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Groundwater was not encountered in any of the borings. A domestic water supply well 1 is located on the property next to the truck washing area. The current water level in this well is reported to be approximately 90 feet below grade. According to Mr. Michael Collins of the San Joaquin County DHS/EHD the water table in the Escalon area was at approximately 50 feet in 1986. 5.2 Borings and Analytical Results The highest hydrocarbon concentrations reported from the preliminary sampling occurred at the north end of the former diesel tank. The tank excavation was never filled and was open at the time of this investigation. Little caving had occurred; the sides of the pit remained sheer and its overall depth was 10 to 12 feet. A dark hydrocarbon stain was observed on the north wall of the excavation extending from the east side of the wall to within a few feet of the west wall at a depth of five to the bottom. The former dispenser was also located at this point and a fuel leak associated with this equipment was known to have.occurred in the past. Accordingly, Boring D-1 (Exhibit 6) was located at the north end of the excavation in an effort to define the vertical extent of impacted.soil at the point of origin. of the fuel discharge (Exhibit 3). A jack hammer was used to break a hole in the concrete pad and the boring was directed southward under the tank at a'30 degree angle. The first indications of hydrocarbons occurred at a depth of 13 feet where a distinct petroleum odor and 98 unit FID reading was noted. Odor and elevated instrument readings persisted to 28 feet, the highest FID reading occurred at 23 feet (700 units). A slight FID increase over background was recorded when testing the 33 foot sample, below which no hydrocarbons were evident to a total measured depth of 40 feet (equivalent to 37.2 feet, true vertical depth. At this depth, the bottom of the boring was 21.5 feet from its surface location or about 5 to 10 feet from north end of the former tank. Samples from a depth of 23, 28, 33 and 43 feet were submitted for analysis. The results substantiated field indicators. A TPH(diesel) concentration of 4100 ppm at 23. feet, 3900 ppm at 28 feet, 410 ppm at 33 feet and None Detected at 43 feet were reported. BTEX constituents were found at very low concentrations in the 23 and 28 foot samples. Analytical results are tabulated in Table 2 and complete laboratory reports are provided in Appendix A. The mobile lab also ran samples from depths of 18 and 33 feet. Hydrocarbons were detected in the 18 foot sample, but not at 33 feet. The chromatograms are provided in Appendix B. _ 1 - r I t ' 7