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samples that have been collected from boreholes. However, concentrations exceeding 2,700 ppm in <br /> samples collected from directly beneath the tanks confirm that the tanks were a source of <br /> contamination. The contaminants did not migrate widely in the vadose zone, which extended to a <br /> depth of more than 25 feet until the past few years. The rise of the water table since 1996 has <br /> reduced the vadose zone to less than 10 feet. <br /> Hydrocarbon concentrations in groundwater, particularly in wells located in the southwestern <br /> portion of the site area, suggest that other, off-site sources may have contributed more gasoline to <br /> the plume than the tanks that were present at the Kwikee site. Concentrations increase to the south <br /> and west of the site, rather than decreasing as expected if the Kwikee tanks were the principal <br /> source. We recommend coordinated monitoring and sampling of the Chevron and Kwikee sites in <br /> order to better map the contaminant plume and interpret its origin and migration path. We also <br /> recommend that PHS/EHD take steps to identify other potential Responsible Parties for <br /> contamination that may have originated on the south side of Country Club Boulevard. <br /> Groundwater monitoring should continue on a quarterly basis through 2001 to confirm the <br /> groundwater gradient and provide additional data on contaminant movement. We do not <br /> recommend any further assessment activities or feasibility testing until a clearer picture of the <br /> relation between on-site and off-site sources has been developed. <br /> 7 <br />