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52 Results of Assessment <br /> 5 2 1 Subsurface Conditions <br /> Consistent with the soil stratigraphy described in Section 4 0, on-site soils encountered during <br /> the drilling of borings SB-12 and SB-13 consisted predominantly of poorly-graded to well-graded <br /> sand, with some silt to the total depth explored of 40 5 feet bgs In boring SB-14, lean clay <br /> extended from the ground surface to approximately 14 5 feet bgs, and was underlain by <br /> predominantly poorly-graded to well-graded sand to approximately 75 feet bgs Gravel was <br /> present within the poorly-graded sand from approximately 44 5 feet to 75 feet bgs Below 75 <br /> feet to the total depth explored of 80 5 feet bgs in boring SB-14 was a lean clay layer containing <br /> I sand Groundwater was encountered in goring SB-14 at approximately 77 5 feet bgs Updated <br /> cross-sections including soil stratigraphic and analytical data obtained during this investigation <br /> are presented on Figures 5 and 6 <br /> 1 522 Soil Analytical Results <br /> I TPHg was detected in samples collected at approximately 30 feet bgs from borings SB-12 <br /> (1,300 milligrams per kilogram, mg/kg) and SB-13 (29 mg/kg), the 35-foot sample collected from <br /> SB-13 (1 3 mg/kg), and the 50-foot sample collected from SB-14 (110 mg/kg) Xylenes were <br /> 1 also detected in the 30-foot samples collected from borings SB-12 and SB-13, and the 50-foot <br /> . sample collected from boring SB-14 up to a maximum concentration of 18 8 mg/kg <br /> Concentrations of benzene, toluene, ethylbenzene, and fuel oxygenates were not detected at or <br /> above laboratory method reporting limits (MRLs) in the soil samples submitted for analysis Soil <br /> 1 analytical results are presented in Table 2 <br /> 523 Residual Soil Cuttings <br /> 1 A total of seven Department of Transportation (DOT)-approved, 55-gallon steel drums of soil <br /> cuttings were generated during drilling activities These drums were temporarily stored inside <br />' the SVEIAS treatment compound on-site pending waste characterization and disposal Due to <br /> the adequate supply of clean augers provided by the Gregg, the augers used during drilling <br /> were not decontaminated on-site, therefore, no rinsate water was generated during drilling <br /> activities The drums were transferred off-site by Filter Recycling Services, Inc (FRS) of Rialto, <br /> California to their facility for recycling/disposal on December 6, 2004 Documentation <br /> confirming waste disposal is included in Appendix J <br /> 53 Conclusions <br /> Based on the results of this investigation, the presence of residual petroleum hydrocarbons <br /> (specifically TPHg and xylenes) was limited to depths of approximately 30 to 35 feet bgs in the <br /> vicinity of the former USTs, and approximately 50 feet bgs in the vicinity of well MW-1 The <br />' vertical extent of petroleum hydrocarbons remained defined in these areas Residual petroleum <br /> hydrocarbon concentrations in soil from boring SB-14 were significantly lower than historical soil <br /> concentrations in borings W-8 and MW-1, which suggests the effectiveness of historical <br /> remedial efforts in this area <br /> Time IN Asmt&SCM doc 9 March 17 2005 <br /> 770T 41668 00 0015 <br />