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Attachment A:Previous Environmental Activities ' <br /> conservative WQO and ESL concentrations for TPHd, BTEX, and PAHs, indicating that <br /> the water from DW-1 was not affected by petroleum hydrocarbons. <br /> 2010 Soil and Groundwater Investigation 4. SAIC submitted a soil and groundwater ' <br /> investigation work plan to the Central Valley RWQCB in August 20085 for further <br /> delineation of soil and groundwater both on-site and off-site. The work plan proposed <br /> one boring on the Tracy Pump Station property to evaluate the vertical extent of affected <br /> groundwater, and six off-site borings to further evaluate the lateral and vertical extent of <br /> affected soil and groundwater. The Central Valley RWQCB accepted the work plan in a , <br /> September 20081etter6. Due to delays with the off-site property tenant, the investigation <br /> 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 ' <br /> geologist screened the soil cuttings for evidence of crude oil using a photo-ionization <br /> detector to measure hydrocarbon vapors in soil. The boring was intended for vertical <br /> groundwater delineation; therefore, soil samples were not collected for analytical , <br /> sampling. A depth discrete water sample was collected at 50 feet bgs for vertical <br /> delineation of affected groundwater. <br /> The groundwater sample was analyzed for TPHd, BTEX, and PAHs. TPHd and BTEX <br /> were not detected in the depth-discrete groundwater sample. Several PAHs were <br /> detected; however, only benzo(a)pyrene was detected above the WQO and ESL <br /> (0.0029 µg/L and of 0.014 µg/L respectively) with a concentration of 0.026 µg/L. The ' <br /> data usability evaluation determined that all analytical data are usable. <br /> SAIC concluded that the vertical extent of affected groundwater on site has been defined ' <br /> by SB-19 at 50 feet bgs. TPHd and BTEX were not detected. Benzo(a)pyrene was <br /> detected in excess of its WQO and ESL; however, this singular occurrence is not <br /> indicative of a larger-scale presence of PAHs in groundwater in concentrations that may , <br /> pose a risk to human health. The absence of crude-oil related constituents in the <br /> groundwater sample suggest the result is anomalous. The lateral and vertical extent of <br /> affected soil and groundwater on site has been delineated up gradient, cross gradient, and <br /> down gradient(to the property boundary). The lateral and vertical extent of affected soil , <br /> and groundwater have not been delineated off site. SAIC recommended that the <br /> RWQCB accept the proposed site division, and grant approval to proceed with risk <br /> assessment activities for the on-site property. The Central Valley RWQCB concurred ' <br /> with the conclusions and recommendations in a March 2010 letter7. <br /> 4 SAIC,2010. Soil and Groundwater Investigation Report, Tracy Pump Station, 14821 West Grant Line Road, Tracy, <br /> San Joaquin County, California. January. <br /> 5. SAIC,2008. Soil and Groundwater Investigation Work Plan,Former Tracy Pump Station, 14821 West Grant Line <br /> Road, Tracy,San Joaquin County. August. <br /> 6. Central Valley RWQCB,2008. Review—Soil and Groundwater Investigation Workplan,Former Tracy Pump <br /> Station, 14821 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 <br /> West Grant Line Road, Tracy,San Joaquin County. Match 10. <br />