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I s u a H t a a II I Project No 58080-06-02 ' January 5, 1995 Page 8 • Petroleum hydrocarbons reported as gasoline and reported as "unidentified petroleum ' hydrocarbons in the gasoline and diesel fuel range" exist in soil beneath the northern, central and southern portions of the site and extend beyond the northern and eastern site boundaries ' The residual petroleum hydrocarbons in soil beneath the site do not appear to have impacted groundwater based on depths of attenuation ranging from approximately 5 to 45 feet bgs ' • Based on the configuration and size of the petroleum hydrocarbon plume, it appears that petroleum hydrocarbon releases to the environment occurred from UST locations within the site Soil analytical data suggests that separate petroleum hydrocarbon ' releases occurred within the northeast and southern portions of the site and appear to have resulted in � rlappmg plumes T t • The vertical and lateral limits of petroleum hydrocarbons in the vadose zone have been ade uatel delineated to allow for the implementation of a soil remedial action plan ,, • Preliminary evaluation of field data obtained from the VET indicates that vapor extraction Al is a feasible technology for the remediation of impacted soil beneath the site • Based on the distribution of MTBE concentrations in groundwater, the MTBE source appears �,�, AA to be in an upgradient direction from the site • Based on the distribution of "weathered" TPHg concentrations in groundwater, the TPHg evlox--source in groundwater appears to be from an offsite source • Based on the distribution of unidentified hydrocarbons in the diesel fuel range in ' groundwater, the diesel fuel range hydrocarbons in groundwater appear to be from an offsite source RECOMMENDATIONS Geocon recommends that the data and information contained herein be used to prepare a Problem i Assessment Report (PAR) for submittal to the San Joaquin County Environmental Health Division i In addition to the information presented herein, the PAR should include all results obtained for the ' VET and present a discussion of remedial,options I Analytical data obtained from the GUMS analysis of soil gas collected from vapor extraction well ' VW-6 should be reviewed to evaluate and possibly identify the specific type of petroleum hydrocarbons present in soil beneath the northern portion of the site A detailed review of the gas chromatograms for selected soil samples should be performed to attempt to delineate TPHg from non-TPHg petroleum hydrocarbons in soil beneath the site I ; I