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0 <br />3 Report 402.331-86.70 <br />crew. Exploratory borings B-1 and B-2 (fig. 2) were drilled and sampled <br />using a truck mounted drill rig with 6" continuous flight solid stem augers. <br />Drilling was conducted without adding fluids to the boreholes. Soil samples <br />collected from the borings were drive samples taken with a 2" I.D. split <br />spoon sampler with six 2" X 4" brass tube liners. The sampler was driven <br />18" into the tank backfill beyond the tip of the auger by a 140 lb safety <br />hammer with a 30" drop. Prior to each sampling the split spoon sampler and <br />brass tubes were thoroughly cleaned to avoid cross contamination. Samples <br />selected for laboratory analysis were retained in the brass liners, labeled, <br />capped with a polyethylene lid, sealed with electrical tape, and placed on <br />ice. The sampling interval ranged from continuous to 5 feet apart. The <br />samples were logged and visually classified (U.S.C.S. D-2487-83) by the on <br />site geologist. Complete borehole logs are included in Appendix A. Drilling <br />and sampling operations were completed on July 28, 1986 and the boreholes <br />filled with tank backfill. <br />Results <br />Boreholes B-1 and B-2 were drilled and sampled to depths of 11 feet <br />(2.5 feet beyond the bottom of the tank). No ground water was encountered. <br />Soil samples obtained from both borings appeared to be free of <br />contamination. The upper 8.5 to 9 feet of material encountered consists of <br />a reddish brown, moist, loose, well sorted tank backfill sand. The native <br />material that underlies the backfill consists of a brown, moist, medium <br />dense sand with sparse gravel. A single soil sample from each boring, <br />taken at 10.5 feet, was selected for chemical analysis. The samples were <br />analyzed by EPA method 8015 (GC -FID Purge and Trap) for gasoline and <br />kerosene and EPA method 8100 (GC -FID extractable hydrocarbons) for diesel <br />and oil. Results of these analyses are presented in the attached <br />laboratory test report from McKesson Environmental Services, Inc. (Appendix <br />B). Both of the soil samples tested showed a total gasoline, kerosene, and <br />diesel concentration below the detectable range (0.05 ppm for gasoline and <br />kerosene and 10 ppm for diesel). The concentration of oil was non-detectabe <br />(detectable range less than 100 ppm) in the sample tested from borehole B-2 <br />but showed a concentration of 170 and 200 ppm in separate tests run on the <br />sample obtained from borehole B-1. The results of the laboratory chemical <br />analyses indicates that no significant gasoline tank leakage has occurred. <br />However, the presence of oil hydrocarbons in the sample tested from borehole <br />B-1 suggests that some contamination, in the vicinity of the tank, from an <br />indeterminate source has occurred. Additional drilling and sampling is <br />needed to adequately define and identify the source as well as the vertical <br />and horizontal extent of the oil contamination. <br />RafnrnnPnc <br />Calif. Division of Mines and Geology, 1966, Geologic Map of California - <br />Sacramento Sheet. <br />