SITE INFORMATION AND CORRESPONDENCE

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Soil and Groundwater Investigation Report Mountain House Development Site#6 July 2008 • Total Dissolved Solids(TDS)using EPA Method 160.1; sulfate, chloride,nitrate (as nitrogen), and nitrite(as nitrogen)using EPA 300.0; specific conductance using EPA 120.1; Kjeldahl nitrogen using EPA 351.2;total phosphorus using EPA 365.1; ammonia(as nitrogen)using 350.2; alkalinity(as CaCO3),bicarbonate (as CaCO3), carbonate(as CaCO3), and hardness(as CaCO3)using SM 20 2320B;boron, sodium, calcium, iron,magnesium, manganese, and potassium using SW846 6010B. Refer to Appendix D for more information regarding the field, sampling, and analytical methods employed during the field investigation. 3.3 QUALITY ASSURANCE/QUALITY CONTROL AND DATA USABILITY Field sampling was conducted in accordance with SAIC's Quality Assurance and Quality Control Sample Collection, Handling, and Analysis procedures (SAIL, 2007a). In accordance with those procedures, quality assurance samples were also collected and analyzed. SAIC performed a data usability evaluation after receipt of all final laboratory reports to determine whether the data can be used for the intended purposes. The evaluation is summarized in the Data Usability Summary found in Appendix E. 3.4 INVESTIGATION-DERIVED WASTE(IDW) To properly store, characterize,and dispose of IDW, SAIC conducted the following: • Placed all IDW(soil cuttings and unused soil sample, disposable sampling equipment,used personal protective equipment, and decontamination water) in U.S. Department of Transportation(DOT) approved 55-gallon drums; • Properly labeled, secured, and stored IDW-containing drums on site pending disposal by Sturgeon& Son, Inc.; and • Collected composite IDW samples and submitted them to Lancaster for profiling. IDW was segregated, sampled, analyzed, and disposed of consistent with Chevron's Operational Excellence Process document entitled HPP-BTR Waste Management Process(Chevron, 2006). 4. FINDINGS 4.1 DWR FILE REVIEW SAIC conducted a search of DWR files to identify water supply wells within a 2,000-foot radius of the site. The search covered portions of Township 2-South,Range 4-East, and Sections 2, 3, 10, and 11. A total of seven wells were identified: five wells are located northwest of the site; and two wells are located southeast of the site. Two of the wells located northwest(approximately 1,500 feet cross gradient)were sampled during the recent investigation at Mountain House Development Site#3. Analytical results of the groundwater samples collected from the two wells were below laboratory reporting limits. A summary of the water well search results is provided in Table 1. Approximate locations of the water wells are shown on Figure 1. This figure also shows the presence of various aqueducts, surface irrigation canals, and other waterways within a 1-mile radius from the site. 4.2 SUBSURFACE CONDITIONS Soil encountered in the borings consisted predominantly of mixtures of clay, silt, and sand. Boring logs, which describe USCS soil characteristics,PID readings, and observations of residual crude oil in soil and/or in groundwater, are provided in Appendix C. Groundwater was encountered at depths ranging from 4.9 to 12 feet bgs. 5 From Science to Solutions