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Well Installation and Soil Boring Report-Tosco(former Unocal)Service Station#6981, Stockton, CA <br /> November 15, 1999 <br /> RESULTS <br /> Soil chemical analytical data are summarized in Table 1 Groundwater chemical analytical data are <br /> summarized in Table 2 Laboratory reports and chains-of custody forms are included in Appendix E <br /> Subsurface Conditions <br /> Soil encountered in borings MW-14,MW-15,VW-7,VW-8,and VW-9 consisted predominantly of clay and <br /> silt with lesser amounts of sand to a maximum depth of approximately 86 feet bgs Groundwater was <br /> encountered in each of the borings at depths between 27 and 29 feet bgs Detailed descriptions of the <br /> subsurface materials encountered during drilling are presented on the boring logs in Appendix D These <br /> conditions appear similar to those encountered during previous investigations at the site During this <br /> investigation groundwater was encountered between approximately 27 and 29 feet bgs <br /> Laboratory Analyses <br /> Soil samples were analyzed by Sequoia Analytical in Sacramento,California(ELAP#1624) Selected soil <br /> samples from each boring were analyzed for Total Petroleum Hydrocarbons quantified as gasoline(TPHg), <br /> benzene, toluene, ethylbenzene and xylenes (BTEX) and methyl tertiary-butyl ether(MtBE)by the DHS <br /> . LUFT methodology <br /> Groundwater samples were analyzed by Sequoia Analytical in Walnut Creek, California(ELAP # 1271) <br /> The collected samples from each well were analyzed for TPHg, BTEX, and MtBE by the DHS LUFT <br /> methodology,and for oxygenates(MtBE,DIPE,TAME,TBA,ETBE, and ethanol)by EPA Method 8260 <br /> Soil Analytical Results <br /> A total of 41 soil samples were analyzed All analyzed samples from borings MW-14,MW-15,and VW-9 <br /> were non detect (ND) for all measured analytes Minor concentrations of petroleum hydrocarbons were <br /> identified in samples from boring VW-8 with a maximum TPHg concentration of 7 24 parts per million <br /> (ppm)and a maximum benzene concentration of 0 0498 ppm High concentrations of TPHg and BTEX were <br /> detected in samples from boring VW-7 between 31 and 46 feet bgs,with a maximum TPHg concentration <br /> of 19,200 ppm and a maximum benzene concentration of 166 ppm Each of these concentrations were <br /> detected in the sample collected at 41 feet bgs Concentration levels dropped significantly below this depth <br /> -- until both reached ND levels by 81 feet bgs MtBE was not detected in any of the soil samples analyzed <br /> Groundwater Analytical Results <br /> No measurable concentrations of TPHg or BTEX were detected in samples collected from monitoring wells <br /> MW-14 or MW-15 TPHg and benzene were each detected in wells MW-16 and VW-7 at maximum <br /> concentrations of 37,000 parts per billion (ppb) and 2,500 ppb respectively (from VW-7) MtBE was <br /> detected in all wells at concentrations ranging from 2 0 ppb in MW-15 to 510 ppb in VW-7 <br /> 140124 05 4 <br />