8/19/1997 BOARD OF SELECTMEN Minutes

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Compliance with Applicable or Relevant and contaminants will degrade with time. Because this Appropriate Requirements (ARARs): This alter- alternative includes no active treatment, there will native does not comply with the Interim Record of be no treatment residuals. This alternative does not Decision (IROD)which requires containment of the satisfy a statutory preference for treatment as a 1 lame, principal element. C p Effectiveness and Permanence of Response Alter- Implementability: Because this alternative in- natives:Ives: The table on page 3 summarizes plume volves no active treatment, there is no system y masa.f capture b or all alternatives. A similar table startup time or anticipated period of operation. mmarizin lume capture by volume is included in Monitoring activities would be performed for more sugp the matrix document. than 50 years. Alternative E has no contaminants are Minimal property access would be required for Under Altera p p captured by active systems. Approximately 61 sampling existing monitoring wells and installing percent of the total contaminant mass would be new monitoring wells. caught in silts and the remainder would continue to Manageable risks to human health are anticipated migrate , downgradient in the coarser, more duringconstruction and sampling of monitoring sands. This alternative • does not permeable wells. effectively remove contaminants. It does not affect r e percentage 39 Environmental impacts associated with installing 1 other plumes. A relatively a g p g percent)of the contaminant mass would continue to and sampling monitoring wells is expected to be low mi rate down adient of the current footprint. because of flexibility in the location of wells. g �' However, human health and ecological risk factors Socioeconomic impacts would be low and associ- associated with that portion are low. ated only with installation of monitoring wells and Socioeconomic impacts associated with the periodic sampling. uncaptured portion of the plume, such as impacts on Cost: Total,capital cost.is estimated to be $1.0 commercial or residential interests, recreation, and million. Annual monitorin and reporting cost is g historical and archeological sites, are expected to be estimated to be $0.3 million. Life-cycle cost, moderate because of the relatively large uncaptured including capital cost, based on 20 years of moni- p portion of the plume. Institutional controls will pro- toring (for cost-estimating purposes only) is esti- hibit drilling of new wells within, or in the direct mated to be$8 million. path of, the CS-10 groundwater plume. Residences over or directly downgradient of the fume have Public Acceptance: The public acceptance of all d y g p o been or are scheduled to be connected t public the response alternatives will be determined water supply. There may not be adequate controls throughout the public comment period. The respec- pp Y Y q • tive organizations, agencies, and community groups on existing we 1 Is. (acceptance groups)will review the information and Effectiveness of Treatment Systems: Natural indicate a preferred choice, acceptable second and attenuation will not effectively remove VOCs,EDB., third choices, and any unacceptable alternatives. semi-volatiles, or inorganics; however the primary CS=10PLUME RESPONSE ALTERNATIVE F This new alternative is described in the accom•- contaminants from migrating to the silts in the area. to an in fact sheet ""Introduction""Introduction Additional CS'- Once in the low conductivity silts, contamination is P Y g t 10 Plume Res onse Alternatives." significantly more difficult to remove. The extrac- p Alternative F is identical to Alternative C except tion wells north of Sandwich Road provide for expedited capture of a portion of the plume that is that the Northwest Extraction Fence is extended relativelyhighly contaminated in that area. to�the plume and eastward in several extraction wells g Y are added north of Sandwich Road. The extended The system would operate at a total flow rate of Northwest Extraction Fence results in increased approximately 9.1 mgd, and would include ca tore of a portio he plume north of the fence approximately 38,000 linear feet of piping, and a P portion of t that is relatively highly contaminated, and prevents I1 s