8/19/1997 BOARD OF SELECTMEN Minutes

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be low. The alternative satisfies a statutory Pref- Adverse impacts to rare species, to rare r treatment as aprincipal element. habitats,to a coastal plain pond community, erence for wetlands complex are expected, but can Implementability: Full system startup would begin gated with a moderate level of scheduling f le milestone of June 2S, 1999. g • by the EPA-enforceable struction panning. The impacts assocla Partials stem startup may be achievable in less than ion along the Ashumet Pond �' construct g 12 months because recirculating well systems are would be less for recirculating well techno] designed and installed as individual or small groups for ETR. Also, this alternative does not in of mini-treatment systems. It is estimated that the orthwest Extraction Fence or East Rc N S ystem will operate for at least So years. This alter- Fence thus reducing environmental impact; la g native relies on recirculating well technology,which is a developing but ted technology. Although Construction and operation would cause P g accepted culatin well pilot tests are be" conducted socioeconomic impacts on the residential recur g p g with the support and approval of regulatory and hood near Ashumet Pond. oversight agencies, full-scale application will Cost: Total capital cost is estimated to require additional regulatory and agency million. Annual operating and maintenani involvement. estimated to be $3.4 million. Life-cy 'n wells would be installed on including capital cost, based on 20 years Most of the recirculating ' access to these tion (for cost-estimating purposes only) is MMR property, greatly simplifying ations. Some.wells however, would be installed to be$149 million. lac. t on private property between Sandwich Road and Public Acceptance: The public acce tai Ashumet Pond. Because recirculating wells are the response alternatives will be do { somewhat less intrusive than ETR technology, it is throughout the public comment period. Tl anticipated that property access is possible, though tiVe organizations, agencies, and communi perhaps difficult. (acceptance groups)will review the inform Manageable risks to human health are anticipated indicate a preferred choice; accepta a se during construction and operation of the system. third choices, and any unacceptable alterna Recirculating wells would present low risk to the off--base neighborhood. a CS=10 PLUME RESPONSEALTERNATIVE E Alternative E relies on natural attenuation. Natural is protected by including institutional cor subsurfaceP rocesses that contribute to natural will minimize exposure to contaminants. attenuation include_ dilution, volatilization, bio- tional controls will include prohibiting c de gradation (e.g., anaerobic dechlorination), ad- new wells within, or in the direct path of, sorption, and chemical reactions (e.g., hydrolysis). groundwater plume. This alternative These processes may reduce contamination to however, address the migration of con acceptable levels over time. Natural attenuation is within the aquifer or from groundwater i not a technology, but rather a strategy that uses water.. Therefore,potential risk is not elim ' natural processes to reduce contaminant concentra- Hydrological and ecological thresholds tion, often in conjunction with other source control because there is no construction. Lilo measures. Monitoring and institutional controls are . used to manage a known condition of contamina- impact on species and habitats i's minimal. tion. This alternative fails the threshold triter ever, it has been carried through the This alternative includes no active plume capture process in artier to allow comparison y} components. be alternatives. Thi's alternative could Matrix riteria with other alternative to address areas of contamination. Overall Protection of Human Health and the Environment: Under this alternative,human health 10