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o The depths and lengths of the screened intervals in he <br /> initial nest of wells near CWS Well 20-01 will be determined <br /> based on lithologic conditions encountered. An exploratory <br /> borehole will be,included in the investigation. The screen <br /> length for each well installed will generally not exceed <br /> 30 feet. The number of wells in the initial nest will be <br /> determined by results of analyses. <br /> o Additional upgradient and downgradient wells will be <br /> constructed in the zone or zones determined to be <br /> contributing chromium to CWS Well 20-01 by chemical analysis <br /> of groundwater samples from the initial well nest . Nests of <br /> wells at upgradient and downgradient locations will only be <br /> constructed if multiple zones of contribution are, discovered <br /> near CWS Well 20-01 or if additional deep or shallow wells <br /> are required to complete plume characterization. <br /> o Special well construction methods will be deleted. <br /> Through the implementation of Phase IV MCTC intends to complete <br /> the characterization of contamination in the aquifer beneath the <br /> site to the extent necessary to evaluate feasible remedial <br /> alternatives. The proposed modifications to Phase IV will enable <br /> this characterization process to be completed in a technically <br /> sound and economical manner. <br /> Specific objections to the DHS suggested modifications are as <br /> follows: <br /> o Screen lengths will be tailored to best provide adequate <br /> vertical section for the collection of consistent and <br /> representative samples. Ten foot screened intervals do not <br /> provide adequate length for this hydrogeologic setting and <br /> may not yield data which can be correlated with the existing <br /> data. <br /> o Well elevations will be determined based on technical <br /> evaluation of available data. Shallow and deep wells may <br /> not be re wired in all locations. <br /> DHS Comment: <br /> Figure 4-4 Delete "peagravel" and add "neat ce ent" , "grout", <br /> "sand-cement grout" , or "concrete" . Ref: State of <br /> California Water Well Standards, Bulletin 74-81, December <br /> 1981. Be advised too that centralizers must be installed at <br /> intervals not to exceed 40 feet. <br /> MCTC Response: <br /> MCTC will corply. Figure !-4 .ill be revised as necessary. <br /> 11654 6 <br />