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f ��f r The UST's along with product dispensers and associated piping were removed under permit from San Joaquin County PHS/EHD on January 19, 1999 Analytical results of the soil samples collected from beneath the UST's and the former dispenser island indicated contamination by petroleum hydrocarbons Analytical results from the tank removal are summarized in Table 1 Sample locations are depicted on Figure 2 Soil Boring Investigation On April 19 and April 20, 1999, Ground Zero conducted a subsurface investigation in order to determine the lateral and vertical extent of contamination Two borings, SBI and SB2, were advanced to a depth of approximately 16 feet bgs in the area proposed for installation of new UST's in order to determine the suitability of the material for backfilling the excavation These borings were located west of the office building on the property (Figure 2) The remaining six soil borings, SB3 through SB8, were advanced to Investigate the lateral and vertical extent of residual soil contamination, as well as the potential Impact to groundwater Bonngs SB3 through SB8 were located around the perimeter of the UST excavation and in the area of the former lines and dispensers Soil and groundwater samples collected from borings SB3 and SB5-SB8 had non-detectable levels for the target analytes However, boring SB4ISB4A had elevated petroleum hydrocarbon concentrations in soil at a depth of 15 feet Soil at a depth of 20 feet did not contain detectable concentrations Petroleum hydrocarbons were also detected in the groundwater sample collected from this boring The data obtained from this investigation indicated that the vertical extent of contamination did not exceed 20 feet below ground surface (bgs) and defined the lateral extent of soil contamination 'The contaminants consisted primarily of diesel and MTBE Soil results summarized in Table I Groundwater results are summarized in Table 2 Sample locations are depicted on Figure 2 Based on the results of this investigation, source removal excavation was proposed in the Corrective Action Workplan dated June 2, 1999 Hydrogeological Setting _ The site is located in southwestern Stockton approximately 6,500 feet south of the Stockton Deepwater Channel, the nearest body of surface water Surface elevation at the site is approximately five feet above sea level Based on historical information provided by San Joaquin County Flood Control and Water Conservation District, groundwater beneath the site was expected to be encountered at approximately 20 feet (bgs), and flow in a northeasterly direction 1. Woolseylreportslsoilxsum doc 2