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Attachment B: Previous Environmental Activities ' <br /> Central Valley RWQCB accepted the work plan in a September 2008 letter6, Due to delays with <br /> the off-site property tenant,the investigation was limited to the proposed on-site activities. <br /> SAIC advanced soil boring SB-19 using a direct push drill rig to 55 feet bgs. An SAIC geologist <br /> screened the soil cuttings for evidence of crude oil using a photo-ionization detector to measure <br /> hydrocarbon vapors in soil. The boring was intended for vertical groundwater delineation; ' <br /> therefore, soil samples were not collected for analytical sampling. A depth discrete water sample <br /> was collected at 50 feet bgs for vertical delineation of affected groundwater. <br /> The groundwater sample was analyzed for TPHd,BTEX,and PAHs. TPHd and BTEX were not ' <br /> detected in the depth-discrete groundwater sample. Several PAHs were detected; however, only <br /> benzo(a)pyrene was detected above the WQO and ESL(0.0029 gg/L and of 0.014 µg/L <br /> respectively)with a concentration of 0.026 gg(L. The data usability evaluation determined that ' <br /> all analytical data are usable. <br /> SAIC concluded that the vertical extent of affected groundwater on site has been defined by SB- ' <br /> 19 at 50 feet bgs. TPHd and BTEX were not detected. Benzo(a)pyrene was detected in excess <br /> of its WQO and ESL; however,this singular occurrence is not indicative of a larger-scale <br /> presence of PAHs in groundwater in concentrations that may pose a risk to human health. The <br /> absence of crude-oil related constituents in the groundwater sample suggest the result is <br /> anomalous. The lateral and vertical extent of affected soil and groundwater on site has been <br /> delineated up gradient, cross gradient,and down gradient(to the property boundary). The lateral ' <br /> and vertical extent of affected soil and groundwater have not been delineated off site. SAIC <br /> recommended that the RWQCB accept the proposed site division, and grant approval to proceed <br /> with risk assessment activities for the on-site property. The Central Valley RWQCB concurred <br /> with the conclusions and recommendations in a March 2010 letter 7. <br /> 1 <br /> 6_ Central Valley RWQCB,2008. Review—Soil and Groundwater Investigation Workplan,Former Tracy Pump Station, 14821 , <br /> West Grant Line Road, Tracy,San Joaquin County. September. <br /> 7_ Central Valley RWQCB,2010_ Review-Soil and Groundwater Investigation,Former Tracy Pump Station, 14821 West Grant <br /> Line Road, Tracy,San Joaquin County. March 10. <br /> B-4 , <br /> SAIC <br /> 1 <br />