| Under Alternative A, 68 percent of
the contaminants (by mass) would be captured by the treatment system. The system
effectively removes contaminants from the groundwater, and the layout of wells would have
a minimal effect on other plumes. Thirty-two percent of the contaminant mass would not be
captured. The uncaptured portion of the plume is expected to discharge to Johns Pond,
Ashumet Pond, and the Quashnet River, or continue to migrate through the aquifer
downgradient of Johns Pond. However, there is no indication that surface water bodies will
be adversely affected. The plume has been adjacent to or under the ponds for many years,
and no SD-5-related contaminants have yet been detected in the ponds. Studies are
currently ongoing between Ashumet and Johns Pond and on the east side of Johns Pond to
determine the potential impacts, if any, of contaminants moving beyond the ponds. Human
health and ecological risk associated with the uncaptured portion of the plume is very
low. Socioeconomic impacts associated with the uncaptured portion of the plume (e.g., impacts on commercial or residential interests, recreation, and historical and archeological sites, resulting from not capturing all of the plume) are expected to be moderate because part of the plume will continue to migrate into or under Johns Pond, Ashumet Pond, and the Quashnet River. Although no adverse impacts to human health or the environment are anticipated, the perception of downgradient residents and users of surface water bodies are expected to cause a moderate socioeconomic impact. Institutional controls will prohibit drilling of new wells within, or in the direct path of, the SD-5 South groundwater plume. All residences within the SD-5 South footprint have been connected to public water; and the Mashpee Board of Public Health has imposed a moratorium on new drinking water wells within areas of known contamination. Wells used for purposes other than drinking water may not be controlled adequately; however, private wells are commonly shallower than the contaminated groundwater. Numerous residences downgradient of the plume (i.e., located in the area toward which groundwater is flowing) are using private wells. It is Air Force policy at the MMR to connect all users of private wells to public water supply in areas where groundwater is known to be contaminated or threatened. Effectiveness of Treatment Systems: The ETR treatment systems (which include pre-treatment and carbon filtration) are capable of removing volatile organic compounds (VOCs) to below detection limits (the lowest levels at which laboratories can accurately detect contaminants). Once the ETR system is started up, the treatment efficiency (the percentage of contaminant mass that is removed by the system before water is reinjected) is 100 percent. The recirculating wells will remove significant contaminant mass, although VOCs may not be removed to below detection limits. The treatment efficiency of recirculating wells is assumed to be 90 percent. The SD-5 South plume does not contain inorganic compounds at levels exceeding drinking water standards. However, the ETR systems will be designed to capture and treat naturally occurring iron and manganese to below secondary drinking water standards. If other inorganics are present above drinking-water standards and are part of the plume, they would be treated to background levels, if technically and economically feasible. Ethylene dibromide (EDB) has been detected sporadically at low levels within the plume, and is not expected to be present in extraction wells at concentrations requiring action. If EDB is detected, the ETR system is capable of removing it to below detection limits. Recirculating well technology will not effectively remove EDB without additional out-of-well treatment processes, which are not included in this alternative. If EDB is detected in the plume at levels requiring action, additional treatment system components would be added. Implementability: Full system startup would begin by the EPA-enforceable milestone of June 22, 1999. Depending on the nature of the recirculating well treatment system, it is possible that one or more of the recirculating wells could be started up 12 to 24 months after the decision date. It is estimated that the system would operate for more than 20 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. Recirculating well technology, which is a developing but accepted technology, would be used only for a small area for additional plume capture. It is not expected that this alternative will require extensive regulatory or agency involvement to obtain approval. Because all systems, with the exception of the treatment plant, would be constructed off MMR property, property access is anticipated to be potentially difficult. To overcome access difficulties, the locations of treatment system components may require adjustment during detailed design. Access for Extraction/Reinjection Fence 1 and Extraction Fence 2 may be possible along Hooppole and Highland Roads, assuming construction is limited to the road easements. If construction activities require additional space beyond road easements, access may be difficult. Access for the pipeline to and from the ETR treatment facility (which would probably be located on MMR property adjacent to the SD-5 North system) should be possible along road easements (Hooppole and Back Roads). For the three recirculating wells along the Johns Pond shoreline, access may be possible at the public boat ramp property and Briarwood Homeowners Association beach property. However, access for a middle recirculating well may be difficult because there is not any vacant land available on which to install the well. There may not be enough area near the Johns Pond shoreline to install below-ground vaults for recirculating wells. However, the Briarwood subdivision’s covenants and restrictions prohibit the construction of outbuildings, thereby requiring a waiver before placing the treatment units above-ground. The wells could be connected by a buried pipeline to a common treatment unit nearby. This unit could be placed above ground or in an underground vault, and would be located in a less populated area acceptable to the local residents. This approach would involve trenching along local roadways for the pipeline to and from the treatment unit. Obtaining access for a separate treatment system may be difficult. Minimal risks to human and ecological health are anticipated during construction and operation of the system. Risks to residents during construction would be minimized by implementing construction safety programs. Risks to residents during and long-term operation would be minimized by placing most of the equipment underground. Environmental impacts associated with construction are anticipated to be moderate. Construction of recirculating wells along the shoreline of Johns Pond may reduce wildlife habitat and negatively affect the shore environment. Clearing of vegetation, alteration of topography, destabilization of adjacent soil and sand, and heavy vehicle and foot traffic associated with construction would alter the vegetative community, resulting in increased runoff and sedimentation of the pond and the potential invasion of non-native plant species. The developed nature of the area reduces the likelihood that impacts would be significant. Environmental impacts associated with construction of Extraction Fences 1 and 2, and Reinjection Well Fence 1 will be minimal due to the developed nature of the area and the potential for construction along existing roads. Impacts would likely include alteration of neighborhood woodlots that provide habitat for common species of wildlife; however, these alterations are not expected to significantly affect wildlife populations. Long-term system operation is not anticipated to cause environmental impacts. Socioeconomic impacts associated with construction are expected to be high. This alternative involves extensive trenching and drilling along roadways for several months. Residents along Hooppole and Back Roads and Highland Avenue, in particular, would be disrupted by construction activities. Trenching would also be required for the pipeline between the wells and the treatment plant. The pipeline would probably be placed along Hooppole and Back Roads, affecting additional residents of those roads. Socioeconomic impacts of construction include noise, dust, temporarily closed streets, reduced use of property, and potential physical safety hazards. Operation of the treatment system would include periodic maintenance of wells, pumps, and pipelines; sampling of monitoring wells; and continuous operation of a treatment plant near the existing SD-5 North plant. For the recirculating wells, operation of a small central treatment unit within the Briarwood neighborhood would also be required. These activities would affect residents moderately for many years. Cost: Total capital cost is estimated to be approximately $16 million. Annual operating and maintenance cost is estimated to be approximately $2 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $44 million. After approximately 2 years, the recirculating wells along the Johns Pond shoreline would be shut off. Life-cycle costs reflect reduced annual operating costs for years 3 through 20. 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 and any acceptable or unacceptable alternatives. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE B Alternative B would use ETR technology. This alternative has extraction wells northwest of Johns Pond along Hooppole Road. Treated groundwater would be reinjected along Hooppole Road using either the same well casing used for extraction, but at a different depth, or in a close-coupled reinjection well (the reinjection well would be within approximately 10 feet of the extraction well). The system would operate at a total flow rate of approximately 0.6 mgd, and would include approximately 8,800 linear feet of piping, and a total of approximately 10 extraction and reinjection wells. Matrix Criteria Overall Protection of Human Health and the Environment: Same as Alternative A. Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): Same as Alternative A. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative B, 65 percent of the contaminants (by mass) would be captured by the treatment system. The system effectively removes contaminants from the groundwater, and the layout of wells would have a minimal effect on other plumes. Thirty-five percent of the contaminant mass would not be captured. Effects of uncaptured portion of the plumež same as Alternative A. Socioeconomic impacts associated with the uncaptured portion of the plumež same as Alternative A. Institutional controls and drinking waterž same as Alternative A. Effectiveness of Treatment Systems: The ETR treatment systems (which include pre-treatment and carbon filtration) are capable of removing VOCs to below detection limits. Once the ETR system is started up, the treatment efficiency (the percentage of contaminant mass that is removed by the system before water is reinjected) is 100 percent. The SD-5 South plume does not contain inorganic compounds at levels exceeding drinking water standards. However, the ETR systems will be designed to capture and treat naturally occurring iron and manganese to below secondary drinking water standards. If other inorganics are present above drinking-water standards and are part of the plume, they would be treated to background levels, if technically and economically feasible. EDB has been detected sporadically at low levels within the plume, and is not expected to be present in extraction wells at concentrations requiring action. If EDB is detected, the ETR system is capable of removing it to below detection limits. Implementability: Full system startup would begin by the EPA-enforceable milestone of June 22, 1999. Partial system startup is not anticipated prior to full system startup. It is estimated that the system would operate for more than 20 years. ETR is an accepted, proven technology that can be expected to perform reliably with proper maintenance. It is not expected that this alternative will require extensive regulatory or agency involvement to obtain approval. Because all systems, with the exception of the treatment plant, would be constructed off MMR property, property access is anticipated to be potentially difficult. To overcome access difficulties, the locations of treatment system components may require adjustment during detailed design. Access for Extraction/Reinjection Fence 1 may be possible along Hooppole Road, assuming construction is limited to the road easement. If construction activities require additional space beyond the road easement, access may be difficult. Access for the pipeline to and from the ETR treatment facility (which would probably be located on MMR property adjacent to the SD-5 North system) should be possible along road easements (Hooppole and Back Roads). Risks to human and ecological health during construction and operationž same as Alternative A. Environmental impacts associated with construction are anticipated to be low. Potential impacts associated with construction will be minimal due to the developed nature of the area and the potential for construction along existing roads. Impacts would likely include alteration of neighborhood woodlots that provide habitat for common species of wildlife; however, these alterations are not expected to significantly affect wildlife populations. Long-term system operation is not anticipated to cause environmental impacts. Socioeconomic impacts associated with construction are expected to be moderate. This alternative involves extensive trenching and drilling along roadways for several months. Residents along Hooppole and Back Roads, in particular, would be disrupted by construction activities. Trenching would also be required for the pipeline between the wells and the treatment plant. The pipeline would probably be placed along Hooppole and Back Roads, affecting additional residents of those roads. Socioeconomic impacts of construction include noise, dust, temporarily closed streets, reduced use of property, and potential physical safety hazards. Impacts are considered to be somewhat less than for other active alternatives because construction activities are limited to one area and confined to the roadway. This alternative involves fewer wells, shorter piping runs, fewer streets disrupted by construction activities, and a shorter duration for construction. Operation of the treatment system would include periodic maintenance of wells, pumps, and pipelines; sampling of monitoring wells; and continuous operation of a treatment plant near the existing SD-5 North plant. These activities would affect residents moderately for many years. Cost: Total capital cost is estimated to be approximately $12 million. Annual operating and maintenance cost is estimated to be approximately $1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $35 million. Public Acceptance: See Alternative A. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE C Alternative C would use recirculating well technology. This alternative uses a line of recirculating wells along Hooppole Road, on the northwest side of Johns Pond. Recirculating wells could be constructed with treatment systems housed either above-ground in a small shed or in an underground vault. The system would include approximately 5 recirculating wells. Matrix Criteria Overall Protection of Human Health and the Environment: Same as Alternative A. Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): Same as Alternative A. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative C, 58 percent of the contaminants (by mass) would be captured by the treatment system. The system effectively removes contaminants from the groundwater, and the layout of wells would have a minimal effect on other plumes. Forty-two percent of the contaminant mass would not be removed or treated. Effects of uncaptured portion of the plumež same as Alternative A. Socioeconomic impacts associated with the uncaptured portion of the plumež same as Alternative A. Institutional controls and drinking waterž same as Alternative A. Effectiveness of Treatment Systems: The recirculating well 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 non-detectable levels. The treatment efficiency of recirculating wells is assumed to be 90 percent. The SD-5 South plume does not contain inorganic compounds at levels exceeding drinking water standards. If inorganic removal is required, external treatment processes would need to be added. External treatment is not included in this alternative. EDB has been detected sporadically at low levels within the plume, and is not expected to be present in recirculating wells at concentrations requiring action. Recirculating well technology will not effectively remove EDB without additional out-of-well treatment processes, which are not included in this alternative. If EDB is detected in the plume at levels requiring action, additional treatment system components would be added. Implementability: Full system startup would begin by the EPA-enforceable milestone of June 22, 1999. Depending on the nature of the recirculating well treatment system, it is possible that one or more of the recirculating wells could be started up 12 to 24 months after the decision date. It is estimated that the system would operate for more than 20 years. Recirculating well technology is a developing but accepted technology. It is expected that this alternative would require more regulatory or agency involvement than other active alternatives using ETR technology. Because all systems would be constructed off MMR property, property access is anticipated to be potentially difficult. To overcome access difficulties, the locations of treatment system components may require adjustment during detailed design. Access for Recirculating Well Fence 1 may be possible along Hooppole Road, assuming construction is limited to the road easement. If construction activities require additional space beyond the road easement, access may be difficult. The roadway may not be wide enough to allow installation of below-ground vaults at each recirculating well containing the treatment equipment. However, the Briarwood subdivision’s covenants and restrictions prohibit the construction of outbuildings, thereby requiring a waiver before placing the treatment units above-ground. The wells could be connected by a buried pipeline to a common treatment unit nearby. This unit could be placed above ground or in an underground vault, and would be located in a less populated area acceptable to the local residents. This approach would involve trenching along local roadways for the pipeline to and from the treatment unit. Obtaining access for a separate treatment system may be difficult. Risks to human and ecological health during construction and operationž same as Alternative A. Environmental impacts associated with construction and operationž same as Alternative B. Socioeconomic impacts associated with construction are expected to be moderate. This alternative involves extensive trenching and drilling along roadways for several months. Residents along Hooppole Road, in particular, would be disrupted by construction activities. Trenching would also be required to run a pipeline from each recirculating well to a small treatment system located nearby. Socioeconomic impacts of construction include noise, dust, temporarily closed streets, reduced use of property, and potential physical safety hazards. Impacts are considered to be somewhat greater than for Alternative B because of the treatment unit located nearby, and somewhat less than for Alternatives D and E because the wells are limited to Hooppole Road. Operation of the treatment system would include periodic maintenance of wells, pumps, and pipelines; sampling of monitoring wells; and continuous operation of small central treatment unit within the Briarwood neighborhood. These activities would affect residents moderately for many years. Cost: Total capital cost is estimated to be approximately $8 million. Annual operating and maintenance cost is estimated to be approximately $1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $23 million. Public Acceptance: See Alternative A. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE D Alternative D would use ETR technology. This alternative uses an extraction well fence aligned with the direction of groundwater flow (referred to as "axial") in the body of the plume. Two additional extraction wells would be installed along Hooppole Road to provide additional plume capture. Treated groundwater would be reinjected northeast and southwest of the plume. The system would operate at a total flow rate of approximately 0.8 mgd, and would include approximately 14,700 linear feet of piping, and a total of approximately 10 extraction and reinjection wells. Matrix Criteria Overall Protection of Human Health and the Environment: Same as Alternative A. Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): Same as Alternative A. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative D, 64 percent of the contaminants (by mass) would be captured by the treatment system. The system effectively removes contaminants from the groundwater, and the layout of wells would have a minimal effect on other plumes. Thirty-six percent of the contaminant mass would not be captured. Effects of uncaptured portion of the plumež same as Alternative A. Socioeconomic impacts associated with the uncaptured portion of the plumež same as Alternative A. Institutional controls and drinking waterž same as Alternative A. Effectiveness of Treatment Systems: Same as Alternative B. Implementability: Same as Alternative B. Because all systems, with the exception of the treatment plant, would be constructed off MMR property, property access is anticipated to be potentially difficult. To overcome access difficulties, the locations of treatment system components may require adjustment during detailed design. Access for the ETR wells and pipelines may be possible along Hooppole, Highland, Pinecrest, Back, and Wheeler Roads, assuming construction is limited to road easements. If construction activities require additional space beyond road easements, access may be difficult. Access for the pipeline to and from the ETR treatment facility (which would probably be located on MMR property adjacent to the SD-5 North system) should be possible along road easements (Hooppole and Back Roads). This alternative requires substantially more trenching than Alternatives B and C where well fences are limited to Hooppole Road. Risks to human and ecological health during construction and operationž same as Alternative A. Environmental impacts associated with construction and operationž same as Alternative B. Socioeconomic impacts associated with construction are expected to be high. This alternative involves extensive trenching and drilling along roadways for several months. Residents along Hooppole Road, Hillside Avenue, Highland Avenue, Pinecrest Road, Back Road, and Wheeler Road, in particular, would be disrupted by construction activities. Trenching would also be required for the pipeline between the wells and the treatment plant. The pipeline would probably be placed along Hooppole and Back Roads, affecting additional residents of those roads. Socioeconomic impacts of construction include noise, dust, temporarily closed streets, reduced use of property, and potential physical safety hazards. Operation of the treatment system would include periodic maintenance of wells, pumps, and pipelines; sampling of monitoring wells; and continuous operation of a treatment plant near the existing SD-5 North plant. These activities would affect residents moderately for many years. Cost: Total annual capital cost is estimated to be approximately $16 million. Annual operating and maintenance cost is estimated to be approximately $1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $43 million. Public Acceptance: See Alternative A. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE E Alternative E would use recirculating well technology. This alternative uses recirculating wells aligned with the direction of groundwater flow (referred to as "axial") in the body of the plume. Two additional recirculating wells would be installed along Hooppole Road to provide additional plume capture. Recirculating wells could be constructed with treatment systems housed either above-ground in a small shed or in an underground vault. The system would include approximately 5 recirculating wells. Matrix Criteria Overall Protection of Human Health and the Environment: Same as Alternative A. Compliance with Applicable or Relevant and Appropriate Requirements (ARARs): Same as Alternative A. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative E, 62 percent of the contaminants (by mass) would be captured by the treatment system. The system effectively removes contaminants from the groundwater, and the layout of wells would have a minimal effect on other plumes. Thirty-eight percent of the contaminant mass would not be captured. Effects of uncaptured portion of the plumež same as Alternative A. Socioeconomic impacts associated with the uncaptured portion of the plumež same as Alternative A. Institutional controls and drinking waterž same as Alternative A. Effectiveness of Treatment Systems: Same as Alternative C. Implementability: Same as Alternative C. Because all systems would be constructed off MMR property, property access is anticipated to be potentially difficult. To overcome access difficulties, the locations of treatment system components may require adjustment during detailed design. Access for recirculating wells and pipelines may be possible along various roadways, assuming construction is limited to the road easements. If construction activities require additional space beyond road easements, access may be difficult. The roadways may not be wide enough to allow installation of below-ground vaults at each recirculating well containing the treatment equipment. However, the Briarwood subdivision’s covenants and restrictions prohibit the construction of outbuildings, thereby requiring a waiver before placing the treatment units above-ground. The wells could be connected by a buried pipeline to a common treatment unit nearby. This unit could be placed above ground or in an underground vault, and would be located in a less populated area acceptable to the local residents. This approach would involve trenching along local roadways for the pipeline to and from the treatment unit. Obtaining access for a separate treatment system may be difficult. This alternative would require substantially more trenching than Alternatives B and C where well fences are limited to Hooppole Road. Risks to human and ecological health during construction and operationž same as Alternative A. Environmental impacts associated with construction and operationž same as Alternative B. Socioeconomic impacts associated with construction are expected to be high. This alternative involves extensive trenching and drilling along roadways for several months. Residents along Hooppole Road, Hillside Avenue, Highland Avenue, Pinecrest Road, Back Road, and Wheeler Road, in particular, would be disrupted by construction activities. Trenching would also be required to run a pipeline from each recirculating well to a small treatment system located nearby. Socioeconomic impacts of construction include noise, dust, temporarily closed streets, reduced use of property, and potential physical safety hazards. Operation of the treatment system would include periodic maintenance of wells, pumps, and pipelines; sampling of monitoring wells; and continuous operation of small central treatment unit within the Briarwood neighborhood. These activities would affect residents moderately for many years. Cost: Total capital cost is estimated to be approximately $9 million. Annual operating and maintenance cost is estimated to be approximately $1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $26 million. Public Acceptance: See Alternative A. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE Y Alternative Y relies on the process of monitored natural attenuation. Natural subsurface processes that contribute to natural attenuation include dilution, volatilization, biodegradation, adsorption, and chemical reactions with subsurface materials. 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 concentrations. 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 would be protected by including institutional controls that will minimize exposure to contaminants. Institutional controls would be required to prohibit drilling of new wells within, or in the direct path of, the SD-5 South groundwater plume. This alternative does not, however, address the migration of contaminants within the groundwater or from groundwater to surface water. Therefore, potential risk would be not eliminated. Hydrological and ecological thresholds are met because there would be no construction. No rare, threatened, or endangered species are known to inhabit the areas likely to be affected by this alternative. 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 SD-5 South plume. Therefore, 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 alternatives to address areas of low-level contamination. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative Y, 3 percent of contaminants (by mass) are captured by active systems, as a result of contaminants being drawn northward by the existing SD-5 North extraction wells. This alternative does not affect other plumes. Ninety-seven percent of the plume contaminants would continue to migrate. Effects of uncaptured portion of the plumež same as Alternative A. Socioeconomic impacts associated with the uncaptured portion of the plume are expected to be high because a large percentage of the plume will migrate into or under Johns Pond, Ashumet Pond, and the Quashnet River. Although no adverse impacts to human health or the environment are anticipated, the plume will migrate farther and adversely affect more area than with alternatives involving active treatment. Therefore, due to the perception of downgradient residents and users of surface water bodies, the socioeconomic impact is expected to be high. Institutional controls will prohibit drilling of new wells within, or in the direct path of, the SD-5 South groundwater plume. All residences within the SD-5 South footprint have been connected to public water; and the Mashpee Board of Public Health has imposed a moratorium on new drinking water wells within areas of known contamination. Wells used for purposes other than drinking water may not be controlled adequately; however, private wells are commonly shallower than the contaminated groundwater. Numerous residences downgradient of the plume are using private wells. It is Air Force policy at the MMR to connect all users of private wells to public water supply in areas where groundwater is known to be contaminated or threatened. Under this alternative, the plume will migrate further than with the other active alternatives. As a result, more land area will be affected, and more institutional controls will be required to prevent exposure to contaminants. Effectiveness of Treatment Systems: Natural attenuation would not effectively remove VOCs to below detection limits; however, the primary contaminants would degrade with time. Implementability: Because this alternative involves no active treatment, there would be no system startup time or anticipated period of operation. Monitoring activities would be performed for more than 20 years. Minimal property access would be required to sample existing monitoring wells and install new ones. Flexibility in sampling and drilling locations would enable the required access to be obtained. Minimal 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 approximately $1 million. Annual monitoring and reporting cost is estimated to be approximately $0.2 million. Life-cycle cost, including capital cost, based on 20 years of monitoring (for cost-estimating purposes only) is estimated to be approximately $6 million. Public Acceptance: See Alternative A. SD-5 SOUTH PLUME RESPONSE ALTERNATIVE Z Alternative Z 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 SD-5 South, 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; therefore, human health would not be protected. Hydrological and ecological thresholds are met because there would be no construction. No rare, threatened, or endangered species are known to inhabit the areas likely to be affected by this alternative. 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 SD-5 South plume. 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. The highest percent of mass capture that can be expected from any of the alternatives is slightly less than 70 percent. Under Alternative Z, 3 percent of contaminants (by mass) are captured by active systems, as a result of contaminants being drawn northward by the existing SD-5 North extraction wells. This alternative does not affect other plumes. Ninety-seven percent of the plume contaminants would continue to migrate downgradient of the current location of the plume. Studies are currently ongoing between Ashumet and Johns Pond and on the east side of Johns Pond to determine the potential impacts, if any, of contaminants moving beyond the ponds. Human health and ecological risk factors associated with the uncaptured portion of the plume are high because there would not be any institutional controls to prevent exposure to contaminants. Socioeconomic impacts associated with the uncaptured portion of the plume (e.g., impacts on commercial or residential interests, recreation, and historical and archeological sites, resulting from not capturing all of the plume) are expected to be high because a large percentage of the plume will migrate into or under Johns Pond, Ashumet Pond, and the Quashnet River. Although no adverse impacts to human health or the environment are anticipated, the plume will migrate farther and adversely affect more area than with alternatives involving active treatment. Therefore, due to the perception of downgradient residents and users of surface water bodies, the socioeconomic impact is expected to be high. No new institutional controls would prohibit drilling of new wells within, or in the direct path of, the SD-5 South groundwater plume. All residences within the SD-5 South footprint have been connected to public water; and the Mashpee Board of Public Health has imposed a moratorium on new drinking water wells within areas of known contamination. Wells used for purposes other than drinking water may not be controlled adequately; however, private wells are commonly shallower than the contaminated groundwater. Numerous residences downgradient of the plume (i.e., located in the area toward which groundwater is flowing) are using private wells. However, no connections to public water would be implemented under this alternative. Effectiveness of Treatment Systems: The no- action alternative would not remove VOCs to below detection limits; however, the primary contaminants would degrade with time. Implementability: Because this alternative involves no action, there would be 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 or ecological health, nor any socioeconomic or environmental impacts, as a result of construction and operation. Cost: Total capital cost is estimated to be approximately $0. Annual monitoring cost is estimated to be approximately $0.1 million. Life-cycle cost, including capital cost, based on 20 years of operation (for cost-estimating purposes only) is estimated to be approximately $2 million. Public Acceptance: See Alternative A.
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