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I <br /> Proposal for of Site Cleanup Confirmation May 5, 1992 <br /> Southland, 7-Eleven No 20680, 9110 Thornton Road. Stockton, CA 3 <br /> 3) Collection of soil samples to further confirm the effectiveness of the sod venting <br /> system, soil samples were collected from beneath the tank, adjacent to tank lines <br /> and from the boring conducted for installation of the on-size monitoring well <br /> The results associated with analysis of sod samples collected during removal of the underground <br /> tank and associated piping were presented in correspondence to the SJPH dated October 4, 1992 <br /> The soil and groundwater analytical results were presented In the February 21, 1992, report titled <br /> Protect Quarteriy Update and Well Installation Report, 7-Eleven Store9110 Thornton Road <br /> Stockton, California <br /> I22 Groundwater Remediation Results Overview <br /> 2.21 Monitoring Wells <br /> The groundwater extraction and remediation system operated from 1986 to October 1990 Seven <br /> hundred sixty gallons of separate-phase gasoline were removed from the site, and dissolved <br /> hydrocarbon concentrations in the groundwater have been reduced significantly since work was <br /> initiated As of October 1990, the benzene, toluene, ethylbenzene, xylene (BTEX) concentrations in <br /> groundwater samples collected from the site monitoring wells have been below detection limits for <br /> BTEX compounds The only concentration of TPH-as-gasoline detected in October 1990 was 51 <br /> parts per billion (ppb) in the sample collected from well MW-1, which had historically contained <br /> separate-phase gasoline <br /> Quarterly sampling and analysis of groundwater samples collected from all the monitoring wells that <br /> Icontain water continued to the present after October 1990 In addition, three new wells were <br /> installed to provide additional on-site and off-site downgradient data With the exception of the <br /> IFebruary 24, 1992, sampling event, petroleum hydrocarbon concentrations in groundwater samples <br /> f collected from all wells have been below detectable levels since the October 1990 sampling event <br /> Low petroleum hydrocarbon concentrations were detected in nine oft he groundwater sampleSl <br /> 6ollected on February 24, 1992 Because petroleum hydrocarbon concentrations had been below <br /> detectable levels in recently collected groundwater samples, a second set of samples were collected <br /> Ion March 30, 1992, to confirm the analytical results of the February 24, 1992, samples <br /> 4"GROUNDWATER <br /> TECHNOLOGY INC <br /> C <br />