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l I 1993 , when groundwater was first encountered at a depth of between 65 and 70 feet and subsequently stabilized at a depth of approximately 68 feet. In an earlier letter to Mr. Ed Gotelli, ' dated December 11, 1992 , the PHS/EHD reported that seasonal high groundwater (1986) at this site was estimated to be between 45 and 50 feet. ' 2 .4 Initial Assessment and Drilling On 9 October 1992 , a soil boring was installed in the center of the ' gasoline tank cavity (Boring #l, see Figure 2) . This boring was advanced to a depth of 60 feet. Samples were collected at five-foot intervals and analyzed for total petroleum hydrocarbons (TPH as ' gasoline) and volatile aromatics (BTE&X) . TPH as gas was detected in samples B1-20 (93 µg/g) , Bl--30 (6, 100 ' µg/g) and B1-40 (13 µg/g) . Benzene, toluene and xylene were detected in all samples except B1-60, at levels ranging from 0. 007 µg/g (xylene, B1-50) to 520 µg/g (toluene and xylene, B1-30) . Ethylbenzene was detected in samples B1-20 (3 . 5 gg/g) , Bl--30 (170 µg/g) and B1-40 (0. 37 µg/g) . The results were described in, a report dated 16 November 1992 , submitted by GeoAudit to San Joaquin County PHS/EHD. M3.0 PROCEDURES ' 3. 1 Drilling and Sampling On 9 and 10 March 1993 , three soil borings were drilled, using a I truck-mounted drill rig equipped with 8-inch-diameter hollow-stem augers. Each boring was drilled to a depth of 77 feet. Woodward Drilling of Rio Vista, California provided the drill rig and 2-man Idrilling crew. Discrete soil samples were collected ahead of the drill bit using a split-tube sampler loaded with three pre-cleaned 2 by 6-inch brass tubes. The samples were collected at five-foot intervals beginning at a depth of 10 feet. To avoid cross contamination, the sampling equipment was washed in a tri-sodium phosphate (TSP) ' solution and rinsed twice with water prior to each sampling run. Augers were steam cleaned between borings. For each sample, both ends of the lead tube were covered with aluminum sheets, capped and sealed with tape. The samples were labeled, logged on a chain of custody and stored on ice pending transmission to WEST Laboratories in Davis for analysis. Soil in the second and third tubes was then extruded and described in accordance with the Unified Soil Classification System. Descriptions were recorded on the boring logs. Auger returns and soil in the second tube were screened for the presence of organic 2