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Soil and Groundwater Investigation Report ARCO Facility No 6100 Tracy, California . Page 6 RESULTS OF INVESTIGATION Site Geology and HydrogeoloZy Silt and clayey silt were encountered in the boring from 0 to 57 feet bgs, with sand lenses present from 16 to 18 feet, 25 to 26 feet, and 43 to 45 feet bgs Silty sand was encountered from approximately 57 to 70 feet bgs Silt and sandy silt were present from approximately 70 to 83 feet bgs Salty sand was present from 83 to 106 feet bgs Silt and clayey silt were encountered from 106 to 202 feet bgs Moisture content of the soil samples collected from the borehole varied from dry to moist A geologic log detailing soil types encountered while advancing the boring is presented in Appendix A Material encountered during drilling was relatively consistent with the soil logged from vapor extraction wells located in the immediate vicinity (VW-17 through VW-20) The total depth drilled for vapor extraction well VW-17 is approximately 110 feet bgs The total depths of vapor extraction wells VW-18 through VW-20 range from approximately 73 to 88 feet bgs, though their surface elevation is approximately 15 to 20 feet lower than • the surface elevation of monitoring well MW-1 A Delta representative measured water levels in 18 of the 20 vapor extraction wells at the site on October 3, 2000 Two wells could not be accessed due to the condition of the well head (well box lids rusted shut) Table 1 presents depth to water and total depth of the vapor extraction wells Eight of the 18 vapor extraction wells measured had water levels greater than 0 5 feet in the bottom of the casing Typical threaded PVC bottom caps are four to six inches in length Depth to water in these eight wells ranged from 24 15 to 58 00 feet bgs Monitoring well MW-1 had water levels of approximately 106 to 108 feet bgs, depending on product thickness, during September and October, 2000 Vapor extraction well VW-17 located approximately 8 feet northeast of monitoring well MW-1, and other vapor extraction wells in the vicinity do not contain water with the exception of VW-20 (approximately 1 foot of water in the well) The field data sheet showing water levels and total depths of the wells is presented in Appendix B Laboratory Results Results of soil laboratory analysis are presented in Table 2 Chain-of-custody forms and certified analytical reports for the soil samples are presented in Appendix C The highest concentrations of TPHG and BTEX compounds were detected in the sample collected from 111 feet bgs at concentrations of 4,440 mg/kg (TPHG), 22 3 mg/kg (benzene), 188 mg/kg (toluene), 76 3 mg/kg (ethylbenzene), and 391 mg/kg (total xylenes) TPHG was detected in the soil samples from 50 to 142 feet bgs, and benzene from 50 to 131 feet bgs