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16 August 2001 AGE-NC Project No 97-0312 Page 3 bf 20 t 2 4 , GROUND WATER DEPTH AND FLOW DIRECTION Review ofhistorca1 depth to ground wa_termaps published b the San Joaquin County Flood Control , and Water Conservation District(FCD&WCD)dating back to 1971 suggests that groundwater depth ' near the site has fluctuated between approximately 40 and 85 feet bsg, review of regional ground water elevation maps published by the FCD&WCD (1998) suggest a southeast to northeast ground ' water flow direction Based on twenty-six ground water monitoring events recorded at the site between October 1996 and ' March 2001, depth to ground water measurements have fluctuated between 49 and 69 feet bsg, gradient has been relatively horizontal at the site ranging between 0 00035 and 0 005 ft/ft Ground water flow direction has-been inferred to be towards the northeast on all but one occasion (June ' 2000, flow direction toward the northwest) Depth to ground water and ground water elevation data are summarized in Table 1 ' 3.0. SUMMARY OF PRELIMINARY INVESTIGATION AND EVALUATION ' Site assessment activities summarized below were originally reported in quarterly reports prepared by Environrnental Science & Engmgeering, Inc (ESE) between June 1990 and February 1997 and by AGE between March 1997 and May 2001 Appendix A contains a list of reports referenced in ' preparing this summary The following is a summary of significant assessment activities conducted to date at the Cherokee Truck Ston site ' May 1990- Review of San Joaquin County Public Health Services -Environmental Health x' Division (PHS-EHD) files for the site indicated fourteen soil borings (B1 through B13, HA-1) were advanced near the UST, piping and dispenser areas to assess the lateral and ' vertical extent of impacted soil Petroleum hydrocarbon compounds were detected in 15 of the twenty samples collected from the borings Total petroleum hydrocarbons quantified as gasoline (TPH-g) and diesel (TPH-d) ,were detected at concentrations as high as 5,800 ' milligrams per kilogram (mg/kg) and 12,000 mg/kg, respectively Petroleum hydrocarbons were found to extend to a depth of approximately 50 feet below surface grade (bsg)near the fueling island location Soil boring locations are depicted in Figure 4 A summary of soil sample analysis is presented in Tables 2 and 3 As-built well diagrams and boring logs, where available, are included in-Appendix B ' September/October 1990-One ground water monitoring well(UST-1)was installed on-site u to a depth of approximately 102 feet bsg ,Laboratory analysis of soil samples collected from ' UST-I contained concentrations of petroleum hydrocarbon compounds to a depth of at least 85 feet bsg Laboratory analysis ofthe initial ground water sample collected from UST-1 also , Advanced GeoEovironmental,Inc