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Attachment$Previous Environmental Activities 1 irrigation, industrial, and municipal water supply wells within 2,000 feet of the site. The well search covered portions of Township 2-South, Range 4-East,sections 11, 13, and 14. SAIC reviewed water well completion reports for each section. Two water supply wells were located within the search area; both were listed as domestic wells. One of the wells was on site (DW-1) ' and screened from 124 feet to 144 feet with a 50-foot sanitary seal. The off-site well was approximately 1,300 feet west of the site and screened from 260 feet to 280 feet with a 100-foot sanitary seal. No other wells were identified within the search radius. May 2007 and March 2008 Investigation.3 The field investigation was conducted in two phases. The first phase was conducted in May 2007 and consisted of advancing nine shallow hand-auger borings (HA-1 through HA-9) and three step-out hand-auger borings (HA-IA, HA- 4A and 14A-6A) in the general vicinity of the former blow-off pond, the former large AST, and the former small AST in the southwest area of the site. The second phase of the field investigation was conducted in March 2008 after a right of way agreement was obtained from the ' Union Pacific Railroad to access the off-site property. The second phase consisted of advancing one on-site soil boring(SB-14)and four off-site soil borings(SB-15 through SB-18). Soil and groundwater samples were collected from all borings and analyzed for TPHc, BTEX, and PAHs. SAIC also sampled water supply well DW-1 for General Minerals, TPHd, BTEX, and PAHs to confirm previous results. Various soil and groundwater sample analytical results exceeded screening levels. TPHc exceeded screening levels in 10 soil samples with the highest concentration of 9,600 mg/kg in HA-4, and PAHs exceeded levels in four soil samples. TPHd exceeded screening levels in five groundwater samples with the highest concentration of 4,400 pg/L in S13-18. PAHs did not exceed screening levels in groundwater. Boring SB-l6 was not sampled due to the presence of separate-phase oil (SPO). The groundwater sample collected from DW-1 indicated no TPHd or PAH exceedances and a TDS value of 1,640 mg/L. ' The investigation report concluded that the lateral extent of affected soil still was not delineated down gradient(north and northeast)of the site. Additional soil investigation was recommended. The lateral extent of affected groundwater was not delineated down gradient(north and north east)of the site as indicated by SPO in SB-16 and concentrations of TPHd above Water Quality Objectives (WQOs) and/or Environmental Screening Levels(ESLs)for samples collected from SB-17 and SB-I8. Additional groundwater investigation was recommended. ' Results from a grab groundwater sample collected from well DW-1 during the 2004 and 2007/2008 investigation continued to be at non-detect levels at or above the lowest, most conservative WQO and ESL concentrations for TPHd, BTEX, and PAHs, indicating that the water from DW-1 was not affected by petroleum hydrocarbons. 2010 Soil and Groundwater Investigation¢. SAIC submitted a soil and groundwater ' investigation work plan to the Central Valley RWQCB in August 20085 for further delineation of soil and groundwater both on-site and off-site. The work plan proposed one boring on the Tracy Pump Station property to evaluate the vertical extent of affected groundwater, and six off-site borings to further evaluate the lateral and vertical extent of affected soil and groundwater. The " SAIC,2008. Soil and Groundwater Investigation Report,Tracy Pump Station, Tracy, California. lune. ' 4 SAIC,2010_ Soil and Groundwater Investigation Report, Tracy Pump Station, 14821 West Grant Line Road, Tracy, San Joaquin County, California. January. 5. SAIC,2008. Soil and Groundwater Investigation Work Plan Former Tracy Punip Station, 14821 West Grant Line Road, Tracy,San Joaquin County. August. ' B-3 SAIC