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Upon completion of the groundwater sampling, the borings were grouted in the presence of a San Joaquin County inspector using a cement-bentonite mixture in accordance with San Joaquin County permit requirements. Soil Gas Sample Analytical Results Soil gas sample analytical results are summarized in Table 2. Appendix A contains the complete laboratory analytical reports and chain-of-custody documentation. For screening purposes, the reported chemical concentrations are compared to California Human Health Screening Levels (CHHSLs) established by DTSC as levels that are protective of human health. CHHSLs are guidance or advisory screening levels and are not mandated cleanup levels. It should be noted that CHHSLs were developed to represent a very conservative scenario, and thus exceeding a CHHSL does not necessarily mean that the site presents an unacceptable risk. Twenty-one VOCs were reported in soil vapor samples. The highest concentrations were generally reported in the soil vapor collected at SV-1. • Benzene was reported in all four soil vapor samples at concentrations ranging from 7.0 to 37 micrograms per cubic meter (µg/m). The concentration of benzene reported at SV-1 (37 µg/m) is slightly above the residential land use CHHSL of 36.2 pg/m3 and below the commercial/industrial land use CHHSL of 122 µg/m3 for benzene. To determine a more site-specific assessment of the potential risk which may be represented by the maximum concentration of benzene detected in soil vapor, the DTSC version of the Johnson and Ettinger (J&E) indoor air model was used. The J&E model was run using default values for the exposure parameters and an assumption that the soil type was sand. The resulting cancer risk was 6E-07. If the model is run assuming a more site- specific soil type (i.e., silty clay), the cancer risk is further reduced to 3E-07. Thus, even though the maximum concentration of benzene in soil vapor exceeds the CHHSL for indoor air, this comparison over-estimates the potential risk. As shown, the J&E model conservatively estimates the potential risk to be significantly less than 1 E-06. • Toluene was reported in all four soil vapor samples at concentrations ranging from 24 to 1,700 µg/m3. All of the reported toluene concentrations are below the residential land use CHHSL for toluene of 135,000 µg/m3. • Ethyl benzene was reported in all four soil vapor samples at concentrations ranging from 4.4 to 430 µg/m3. CHHSLs for ethyl benzene have not been established. • m,p-Xylene was reported in all four soil vapor samples at concentrations ranging from 20 to 1,800 µg/m3. All of the reported m,p-xylene concentrations are below the residential land use CHHSL for m,p-xylene of 315,000 µg/m3. • o-Xylene was reported in all four soil vapor samples at concentrations ranging from 6.8 to 390 pg/m3. All of the reported o-xylene concentrations are below the residential land use CHHSL for o-xylene of 135,000 µg/m3. • Hexane was reported in all four soil vapor samples at concentrations ranging from 7.3 to 4,300 µg/m3. CHHSLs for hexane have not been established. • Fifteen additional VOCs were reported in one or more soil vapor samples at relatively low concentrations. These VOCs include 1,3,5-trimethylbenzene, Page 3 of 4 January 2006