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ERI 205503 R01 Unocal Service Station 5886 Stockton California June 3 1997 <br /> i4,0 RESULTS OF INVESTIGATION <br /> 4-1 Site Geology and Hydrolgeology <br /> Sediments encountered beneath the site typically consist of clayey silt, silty clay, and fine-grained <br /> sand Groundwater was encountered approximately 9 to 14 feet bgs in the borings Static <br /> groundwater elevations ranged from approximately 6 to 9 5 feet bgs (MPDS, May 1997) During <br /> May 1997, groundwater flowed towards the southwest at a hydraulic gradient of 0 002 (MPDS, May <br /> 1997) <br /> 42 Soil Conditions <br /> Concentrations of TPHg were not detected in hand-augured borings except for 3 3 milligrams per <br /> kilogram (mg/Kg) TPHg detected in HA2 Concentrations of TEPHd were detected up to S 4 mg/Kg <br /> in HA2 Concentrations of MTBE were detected up to 12 mg/Kg in HA3 <br /> Residual gasoline and diesel hydrocarbons were not detected at or above stated laboratory detection <br /> limits in soil samples collected from borings B4 through B7 except for 1 0 mg/Kg TEPHd detected at <br /> 5 5 feet bgs in boring B5 Copies of laboratory reports for soil samples obtained during this <br /> investigation are included in Appendix F Results of laboratory analyses of soil samples are <br /> summarized in Table 1 <br /> 43 Groundwater Conditions <br /> Results of laboratory analyses of groundwater samples collected from wells MW1 through MW3, <br /> MW41) through MW7D, and MW4S through MW7S did not detect TPHg and BTEX above stated <br /> laboratory method detection limits except for benzene detected in wells MW2 and MW3 up to 4 3 <br /> micrograms per liter (ug/L) <br /> Diesel range hydrocarbons were not detected in groundwater samples collected from wells MW1, <br /> MW4S though MW7S, MW6D, and MW71) Diesel range hydrocarbons were detected in wells <br /> �� 6 <br />