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Attachment A:Previous Environmental Activities <br /> The results of the investigation indicated that soil and groundwater were adequately <br /> delineated up gradient(south) and cross gradient(west) of the site. However,the lateral <br /> extent of affected soil and groundwater was not delineated down gradient(north and east) <br /> of the site, and the vertical extent of affected groundwater was not delineated. <br /> January 2004 and April 2006 California Department of Water Resources (DWR) <br /> Well Search. SAIC conducted a well search of DWR files to review well driller logs for <br /> domestic, irrigation, industrial, and municipal water supply wells within 2,000 feet of the <br /> site. The well search covered portions of Township 2-South, Range 4-East, sections 11, <br /> ' 13, and 14. SAIC reviewed water well completion reports for each section. Two water <br /> supply wells were located within the search area; both were listed as domestic wells. One <br /> of the wells was on site(DW-1) and screened from 124 feet to 144 feet with a 50-foot <br /> sanitary seal. The off-site well was approximately 1,300 feet west of the site and <br /> screened from 260 feet to 280 feet with a 100-foot sanitary seal. No other wells were <br /> identified within the search radius. <br /> ' May 2007 and March 2008 Investigation.3 The field investigation was conducted in <br /> two phases. The first phase was conducted in May 2007 and consisted of advancing nine <br /> shallow hand-auger borings (HA-I through HA-9) and three step-out hand-auger borings <br /> (HA-IA, HA-4A and HA-6A) in the general vicinity of the former blow-off pond,the <br /> former large AST, and the former small AST in the southwest area of the site. The <br /> second phase of the field investigation was conducted in March 2008 after a right of way <br /> agreement was obtained from the Union Pacific Railroad to access the off-site property. <br /> The second phase consisted of advancing one on-site soil boring(SB-14) and four off-site <br /> soil borings (SB-15 through SB-18). Soil and groundwater samples were collected from <br /> all borings and analyzed for TPHc, BTEX, and PAHs. SAIC also sampled water supply <br /> well DW-1 for General Minerals, TPHd, BTEX, and PAHs to confirm previous results. <br /> Various soil and groundwater sample analytical results exceeded screening levels. TPHc <br /> exceeded screening levels in 10 soil samples with the highest concentration of <br /> 9,600 mg/kg in HA-4, and PAHs exceeded levels in four soil samples. TPHd exceeded <br /> screening levels in five groundwater samples with the highest concentration of <br /> 4,400 gg/L in SB-18. PAHs did not exceed screening levels in groundwater. Boring <br /> SB-16 was not sampled due to the presence of separate-phase oil(SPO). The <br /> groundwater sample collected from DW-1 indicated no TPHd or PAH exceedances and a <br /> TDS value of 1,640 mg/L. <br /> The investigation report concluded that the lateral extent of affected soil still was not <br /> delineated down gradient(north and northeast)of the site. Additional soil investigation <br /> was recommended. The lateral extent of affected groundwater was not delineated down <br /> gradient(north and north east) of the site as indicated by SPO in SB-16 and <br /> ' concentrations of TPHd above Water Quality Objectives (WQOs) and/or Environmental <br /> Screening Levels (ESLs) for samples collected from SB-17 and SB-18. Additional <br /> groundwater investigation was recommended. <br /> Results from a grab groundwater sample collected from well DW-I during the 2004 and <br /> 2007/2008 investigation continued to be at non-detect levels at or above the lowest,most <br /> 3. SAIC,2008. Soil and Groundwater Investigation Report, Tracy Pump Station, Tracy, California. June. <br /> 1 <br />