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I Previous Investigations SSB Environmental Consultants, Inc performed the initial investigation at the site in July of 1991 The preliminary investigation consisted of the installation of four 2-inch diameter PVC groundwater monitoring wells (MW1 - MW4) to about 75 feet below grade at the locations shown on Figure 2 Results of analyses indicated the highest concentrations of gasoline range hydrocarbons (TPH) in soil were found between depths of 20 and 45 feet in well MW2 (37 mg/kg to 560 mg/kg) TPH concentrations in soils from well MW1 ranged from 0 4 to 37 mg/kg The other wells had TPH concentrations less than 7 mg/kg in the soil samples collected during drilling Gasoline range hydrocarbons were detected in groundwater from each of the wells with benzene concentrations ranging from 36 4 to 5,270 ugA The details of this investigation are presented in the SSB report titled "Preliminary Assessment of Soil and Groundwater Quality at Thrifty Oil Co Station No 172, 7647 Pacific Avenue, Stockton, California", dated July 17, 1991 In April 1994, Thrifty conducted an additional investigation at the site Three vadose wells (VWA, VWB and VWC) and two groundwater monitoring wells (MW7 and MW8) were installed at the property The vadose wells were located immediately adjacent to the underground tanks and were intended for use in a vapor extraction system The groundwater monitoring wells were located along the southwest and southeast corners of the site This work was the first phase of the original proposed scope of work described in the Revised Workplan Results of analysis from soil sampling indicate up to 21,000 mg/kg TPH was detected in soils from well VWC at 30 feet below grade Soil samples from wells VWA and VWB contained 23 mg/kg TPH or less Soils from wells MW7 and MW8 had less than 1 mg/kg TPH Results of quarterly groundwater sampling indicate well MW8 consistently has had high dissolved hydrocarbon concentrations, which is interesting since it is located in an upgradient position and the soil samples did not contain significant hydrocarbon Page 2