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June 16, 1997 <br /> Page 5 <br /> shallow groundwater into the well, so deeper water beanng zones are protected from <br /> cross contamination Based on the above information, the likelihood of shallow site <br /> groundwater impacting a drinking water source appears to be remote <br /> RATIONALE FOR SITE CLOSURE <br /> In summary, PACIFIC believes the site is a good candidate for closure Our request for <br /> closure or no further action status for this site is based on the following rationale <br /> • USTs and associated facilities were removed from the site in September 1995 Soil <br /> samples collected during removal activities indicated nondetectable to low <br /> concentrations of residual petroleum hydrocarbons in soil beneath the site <br /> • Soil analytical results reported nondetectable concentrations of TPH-g and BTEX <br /> compounds in all eight borings throughout the total explored, and only trace <br /> concentrations of TPH-d(1 0 and 1 3 ppm reported as unidentified hydrocarbons) <br /> and MtBE(0 18 ppm) in 3 of 28 samples <br /> • Groundwater sampling analytical results reported nondetectable concentrations for <br /> all constituents analyzed over the last three quarters Analytical groundwater data <br /> generated from previous sampling events prior to the last three quarters indicated <br /> • nondetectable concentrations of hydrocarbons in groundwater, with exception of <br /> very low hydrocarbon concentrations reported in samples from Wells MW-1 and <br /> MW-2 <br /> • The City of Ripon derives one hundred percent of it's water supply from municipal <br /> groundwater wells that have a screened interval approximately between 70 and 200 <br /> feet bgs There are no known municipal wells located within a 1/2-mile radius <br /> downgradient of the site Since groundwater has not been impacted, potential <br /> impact to health or other beneficial use is considered remote <br /> The known potential petroleum hydrocarbon sources have been removed from the site <br /> and groundwater analysis indicates that groundwater beneath the site has not been <br /> significantly impacted Residual hydrocarbons in the soil will likely bio-attenuate over <br /> time Based on the above data, PACIFIC recommends unconditional site closure <br /> 9201026A/CLOSERPT <br />