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1 1444 MARIPOSA ROAD WKA No 2307 02 December 15, 1993 Page 2 I November 9, 1992 At 36 feet below grade, petroleum hydrocarbon odors were still noticeable ' in the soils, so an exploratory trench was dug in the center of the excavation to a depth of approximately 44 feet below grade Because further excavation would require sloping of the side walls, the decision was made to drill exploratory soil borings to further evaluate the vertical and ' lateral extent of hydrocarbon contamination ' In accordance with our Site Contanunation Workplan dated December 4, 1992, four soil borings (B1 through B4) were drilled between March 29-31, 1993 at the locations shown on Plate 2 ' Boring B1 was constructed approximately five feet easterly of the excavation and extended to a depth of 86 5 feet Drilling was discontinued when ground water was encountered in the boring ' at a depth of approximately 85 feet Soil borings B2 and B3 were drilled at approximate 30° angles from vertical beneath the location of former underground storage tanks to vertical depths of 71 and 81 feet below site grade The sods in these borings consisted primarily of silty clays and clayey silts, two thin sand,layers were ' observed at depths of approximately 49 to 53 feet and 63 to 68 feet Boring B4 was constructed approximately ten feet westerly of the excavation to a depth of 49 5 feet A slight petroleum odor was noted in each of the four soil borings ' Analytical results of the selected soil samples from the four soil borings revealed relatively low concentrations of petroleum constituents at a depth of 75 feet below surface grade Cross- sectional diagrams depicting the estimated extent of petroleum hydrocarbon contaminated soil are shown on Plates 3 and 4 A comprehensive discussion of our field procedures and findings is ' included in our May 24, 1993 Report of Findings on file with the San Joaquin County Public Health Services i WALLACE•KUHL R ceded paper S ASSOCIATES INC