SITE INFORMATION AND CORRESPONDENCE

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' M. Scott Mansholt - 4 - 12 November 2008 Chevron Mountain House Development Site #6 Two groundwater samples were analyzed for total dissolved solids (TDS) and general ' minerals. The TDS values reported were 2,260 and 2,560 milligrams per liter (mg/L). These values exceed California Department of Health Services (CaIDHS) Maximum Contaminant Level (MCL) for TDS (500 mg/L), which is based on aesthetic (taste and odor) and technical (staining and corrosion) characteristics 3. Additionally, the reported values also exceed the ' CaIDHS "upper" and "short term" TDS values of 1,000 and 1.500 mg/L, respectively. ' SAIC summarized and concluded the fallowing: • The vertical extent of affected soil has been defined in Area 1, but not laterally downgradient. Additional soil investigation is needed. Affected groundwater has been ' adequately defined. • The vertical extent of affected soil has been defined at 35 to 40 feet bgs in Area 2. Lateral and additional downgradient soil characterization is needed. Upgradient, affected groundwater has been defined. Additional groundwater delineation is needed downgradient to the east-northeast. ' The extent of affected groundwater was defined u and downgradient of Area 3. • 9 p 9 Vertically, the extent of affected soil was defined at 28 to 32 feet bgs, Laterally, ' downgradient it has not been defined to the east-northeast and further investigation is needed. SSAIC proposed 13 additional borings at the areas described above to evaluate/define affected soil and/or groundwater. They proposed four stepout borings for Area 1, six for Area 2, and three at Area 3. Site access has been difficult and SAIC has indicated that Central Valley ' Regional Water Quality Control Board staff assistance may be needed to communicate with the property owner. ' I have the following comments: • 1 concur that the lateral extent of affected soil and groundwater has been partially ' defined and that additional characterization is needed. • 1 concur with the approximate proposed boring locations with the exception of ' location J which should be relocated further from the boring containing SPO. Two borings should be completed approximately 50 feet further east-northeast of location J, approximately 50 feet to the northwest and southeast, respectively. 1 3- California DHS, Title 22 California Code of Regulations, California Safe Drinking Water Act and Related Laws and Regulations, March 2008.