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ERI 205503 R01 Unocal Service Station 5886 Stockton California June 3 1997 <br /> • MW2, MW3, MW4D, and MWSD up to 170 ug/L Sequoia notes indicate diesel range hydrocarbons <br /> detected are discrete peaks Additionally, Mr Alan Kemp of Sequoia indicated that select diesel <br /> range peaks in groundwater samples collected from wells MW2, MW3, MW4D, and MWSD are a <br /> result of sodium sulfate originating in the laboratory Diesel range chromatograms of groundwater <br /> samples collected from these wells and the method blank chromatogram are provided in Appendix F <br /> Concentrations of MTBE were not detected in groundwater samples collected from wells MW4, <br /> MWS, and MW7 (both shallow and deep casings) above stated laboratory method detection limits but <br /> were detected in wells MW1 through MW3, MW6D, and MW6S up to 8,000 ug/L <br /> 50 SUMMARY AND CONCLUSIONS <br /> The data obtained during this investigation indicate the following <br /> • Banks did not note any leaks in the existing piping or in UST interstitial spaces during their <br /> March 20, 1997 inspection Data are currently unavailable to evaluate whether MTBE was <br /> present in groundwater prior to tank replacement <br /> • Sediments encountered in soil borings typically consisted of silty clay, clayey silt, and fine- <br /> grained sand <br /> • Residual gasoline hydrocarbons (TPHg) were not detected at or above the stated laboratory <br /> method detection limits in soil samples collected from hand-augured borings HAI through <br /> HA3 except for 3 3 mg/Kg in HA2 Concentrations of TEPHd were detected up to 8 4 <br /> mg/Kg and MTBE up to 12 mg/kg <br /> • Residual gasoline and diesel hydrocarbons were not detected above stated laboratory detection <br /> limits in soil samples collected from borings B4 through B7 except for 1 0 mg/Kg TEPHd <br /> detected at 5 5 feet below ground surface in boring B5 <br /> • Residual hydrocarbons in soil appear to have been delineated beneath the site <br /> 7 <br /> I <br />