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. Soil and Groundwater Investigation Report ARCO Facility No 2168 Stockton, California Page 7 and 1C96, classified onsite as silt, were tested to have permeability values of 3 1 x 10-6 cm/sec (0 98 m/yr) and 9 3 x 10-7 cm/sec (0 29 m/yr), respectively Sample 8C40, classified onsite as silty sand, was tested to have a permeability value of 2 6 x 10-5 cm/sec (2 46 m/yr) The laboratory report for permeability testing is included in Appendix C Laboratory Results Total petroleum hydrocarbons as gasoline and BTEX compounds were detected between 25 and 65 feet bgs in the samples collected from boring/well MW-1C and between 35 and 75 feet bgs in the samples collected from boring/well MW-8C The highest concentrations of TPHG and benzene were detected to samples collected from bonng/well MW-1C TPHG was detected at 100 mg/kg at 35 feet bgs and benzene was detected at 0 719 mg/kg at 45 feet bgs (see Table 3) MTBE was detected only in two soil samples collected from MW-8C (1 07 mg/kg at 35 feet bgs using Method 8260 and 0 266 mg/kg at 45 feet bgs, using Method 8015/8020) Methanol was detected to samples 8C35 (1 07 mg/kg), 8C50 (2 39 mg/kg), and 8C75 (5 08 mg/kg) TBA, DIPE, ETBE, TAME, EDB, 1,2 DCA, and ethanol were not detected in any of the soil samples Soil analytical results are summarized in Table 3 Figure 3 summarizes TPHG and benzene concentrations detected in soil Certified analytical reports with chain-of-custody documentation are located in Appendix C Groundwater samples were collected from momtonng wells MW-I through MW-8, MW- 1B, MW-1C, MW-8B, and MW-8C (Figure 2) TPHG was detected in all water samples collected at concentrations ranging from 53 7 µg/l (MW-1C) to 37,900 µg/1 (MW-6) Benzene was also detected in all water samples collected, except MW-8, at concentrations ranging from 15 6 pg/l (MW-8C) to 9,540 µg/l (MW-3) MTBE was detected in samples collected from MWA (2 28 µg/1), MW-3 (12 7 µg/1), and MW-4 (90 µg/1) TBA was detected in samples collected from MW-3 (244 µg/1) and MW-4 (392 µg/1) 1,2-DCA was detected in samples collected from various monitoring wells with the highest concentration detected in upgradient and offsite well MW-6 ETBE, TAME, EDB, ethanol and methanol were not detected in any of the water samples Groundwater analytical results are detailed in Table 4 and Figure 5 provides a summary of TPHG, benzene, and MTBE concentrations Certified analytical reports with chain-of-custody documentation are located in Appendix C Summary of Findings The following summarizes the results of the investigation • The soil beneath the site is predominately fine grained (clayey silt, silt, silty sand, and fine-grained sand) to a depth of approximately 55 feet bgs, and becomes