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' Problem Assessment Report Page 4 Ranch Market,23569 South Santa Fe Road,Riverbank,CA November 8,2000 ' 2.5 Lithology ' Based on the description of the soil samples collected from the soil bonngs, the lithology at the Site consists mainly of sands and silts The lithology generally coarsens downward from sandy silt towards the groundwater surface to silty sand and sand found at depth Figures 4, 5, ' and 6 show the layout of the two geologic cross-sections through the Site, geologic cross- section A to A', and geologic cross-section B to B', respectively No obvious low permeability, confining layer of clay or silty clay was observed in the continuous core ' samples collected from the soil borings SB-1 or SB-2 Boring logs of the all soil bonngs drilled at the Site are included in Appendix B ' 2.6 Hydrogeologic Setting 2.6.1 Groundwater Gradient and Flow Direction Since December 1998, the depth to water in the Site well MW-1 has varied from 25 87 to 27 99 feet bgs (Table 3) The groundwater flows toward the South with a gradient of ' approximately 0 0028 feet per foot (Figure 7) 2.6.2 Sensitive Receptor Survey ' SECOR performed a field survey and a Department of Water Resources (DWR) records search to identify industrial, municipal, or domestic wells within a 2000-foot radius of the Site Due to the presence of the Stanisluas River south of the site, and the fact that no wells ' were observed during the field search South of the river in Riverbank, California, the DWR well search was limited to north of the Stanislaus River, in San Joaquin County ' Well logs were not found at the DWR for the wells on the properties adjacent to the Ranch Market (wells DW-1 through DW-4, Figure 2) or the wells observed at distances greater than 1,700 feet North of Ranch Market (Figure 8) Only three wells were identified during the records review within the 2,000-foot search radius The wells identified are all South and down gradient from Ranch Market one at Jacob Meyers Park, approximately 700 feet away, one West of the Park, approximately 1,000 feet from the Site, and one to the East of the Park ' and East of Santa Fe Road, approximately 1,500 feet from the Site Table 4 presents a summary of the wells located during the DWR records review and field search A field check to identify sensitive receptors within a 2000-foot radius of the Site was conducted on August 11, 2000 A search was conducted for bodies of water that provide I ecological habitat, schools and residential areas, and industrial, municipal, or domestic wells Sensitive receptors identified during the field search include the following • The Stanislaus River located approximately 1,200 feet to the South of the Site • The domestic wells used by the Ranch Market and three adjacent residential homes to supply shallow groundwater as the primary source of water • A well operated by the City of Riverbank is located in the Jacob Meyers Park, 700 feet south of the Site City of Riverbank Public Works Department reports the well has been tested and contains concentrations of nitrates above the maximum contaminant Ilevel of 45 mg/kg File PAR-report doe SECOR International Incorporated