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w IWO/ regular gasoline were removed from the tank at this time. One sample was collected from two feet below the bottom of the excavation, and a second sample was collected from the west wall of the excavation where soil staining was observed. Total petroleum hydrocarbons (TPH as gasoline), ethylene dibromide (EDB) and lead were detected in the bottom sample at 15,000 ppm, 1,800 ppm and 13 ppm, respectively. The sample from the west sidewall contained TPH as gasoline, EDB and lead at 13,000 ppm, 2,300 ppm and 38 ppm, respectively. It was determined that an unauthorized release of hydrocarbons had occurred, and further investigation would be required. 2.4 Groundwater Depth and Gradient According to the San Joaquin County Flood Control Map(Fall, 1990), depth to groundwater in the area is between 60 and 70 feet. The regional groundwater gradient is towards the south or southwest. Monitoring wells, located approximately 1/4 mile south of the subject site, installed and maintained by GeoAudit, indicated a depth to groundwater of approximately 55 feet in April of 1993. 2.5 Soil Boring Drilling, September 1993 On September 28, 1993, one soil boring was drilled at the site by GeoAudit. The boring (B3) was drilled in the former UST excavation. Samples from depths of 20, 30 and 35 feet were analyzed for TPH as gasoline and BTE&X (B3-20, 133-30 and 133-35). TPH and BTE&X con t amination were detected in sample 133-20 at concentrations to 5.7 ppm (Table 1). However, no contamination was detected at depths of 30 and 35 feet. In a letter dated October 21, 1993, GeoAudit recommended excavation of the hydrocarbon impacted soil. TABLE 1 Analytical Results of Soil Samples September 28, 1993 mg/kg Sample I.D. TPH as Ethyl- Gasoline Benzene Toluene benzene Xylene 113-20 5.7 0.092 0.45 0.11 0.61 B3-30 ND ND ND ND ND B3-35 ND ND ND ND ND Not detected mg/kg=parts per million(ppm) 0.1.0.1 n.&s—i...1— 2 73S/34 YnYBR-.wpl