Decision Criteria Matrix

Overview of the Analysis of Alternatives

The decision criteria matrix is a tool presenting criteria against which plume response alternatives are measured, compared, and evaluated. Basically, the criteria answer the following questions about each alternative:

Does it meet basic requirements? (called "threshold" criteria)
How well will it work? (called "primary balancing" criteria)
Is it acceptable to stakeholders? (called "acceptance" criteria)

The remedial project managers, in cooperation with hydrological, ecological, human health, and other technical specialists, have evaluated how well each CS-10 plume response alternative meets each of the threshold and primary balancing criteria, and have used "Consumer Reports" type symbols to fill in the matrix. Their analysis is contained in the document entitled "CS-10 Plume Response Decision Document" and summarized in this fact sheet.

Does it meet basic requirements? Threshold criteria apply to two basic requirements that an alternative must meet in order to be considered further. The two threshold criteria are: (1) overall protection of human health and the environment; and (2) compliance with Applicable or Relevant and Appropriate Requirements (ARARs), which are the federal and state requirements that apply to MMR.

How well will it work? The primary balancing criteria are used to evaluate alternatives using both qualitative and quantitative information. The primary balancing criteria present the strengths and weaknesses of each alternative for comparison among alternatives.

Is it acceptable? The acceptance criteria portion of the draft matrix has been purposely left blank. Acceptance criteria will be evaluated by acceptance groups, which include the public-at-large, affected neighborhoods, citizen teams, Senior Management Board selectmen, the Massachusetts Department of Public Health, the U.S. Agency for Toxic Substances and Disease Registry, Natural Resource Trustees, EPA, DEP, and Department of Defense.

The acceptance groups will review and discuss the matrix and recommend a preferred alternative, acceptable second and third choices, and any unacceptable alternatives. AFCEE staff will work with the acceptance groups to provide necessary information and receive input.

Once the acceptance criteria part of the matrix is complete and the public comment period has ended, the remedial project managers will recommend a course of action. Ideally, an alternative that is protective of human health and the environment, meets regulatory requirements, and has widespread acceptance, will be identified. In the event that consensus is not reached, the remedial project managers will further investigate stakeholders’ preferences and make every attempt to understand the nature of objections and preferences. They will ensure that all the acceptance groups’ concerns and comments are heard and understood. They will determine whether an alternative can be modified to meet the needs of the acceptance groups or if changes can be incorporated to make an alternative more attractive to the majority of the groups.

After this process, the remedial project managers will make the final decision and respond to written comments in a document called a "responsiveness summary." The scheduled date to announce the decision and release the responsiveness summary for CS-10 is August 22, 1997.

The plume response action taken will address the areas of greatest need. No additional studies are required to be able to take action on all or most of the plume. However, additional studies to further define the plume will be completed and additional action will be taken if necessary.

CS-10 Plume Response Alternative A
CS-10 Plume Response Alternative B
CS-10 Plume Response Alternative C
CS-10 Plume Response Alternative C1
CS-10 Plume Response Alternative D
CS-10 Plume Response Alternative E
CS-10 Plume Response Alternative F
CS-10 Plume Response Alternative G

CS-10 PLUME RESPONSE ALTERNATIVE A

Alternative A would use extraction, treatment, and reinjection (ETR) technology. This alternative is designed for maximum plume capture. Extraction fences (lines of wells) would be located along the leading edge of the plume, including the area adjacent to Ashumet Pond.

The system would operate at a total flow rate of approximately 7.2 million gallons per day (mgd), and would include approximately 35,000 linear feet of piping, and a total of approximately 96 extraction and reinjection wells.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health would be protected because the groundwater plume is captured, further migration of contaminants is prevented, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Portions of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured.

Hydrological thresholds, such as minimizing drawdown in surface water bodies and minimizing the amount of treated water that flushes through the ponds, would be met. However, the extensive construction required for this alternative would affect several sensitive habitats and rare animal species. These impacts would require extensive mitigation.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative complies with all ARARs.

Effectiveness and Permanence of Response Alternatives: The table at right summarizes plume capture by mass for all alternatives, based on the results of modeling. A similar table summarizing plume capture by volume is included in the matrix document.

Under all alternatives, a portion of the plume will be caught in silts underlying the aquifer. It is difficult to remove contaminants from silts because water moves extremely slowly through them. Contaminants are expected to break down significantly through natural processes while trapped or slowed by the silts.

Percent Plume Capture by Mass for All Alternatives

Alt	Capture by ETR	Capture by Recirc	Total Capture by System	Caught in Silts	Total not Captured or Caught in Silts	Total Captured or Caught in Silts
A	88	0	88	11	1	99
B	79	0	79	19	2	98
C	84	2	86	13	2	98
C1	90	2	92	6	2	98
D	0	73	73	19	8	92
E	na	na	na	61	39	61
F	92	1	93	6	1	99
G	na	na	na	61	39	61

Under Alternative A, 99 percent of the contaminants (by mass) is captured by the treatment system or caught in silts. The system effectively removes contaminants, and the configuration would have a minimal effect on other plumes. A very small percentage (1 percent) of the contaminant mass would not be captured or caught in silts; however, human health and ecological risk associated with that portion is very low.

Socioeconomic impacts associated with the uncaptured portion of the plume, such as impacts on commercial or residential interests, recreation, and historical and archeological sites, are expected to be low. Institutional controls will prohibit drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Residences over or directly downgradient of the plume have been or are scheduled to be connected to public water supply. There may not be adequate controls on existing wells.

Effectiveness of Treatment Systems: The treatment system (which involves activated carbon and pretreatment) is capable of removing volatile organic compounds (VOCs) and ethylene dibromide (EDB) to below detection limits. Other contaminants, such as semi-volatiles and inorganics, would also be treated to background levels, if technically and economically feasible, if they appear in the extracted water. Spent carbon produced by the system would be transferred offsite for regeneration, which destroys the contaminants. Residual solid wastes would be transferred offsite and disposed of in an appropriate manner. The residual solid wastes are not expected to be a hazardous waste. Risks to workers associated with handling, treating, and disposing of residuals would be low. The alternative satisfies a statutory preference for treatment as a principal element.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup will not be achievable in less than 12 months from the decision date. It is estimated that the system will operate for at least 50 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Because it is a proven technology, regulatory agency involvement to obtain approval will be minimal.

Access to property to install wells between Sandwich Road and Ashumet Pond could be difficult to obtain, due to the intrusive nature of the construction work required.

Manageable risks to human health are anticipated during construction and operation of the system. Treatment plants would be located on base, thus minimizing potential risks to the off-base neighborhood.

Significant adverse impacts to rare species, to rare species habitat, to a coastal plain pond community, and to a wetlands complex are expected. These impacts would require extensive mitigation and planning to minimize construction damage to habitats and impacts to rare species.

Construction and operation would have significant socioeconomic impacts on the residential neighborhood near Ashumet Pond because of the intrusive nature of the system and the need for long-term maintenance of wells, pumps, and pipelines in the community.

Cost: Total capital cost is estimated to be $41.8 million. Annual operating and maintenance cost is estimated to be $3.6 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $113 million.

Public Acceptance: The public acceptance of all the response alternatives will be determined throughout the public comment period. The respective organizations, agencies, and community groups (acceptance groups) will review the information and indicate a preferred choice, acceptable second and third choices, and any unacceptable alternatives.

CS-10 PLUME RESPONSE ALTERNATIVE B

Alternative B would use ETR technology. This alternative is designed with consideration of property access issues and potential adverse impacts to sensitive ecological areas along the shoreline of Ashumet Pond. Instead of an extraction fence along the pond, this alternative would use an extraction fence along Sandwich Road. Because the fence is upgradient of the leading edge of the plume near Ashumet Pond, a portion of the plume would not be captured.

The system would operate at a total flow rate of approximately 6.9 mgd, and would include approximately 32,000 linear feet of piping, and a total of approximately 94 extraction and reinjection wells.

Matrix Criteria

Overall Protection of Human Health and the Environment:Under this alternative, human health would be protected because a high percentage of the groundwater plume is captured, further migration of contaminants is greatly reduced, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Most of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured. Contaminant concentrations downgradient of the system south of Sandwich Road would decline over time.

Hydrological thresholds, such as minimizing drawdown in surface water bodies and minimizing the amount of treated water that flushes through the ponds, would be met. Construction would affect sensitive habitats and rare upland animal species but impacts can be mitigated by planning and scheduling. Impacts to Ashumet Pond habitats would be avoided by placing the extraction fence along Sandwich Road.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs):This alternative complies with all ARARs.

Effectiveness and Permanence of Response Alternatives: The table on page 3 summarizes plume capture by mass for all alternatives. A similar table summarizing plume capture by volume is included in the matrix document.

Under Alternative B, has the 98 percent of the contaminants (by mass) is captured by the treatment system or caught in silts. The system effectively removes contaminants, and the configuration would have a minimal effect on other plumes. A small percentage of the contaminant mass (2 percent) would not be captured or caught in silts; however, human health and ecological risk associated with that portion is very low.

Effectiveness of Treatment Systems: The treatment system is capable of removing VOCs and EDB to below detection limits. Other contaminants, such as semi-volatiles and inorganics, would also be treated to background levels, if technically and economically feasible, if they appear in the extracted water. Spent carbon produced by the system would be transferred offsite for regeneration, which destroys the contaminants. Residual solid wastes would be transferred offsite and disposed of in an appropriate manner. The residual solid wastes are not expected to be a hazardous waste. Risks to workers associated with handling, treating, and disposing of residuals would be low. The alternative satisfies a statutory preference for treatment as a principal element.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup may be achievable for the Sandwich Road extraction fence in less than 12 months from the decision date, given funding and regulatory approval. It is estimated that the system will operate for at least 50 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Because it is a proven technology, regulatory agency involvement to obtain approval will be minimal.

Access to property to install wells would be simplified because the majority of wells would be installed on MMR property.

Adverse impacts to rare habitats are expected but can be mitigated with a moderate level of scheduling and construction planning. The impacts associated with construction along the Ashumet Pond shoreline and the Northwest Extraction Fence would be eliminated for this alternative.

Construction and operation would cause low socioeconomic impacts on the residential neighborhood near Ashumet Pond because most construction and operation would take place on base.

Cost: Total capital cost is estimated to be $39.8 million. Annual operating and maintenance cost is estimated to be $3.4 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $108 million.

CS-10 PLUME RESPONSE ALTERNATIVE C

Alternative C combines ETR and recirculating well technology. This alternative is designed with consideration of property access issues and potential adverse impacts to sensitive ecological areas along the shoreline of Ashumet Pond. Instead of an extraction fence along the pond, this alternative would use an extraction fence along Sandwich Road and recirculating wells to reduce contaminant mass between Sandwich Road and Ashumet Pond.

The system would operate at a total flow rate of approximately 7.5 mgd, and would include approximately 35,000 linear feet of piping, and a total of approximately 93 extraction and reinjection wells, and 5 recirculating wells.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health would be protected because a high percentage of the groundwater plume is captured, further migration of contaminants is greatly reduced, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Much of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured. Contaminant concentrations downgradient of the system south of Sandwich Road are reduced by recirculating wells.

Hydrological thresholds would not be met, because the amount of treated water that flushes through the ponds is anticipated to be slightly above the threshold. However, the recirculating well pilot study suggests that treated water will not significantly alter ambient water quality. In addition, it is believed that final design could bring Ashumet Pond treated water flows within guidance thresholds. System construction would affect sensitive habitats and rare upland animal species. Impacts to Ashumet Pond habitats would be reduced by using recirculating wells. The remaining impacts would require moderate mitigation.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative complies with all ARARs.

Under Alternative C, 98 percent of the contaminants (by mass) is captured by the treatment system or caught in silts. The system effectively removes contaminants, and the configuration would have a minimal effect on other plumes. A small percentage (2 percent) of the contaminant mass would not be captured or caught in silts; however, human health and ecological risk associated with that portion is very low.

Effectiveness of Treatment Systems: The ETR portion of the treatment system is capable of removing VOCs and EDB to below detection limits. Other contaminants, such as semi-volatiles and inorganics, would also be treated to background levels, if technically and economically feasible, if they appear in the extracted water. The recirculating wells remove only VOCs and will not effectively remove EDB, semi-volatiles, or inorganics without additional above-ground processes, which are not included in this alternative. These contaminants are not anticipated in the vicinity of the recirculating wells. If EDB, semi-volatiles, or inorganics are detected in the plume at levels requiring action, additional treatment systems would be added.

Spent carbon produced by the system would be transferred offsite for regeneration, which destroys the contaminants. Residual solid wastes would be transferred offsite and disposed of in an appropriate manner. The residual solid wastes are not expected to be a hazardous waste. Risks to workers associated with handling, treating, and disposing of residuals would be low. The alternative satisfies a statutory preference for treatment as a principal element.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup may be achievable for the Sandwich Road extraction fence in less than 12 months from the decision date, given funding and regulatory approval. It is estimated that the system will operate for at least 50 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Recirculating well technology is used only for contaminant mass removal south of Sandwich Road. Because ETR is a proven technology, regulatory agency involvement to obtain approval will be minimal.

Most of the ETR wells would be installed on MMR property, greatly simplifying access to these locations. Recirculating wells, however, would be installed on private property between Sandwich Road and Ashumet Pond. Because recirculating wells are somewhat less intrusive than ETR technology, it is anticipated that property access is possible, though perhaps difficult.

Adverse impacts to rare species, to rare species habitats, to a coastal plain pond community, and to a wetlands complex are expected, but can be mitigated with a moderate level of scheduling and construction planning. The impacts associated with construction along the Ashumet Pond shoreline would be less for recirculating well technology than for ETR.

Construction and operation would cause moderate socioeconomic impacts on the residential neighborhood near Ashumet Pond because of the recirculating wells in the neighborhood.

Cost: Total capital cost is estimated to be $44.3 million. Annual operating and maintenance cost is estimated to be $3.8 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $119 million.

CS-10 PLUME RESPONSE ALTERNATIVE C1

This new alternative is described in the accompanying fact sheet, "Introduction to Additional CS-10 Plume Response Alternatives."

Alternative C1 is identical to Alternative C except that the Northwest Extraction Fence is extended eastward into the plume. The extended fence results in increased capture of a portion of the plume north of the fence that is relatively highly contaminated, and prevents contaminants from migrating to the silts in that area. Once in the low conductivity silts, contamination is significantly more difficult to remove.

The system would operate at a total flow rate of approximately 8.5 mgd, and would include approximately 37,000 linear feet of piping, and a total of approximately 101 extraction and reinjection wells, and 5 recirculating wells.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health would be protected because a high percentage of the groundwater plume is captured, further migration of contaminants is greatly reduced, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Portions of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured. Contaminant concentrations downgradient of the system south of Sandwich Road are reduced by recirculating wells.

Hydrological thresholds would not be met, because the amount of treated water that flushes through the ponds is anticipated to be slightly above the threshold. However, the recirculating well pilot study suggests that treated water will not significantly alter ambient water quality. In addition, it is believed that final design could bring Ashumet Pond treated water flows within guidance thresholds. Extensive construction would affect sensitive habitats and rare upland animal species. Impacts to Ashumet Pond habitats would be reduced by using recirculating wells. The remaining impacts would require moderate mitigation.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative complies with all ARARs.

Under Alternative C1, 98 percent of the contaminants (by mass) is captured by the treatment system or caught in silts. The system effectively removes contaminants, and the configuration would have a minimal effect on other plumes. A small percentage (2 percent) of the contaminant mass would not be captured or caught in silts; however, human health and ecological risk associated with that portion is very low.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup may be achievable for the Sandwich Road extraction fence in less than 12 months from the decision date, given funding and regulatory approval. It is estimated that the system will operate for at least 50 years. ETR technology is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Recirculating well technology is used only for contaminant mass removal south of Sandwich Road. Because ETR is a proven technology, regulatory agency involvement to obtain approval will be minimal.

Construction and operation would cause moderate socioeconomic impacts on the residential neighborhood near Ashumet Pond because of the recirculating wells in the neighborhood.

Cost: Total annual capital cost is estimated to be $45.8 million. Annual operating and maintenance cost is estimated to be $3.8 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $122 million.

CS-10 PLUME RESPONSE ALTERNATIVE D

Alternative D uses recirculating well technology. It is designed with some consideration of property ownership, property access, and ecological impacts. Recirculating well fences would be located along the leading edge of the plume, except for the area adjacent to Ashumet Pond. Some recirculating wells would be placed near the shore of the pond and a fence of recirculating wells would be placed along Sandwich Road.

The system would include approximately 102 recirculating wells.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health would be protected because a high percentage of the groundwater plume is captured, further migration of contaminants is greatly reduced, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Most of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured. Although groundwater intercepted by recirculating wells would be substantially treated, it may not be cleaned to background concentrations or drinking water standards due to limitations in the treatment technology.

Hydrological thresholds would not be met, because the amount of treated water that flushes through the ponds is anticipated to be slightly above the threshold. However, the recirculating well pilot study suggests that treated water will not significantly alter ambient water quality. Although this alternative requires less construction than others, construction would still affect sensitive habitats and rare upland animal species. Construction of recirculating wells close to the shore of Ashumet Pond may affect sensitive habitats. Moderate mitigation would be required.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative complies with all ARARs.

Under Alternative D, 92 percent of the contaminants (by mass) is captured by the treatment system or caught in silts. The system removes contaminants somewhat effectively, and the configuration would have a minimal effect on other plumes. A slightly larger percentage (8 percent) of the contaminant mass would not be captured by the recirculating wells or caught in silts; however, human health and ecological risk associated with that portion is very low.

Effectiveness of Treatment Systems: The treatment system is designed to remove VOCs through in-well air stripping followed by vapor-phase granular activated carbon. While significant mass removal will be accomplished, concentrations may not be reduced to background levels and some residual contamination may be left. Semi-volatiles and inorganics, which have not been detected at levels requiring action, would not be removed without the addition of external treatment processes, which are not included under this alternative. EDB, which has been detected sporadically at low levels, will not be removed from groundwater without special liquid-phase carbon treatment systems, which are not included in this alternative. If EDB, semi-volatiles, or inorganics are detected in the plume at levels requiring action, additional treatment systems would be added, although they are not incorporated into this alternative.

Spent carbon produced by the system would be transferred offsite for regeneration, which destroys the contaminants. There will not be any residual solid wastes. Risks to workers associated with handling, treating, and disposing of residuals would be low. The alternative satisfies a statutory preference for treatment as a principal element.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup may be achievable in less than 12 months because recirculating well systems are designed and installed as individual or small groups of mini-treatment systems. It is estimated that the system will operate for at least 50 years. This alternative relies on recirculating well technology, which is a developing but accepted technology. Although recirculating well pilot tests are being conducted with the support and approval of regulatory and oversight agencies, full-scale application will require additional regulatory and agency involvement.

Most of the recirculating wells would be installed on MMR property, greatly simplifying access to these locations. Some wells, however, would be installed on private property between Sandwich Road and Ashumet Pond. Because recirculating wells are somewhat less intrusive than ETR technology, it is anticipated that property access is possible, though perhaps difficult.

Manageable risks to human health are anticipated during construction and operation of the system. Recirculating wells would present low risk to the off-base neighborhood.

Construction and operation would cause moderate socioeconomic impacts on the residential neighborhood near Ashumet Pond.

Cost: Total capital cost is estimated to be $41.5 million. Annual operating and maintenance cost is estimated to be $3.4 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $109 million.

CS-10 PLUME RESPONSE ALTERNATIVE E

Alternative E relies on natural attenuation. Natural subsurface processes that contribute to natural attenuation include dilution, volatilization, biodegradation (e.g., anaerobic dechlorination), adsorption, and chemical reactions (e.g., hydrolysis). These processes may reduce contamination to acceptable levels over time. Natural attenuation is not a technology, but rather a strategy that uses natural processes to reduce contaminant concentration, often in conjunction with other source control measures. Monitoring and institutional controls are used to manage a known condition of contamination.

This alternative includes no active plume capture components.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health is protected by including institutional controls that will minimize exposure to contaminants. Institutional controls will include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. This alternative does not, however, address the migration of contaminants within the aquifer or from groundwater to surface water. Therefore, potential risk is not eliminated.

Hydrological and ecological thresholds are met because there is no construction. Likewise, the impact on species and habitats is minimal.

This alternative fails the threshold criteria. However, it has been carried through the evaluation process in order to allow comparison with other alternatives. This alternative could be combined with other alternative to address areas of low-level contamination.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative does not comply with the Interim Record of Decision (IROD) which requires containment of the CS-10 plume.

Under Alternative E, has no contaminants are captured by active systems. Approximately 61 percent of the total contaminant mass would be caught in silts and the remainder would continue to migrate downgradient in the coarser, more permeable sands. This alternative does not effectively remove contaminants. It does not affect other plumes. A relatively large percentage (39 percent) of the contaminant mass would continue to migrate downgradient of the current footprint. However, human health and ecological risk factors associated with that portion are low.

Socioeconomic impacts associated with the uncaptured portion of the plume, such as impacts on commercial or residential interests, recreation, and historical and archeological sites, are expected to be moderate because of the relatively large uncaptured portion of the plume. Institutional controls will prohibit drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Residences over or directly downgradient of the plume have been or are scheduled to be connected to public water supply. There may not be adequate controls on existing wells.

Effectiveness of Treatment Systems: Natural attenuation will not effectively remove VOCs, EDB, semi-volatiles, or inorganics; however the primary contaminants will degrade with time. Because this alternative includes no active treatment, there will be no treatment residuals. This alternative does not satisfy a statutory preference for treatment as a principal element.

Implementability: Because this alternative involves no active treatment, there is no system startup time or anticipated period of operation. Monitoring activities would be performed for more than 50 years.

Minimal property access would be required for sampling existing monitoring wells and installing new monitoring wells.

Manageable risks to human health are anticipated during construction and sampling of monitoring wells.

Environmental impacts associated with installing and sampling monitoring wells is expected to be low because of flexibility in the location of wells.

Socioeconomic impacts would be low and associated only with installation of monitoring wells and periodic sampling.

Cost: Total capital cost is estimated to be $1.0 million. Annual monitoring and reporting cost is estimated to be $0.3 million. Life-cycle cost, including capital cost, based on 20 years of monitoring (for cost-estimating purposes only) is estimated to be $8 million.

CS-10 PLUME RESPONSE ALTERNATIVE F

This new alternative is described in the accompanying fact sheet, "Introduction to Additional CS-10 Plume Response Alternatives."

Alternative F is identical to Alternative C except that the Northwest Extraction Fence is extended eastward into the plume and several extraction wells are added north of Sandwich Road. The extended Northwest Extraction Fence results in increased capture of a portion of the plume north of the fence that is relatively highly contaminated, and prevents contaminants from migrating to the silts in the area. Once in the low conductivity silts, contamination is significantly more difficult to remove. The extraction wells north of Sandwich Road provide for expedited capture of a portion of the plume that is relatively highly contaminated in that area.

The system would operate at a total flow rate of approximately 9.1 mgd, and would include approximately 38,000 linear feet of piping, and a total of approximately 104 extraction and reinjection wells, and 5 recirculating wells.

Matrix Criteria

Overall Protection of Human Health and the Environment: Under this alternative, human health would be protected because a high percentage of the groundwater plume is captured, further migration of contaminants is greatly reduced, and institutional controls will minimize future exposure to contaminants. Institutional controls include prohibiting drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Most of the plume that might otherwise migrate under or into Ashumet and Johns Ponds would be captured. Contaminant concentrations downgradient of the system south of Sandwich Road are reduced by recirculating wells.

Hydrological thresholds, such as minimizing drawdown in surface water bodies and minimizing the amount of treated water that flushes through the ponds, have not been met. This would require design improvements to redistribute reinjected water along the proposed reinjection fences. Extensive construction would affect sensitive habitats and rare upland animal species. Impacts to Ashumet Pond habitats would be reduced by using recirculating wells. The remaining impacts would require moderate mitigation.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative complies with all ARARs.

Under Alternative F, 99 percent of the contaminants (by mass) captured by the treatment system or caught in silts. The system effectively removes contaminants, and the configuration would have a minimal effect on other plumes. A small percentage (1 percent) of the contaminant mass would not be captured or caught in silts; however, human health and ecological risk associated with that portion is very low.

Implementability: Full system startup would begin by the EPA-enforceable milestone of June 28, 1999. Partial system startup may be achievable for the Sandwich Road extraction fence in less than 12 months from the decision date, given funding and regulatory approval. It is estimated that the system will operate for at least 50 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Recirculating well technology is used only for contaminant mass removal south of Sandwich Road. Because ETR is a proven technology, regulatory agency involvement to obtain approval will be minimal.

Adverse impacts to rare species, to rare species habitats, to a coastal plain pond community, and to a wetlands complex are expected, but can be mitigated with a moderate level of scheduling and construction planning. However, the impacts associated with construction along the Ashumet Pond shoreline would be less for recirculating well technology than for ETR.

Construction and operation would cause moderate socioeconomic impacts on the residential neighborhood near Ashumet Pond.

Cost: Total capital cost is estimated to be $47.0 million. Annual operating and maintenance cost is estimated to be $4.0 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $127 million.

CS-10 PLUME RESPONSE ALTERNATIVE G

Alternative G is the No-Action Alternative. It involves leaving the site in its present condition without any remediation system. No further activities would be conducted to comply with the EPA or MassDEP groundwater standards at the site. No institutional controls would be instituted to prevent exposure to contaminants.

Some groundwater monitoring would be performed in order to complete a five-year review. This review, required by federal regulation, would be conducted to determine if there are any impacts to public health or the environment five years after implementation of the alternative.

The no-action alternative is developed for each Superfund site to assess impacts on human health and the environment if no measures are taken to address current conditions. It also serves as a benchmark for comparison to other cleanup alternatives being considered. The no-action alternative is selected only at sites that pose little or no risk to human health and the environment. For CS-10, the no-action alternative would not provide adequate protection of human health and the environment. Therefore, it is included for comparison purposes only.

Matrix Criteria

Overall Protection of Human Health and the Environment: This alternative contains no provision for eliminating or reducing exposure pathways.

Hydrological and ecological thresholds are met because there is no construction. Likewise, there is no impact on species or habitats.

This alternative fails the threshold criteria. However, it has been carried through the evaluation process in order to allow comparison with other alternatives.

Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): This alternative does not comply with the IROD which requires containment of the CS-10 plume.

Under Alternative G, no contaminants are captured by active systems. Approximately 61 percent of the total contaminant mass would be caught in silts and the remainder would continue to migrate downgradient in the coarser, more permeable sands. This alternative does not remove contaminants. It does not affect other plumes. A relatively large percentage (39 percent) of the plume contaminants would continue to migrate downgradient of the current footprint; however, human health and ecological risk factors associated with that portion are low.

Socioeconomic impacts associated with the uncaptured portion of the plume, such as impacts on commercial or residential interests, recreation, and historical and archeological sites, are expected to be high. Institutional controls will prohibit drilling of new wells within, or in the direct path of, the CS-10 groundwater plume. Residences over or directly downgradient of the plume have been or are scheduled to be connected to public water supply. There may not be adequate controls on existing wells.

Effectiveness of Treatment Systems: The no- action alternative will not remove VOCs, EDB, semi-volatiles, or inorganics. Because this alternative includes no active treatment, there will be no treatment residuals. This alternative does not satisfy a statutory preference for treatment as a principal element.

Implementability: Because this alternative involves no action, there is no system startup time or anticipated period of operation. Monitoring activities would be performed in order to conduct five-year reviews.

No property access would be required. Because there would be no construction, there would be no risk to human health or the environment, nor any socioeconomic impacts, as a result of construction and operation.

Cost: Total capital cost is estimated to be $0. Annual monitoring cost is estimated to be $0.1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be $2 million.