8/19/1997 BOARD OF SELECTMEN Minutes

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��o F�LU�IIE RESPONSE ALTERNATIVE A Alternative A would use extraction, treatment, and Percent Plume Capture by Mass for All Alternatives . This alternative �5 Alt Capture Capture Total Caught Total'not:: Total reinjection [ETR} technology. by ETR by ::: apre in Silts Captured Ciptured-. ed for maximum plume capture. Extraction Recirc :::::::::ti .. 94 deet :.....Y:.:::: :or or Cau es (lines of wells) would be located along the :: y :::: an.fent n silts adin edge of the plume, including the area adja- E le g g A S8 U :5�... 1 l 99 .. cent to Ashumet Pond. ...:..:. 19 The system would operate at a total flow rate of approx. 7.2 million gallons per day (mgd), 84 :.:::; 3 Y and would include approximately 35,000 linear feet C1 90 2 9 :::::.:::: 6 .....:::...:. ::::.9�.: and a total of approximately 9 6 extraction of piping, D 0 73 = 3:: : i98:; 9...... ...2: and reinjection wells. ... E na na :ria 61 39... . �1. Matrix CriteriaF 92 Overall Protection of Human Health and thena na nal 519 G1 Environment: Under this alternative,human health would be protected because the groundwater plume migration of contaminants is Under Alternative A, 99 percent of the contaminants is captured, further g • ted and institutional -controls will minimize Eby mass) is captured by the treatment system or prevented, caught in silts. The system effectively removes future exposure to contaminants. Institutional con- contaminants, prohibiting drilling of new wells contaminants, and the configuration would have a trots include pro g g • f the CS-1 o round- minimal effect on other plumes. A very small w�thln, or the direct path o , g plume. Portions of the plume that might percentage (1 percent) of the contaminant mass waterp p g to under or rota Ashumet and Johns would not.--be captured or caught in silts; however, otherwise rnigra ' Ponds would be captured. human health and ecological risk associated with that portion is very low. Hydrological thresholds, such as minimizing draw- ' and minimizing the socioeconomic impacts associated with the dawn 1n surface water bodes g e water that flushes through the uncaptured portion of the plume, such as impacts on amount of treated g extensive con- commercial or residential interests, recreation, and ponds, would be met. However, the e . • historical and archeological sites, are expected to be structlon required for this alternative would affect se ' ' nd rare animal s ecies. low. Institutional controls will prohibit drilling o neral sensitive habitats a p These impacts would require extensive mitigation. new wells within, or in the direct path of, the CS-10 groundwater plume. Residences over or directly Compliance with Applicable or Relevant and downgradient of the plume have been or are sched- Appropriate Requirements (ARARs): This alter- uled to be connected to public water supply. There nature complies with all ARARs. may not be adequate controls on existing wells. Effectiveness and Permanence of Response Alter- Effectiveness of Treatment Systems: The treat Effectiveness The table at right summarizes plume cap- ment system (which involves activated carbon and ture by mass for all alternatives, based on the pretreatment) is capable of removing volatile results of modeling. A similar table summarizing organic compounds (VOCs) and ethylene dibromide plume capture by volume is included in the matrix (EDB) to below detection limits. Other document. • contaminants, such as semi-volatiles and inorganics, lIl • would also be treated to background levels, if In Under all alternatives, a portion of the plume will be caught in e aquifer. .fit is technically and economically feasible,Lf they appear g silts underlying th because in the extracted water. Spent carbon produced by difficult to remove contaminants from silts b mon through them. the system would be transferred offsite for regen- water extremely slowly th g contaminants. Residual Contam• es nants are expected to break down erat�on, which destroys the } p solid wastes would be transferred offsite and significantly through natural processes while � residual trapped or disposed of in an appropriate manner. The Pp slowed by the.silts. solid wastes are not expected to be a hazardous waste. Risks to workers associated with handling, 3