8/19/1997 BOARD OF SELECTMEN Minutes

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CS=10 PLUME RESPONSE ALTERNATIVE D ' D uses recirculating well technology. It summarizing plume capture by volume is included in Alternative g is designed ed with some consideration of property the matrix document. ownership, property access, and ecological impacts. Under Alternative D 92ercent of the contaminants be Located along p Recirculating well fences wouldg (by mass) is captured by the treatment system or the leading edge of the plume, except for the area caught in silts. The system removes contaminants Some recirculating g Y adjacent to Ashumet Pond. S g somewhat effectively, and the configuration would wells would be placed near the shore of the pond have a minimal effect on other plumes. A slightly and a fence of recirculating wells would be placed larger ercent, a (S percent) of the contaminant g p g along Sandwich Road. mass would not be captured by the recirculating The system would include approximately 102 wells or caught in silts; however, human health and recirculating wells. ecological risk associated with that portion is very low. Matrix Criteria Socioeconomic impacts associated with the un Overall Protection of Human Health and the captured portion of the plume, such as impacts on Environment: Under this alternative,human health commercial or residential interests, recreation, and would be protected because a high percentage of the historical and archeological sites, are expected to be groundwater plume is captured, further migration of low. Institutional controls will prohibit drilling of contaminants is greatly reduced, and institutional new wells within, or in the direct path of,rthe CS-10 controls will minimize future exposure to contami- groundwater plume. Residences over or, directly nants. Institutional controls include prohibiting downg radient of the plume have been or are drilling of new wells within,or-in the direct path of, scheduled to be connected to public+water supply. the CS-10 groundwater plume. Most of the plume There may not be adequate controls on existing �' Y that might otherwise migrate under or into Ashumet wells. and Johns Ponds would be captured. .Although Ile Effectiveness of Treatment Systems: The treat- groundwater Intercepted by recirculating we ment system is designed to remove VOCs through i would be substantially treated, t may not be cleaned to background concentrations or drinking water in-well air stripping followed by vapor-phase standards due to Limitations in the treatment granular activated carbon. While significant mass technology. removal will be accomplished, concentrations may not be reduced to background levels and some Hydrological thresholds would not be met, because residual contamination may be left. Semi-volatiles the amount of treated water that flushes through the and inorganics, which have not been detected at ponds is anticipated to be slightly above the levels requiring action, would not be removed with- threshold. However, the recirculating well pilot out the addition of external treatment processes, study suggests that treated water will not signifi- which are not included under this alternative. EDB, cantly alter ambient water quality. Although this which has been detected sporadically at low levels, alternative requires less construction than others, will not be removed from groundwater without construction would still affect sensitive habitats and special liquid-phase carbon treatment systems, rare upland animal species. Construction of which are not included in this alternative. If EDB, p recirculating wells close to the shore of Ashumet semi-volatiles, or inorganics are detected in the Pond may-affect sensitive habitats. Moderate plume at levels requiring action, additional treat- mitigation would be required.. ment systems would be added, although they are not Compliance with Applicable or Relevant anincorporated into this alternative.d Appropriate Requirements ): This alter- Spent carbon produced by the system would be native complies with all ARARs. transferred offsite for regeneration, which destroys • the contaminants. There will not be any residual Effectiveness and Permanence of Response Alter- • solid wastes. Risks to workers associated with natives: The table on page 3 summarizes plume of residuals would capture f� �[ similar.table handling, treating, and disposing p y mass far all alternatives 5 9 t S t t