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Soil and Groundwater Investigation Report Catellus Property September 2006 longer observed in the soil samples. Soil samples were collected from beneath the affected soil in these borings. Additionally,in order to evaluate the vertical extent of affected groundwater, a grab groundwater sample was collected from boring SB-20 beneath the zone of affected soil, using a discrete-depth Hydropunce sampling device. • Evaluated project data to determine the extent of affected soil and groundwater. • Prepared this Soil and Groundwater Investigation Report,which describes the investigation results and makes recommendations for future site assessment activities. The field investigation was implemented in accordance with the RWQCB-approved work plan,except for the following variations: • As mentioned above,the investigation excluded analysis for TPHg and MTBE. • Laboratory detection limits were elevated above the limits proposed in the work plan. However, the TDS results,with concentrations up to 9,680,000 pg/L, indicate that the shallow groundwater in the area of investigation is potentially not suitable for municipal or domestic water supply; thus,the Central Valley RWQCB Water Quality Objectives(WQOs)are likely inapplicable. Moreover,benzene is rarely detected at HPP sites,and the results of this investigation indicate benzene in soil and groundwater is not a concern at this site. For more information regarding the field and sampling methods employed during the field investigation, refer to Appendix C. 4. FINDINGS 4.1 SUBSURFACE CONDITIONS Review of the boring logs prepared for each of the 31 total borings indicates that soils encountered at the site range from low-plasticity clays and silts,to clayey or silty sands,to poorly graded sands and gravels with fine-grained sediments. Boring locations are depicted on Figure 2. The boring logs,which describe soil classifications and observations of petroleum-affected soil or groundwater,are provided in Appendix D. Based on comparison of the observed depths at which saturated soils were encountered and the depth-to- groundwater measurements in the boreholes, shallow groundwater appears to be unconfined. Static water-level measurements ranged from 4.6 to 10.6 feet bgs. 4.2 DWR FILE REVIEW RESULTS SAIC conducted a search of DWR files to identify water supply wells within a 'h-mile radius of the site. The search covered portions of Township 2-South,Range 4-East, Sections 13, 14, 18,and 24. A total of 10 water supply wells were identified. Based on review of the DWR Water Well Drillers reports,all identified wells are used for domestic purposes,and none are public supply wells. A summary of the water supply well search results is presented in Table 1. Approximate locations of the water supply wells are shown on Figure 1. 4.3 SOIL ANALYTICAL RESULTS Summarized in Tables 2 and 3 are the soil sample analytical results and the PRGs and ESLs to which they were compared to assess the presence of affected soil and whether any further soil characterization is appropriate. Maps of soil analytical results are provided on Figures 3a and 3b. Copies of the soil laboratory analytical reports are included in Appendix E,following the Data Usability Summary. 4 From science to 711171111