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Monitoring Well Destruction and Soil and Groundwater Investigation Report US Can—Welty Road December 28,2010 west(up gradient)of Areas 1 and 2 has been delineated by borings SB-44 and SB-45, respectively. The down-gradient(northeastern) extent of affected groundwater can be inferred based on borings from the current investigation(SB-47) and previous investigations(SB-35 and SB-42). Maps depicting concentrations of COPCs in soil and groundwater samples collected from the previous investigation are included as Appendix G. The area of affected groundwater northeast of SB-46 (CPS property)has been defined to the extent practicable. Additional delineation to the northeast is not possible due to property-access issues. A previously existing access agreement was cancelled by CPS in 2009. The areas of affected groundwater northwest of the US Can property boundary (borings SB-38 through SB-41 and SB-43)will be investigated separately as part of the Ahern Road—Vernalis site. SAIC-Benham submitted a work plan for Ahern Road—Vernalis on August 26, 2010 (SAIC-Benham, 2010), and it was accepted in a September 2010 letter from the Central Valley RWQCB (Central Valley RWQCB, 2010b). The extent of crude-oil affected soil and groundwater depicted on Figure 3 was derived from SAIC-Benham's evaluation of the data collected during this and previous investigations. 5.1.1 Suitability of the Groundwater for Drinking SAIC-Benham submitted one grab groundwater sample (SB-44) for TDS and General Minerals analysis. The TDS concentration was 1,280 milligrams per liter(mg/L),which exceeds the following current CDPH MCLS and Central Valley RWQCB Water Quality Goals(WQG; Central Valley RWQCB, 2000) for drinking water: • CDPH MCL: 500 mg/L,recommended; 1,000 mg/L,upper; 1,500 mg/L, short term. • Central Valley RWQCB WQG, CDPH, and EPA drinking water standards: 500 mg/L. • Central Valley RWQCB WQG, Agricultural Water Quality Goal: 450 mg/L. • Central Valley RWQCB WQG,EPA Ambient Water Quality Criteria for Taste and Odor or Welfare: 250 mg/L. The results of the General Minerals analyses indicated boron, chloride,manganese, nitrate as nitrogen, sodium, and sulfate in concentrations in excess of their respective WQOs; the chloride and manganese concentrations also exceeded their respective MCLS. The sample exceeded the WQO levels for adverse taste and odor for boron, chloride, manganese, sodium, and sulfate. The groundwater is thus considered to contain certain taste-or odor-producing substances in concentrations that cause nuisance or adversely affect beneficial uses (California Code of Regulations, Title 22). These exceedances indicate that the uppermost water-bearing zone is not suitable for drinking-water use. Groundwater analytical results for General Minerals are provided in Table 5. 5.2 CALIFORNIA DEPARTMENT OF WATER RESOURCES FILE REVIEW On November 1, 2010, SAIC-Benham conducted a search of the DWR files to identify water- supply wells within a 2,000-foot radius of the site. The search covered portions of Township 3-South, Range 6-East, Sections 26, 27, 34, and 35, and portions of Township 4-South,Range 6-East, Sections 2 and 3. A total of nine water-supply wells were identified within the search area. A summary of the water well search results is provided in Table 6. Locations of the water wells are shown on Figure 1. 5 Benham Congmk,LLC ��` AWh.11y Owned S.bsidiary