SITE INFORMATION AND CORRESPONDENCE

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Soil and Groundwater Investigation Report Mountain House Development Site#6 February 25,2010 It should be noted that the central portion of Area 2 consists of five borings with groundwater analytical results less than ESLs and WQOs (previous borings GP158 through GP 160 and SB- 12; and current boring SB-39). The southern affected groundwater area was included in Area 2 for consistency. The concentrations detected in the groundwater samples collected from S13-1, SB-2, SB-3, and SB-38 exceed, but are very close to, the WQOs and/or ESLs; therefore, it is likely that the crude- oil constituent concentrations decrease to below screening levels in close proximity to the boring locations. The extent of crude-oil affected groundwater is delineated on Figure 3,which was derived from SAIC-Benham's evaluation of the data collected during the previous and current investigations. 5.2.1 Suitability of the Groundwater for Drinking A grab groundwater sample collected from SB-42 was submitted for TDS and General Minerals analysis. The TDS concentration was 2,190 mg/L which exceeds the following current California Department of Public Health(CDPH) maximum contaminant levels (MCLs; CDPH, 2004) and RWQCB Water Quality Goals (WQG; RWQCB, 2000) for drinking water: • CDPH MCL: 500 mg/L, recommended. • CDPH MCL: 1,000 mg/L,upper. • CDPH MCL: 1,500 mg/L, short term. • RWQCB WQG, CDPH, and EPA drinking water standards: 500 mg/L. • RWQCB WQG, Agricultural Water Quality Goal: 450 mg/L. • RWQCB WQG, EPA Ambient Water Quality Criteria for Taste and Odor or Welfare: 250 mg/L. In addition, the results of the General Minerals analyses for SB-42 indicated boron, chloride, manganese, nitrate as nitrogen, sodium, and sulfate in concentrations in excess of the respective MCLs and/or WQOs. The results exceeded the WQO levels for adverse taste and odor for manganese and sodium. The groundwater is thus considered to contain certain taste- or odor- producing substances in concentrations that cause nuisance or adversely affect beneficial uses (California Office of Administrative Law, 2008). These exceedances indicate that the uppermost water-bearing zone is not suitable for drinking water use. Groundwater analytical results for General Minerals and TDS are provided in Table 5. 5.2.2 Water Supply Well of Interest The Foster Well is currently in use by a nearby residence. The construction details of this well, including total depth and screened intervals, are unknown. The Foster Well is located up gradient of the previously advanced boring SB-19. The Foster Well sample (FosterWell-1) did not contain concentrations of TPHd, BTEX, or PAHs exceeding the laboratory reporting limits, WQOs, or ESLs. Various water-quality parameter analytical results from the Foster Well, such as General Minerals and TDS, exceeded screening levels. Groundwater analytical results for General Minerals and TDS are provided in Table 5. 8 Fmin Science to Solutions