwater. The system operates in a manner simUar to air stripper towers, countercurrent groundwater and air flow whereby air is bubbled through the groundwater. Tray aerators are physicaUy much smaUer than air stripper towers but provide more surface area due to the use of multiple intemal trays. A greater air-to-water ratio of approximately 100:1 and air flow of approximately 2000 cfm is required to achieve the removal efficiencies of air stripper towers. An advantage of tray aerators is cleaning of metal oxide deposits is easUy accompUshed.

4.2.2.3 UV/ Chemical Oxidation

UV/chemical oxidation is a technology implemented for the treatment of low level (<5ppm) organic compounds found in groundwater. Chemical oxidation uses an oxidizing agent to convert organic chemicals into carbon dioxide and water. Strong oxidizing agents commonly used to treat groundwater include hydrogen peroxide, chlorine gas, chlorine dioxide, sodium hypochlorite, ozone, ultraviolet Ught, and potassium permanganate.

The process involves mixing the influent water with one or more chemical oxidizers, then frradiating the water with ultraviolet (UV) radiation to induce the breakdown of contaminants. As a result of these reactions the contaminants are reduced to less harmful compounds. An advantage of this process over air stripping is that it does not generate significant air emissions or other residual wastes which would require additional treatment.

Initial estimates indicate that the cost of UV/chemical oxidation treatment is substantiaUy higher than air stripping when off-gas treatment is not required. The energy and chemical costs would be significant. In addition the potential for high VOC concentrations are a concem as this technology is better suited for low VOC concentration streams. Several chemicals of concem at the OK Tool site may not be effectively treated by this method.

4.2.2.4 Fluidized Bed

Fluidized bed technology is used to remove volatUe organics from groundwater in a manner simUar to an air stripper tower and low profUe air stripper technology. A tower, sUghtly smaUer than an air stripper tower and sized for a similar flow rate, is loaded with eUipsoidal­shaped packing material.

Operation consists of fluidizing the packing material, air stream and groundwater by introducing a high volume, low pressure air stream to the bottom of the tower. The lifting effect of the air stream causes the packing material to rotate and rise in the fluidized tower. This results in an increase of the actual surface area of the packing material. Mass transfer of VOCs from the Uquid phase to the vapor phase occurs along the surface of the packing material.

A major advantage of fluidized bed technology is pretreatment for removal of metals is not necessary. The flooded condition of the tower and scouring action of the air stream minimize the propensity of metal oxides to form and accumulate.

Disadvantages include the need of a high air to water ratio to achieve desired VOC removal efficiencies and subsequent increases in utiUty costs and off gas treatment costs (if required).

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4.2.3 Vapor Treatment

Off gas streams produced by the groundwater remediation equipment and soU vapor exfraction equipment wUl require treatment prior to discharge to the atmosphere. The off gas treatment process would handle approximately 1000 - 2000 cfm of air containing PCE, TCE, 1,1,1 TCA and trans-1,2 DCE as weU BTEX compounds.

Based on off gas emissions from an air stripper tower system designed to freat 250 gpm, a vapor flow of 1000 cfm (30 to 1 air/water ratio) would be required and could release up to 40 pounds of VOCs per day. An air stripper tower designed to treat 60 gpm of groundwater with an air flow of 240 cfm (30 to 1 air/water ratio) could release up to 10 lbs. of VOCs per day. Under OSWER Directive Number 9355.0-28, air emissions of less than 15 lbs/day do not require treatment prior to discharge to atmosphere. The off gas stream generated by pumping at a rate of 60 gpm or 75 gpm, and removing VOCs with an air stripper tower may not require treatment prior to discharge. However, implementation of vapor extraction or other enhancements would likely require vapor treatment. Therefore, vapor treatment was retained for these scenarios.

If off gas freatment is required, a minimum of 90 percent removal of total volatUe organics from the off gas stream is a Ukely scenario. Removal of chlorinated solvents and BTEX compounds from air sfreams can be accompUshed with a variety of treatment aitematives. Three such aitematives are discussed in the foUowing section

4.2.3.1 Vapor Phase Carbon

Vapor phase carbon is the most commonly used treatment system for removing VOCs from off gas streams. Carbon adsorption is typically employed when the contaminant concentrations are less than 1000 ppmv. Pore spaces inherent to activated carbon adsorb VOC molecules from the air stream and retain the molecules untU the carbon is incinerated or regenerated. The systems are readUy avaUable in many sizes so custom designing is generaUy not necessary. Vapor phase carbon removes VOCs with varying efficiency depending on several parameters such as boUing point, Henry's Law constant and molecular weight. Removal efficiencies of the contammants present at the OKTSA have been removed in excess of 90% with vapor phase carbon treatment in simUar appUcations. Carbon has a high affinity for water molecules, higher than its affinity for VOC molecules. Reducing the water content of the off gas stream prior to vapor phase carbon treatment greatly enhances the VOC adsorption capacity of the carbon.

Spent carbon may be regenerated either on site or off site for further use. Initial estimates indicate that greater than 500 pounds per day of carbon may be required to effectively treat the off gas stream generated by groundwater containing the maximum groundwater concentrations presented in Table 4-6. Under these conditions, on-site regeneration wiU be further considered. On-site regeneration requires a steam source to strip the VOCs from the vapor phase carbon. The VOC laden steam is condensed and the solvent coUected for disposal. The carbon is dried with warm, dry air before being put back on-line.

Use of vapor phase carbon as a biofUter to treat the off gas stream of the VOC-removing remediation equipment is not a feasible option for this appUcation. Biofiltration involves the introduction of a VOC-containing air stream into a porous medium containing appropriate bacteria. The bacteria, aided by introduction of nutrient supplements, utUize the VOCs in the air stream as a food source and breakdown the compounds into harmless components.

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Degradation of the most common chemicals present at OKTSA, chlorinated solvents occurs most efficiently and quickly via anaerobic pathways. Biofiltration typicaUy utUizes aerobic conditions to degrade contaminants. This option is not appUcable for this site.

4.2.3.2 Resin Adsorption

Resin adsorption is a relatively new altemative for treating VOC-containing off gas streams. The technology employs a synthetic adsorbent material, consisting of pyrolyzed sulfonated styrene-divinylbenzene copolymer, housed in an adsorption bed. Reportedly the synthetic material is 3 to 4 times more hydrophobic than vapor phase carbon, so its adsorptive capacity is not affected by the presence of water vapor in high humidity off gas streams.

VOC removal efficiencies exceeding 90% have been reported by the manufacturer. Spent resins are regenerated on site using a process consisting of a vacuum evacuation to the adsorption bed foUowed by introduction of nitrogen gas into the bed. Electric coUs buUt into the bed are activated and VOCs thermaUy purged from the resin. The VOC vapors are coUected and condensed for disposal. The beds are cooled to ambient temperature prior to going on-line.

4.2.3.3 Thennal Oxidation

Thermal oxidation involves the combustion of VOC vapors in the presence of oxygen. Complete destmction of the VOCs requires high temperatures in the 1400 to 1800 degree F range. Thermal oxidation is capable of VOC destmction at efficiencies ranging from 95% to greater than 99% depending on operating parameters and the chemical composition of the influent stream. AuxUiary fuel, such as natural gas, is suppUed to a thermal oxidizer to supplement the BTU value of the off gas stream and increase the incineration temperature to the oxidation temperature of the VOCs.

FoUowing oxidation of chlorinated solvents in a thermal oxidizer, the exiting off gas stream requires treatment through a scrubber tower to remove hydrochloric gas generated during destruction of the chlorinated solvents.

4.2.3.4 Catalytic Oxidation

Catalytic oxidation is a thermal process used to destroy vapor phase contaminants. A variation of direct incineration, this technique employs a catalyst (typically a precious metal formulation such as paUadium or platinum) to promote rapid oxidation and decrease the temperature required for destruction. Operating temperatures are typicaUy between 600 and 900 degrees F.

VOC-containing air enters the system as natural gas is fired into the front of a catalyst chamber to increase and maintain the optimum temperature required for the catalytic reaction to take place. The exothermic reaction across the catalytic bed oxidizes the VOCs into carbon dioxide, water vapor and inorganic acids. Additional treatment of the off gas from the catalytic oxidizer is required to remove hydrochloric gas generated during destruction of chlorinated solvents.

4.2.4 Expansion Capability

The remediation system must have buUt in flexibiUty to aUow for the addition of enhanced treatment equipment and to handle a groundwater flow rate ranging from 60 to 250 gpm. Equipment to enhance VOC removal from the groundwater and vadose zone may be assessed by CDM in the future. Part of the assessment includes compatibiUty between the enhanced

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treatment equipment and the current treatment train. The unit processes chosen as part of the current treatment train must have the abiUty to accept additional flow and possibly different physical parameters and chemical compositions from future implementation of enhanced extraction processes.

For example, an air stripper tower may be sized to accept a range of flows and VOC concentrations by adjusting the height of the packed tower or the air/water ratio.

4.3 Preliminary Technology Screening

The results of the preliminary technology screening are presented . The discussion to foUow wUl expand on the reasons why certain processes were retained or eliminated from further consideration.

4.3.1 Metals Removal

Precipitation / Sedimentation - One of the more commonly used methods for removing metals from groundwater. The relatively low concentrations of metals and total suspended soUds in the OKTSA groundwater wiU generate minimal quantity of sludge. Precipitation/sedimentation would work effectively, however, metal concentrations are not expected to sustain elevated levels, therefore this technology has been eliminated from further consideration.

Green Sand FUters - This treatment altemative is best used to remove metals from groundwater containing less than 5 mg/l of total metals. Backwash water wiU require disposal. This process wUl require high capital and O&M costs. This technology has been eliminated from further consideration.

Ion Exchange - This treatment process is traditionaUy used by electronic equipment manufacturers to provide deionized makeup water for manufacturing processes. Resins designed for groundwater remediation systems are capable of removing metals to meet discharge criteria. Resin regeneration can be conducted either on-site or off-site. Backwash water requires disposal. This technology is appUcable for removal of metals from flows containing low metal concentrations and has been retained for further consideration.

Sequestering Agents - This treatment process does not reduce metal concentrations in the groundwater stream. It serves to hold the metal in solution and prevent precipitation. The cost of the sequestering agent is expensive. Since metal concentrations may need to be reduced prior to discharge this technology is not appUcable for this site and has been eliminated from further consideration.

No Treatment - Depending upon the effluent discharge requirements imposed on the treatment system and the VOC removal equipment best suited for this appUcation, metals removal may not be necessary. This option is retained for future consideration.

4.3.2 Organic Removal

Air Stripper Tower - This freatment process can effectively remove the VOCs of concem from the groundwater. Air stripper towers are also flexible conceming variations in flow and contaminant concentration. Periodic cleaning of packing material may be necessary if metals pretreatment is not implemented. This treatment process wUl be retained for future consideration.

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Tray Aerator - Their compact size and ease of cleaning make this an attractive altemative to an air stripper tower. Tray aerators offer flexible operation, easy instaUation of additional trays to increase surface area and VOC removal efficiency. One drawback is the high air/water ratio needed to realize desired removal efficiencies. This treatment process wiU be retained for future consideration.

UV/Oxidation - This technology effectively treats low level (<10 ppm) unsaturated compounds with the potential for no air emissions. This technology is energy intensive. The likelihood of achieving complete oxidation of the chemical of concem may be low. Because of the potential of encountering NAPL and high concentrations of VOCs in the groundwater, and the high cost of treatment, this process wUl not be retained for further consideration.

Fluidized Bed - This technology effectively removes VOCs from groundwater and does not require prior metals removal. One drawback is the high air/water ratio needed to realize desired removal efficiencies. Requires large off gas stream treatment equipment. This process wUl be retained for future consideration.

4.3.3 Vapor Treatment

Vapor Phase Carbon - A proven effective off gas treatment process, it is also flexible regarding treatment of off gas streams having changeable flow rates and varying contaminant concentrations. Adsorption capacity is greatly increased by removing water vapor from the off gas stream prior to treatment. Regeneration of carbon can occur either on site or off site. Either method wUl require disposal of solvent removed from the carbon. This treatment process wUl be retained for further consideration.

Resin Adsorption - Synthetic resin adsorption technology does not have a proven track record. The major equipment manufacturer has significantly scaled back operations recently. This altemative has been eliminated from further consideration.

Thermal/Catalytic Oxidation - These treatment aitematives are best used with highly concentrated (>500 ppmv) VOC off gas streams possessing high BTU values. Varying off gas flow rates and contaminant concentrations can decrease effectiveness of catalyst. The lower the concentration of VOCs and subsequent decrease in BTU value, the more makeup gas, such as natural gas, needs to be introduced to supplement the VOC stream. In addition, treatment of off gas from either oxidation system requires expensive HCI scmbbing. This altemative has been eliminated from further consideration.

Technologies that have been retained for further consideration are:

Metals Removal

• Ion exchange

• No metal treatment

VolatUe Organics Removal

• Air Stripper tower • Tray aerator • Fluidized bed

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Off Gas Treatment

• Vapor Phase Carbon

Based on the preliminary screening objectives two conceptual treatment aitematives were developed. These treatment aitematives are presented in Drawings M-1 and M-IA.

Process Flow Schematic #1 (M-1)

Removal of groundwater from the OKTSA site is accompUshed through four groundwater extraction weUs. The groundwater is pumped at a rate of 250 gpm into the treatment buUding to two 7500 gaUon equalization tanks arranged in series. The lead tank serves as a settling tank to remove suspended soUds prior to overflowing its contents to the second 7500 gaUon equalization tank. Use of two tanks at the beginning of the treatment stabilizes the hydrauUc gradient into the system and aids in removal of particulates from the groundwater.

The groundwater is pumped from the equalization tank to the ion exchange system for reducing metal concentrations including iron, manganese and lead. Reduction of iron and manganese reduces the possibiUty of metal hydroxide precipitate fouUng in downstream treatment equipment. Removal of lead may be necessary to meet guidance discharge concentrations. The ion exchange system is Ukely to contain a cationic resin to remove the positively charged metal ions. The ion exchange system is required to undergo occasional backflushing to remove suspended soUds and regeneration of the resin is required on a regular basis. Backwash water is directed to the 7500 equalization tanks. Currently, CDM is assessing the possibiUty of regenerating the ion exchange regeneration water offsite. This option avoids the need for caustic and acid feed systems and a regeneration water coUection tank.

Upon exiting the ion exchange system, the groundwater enters the air stripper tower system. The system consists of two towers, aUgned for operation in either series or paraUel flow, depending on the demands of the site. Series flow may be utilized to treat the more highly-contaminated groundwater likely to be present in the extraction weUs at startup whUe the paraUel aUgnment may be used to treat a greater volume of groundwater if necessary. Treated groundwater is coUected in the air stripper tower sump for disposal or reuse as backwash water to clean the ion exchange system.

Off gas from the air stripper tower travels through ductwork into a conrunon header with the off gas from the soU vapor extraction system. The combined flow passes through an influent heater prior to entering the vapor phase carbon system. CDM is assessing the addition of a chUler coU to further reduce the relative humidity of the combined off gas streams. The vapor phase carbon system wiU be designed for on-site regeneration using steam and condensed air flow. The steam regeneration system wUl provide periodic regeneration of the vapor carbon beds and reduce the possibiUty of dovmtime due to carbon change over requirements. Solvents stripped from the carbon during steam regeneration wiU be condensed and coUected for offsite disposal.

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This treatment scheme does not include metals pretreatment. Two 7500 equalization tanks are used to coUect flow from the groundwater extraction weUs to stabUize flow.

From the second equalization tank, centrifugal pumps deUver the flow to a fray aerator. Two tray aerators are utUized and arranged for operation in either series or paraUel flow. This aUgnment aUows for series treatment of groundwater Ukely to contain higher concentrations of VOCs immediately after startup and provides added capacity to treat greater volumes of groundwater in the paraUel aUgnment. Treated groundwater is coUected in the tray aerator sump prior to discharge.

Off gas from the tray aerator wiU combine in a common header with off gas from the soU vapor extraction system. The combined off gas flow wUl pass through a preheater to reduce the relative humidity of the stream. The need for a chiller coU to further reduce the relative humidity is currently being assessed. The vapor phase carbon system wUl be designed for on-site regeneration using steam and compressed air. Solvent stripped from the carbon during the steam regeneration process wUl be condensed and coUected for offsite disposal.

4.4 Nature of Treatability Test to be Conducted

In order to more thoroughly assess the appUcabUity of ion exchange technology for possible use in the treatment process, a bench scale test has been proposed. Vendors wUl conduct the ion exchange testing. FoUowing is vendor information and descriptions of the goals and nature of the test.

Ion Exchange - Resintech or US FUter wUl conduct bench scale ion exchange tests to assess the metals removal effectiveness of an ion exchange bed. Ion exchange technology wUl be assessed to determine if metal concentrations can be cost effectively removed from the site groundwater to meet the guidance discharge criteria.

The tests wUl provide information to determine the appropriate resin, the capacity of the resin, the usage rate of the resin and composition of backwash water so that operating costs may be estimated. Up to 50 gaUons of groundwater coUected from the site wiU be sent to the vendor selected to conduct the tests.

The test wiU be conducted as foUows: The groundwater sample is passed through several different ion exchange resins to determine if the resin can successfuUy remove the metals, the capacity of the resin, and the concenfration of the metals in the effluent. In addition, backwashing and resin regeneration cycles and metal concentrations may be estimated. The tests are run untU the resins are exhausted and no longer remove the metals. The order of breakthrough of the metals may be identified during the testing. Resin performance is evaluated by the vendor and a recommendation of the best performing resin is provided.

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5.0 ENHANCED DNAPL EXTRACTION/TREATMENT TECHNOLOGIES

Dense non-aqueous phase Uquids (DNAPLs) are water immiscible Uquids that have a density significantly greater than water. In the case of chlorinated solvents, PCE has a specific gravity of 1.62 and TCE has a specific gravity of 1.46. The presence of DNAPL contamination may have significant impact on site investigations and the abUity to restore contaminated portions of the subsurface to required cleanup levels. The CDM team has evaluated several innovative DNAPL extraction/treatment technologies investigated at other sites. Many of these techniques are not yet "tried and true" and require site-specific testing to determine their feasibUity.

Residual DNAPL is defined as immiscible Uquid which is contained within the pore structure of the soU held up by capUlary forces. Residual saturation in the vadose zone is typicaUy present in 10 to 20% of the void space. Residual saturation in the saturated zone generaUy exceed those in the vadose zone due to increased buoyancy and surface tension effects and range from 10 to 50% of the void space.

CDM has reviewed the state of the art techniques for both DNAPL investigations and site remediation. Key to understanding of DNAPL behavior in the subsurface is our effort to potentiaUy enhance removal. Depending on the specific site conditions, any option should consider gravity gradients, capUlary pressure gradients and the hydrauUc gradients which wUl develop a technicaUy sound remedial system to contain or enhance DNAPL removal. The appUcation of innovative technologies to enhance DNAPL removal wUl also be evaluated for the risks they might pose in spreading the problem.

Key to understanding of any enhanced DNAPL extraction/treatment technologies is the limitations inherent with the removal of saturated Uquids from soU. Even under optimum conditions, removal efficiencies may not approach levels indicative of drinking water standards. Innovative technologies can effectively achieve significant removals of up to 95+%. However, beyond these Umits, other technical considerations would need to be considered.

5.1 Technical Impracticability Analysis

The US EPA and the technical community have recently assessed the state of current remediation technologies. Based on evaluation of data coUected at 28 pump and freat sites, it was determined that:

In the majority of cases, the pumping systems were able to achieve containment of the dissolved phase contaminant plume;

The extractions systems were effective in reducing the mass of contamination in the aquifer;

When extraction systems were started up, contaminant concentrations dropped rapidly but then leveled off (taUing effect). The plateau VOC concentration was typicaUy above remediation goals (e.g., MCLs); and

Cleanup times and cost were severely underestimated. TypicaUy, an 80 percent increase was incurred over original estimates and cleanup times were three times longer than originaUy predicted.

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I Several reasons were presented as to why slow decreases in and taiUng of contamination concenfrations were observed over time. These include:

Heterogeneity in the aquifer causing preferential movement of pumped groundwater through areas of high permeabiUty and tailing, the result of slow diffusion of contaminants from the low to the higher permeabiUty areas.

Slow desorption kinetics also responsible for the observed tailing effect.

Zones of immobUe water exist within the soUs grains (e.g., in micropores or fractures). In such cases, contaminant release is controUed by the slow diffusion from the immobUe to the mobUe zone.

Continuous sources of contamination exist that continuaUy release contamination to groundwater, for instance, residual contamination in the vadose zone or DNAPLs.

If DNAPLs are present, long cleanup times are expected due to the slow rate of release into groundwater which results in long periods of relatively constant concentrations at a pumping weU.

Many site-specific factors can inhibit groundwater restoration such as hydrogeology and the presence of DNAPL. EPA has estabUshed guidance for determining whether groundwater restoration is technicaUy impracticable and what altemative measures should be undertaken to protect human health and the environment. The determination of technical impracticabUity (TI) wUl be made by EPA based upon site specific characterization and where appropriate, remedy performance data. A Tl evaluation may be warranted if the engineering feasibUity and reUabiUty of reaching the specific ARARs or media cleanup standards cannot be met. The Tl evaluation should generaUy include:

1. Specific ARARs of media cleanup standards for which Tl determinations are sought (groundwater cleanup to MCLs, altemative contaminant levels should be considered).

2. Spatial area over which the Tl decision wUl apply. The area contained within the cutoff waU and capture zone (area within OUl).

3. Conceptual model of site geology, hydrology, groundwater contamination sources, transport and fate (vertical profUe, soU gas, soU boring and monitoring weUs).

4. An evaluation of the restoration potential of the site,

a. A demonstration that contamination sources have been identified and have been or wUl be removed and contained to the extent practicable (site investigation complete).

b. An analysis of the performance of any ongoing or completed remedial actions (containment and enhancements).

c. Predictive analyses of the timeframes to attain required cleanup levels using avaUable

l> technologies (non-equUibrium transport modeling may be requfred).

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d. A demonstration that no other remedial technology could reUably, logicaUy or feasibly attain the cleanup levels at the site within a reasonable timeframe (A number of enhanced groundwater extraction and remediation techniques have been evaluated for the OK Tool Source Area since the proposal stages of this project and are discussed in this report. However, the compressed project schedule and absence of funding for pUot testing of two promising groundwater extraction techniques; vertical circulation weUs and steam injection has resulted in a design approach focusing primarUy on conventional mass contaminant removal technologies. Although CDM plans to include both conventional and enhanced contaminant mass removal in the conceptual design for the OK Tool source area, evaluation of enhanced contaminant removal techniques have not been required as a part of the TI waiver process at other Superfund sites in New Hampshire and may not be considered a part of the TI waiver process for the OK Tool site.)

5. Estimates of the cost of the existing or proposed remedy options including construction, operation and maintenance costs.

A TI waiver to AppUcable of Relevant and Appropriate Regulations (ARARs) has been granted to the G.E./Moreau CERCLA site in Saratoga County, New York. The modified remedy included a soU-bentonite cutoff waU around and cap over the source of contamination (source control), continued monitoring of downgradient weUs to ensure that the slurry waU was effectively containing the source and that plume migration was halted, treatment of groundwater where it exits to surface water using the air stripping technology, and natural flushing of the dissolved phase plume downgradient of the source. Groundwater pump and treat of the entire downgradient plume was not considered feasible. The Tl waiver was granted because of hydrogeologic and contaminant related factors (including variation in hydrauUc conductivity, sorption capacity of aquifer material, and desorption non-equUibrium) at the site and, based on EPA contaminant transport modeling, an estimated time of cleanup of greater than 200 years, ranging upward to 500 years regardless of the remedial method employed. The remedy would be accompanied by efforts to prevent exposure to contaminated groundwater and evaluate further risk reduction. The model employed by EPA utUized recent advances in non-equUibrium transport modelling to more accurately estimate restoration timeframes. Natural flushing at this site was evaluated for restoration of downgradient groundwaters and proved to be as effective and substantiaUy more cost effective than pulsed pumping of a pump-and-treat system.

Based on the Tl Guidance, sites where groundwaters are deemed impracticable to remediate "should show that contamination sources have been, or wUl be, identified and removed or treated" to the extent practicable. Where it is not practicable to fuUy locate, remove and/or treat the sources, tor instance where DNAPLs are present, "use of migration control or containment measures should be considered."

The TI guidance states that other appUcable technologies should be evaluated to demonstrate that no other technology or cleanup strategy would be capable of achieving groundwater restoration at the site. This evaluation for enhanced DNAPL technologies was developed to include: 1) a review of the technical Uterature to identify candidate technologies; 2) a screening of the candidate technologies based on general site conditions to identify potentiaUy appUcable technologies; and 3) an analysis, using site hydrogeologic and chemical data, of the capabUity of any of the appUcable technologies to achieve the required cleanup standards. The first two steps are being conducted as part of the technology screening and altemative development steps of this document. Completion of the field investigation and the

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implementation of pUot studies may be required to complete Step 3.

Based upon our understanding of the issues, the CDM team wUl evaluate the site information and future remedial investigations and remedial actions in Ught of this poUcy. Our efforts wUl be to provide the most cost effective and reUable remediation program to contain the migration and enhance the removal of contaminants in the source area.

The evaluation of remediation technologies is discussed in the next section to enhance the cleanup of the OKTSA site. The ineffectiveness of groundwater pump and freat and the complexity of site conditions has resulted in the development of innovative techniques to reduce the toxicity, mobiUty and volume of contaminants.

5.2 Enhanced DNAPL Recovery Aitematives

Based upon our experience with innovative technologies and our understanding of the site conditions, the CDM team has evaluated several promising DNAPL extraction/freatment technologies Usted below for the cleanup of the OKTSA site. In addition, we have provided a brief description of each of these technologies and a brief description of our understanding of limitations and/or advantages of these systems.

Technology Class Technology Description

Enhanced Extraction Vertical circulation weUs

Unterdruck-Verdampfer-Brunnen (UVB) Vacuum Vaporizing WeU

Enhanced Source Removal SoU vapor extraction

SVE/Air sparging

Bioremediation

Steam injection/recovery

Surfactant enhanced groundwater flushing

Zero-valent dechlorination using iron fillings

Based upon a review of the technical Uterature and our work at other DNAPL sites, the CDM team has presented these innovative extraction/treatment remediation technologies as potentiaUy appUcable to the OKTSA site. These technologies, either alone or in combination, may improve contaminant removal and reduce future site risks.

5.2.1 Vertical Circulation Wells

The instaUation of vertical circulation weUs (VCW) particularly within the source area under the buUding, were evaluated. These multiple screened weUs aUow for the simultaneous injection to and exfraction from a common vertical borehole. A circulating flow pattern is created within the saturated zone. The development of these types of weUs have been previously evaluated for petroleum production. VCWs have the foUowing distinct advantages over conventional

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weU clusters:

Reduced instaUation costs over systems involving multiple wells;

Effective hydrauUc control over limited volumes of the formation;

AbiUty to capture DNAPLs that might sink when mobilized;

Reduced volume of groundwater produced for treatment; and

Induced vertical flow can cause additional vertical gradients within the zone.

The relative performance of the VCW system over conventional injection/extraction (two weU) systems has been assessed under a variety of flow conditions, i.e. groundwater flushing, air sparging, steam injection and surfactant enhancements. The VCW system achieved higher mass removal rates due primarUy to reduced dUution by uncontaminated groundwater.

5.2.2 Unterdruck-Verdampfer-Brimnen (UVB) Vacuimi Vaporizing WeU

The UVB technology is an in situ groundwater remediation technique designed to remove VOCs from groundwater within each individual weU system. The UVB process consists of a single weU with two hydrauUcaUy separated screened intervals instaUed within a single aquifer. Groundwater is pumped from the lower section of the aquifer through an aeration chamber within the weU casing, and then reinfiltrated into the upper section of the aquifer. SVE is apphed at the upper screen whUe compressed air is deUvered at the lower screen.The groundwater flow forms a recirculation pattern within the saturated zone to continuously flush contaminants to the lower aquifer. The upflow groundwater passes through a stripping reactor consisting of a fluted and channelized column that facUitates the transfer of VOCs to the gas phase by increasing the contact time between the two phases and by minimizing the coalescence of air bubbles. The UVB system combines VCW recirculation and VOC weU treatment of the groundwater within the weU casing.

The combined withdrawal of groundwater from the lower section of the aquifer and the reinjection of groundwater in the upper section of the aquifer may cause a drculation pattern to develop around the weU. The extent of the circulation pattern is determined by the aquifer properties and is known as the radius of the circulation ceU. The radius of circulation ceU is largely controUed by anisofrophy (horizontal versus vertical hydrauUc conductivity). As a general rule, the developer estimates that the system's radius of circulation ceU would be about 2.5 times the distance between the upper and lower screen intervals. The system provides soU flushing within the circulation ceU.

The system has the advantage that contaminated groundwater is not removed from the aquifer minimizing the permit requirements and the above grade treatment systems. The most ideal conditions for it's appUcation include relatively homogeneous sandy aquifers having a thickness greater than 30 feet. High concentrations of VOCs may not meet stringent treatment standards with one pass through the system. Additional recirculation maybe required; however, concem may arise since a portion of the reinfiltrated groundwater may not be captured by the system.

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During the Site demonstration at March Air Force Base in Califomia, the UVB technology was assessed for appUcabiUty of the UVB system at other contaminated sites. In this case, TCE concentrations from the influent weU ranged form 14 pg/L to 220 pg/L. The UVB system reduced TCE in the groundwater discharged from the treatment system to below 5 pg/L .

The radius of drculation ceU of the groundwater treatment system was estimated by both direct and indirect methods. The radius of circulation ceU was directly measured by conducting a dye trace study. Based on the dye trace study, the radius of circulation ceU was measured to be a least 40 feet in the downgradient direction. However, no dye was observed in wells located 40 feet upgradient or cross gradient of the UVB system. The radius or drculation ceU was indirectly evaluated by (1) modeling the groundwater flow, and 2) analyzing aquifer pump test data. Groundwater flow modeUing results conducted by the developer indicate a radius of circulation ceU of 83 feet. Analysis of aquifer pump test data indicates a radius of drculation ceU of about 60 feet for a traditioned pumping well near this UVB system.

Costs are highly site-specific. EPA estimates that one-time capital costs for a single treatment unit are $180,000; variable annual operation and maintenance costs for the first year were estimated to be $72,000, and for subsequent years, $42,000. Based on these estimates, the total cost for operating a single UVB system for one year was calculated to be $260,000.

The key criteria for evaluation of these systems at the OKTSA site include the relative horizontal and vertical hydrauUc conductivity, the groundwater travel time, the radius of the cfrculation ceU, the drculation percentage recovery, the homogenization of the groundwater within the zone of influence and the effectiveness of the in weU treatment system. The thickness of the aquifer and the distance between the upper and lower portions of the weU screen wiU also affect system performance. A high hydrauUc conductivity of the upper portion of the aquifer may extend the groundwater distribution; however, the recapture of the reinjected groundwater may be very low. Physical barriers may improve the vertical drculation pattems.

5.2.3 Soil Vapor Exfraction

SoU vapor extraction in an in situ remedial technique in which the soU gas within the unsaturated zone is pumped out of the soU pores via an appUed vacuum at one or more extraction weUs (or trenches). Pressure gradients are created in the vadose zone to induce convective airflow through the porous media. As the contaminated soU gas is extracted from the ground, clean air from the surface is drawn into the contaminated zone and the volatUe organics are fransferred from the Uquid or soUd matrix into the soU gas stream. Thus, volatUe contaminants that are present in the soU gas are removed with extracted afr. SVE is most effective in removing VOCs such as PCE and TCE.

SoU properties play a significant role on the appUcabiUty of vapor extraction. SoUs with a high clay and/or sUt fraction may restrict the rate of air movement and, therefore, decrease the effectiveness of vapor extraction. SoU gas concentrations near the leachfield and under the buUding indicate significant residual VOCs in the soUs.

A weU-proven technology, with over 100 appUcations throughout the U.S., and several hundred in Europe. The technology is also used to enhance groundwater remediations such as pump-and-treat technologies by attacking the contamination source.

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5.2.4 Air Sparging/ SVE

Air sparging also referred to as "in situ air stripping" or "in situ volatilization" is a freatment technology for removing VOCs from the saturated zone. Contaminant-free air is injected under pressure into the residual contamination area and the contaminated groundwater to volatilize VOCs from the saturated zone and for effective capture with a SVE system. Pure product within the saturated zone provides a significant source for contaminated groundwater. Due to the volatUe nature of these immisdble organics, the introduction of air into the saturated zone preferentiaUy distributes the VOCs into the air stream.

The use of an afr sparging system results in a net positive pressure in the subsurface, which must be compensated for by the SVE system to prevent migration to previously uncontaminated areas. The major mechanism responsible for afr sparging success is contaminant mass transport. The mass transfer mechanism consists of movement of residual contaminants in the subsurface, dissolution of soU contaminants into the groundwater, and volatUization of contaminants. The sparged afr displaces water in the soU pores and increases the turbulence and mixing in the groundwater.

The effectiveness of an afr sparging/SVE system at the OKTSA site wUl be dependent on control of groundwater elevations. An afr sparging/SVE system has the potential to remove significant quantities of DNAPL within a range of costs that are likely to be an order of magnitude less than conventional pump and treat per pound of contaminant removed. The lowering of the water table below the boulder zone by hydrodynamic controls and/or physical barriers wiU greatly increase the vadose zone and the success of technology on DNAPL source areas. The instaUation of vertical drculation weUs wUl also increase the effectiveness of an afr sparging/SVE system. CDM recommends performing pUot tests of this technology to determine it's effectiveness at the OKTSA site.

5.2.5 Bioremediation

The CDM team has been on the leading edge of bioremediation for chlorinated solvent contamination. Our efforts at other DNAPL sites involve the stimulation of biodegradation of PCE and TCE through the injection of methane and more recently phenol. The process of biostimulation with methane injection is also referred to as biosparging or bioventing. VOCs are volatUized from the groundwater into the vadose zone. The addition of gaseous methane and oxygen stimulates the growth of methanotropic microorganisms which are know to degrade PCE and TCE. Biodegradation occurs in both the groundwater and in the unsaturated zone. Extensive testing of this approach has been conducted by CDM at the Savannah River Demonsfration Project near Savannah Georgia.

Biodegradation of PCE can only occur under anaerobic conditions by reductive dechlorination reactions. Methanogenic bacteria facUitate reductive dechlorination of halogenated aUphatics under anaerobic conditions. PCE is sequentiaUy reduced by microbes to TCE, then to either 1,1­DCE, ds- or trans 1,2-DCE. DCE forms are then reduced to vinyl chloride, ethylene (ETH), and ultimately methane under anaerobic conditions. Biotic reductive dechlorination of trichloroethane (TCA), a breakdown product of HCE, results in 1,2-dichloroethane (1,2-DCA), and chloromethane (CA), which is abioticaUy transformed to ethanol (EtOH).

Optimal conditions for anaerobic microbial degradation have been studies in the laboratory. Laboratory results are summarized below:

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Enhanced reductive dechlorination is not sustainable without addition of a primary substrate and an electron donor. Large amounts of primary substrate and electron donor are requfred.

Sulfate reducers and methanogens facUitate reduction reactions under anaerobic conditions and can utilize methanol, glucose, acetate, hydrogen, or formate as an electron donor and/or primary substrate. AuxUiary substrates must be suppUed in high concenfrations, e.g. Acetate concentrations were 100 mg/L in several experiments.

PCE is rapidly fransformed to lesser chlorinated compounds under anaerobic conditions in the laboratory. For ethenes, the rate Umiting step is generaUy conversion of vinyl chloride to ethylene. At high sulfate concentrations, the reduction of PCE essentiaUy stops at DCE. For ethanes, 1,2-DCA is recalcitrant, it does not readUy degrade unless under strict anaerobic conditions.

A mixture of anaerobes (microbes that are present in anaerobic conditions) such as obtained from activated sludge, is preferable to pure cultures.

In general, reduction of higher chlorinated compounds proceed rapidly to lesser chlorinated compounds (tri-, di- and monchloro-) which biodegrade more rapidly under aerobic than anaerobic conditions if at aU. Therefore, sequential treatment under anaerobic then aerobic conditions is requfred.

Methanotrophic bacteria co-metaboUze chlorinated aUphatics (TCE, DCA, DCE) under aerobic conditions when methane is avaUable as the primary substrate. Conversion of methane to methanol is initiated by activation of the methane mono-oxygenase (MMO) enzyme. Once activated, the MMO enzyme also catalyzes formation of alkene epoxides from alkenes. Epoxides undergo abiotic transformations to nonvolatUe compounds which are subsequently transformed by the consortium of heterotrophs to carbon dioxide, water and chloride. The MMO enzyme can also oxidize alkanes to the corresponding alcohol and methyl ketone. Bacteria that utilize aromatics, including phenol, toluene, and cresols, also are capable of degrading chlorinated aUphatics under aerobic conditions. Research indicates that a mono- or di-oxygenase enzyme is activated during oxidation of the aromatic compounds, which is responsible for oxidizing ethenes potentiaUy via formation of epoxide intermediates. Laboratory results are summarized below:

Methane must be present to initiate and sustain degradation of chlorinated aUphatics by methanotrophs.

Vinyl chloride, 1,2-DCE, and 1,1-DCA are readUy degraded by methanotrophs. TCA and TCE are less easUy degraded by methanotrophs than less chlorinated aUphatics.

At low ceU concentrations, a product of TCE oxidation may be toxic to bacteria as evidenced by a decrease in the rate of degradation with time at low ceU density (0.08 g/L). A rate decrease was not observed at high ceU density (0.8 g/L) in the laboratory. Toxidty to the ceUs may be caused by the epoxide, which can alkylate ceUular nucleophUes (i.e. can substitute the epoxide into ceUular compounds, altering thefr composition and function).

A mixed microbial community is requfred for complete degradation of chlorinated alphatics to carbon dioxide.

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I The effectiveness of biostimulation at the OKTSA site may be benefidal, however, the CDM team does not presently consider this technology to be fuUy developed for use at this site. CDM wiU continue to be on the leading edge of new developments in this area and may consider this option in the future.

5.2.6 Steam Injection

Steam injection also referred to as "soU heating" or "steam venting" is an in situ freatment technology for remediation of organics in both the vadose and saturated zones. Steam is injected into the contaminated zone to thermaUy recover organic vapors and Uquids in conjunction with water and vapor extraction. Steam injection is coupled with an SVE system and a water extraction system in order to capture the contaminants that are Uberated from the porous soU. Steam wUl address the removal of residual contamination and trapped smaU contaminant lenses or pockets within the interstitial pore spaces. The short-term appUcation of steam may effectively release residual products from the pores. The recovery system can then effectively remove these contaminants from the subsurface.

The appUcation of steam to the contaminated soU provides several potential mechanisms for removal of contaminants. The heat increases the vapor pressure of the less volatUe compounds and decreases thefr viscosity, thus making them easier to desorb form soU particles. The condensation of steam on soU particles provides energy to release adsorbed contaminant molecules. The addition of water in the form of steam, dUutes the existing contaminated pore water, causing a soU flushing action that carries dissolved contamination to the extraction weUs.

Favorable site characteristics include primarUy VOCs, (PCE and TCE exceUent candidates), maximum soU concentrations of 200 to 1,000 mg/kg (higher concentrations may cause downward migration, a confining layer below the treatment zone, a confining layer above the area of soU, i.e., a temporary concrete or asphalt cap. The technology is most economical and technicaUy effective on a large volume of moderately contaminated soU.

Steam injection can effectively treat in both the vadose (unsaturated) zone and saturated soUs. Greater amounts of energy is requfred to heat saturated soU, and water recovery would be much higher. However, treatment effectiveness is expected to be as good as or better than that for unsaturated soUs.

The technology is capable of treating soUs to a significant depth, up to 100 feet or more. Steam injection is espedaUy practical and cost-effective for deep contamination because the weUs permit deep access to the treatment area at low cost. The technology is not appUcable for treatment in non-permeable or low permeabUity strata such as rock or thick clay layers. Fractured rock formations and geological structures with high permeabUity "tunnels" within them would cause preferential steam flow and would not aUow most areas of soU to be appropriately treated by the technology.

ShaUow contamination, or very narrow depth intervals of contamination, would not be appropriate to treat due to the difficulty of controlling the steam zone to a narrow range and the high costs per cubic yard based on the area of the site. Capital and mobUization costs for the technology are high enough that only large volumes of soil i.e., greater than 5,000 cubic yards, are economical for freatment.

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The use of steam injection results in the migration of vapors in the steam zone and the flow of DNAPL Uquids ahead of the steam condensate front. Steam injection has the potential to enhance DNAPL removal by physical displacement, reduction in DNAPL viscosity, increased evaporation of DNAPL and increased desorption of DNAPL from soU.

The effectiveness of a steam injection/recovery system at the OKTSA site wUl be dependent on control of groundwater elevations. A steam injection/recovery system has the potential to remove significant quantities of DNAPL within a range of costs that are likely to be an order of magnitude less than conventional pump and treat per pound of contaminant removed. The lowering of the water table below the boulder zone by hydrodynamic controls and/or physical barriers wiU greatly increase the vadose zone and the success of technology on DNAPL source areas. The instaUation of vertical drculation weUs wUl also increase the effectiveness of a steam injection/recovery system. CDM recommends performing pUot tests of this technology to determine it's effectiveness at the OKTSA site.

5.2.7 Surfoctant Enhanced Groundwater Flushing

A number of chemical enhancements to pump and treat remediation have been considered including: complexing agents, surfactant enhanced solubilization and mobUization (microemulsification), oxidation-reduction agents, precipitation-dissolution reagents and ionization agents. An EPA-sponsored workshop enumerated the benefits and limitations of each of these remediation technologies and identified surfactant enhanced groundwater flushing as a promising technology. Surfactant enhanced groundwater flushing involves the addition of surfactants prior to reinjection of treated groundwater to flush the contaminants from the subsurface. Surfactants can significantly increase the aqueous solubUity of contaminants and thus decrease the pore volumes necessary to remove the contaminants.

Surfactant enhanced flushing is based upon two major mechanisms: solubilization, partioning of contaminants into the oU-Uke interior of surfactant miceUes, and microemulsification, the formation of middle phase microemulsions with a concomitant ultra-low interfacial tension between surfactant-rich phase and water or oU phases. Two obstacles to the appUcation of this technology has been regulatory concems regarding injection of surfactants and the economics of the process based largely on the abUity to recycle surfactant in the process. Current research has focused on the use of twin-head anionic surfactants that have U.S. Food and Drug Administration (FDA)dfrect food additive status (commonly referred to as edible surfactants).

The effectiveness of a surfactant enhanced flushing system at the OKTSA site wiU be dependent on the nature of the DNAPL zone. A surfactant enhanced flushing system has the potential to remove significant quantities of DNAPL within a range of costs that are likely to be less than conventional pump and treat per pound of contaminant removed. The instaUation of vertical cfrculation weUs wiU also increase the effectiveness of a surfactant enhanced flushing system. The CDM team does not presently consider this technology to be fuUy developed for use at this site. CDM v continue to be on the leading edge of new developments in this area and may consider this option in the future.

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5.2.8 Reductive Dechlorination Using Iron Filings

Reductive dechlorination, considered an innovative technology, utilizes zero-valent fron to enhance abiotic dehalogenation of chlorinated organics. Dechlorination may occur via the foUowing chemical equation where R-Cl is a chlorinated organic compound:

2Fe° + R-Cl + 3H2O -^ 2Fe2 + 3 OH" + H^ + R-H + Cl'

Half Uves for several chlorinated methane, ethanes, and ethenes have been determined experimentaUy in the laboratory where, of the compounds tested, only dichloromethane was not reduced by a measurable amount. The lowest half Uves (highest reduction in chemical concentration) were observed for PCE, within the range of 0.16 to 3.6 hours. Mid-range half Uves included TCE at 8.6 hours under batch test conditions. Reaction rates increase with the amount of fron in the reaction vessel but decrease as pH increases, which results from the release of hydroxyl ions in the reaction. The process produces low percentages of breakdown products that in tum are dechlorinated (including vinyl chloride) and is effective at reducing PCE and aU higher chlorinated compounds quickly and effectively.

The process would be implemented as an aboveground reactor and would need to be coupled with a second process such as aerobic biodegradation or GAC to remove methylene chloride and any residual contaminants. Though this process appears to be promising, it is screened from further consideration because laboratory test have not been completed and substantial laboratory and field-scale treatabUity/pUot testing would be requfred to determine site-specific design parameters such a Ufe of the fron fiUngs, percent reduction of chlorinated organics, requfred reactor dimensions, flow rates, and effectiveness of the process.

The effectiveness of an fron filing waU at the OKTSA site may be beneficial; however, the CDM team does not presently consider this technology to by fuUy developed for use at this site. CDM wUl continue to be on the leading edge of new developments in this area, and may consider this option in the future.

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6.0 OKTSA REMEDLVTION ALTERNATIVES

Based upon our current understanding of the site conditions and our experience with simUar sites, the CDM team evaluated several remedial aitematives likely to be effective for the OKTSA site. The development of the remedial aitematives were based upon a preliminary screening of the individual components, e.g., hydrauUc pumping, containment barrier, and treatment systems. The objective of preliminary screening was to narrow the Ust of potential aitematives that wUl be evaluated in the preliminary cost estimates. Preliminary screening was based upon each system's abUity to meet the minimum specific remedial objectives, implementabihty, and short-term and long-term effectiveness. A brief description of several promising remedial aitematives and thefr advantages and limitations at the OKTSA site foUows.

6.1 SC-1 Pump and Treat with HydrauUc Control at 250 gpm

This altemative proposes to provide hydrauUc containment of the OKTSA site with two groundwater extraction weUs in accordance with the remedy specified in the Record of Decision. The flow capacity of the pump and treat system was estimated to be up to 250 gaUons per minute (gpm) with treatment of the extracted groundwater via metals removal, afr stripping and vapor phase carbon with discharge of the treated groundwater to the Souhegan River.

This altemative can be easUy implemented with existing avaUable equipment and a limited need for additional data. Groundwater management for this altemative may requfre more than 25 years due to the limitations of using pump and treat technology alone to remediate the site.

6.2 SC-2 Pump and Treat with Limited HydrauUc Confrol at 150 gpm

This altemative proposes to provide hydrauUc containment of the OKTSA site with two groundwater extraction weUs in a more confined area of the site. Based upon our evaluation of the hydrauUc model, the pump and treat system was estimated to be up to 150 gaUons per minute (gpm) with treatment of the extracted groundwater via metals removal, afr stripping and vapor phase carbon with discharge of the treated groundwater to the Souhegan River.

This altemative can be easUy implemented with existing equipment avaUable. Additional data wUl be requfred to better define the extraction weU capture zone. Groundwater management for this altemative may requfre more than 25 years due to the limitations of using pump and treat technology alone to remediate the site.

6.3 SC-3 Partial Physical Barrier aroimd Source Area with Bedrock and Plume Confrol at 75 gpm

This altemative proposes to instaU a partiaUy enclosed containment waU along the Souhegan River and west and north of the OKTSA site to hydrauUcaUy reduce river water recharge through the source area. Groundwater extraction weUs near the containment waU wiU be requfred to lower the groundwater elevations within the source area and create a net upward gradient in the bedrock aquifer. The pump and treat system was estimated to be up to 75 gaUons per minute (gpm) with treatment of the extracted groundwater via metals removal, afr stripping and vapor phase carbon with discharge of the treated groundwater to the Souhegan River.

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This altemative wiU be more difficult to implement due to the boulder zone and fractured bedrock conditions of the site. Additional data wiU be requfred to better define bedrock contours and properties, and the interactions between the overburden and bedrock aquifers. Since minimal source removal is planned, groundwater management for this altemative may requfre more than 25 years due to the limitations of pump and treat alone to remediate the site.

6.4 SC-4 Enclosed Physical Barrier around Source Area with Bedrock and Plimie Confrol at 60 gpm

This altemative proposes to instaU a totaUy enclosed containment waU around the OKTSA to hydrauUcaUy isolate the source area from the regional groundwater flow system. Groundwater extraction weUs wUI be requfred both for hydrauUc control inside the containment waU and downgradient of the source area. The pump and treat system was estimated to be up to 60 gaUons per minute (gpm) with treatment of the extracted groundwater via metals removal, afr stripping and vapor phase carbon with discharge of the treated groundwater to the Souhegan River.

This altemative wUl be more difficult to implement due to the boulder zone and fractured bedrock conditions of the site. Additional data wUl be requfred to better define bedrock contours and properties, the interactions between the overburden and bedrock aquifers and the extraction well capture zone. Since minimal source removal is planned, groundwater management within the slurry waU may requfre more than 25 years to remediate the site, however plume management may be complete within 10 years.

6.5 SC-5 Enclosed Physical Barrier with EiUianced DNAPL Removal at 60 to 75 gpm

This altemative proposes to instaU a totaUy enclosed containment waU around the OKTSA to hydrauUcaUy isolate the source area from the regional groundwater flow system. Vertical cfrculation weUs with the capabiUty to conduct afr sparging, steam injection or other enhanced DNAPL removal techniques wiU be instaUed within the containment waU. The flow component from within the containment waU could range from 0 to 25 gpm depending on the enhanced removal technique implemented. An estimate of up to 20 gaUons per minute (gpm) with treatment of the extracted groundwater via metals removal, afr stripping and vapor phase carbon with discharge of the treated groundwater to the Souhegan River was used for cost estimating purposes. Groundwater extraction weUs outside of the containment waU downgradient of the source area wiU also be requfred. The SVE system was estimated to be up to 100 cubic feet per minute (cfm) with treatment of the solvent ladened afr via vapor phase carbon.

This altemative wUl be as difficult to implement as SC-3 & SC-4 due to the boulder zone and fractured bedrock conditions of the site. Additional data and pUot studies wUl be requfred to develop the enhanced DNAPL treatment program, to better define bedrock contours and properties, the interactions between the overburden and bedrock aquifers and the extraction well capture zone. Contaminant source area mass reduction wHl be significant. The cost per pound removed wUl be highly efficient. Groundwater management for this altemative may be completed in less than 25 years. Additional data from pUot testing of enhanced groundwater extraction technologies are needed to confirm these assumptions and cost estimates.

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I 6.6 Aitematives Summary

This section presents a sunrunary of the five remedial aitematives considered in terms of technical work components, implementabUity and costs. This section also presents a surrunary of each altemative in terms of benefits and potential risks. A detaUed analysis of these source confrol options is provided in Table 6-1. The analysis considered protection of human health and the envfronment, compUance with ARARs, long-term effectiveness, reduction of toxidty, mobiUty and volume, short-term effectiveness, implementabUity and cost.

SC-1 consists of:

Two extraction weUs pumping a total of 250 gpm; Groundwater coUection and treatment system; SoU vapor extraction near the leachfield and existing buUding; New pre-engineered buUding; Continued operation indefinitely.

SC-2 consists of:

Two extraction weUs pumping a total of 150 gpm; Groundwater coUection and treatment system; SoU vapor extraction near the leachfield and existing buUding; New pre-engineered buUding; Continued operation indefinitely.

SC-3 consists of: ! •

• Construction of a partial slurry waU along the west and north sides of the existing OK Tool buUding to reduce the recharge of the Souhegan River undemeath the buUding and leachfield (suspected sources); Four extraction weUs pumping a total of 75 gpm; Groundwater coUection and treatment system; SoU vapor extraction near the leachfield and existing buUding; New pre-engineered buUding; Continued operation indefinitely.

SC-4 consists of:

• Construction of a totaUy enclosed slurry waU around the OK Tool buUding and northem yard to hydrauUcaUy isolate the source area from the regional groundwater flow;

• Two extraction wells within the slurry waU, pumping a total of 25 gpm to hydrauUcaUy containing groundwater by inducing an upward hydrauUc gradient;

• Two extraction weUs outside the slurry waU pumping a total of 50 gpm; • Groundwater coUection and treatment system; • SoU vapor extraction near the leachfield and existing buUding; • New pre-engineered buUding; • Continued operation inside waU determined by best methods avaUable. Downgradient

plume cleanup within 10 years.

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1 r ­New H a m p s h i r e Depar tment of Envi ronmenta l Services

O K Tool Source Area/Savage Well Superfund Site

Table 6-1 Source Control Alternat ive Feasibility

ALTERNATIVES OVERALL PROTECTION OF HUMAN COMPLIANCE W/ARARS LONG TERM EFFECTIVENESS REDUCTION OF TOXICITY SHORTTERM IMPLEMENTABILITY COST HEALTH & THE ENVIRONMENT AND PERMANENCE MOBILITY AND VOLUME EFFECTIVENESS

SC-1 Hydraulic Containment @ LOW LOW LOW LOW MEDIUM HIGH HIGH 250 gpm Vll recharge Groundwater flow contained with MCLs not met in source Not effective at limiting High groundwater flows Source contributions This alternative Cost per pound

river conuibution flushing site groundwater contaminant dissolution required at low VOC to down gradient is easily removed will be management >I00 years management > 100 years concentration plume will be reduced implementable very high

Remedial objectives , are not achieved

SC-2 Hydraulic Containment @ LOW LOW LOW LOW MEDIUM HIGH HIGH ISO gpm w/recharge Groundwater extraction focused MCLs not met in source Not effective at limiting Groundwater VOC Source contributions This alternative Cost per pound

on flow under building groundwater contaminant dissolution concentrations more to down gradient is easily removed will be management >I00 years management >I00 years elevated plume will be reduced implementable significant

Remedial objectives are not achieved

SC-3 Partial physical banier w/ MEDIUM LOW MEDIUM MEDIUM MEDIUM MEDIUM LOW hydraulic pumping @ 75 gpm Groundwater extraction focused MCLs not met in source Effective at limiting Partial containment River contributions River barrier is Capital cost for

on upward vertical gradients at groundwater river contribution to with down gradient (o down gradient easily implementable containment with bedrock interface source area plume capture plume will be reduced Standard construction limited O & M cost management >100 years management >100 years Remedial objectives

are not achieved

SC-4 Full physical barrier w/ MEDIUM MEDIUM MEDIUM MEDIUM MEDIUM MEDIUM MEDIUM hydraulic control @ 60 gpm Groundwater extraction focused MCLs not met in source Effective at limiting Source containment w/ Source contributions While this has been Capital cost for

on upward vertical gradients & groundwater but groundwater contact cleanup of down to down gradient successfully containment downgradient plume control downgradient achieved w/DNAPL gradient plume plume will be reduced implemented at other Plume management

NPL sites, construction < 10 years is often complex

SC-5 Full physical Barrier w/ HIGH HIGH HIGH HIGH HIGH MEDIUM MEDIUM enhanced DNAPL removal & Containment with source MCLs not met in source Groundwater contact Source containment w/ Source contributions While this has been Cost per pound hydraulic control @ SO to removal, plume control & groundwater but limited with active DNAPL effective removal of to down gradient successfully removed will be

7Sgpm control of bedrock contamination source & plume reduced removal & plume control DNAPL & plume cleanup plume will be removed implemented at other effective

signiflcantly Hydraulic control NPL sites, site Plume management effective studies required < 10 yean

i

P

^

SC-5 consists of:

• Construction of a totaUy enclosed slurry waU around the OK Tool buUding and northem yard to hydrauUcaUy isolate the source area from the regional groundwater flow;

• From two to twenty vertical cfrculation/enhanced extraction wells within the slurry waU including vertical cfrculation weUs to enhance DNAPL removal, pumping a total of up to 25 gpm;

• Two extraction weUs outside the slurry waU pumping a total of 50 gpm; • Groundwater coUection and treatment system; • SoU vapor extraction near the leachfield and existing buUding; • New pre-engineered buUding;

• Continued operation inside waU determined by best methods available. Downgradient plume cleanup within 10 years.

6.7 Cost Comparison

A surrunary of the estimated cost for each altemative, itemized by remediation/construction requfrements for each altemative, are presented in Table 6-2 and 6-3. Table 6-2 depicts the altemative present worth analysis based on a 5% discount rate. Table 6-3 presents this analysis without discounting the annual O&M cost.

Based upon the 5% discount rate, the capital cost for implementing SC-1 is estunated to be approximately $2,100,000, and the annual O&M cost is estimated to be approximately $225,000. Based upon a present worth cost for 25 years, the total cost is estimated to be approximately $5,270,000. The capital cost for implementing SC-2 is estimated to be approximately $1,900,00, and the annual O&M cost is estimated to be approximately $175,000. Based upon a present worth cost for 25 years, the total cost is estimated to be approximately $4,350,000. The capital cost for implementing SC-3 is estimated to be approximately $3,400,000, and the annual O&M cost is estimated to be approximately $100,000. Based upon a present worth cost for 10 years, the total cost is estimated to be approximately $4,260,000. The capital cost for implementing SC-4 is estimated to be approximately $4,530,000, and the annual O&M cost is estimated to be approximately $90,000 for 10 years. Based upon a present worth cost for 10 years, the total cost is estimated to be approximately $5,230,000. The capital cost for implementing SC-5 is estimated to be $5,930,000, and the annual O&M cost is estimated to be $120,000 for 10 years. Based upon a present worth cost for 5 years, the total cost is estimated to be $6,450,000. It is noted that some of the itemized costs are only appUcable to specific aitematives. These costs should only be used for cost comparison basis between aitematives since a detaUed conceptual plan has not yet been developed.

A sensitivity analysis was performed for both SC-1 and SC-4 to determine when the estimated present worth costs would be comparable. Figures 6-1 and 6-2 show the estimated present worth cost over time for both scenarios, using a 5% discount and no discount, respectively. The appUcation of present worth costs through a 50-year timeframe would indicate that the total present worth cost for SC-4 would be comparable to SC-1 within approximately 45 years. A dfrect cost analysis would bring the two aitematives in Une within about 23 years.

-70­

1 r ­NEW HAMPSHIRE DEPARTMENT OF ENVIRONMENTAL SERVICES

OK TOOL SOURCE AREA/SAVAGE MUNICIPAL WELL SUPERFUND SFTE

TABLE 6-2 PRELIMINARY COST ESTIMATES FOR REMEDLVL ALTERNATFVES

5% DISCOUNT RATE

Description Altemative #1 Altemative #2 Alternative #3 Altemative #4 Altemative #5 Hydraulic containment- Hydraulic containment- Partial physical Full physical barrier Physical barrier with 250 gpm w/ recharge 150 gpm w/ recharge barrier v/I hydraulic v/I hydraulic control enhanced DNAPL removal w/

pumping @ 75 gpm @ 60 gpm hydraulic control @ 50 to 75 gpm

I Well Installation 76,908 76,908 51,272 51,272 51,272 2 Yard Piping 97,500 58,500 19,500 19,500 19,500 3 Pumps 42,900 42,900 39,000 39,000 39,000 4 Blowers 29,250 29,250 29,250 29,250 29,250 5 Tanks 18,200 18,200 18,200 18,200 18,200 6 Metals Removal System 0 0 0 0 0 7 Air Stripper System 91,000 91,000 45,500 45,500 45,500 8 SVE System 78,000 78,000 78,000 78,000 78,000 9 Vapor Phase Carbon 325,000 325,000 260,000 260,000 325,000 10 Physical barrier wall 0 0 936,000 1,482,000 1,482,000 11 Enhanced DNAPL removal 0 0 0 0 600,000 12 Process Piping 21,000 17,000 15,000 15,000 15,000 13 Pre-engineered building 220,000 160,000 120,000 120,000 120,000

Subtotal Estimated Equipment Cost $999,758 $896,758 $1,611,722 $2,157,722 $2,822,722 Site Work* $499,879 $448,379 $805,861 $1,078,861 $1,411,361 Construction Contingencies** $599,855 $538,055 $967,033 $1,294,633 $1,693,633

Total Estimated Construction Cost $2,099,492 $1,883,192 $3,384,616 $4,531,216 $5,927,716 Annual O&M $225,000 $175,000 $100,000 $90,000 $120,000 Present Worth O&M*** $3,170,250 $2,465,750 $772,200 $694,980 $519,540

Total Present Worth Cost (approx) $5,270,000 $4^50,000 $4,260,000 $5,230,000 $6,450,000

Site work includes sitework, concrete, instrumentation, electrical and contingency (50% of estimated construction costs) ** Construction contingencies include Contractor's OH & P, administration and engineering (40% of sum of estimated construction costs and site work) *** Present Worth Cost for 25 year operation for alternatives 1 and 2 (5% discount rate - Annual cost times 14.09)

Present Worth Cost for 10 year operation for alternatives 3 and 4(5% discount rate - Annual Cost times 7.722) Present Worth Cost for 5 year operation for alternative 5(5% discount rate - Annual Cost times 4.3295) _ _ _ _ _ ^

1 r ­NEW HAMPSHIRE DEPARTMENT OF ENVIRONMENTAL SERVICES

OK TOOL SOURCE AREA/SAVAGE MUNICIPAL WELL SUPERFUND SITE

TABLE 6-3 PRELIMINARY COST ESTIMATES FOR REMEDUL ALTERNATIVES

NO DISCOUNT RATE

Description Altemative #1 Altemative #2 Alternative #3 Altemative #4 Altemative #5 Hydraulic containment- Hydraulic containment- Partial physical Full physical barrier Physical barrier with

250 gpm v/I recharge 150 gpm v/I recharge barrier v/I hydraulic v/I hydraulic control enhanced DNAPL removal w/ pumping @ 75 gpm @ 60 gpm hydraulic control @ 50 to 75 gpm

1 Well Installation 76,908 76,908 51,272 51,272 51,272 2 Yard Piping 97,500 58,500 19,500 19,500 19.500 3 Pumps 42,900 42,900 39,000 39,000 39,000 4 Blowers 29,250 29,250 29,250 29,250 29,250 5 Tanks 18,200 18,200 18,200 18,200 18,200 6 Metals Removal System 0 0 0 0 0 7 Air Stripper System 91,000 91,000 45,500 45,500 45,500 8 SVE System 78,000 78,000 78,000 78,000 78,000 9 Vapor Phase Carbon 325,000 325,000 260,000 260,000 325,000 10 Physical barrier wall 0 0 936,000 1,482,000 1,482,000 11 Enhanced DNAPL removal 0 0 0 0 600,000 12 Process Piping 21,000 17,000 15,000 15,000 15,000 13 Pre-engineered building 220,000 160,000 120,000 120,000 120,000

Subtotal Estimated Equipment Cost $999,758 $896,758 $1,611,722 $2,157,722 $2,822,722 Site Work* $499,879 $448,379 $805,861 $1,078,861 $1,411,361 Construction Contingencies** $599,855 $538,055 $967,033 $1,294,633 $1,693,633

Total Estimated Construction Cost $2,099,492 $1,883,192 $3,384,616 $4,531,216 $5,927,716 Annual O&M $225,000 $175,000 $100,000 $90,000 $120,000 Present Worth O&M*** $5,625,000 $4,375,000 $1,000,000 $900,000 $600,000 1

Total Present Worth Cost (approx) $7,725,000 $6,260,000 $4,500,000 $5,430,000 $6,530,000

* Site work includes sitework, concrete, instrumentation, electrical and contingency (50% of estimated construction costs) * * Construction contingencies include Contractor's OH & P, administration and engineering (40% of sum of estimated construction costs and site work) *** Present Worth Cost for 25 year operation for aitematives 1 and 2 (0% discount rate - Annual cost times life of operation (yrs))

Present Worth Cost for 10 year operation for aitematives 3 and 4(0% discount rate - Annual Cost times life of operation (yrs)) Present Worth Cost for 5 year operation for altemative 5 (0% discount rate - Annual Cost times life of operation (yrs))

NUDE? 3 r ­OK Tool Source Area/Savage Well Superfund Site

Figure 6-1 Altemative Cost Comparison at 5% Discount

$7,000,000 -r

$6,000,000 -­

$5,000,000

"§ $4,000,000

3 ^ $3,000,000 --

Allcmalive 1

" • Allemalive 4

$2,000,000

$1,000,000 -­

$0

o tM

O CO

o o in

o

Years of Operation

o o CO

o cn

o o

NHDiS OK Tool Source Area/Savage Well Superfund Site

Figure 6-2 Alternative Cost Comparison at 0% Discount

$14,000,000

$12,000,000

$10,000,000

o

a

3

$8,000,000

$6,000,000

$4,000,000 ­ -

Alternative

Alternative

1

4

$2,000,000 ­ -

$0 + i n in in in in o

CM CM CO CO in

Years of Operation