8/19/1997 BOARD OF SELECTMEN Minutes

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Road and Ashumet Pond. Because recirculating Construction and operation would cause moderate lls are somewhat less intrusive than ETR tech- socioeconomic impacts on the residential neighbor- we o it is anticipated that property access is hood near Ashumet Pond because of the nol gY? . possible,though perhaps difficult. recirculating wells in the neighborhood. risks to human health are anticipated Cost: Total capital cost is estimated to be $44.3 Manageable p ring construction and operation of the.system. -million. Annual operating and maintenance cost is du g Treatment plants would be located on base, thus estimated to be $3.8 million. Life-cycle cost, inimizin otential risks to the off-base neighbor- including capital cost, based on 24 years of opera- hoo m gP d. Recirculatingwells would present low risk to tion (for cost-estimating purposes only) is estimated the off-base neighborhood. to be$119 million. e species, to rare species Public Acceptance:Adverse impacts to rar p The public acceptance of all p h � p habitats,to a coastal lain pond community, and to a the response alternatives will be determined . wetlands complex are expected, but can be mite- throughout the public comment period. The g respec- with a moderate level of schedulin and con- tive organizations, agencies, and community groups gated struction pg p planning. The impacts associated with (acceptance groups)will review the information and construction along the Ashumet Pond shoreline indicate a preferred choice, acceptable second and would be less for recirculating well technology than third choices, and any unacceptable alternatives. for ETR. .� C� '10 PLUME RESPONSE ALTERNATIVE C1 This new alternative is described in the accom- Ashumet and Johns Ponds would be captured. Pan in fact sheet, "Introduction to Additional CS Contaminant concentrations downgradient of the Y g 10 Plume Response Alternatives." system south -of Sandwich Road are reduced by Alternative CI is identical to Alternative C except recirculating wells. that the Northwest Extraction Fence is extended Hydrological thresholds would not be met, because eastward into thep lume. The extended fence results the amount of treated water that flushes through the in increased a capture of portion of the plume north ponds is anticipated to be slightly above the P of the fence that is relatively highly contaminated, threshold. However, the recirculating well pilot andp revents contaminants from migrating to the study suggests that treated water will not signifi- silts in that area. Once in the low conductivity silts, cantly alter ambient water quality. In addition, it is contamination is significantly more difficult to believed that final design could bring Ashumet Pond remake• treated water flows within guidance thresholds. Extensive construction would affect sensitive The system would operate at a total flow rate of re upland animal species. Impacts to habitats and ra p p approximately 8.5 mgd, and would include Ashumet Pond habitats would be reduced by using approximately 37,000 linear feet of piping, and a recirculating wells. The remaining impacts would total of approximately 101 extraction and rein- . require moderate mitigation. lection wells,and 5 recirculating wells. Compliance with Applicable or Relevant and Matrix Criteria Appropriate Requirements (ARARs): This alter- Overall Protection of Human Health the native complies with all ARARs. Environment: Under this alternative, human health Effectiveness and Permanence of Response Alter- would be protected because a high percentage of the natives: The table on page 3 summarizes plume groundwater plume is captured, further migration of capture by mass for all alternatives. A similar table contaminants iseatl reduced, and institutional summarizing plume capture by volume is included in' � Y controls will minimize future exposure to contami- the matrix document. nants. Institutional controls include prohibiting 1 9g percent of the contami- drillin direct path of, Under Alternative C , g of new wells within, or in the the nants (by mass) is captured by the treatment system CS-14 groundwater plume. Portions of the • or caught in silts. The system effectively removes plume that might otherwise migrate under or into 7