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90189H-ALL CON-7 Woodward-Clyde Consultants <br /> 2.4 GROUNDWATER CONTAMINATION ASSESSMENT <br /> Review of the analytical results for the groundwater samples presented <br /> in the Phase tI RI report (WCC 1987a) and comparison of concentration <br /> ranges and averages with background well data and existing state and <br /> federal health based criteria for potable water, shown In Table 2-2, <br /> indicated the presence of significant groundwater contamination. Total <br /> copper and lead were the primary contaminants with nickel and tin <br /> representing secondary contaminates. The dissolved copper profiles (Figure <br /> 2-3) , derived from monitoring well data presented in the RI report, <br /> indicated that actual aqueous contamination was confined to a relatively <br /> small area. Apparently, due to the effect of metallic adsorption onto <br /> native soils (i.e., clays and silts), the aqueous transport of contaminant <br /> metals is significantly less than if non-attenuating conditions existed. <br /> In addition, the flow of liquids through the breaches in the sump were <br /> occasional and not constant, therefore only slugs of aqueous cortaminants <br /> were injected into the surrounding soils. As a result of the attenuation, <br /> the maximum downgradient distance of dissolved metal transport appears to <br /> be less than 75 feet from the sump with far field values (generally 50 feet <br /> or more from the sump) being an order of magnitude less than maximum <br /> values. <br /> From the time that the RI report was prepared, the moritoring of <br /> groundwater quality has continued. Recent data, presented in Appendix 8, <br /> show substantlal improvements in water quality. Aqueous metal <br /> concentrations are now at the levels of analytical detection and indicate <br /> that dilution and the effects of well purging and sampling have had a <br /> beneficial effect. <br /> 2.5 ENDANGERMENT ASSESSMENT <br /> Cleanup levels for remediation are generally established on the bas's <br /> of site specific conditions and the perceived threat to human health and <br /> the environment. Proposed cleanup levels for soils are often presented in <br /> N 2-s <br /> L d Wd T£:S E66T 'bL'NIf LSOC SSL 916 :-91 BDONJ FaTleil lealuaD ; WOad <br />