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On May 8, 1992, Semco Corporation removed Tanks C and D Soil samples collected for <br /> analysis from both ends of each tank did not contain detectable concentrations of TPH-as- <br /> gasoline, TPH-as-diesel or BTEX compounds The soil sample results are summarized in Table <br /> 6 <br /> Summa�C <br /> Soil beneath only one of the four removed USTs (Tank A) contained significant concentrations of <br /> petroleum hydrocarbons The extent of the impacted soil beneath Tank A was defined and then <br /> excavated Three groundwater monitoring wells were installed and sampled for five consecutive <br /> quarters Dissolved gasoline hydrocarbons were detected at a maximum concentration of 770 <br /> ppb of TPH-as-gasoline and 3 7 ppb of benzene These concentrations generally declined over <br /> the five quarters of sampling <br /> tThe nearest water well is approximately 1,000 feet north of the site Immediately north of the <br /> site is Mormon Slough The surface water in this shallow channel is approximately 10 to 20 feet <br /> above the groundwater surface measured beneath the site <br /> 1 <br /> 5 <br />