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ERI 205503 R01 Unocal Service Station 5886, Stockton California lune 3 1997 <br /> • Groundwater was encountered at approximately 9 to 14 feet bgs During May 1997 static <br /> groundwater elevations ranged from approximately 6 to 9 5 feet bgs and the groundwater <br /> gradient was towards the southwest at a hydraulic gradient of 0 002 Groundwater elevations <br /> were essentially the same In the shallow and deep wells, Indicating hydraulic communication <br /> between the two depths <br /> • Analyses of groundwater samples did not detect TPHg and BTEX above stated laboratory <br /> method detection limits except for up to 4 3 ug/L benzene detected in wells MW2 and MW3 <br /> • TEPHd was not detected in groundwater samples collected from wells MW1, MW4S through <br /> MW7S, MW6D, and MW7D Diesel range hydrocarbons were detected 1n wells MW2, <br /> MW3, MW4D, and MWSD up to 170 ug/L However, Sequoia notes reported diesel <br /> range hydrocarbons were unidentified and do not appear to be diesel Additionally, <br /> Sequoia reported groundwater samples from wells MW2, MW3, MW4D and MWSD <br /> contained sodium sulfate originating in the laboratory <br /> • <br /> MTBE was not detected in groundwater samples collected from wells MW4, MWS, and MW7 <br /> (both shallow and deep casings) above stated laboratory method detection limits MTBE was <br /> detected in wells MW1 through MW3 and MW6S and MW6D up to 8,000 ug/L <br /> I <br /> The lateral and vertical extent of TPHg and BTEX appear to be delineated beneath the site <br /> Concentrations of MTBE have been delineated in each direction except towards the south and <br /> southwest <br /> 6.0 LIMITATIONS <br /> This report was prepared in accordance with generally accepted standards of environmental geological <br /> practice In California at the time this Investigation was performed This Investigation was conducted <br /> solely for the purpose of evaluating environmental conditions of the soil and water with respect to <br /> residual petroleum hydrocarbons No soil engineering or geotechnical references are Implied or <br /> should be Inferred Evaluation of the geologic conditions at the site for the purpose of this <br /> 8 <br />