SITE INFORMATION AND CORRESPONDENCE_FILE 2

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• Comparison of the maximum concentration of each detected chemical to the 2008 Environmental Screening Levels (ESLs) established by the San Francisco Bay Regional Water Quality Control Board • Comparison of the maximum concentration of each detected chemical to the 2010 California Human Health Screening Levels (CHHSLs) established by Office of Environmental Health Hazard Assessment (OEHHA) for California Environmental Protection Agency. • Modeling using the Department of Toxic Substances Control (DTSC)version of the Johnson and Ettinger Model(J&E Model) In January 2000, soil gas samples were collected from nine vapor probes (VI through V9) at 4 feet below ground surface (bgs) from the site (Figure 1). Soil Gas analytical results are shown in Table 1. Total volatile petroleum hydrocarbons (TVPH) were detected at 1,810 and 92 parts per million by volume(ppmv) in V5 and V6, respectively, located to the immediate north of the service shop building. Benzene was detected at 5.4 and 0.17 ppmv in V5 and V6, respectively. Comparison with ESLs The comparison of maximum detected concentrations of each chemical of concern to ESLs is shown in Table 2. It is apparent that the maximum detected concentrations of benzene and MTBE exceed both the residential and commercial ESLs for these chemicals. Comparison with CHHSLs The comparison of maximum detected concentrations of each chemical of concern to CHHSLs is shown in Table 3. It is apparent that the maximum detected concentrations of benzene and MTBE exceed the residential and commercial CHHSLs for these chemicals. J&E Modeling The evaluation of vapor intrusion to indoor air was conducted using the J&E Model. Based on location and use of the site, the assessment of soil gas intrusion to indoor air was conducted for a commercial scenario. The results of J&E modeling are summarized in Table 4. It is apparent that the residential and commercial cancer risks exceed 1 in 1 million(1E-06)by more than an order of magnitude. Therefore,the cancer risk calculated using the maximum detected concentrations of chemicals detected in soil gas would not be considered as acceptable. Conclusion The HHRA confirmed that the 2000 soil gas concentrations represent an unacceptable health risk when compared to ESLs, CHHSLs, and analysis using the J&E Model. In the letter dated October 11, 2010, the SJCEHD approved collection of new soil gas data if the risk was unacceptable using the 2000 soil gas concentrations. AA&A will proceed to collect additional soil gas samples in accordance with our workplan dated August 26, 2010 and approved by the SJCEHD on October 11,2010.