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• A S S a C I A T E S I N C 4.0 . EXISTING CONDITIONS 4.1 Soil Conditions Native sediments encountered in soil borings SBI though SB6 during field activities indicate that the upper 16 to 30 feet of the soil column consists primarily of silt (ML). Apparent fill (silty sand, SM) was observed in the upper 10 to 15 feet of soil borings SB1 and SB4. Groundwater was not encountered during drilling activities. Soil boring/well construction logs are contained in Appendix A. Results of laboratory analyseserformed on selected soil samples from the borings indicate p P g that total lead, detected in all the soil samples analyzed, is present beneath the site at ' concentrations ranging from less than 7 to 20 milligrams per kilogram (mg/kg). The analytical results were compared with the typical U.S. Mean and typical Bay Area concentrations in soil as presented in Summary of Typical Metals Concentrations in Soils and Surficial Materials, from U.S.G.S. Professional Paper 1270 for the Conterminous United States (USGS, April 1992). In comparison, the lead detected appears to be present at background concentrations. Petroleum hydrocarbon constituents were detected in soil samples collected from borings SB 1 P g and SB4. The highest reported constituent concentrations were observed in the soil samples collected at 15 feet bgs. The highest concentrations of petroleum constituents at this depth were detected in sample ET-SB4-15.0 and include toluene (91 mg/kg), ethylbenzene (190 mg/kg), xylenes (800 mg/kg), TPHg (9,100 mg/kg), and TPHd (1,700 mg/kg). The petroleum ' hydrocarbons appear to attenuate rapidly with depth as indicated greatest by soil sample ET- SB4-20, collected from SB4 at 20 feet bgs, which contained only trace levels of toluene (0.0071 mg/kg), ethylbenzene, xylenes (0.021 mg/kg), and TPHg (0.13 mg/kg). Rapid vertical attenuation of hydrocarbons is also evidenced by soil sample ET-SB1-30.0, collected at 30 feet bgs, which contained only trace levels of toluene (0.064 mg/kg), and xylenes 0.012 mg/kg). MTBE was not detected in any of the soil samples analyzed and benzene was detected only in sample ET-SB1-15.0 at a concentration of 0.90 mg/kg. No petroleum hydrocarbons were detected above laboratory method detection limits in soil samples collected from perimeter soil borings SB2, SB3, SB5 and SB6. Laboratory analytical results are consistent with field ' observations and PID readings. Analytical results are summarized in Table 1. Based on the 1997 analytical results of soil samples collected during the advancement of the soil borings, the horizontal and vertical extent of soil impacted by petroleum has been essentially defined and appears to be limited laterally to the immediate vicinity of the former tank pit. w:1943041reportsldosure.doc 3 r�