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' Final Baseline Human Health Risk Assessment <br /> San Joaquin Human Services Agency Building <br />' December 2001 <br /> results Thus, it is highly unlikely that the average concentration of groundwater directly beneath <br />' the building is near the 90th percentile for benzene <br />' Human health exposure parameters for occupational worker exposure were obtained from <br /> regional guidance documents (CalEPA, 1996) Site-specific exposure duration and exposure <br />' frequency parameters similar to default EPA parameters of 25 years and 250 days/year were <br />' used Site-specific human health exposure factors, including California-specific benzene <br /> inhalation toxicity criteria (OEHHA, 2001), and site-specific vapor intrusion modeling <br />' parameters are summarized together in Table 2 Chemical and physical properties for benzene <br /> are summarized in Table 3 Soil properties for various soil types based on the U S Soil <br />' Conservation Service Classification System are summarized in Table 4 <br />' 3.3 Site-Specific Results <br /> The 90' percentile concentration of benzene in groundwater was used as the site-specific <br />' exposure point concentration The corresponding potential cancer risk and hazard level for <br /> indoor workers using the 90' percentile concentration and site-specific human health exposure <br />' and vapor intrusion modeling parameters is summarized below <br /> Table 1:1 Summary of Health Risk � <br />' <br /> drouAdwater( W-21MVIt-2A)tU Indoor Air Risks Exposure Point liiarismental Pizard <br /> Concentration',,' Disk level <br /> Area COPIC (mg1L) tlnitliess) (Unitiess) <br />' Human Services Agency Building Benzene 12 9 8 5E-7 < 1 <br /> Notes <br />' ' Represents the 901h percentile concentration as calculated from combined groundwater data from wells MW-2 and MW-2A <br /> z Groundwater sampling events used for well MW-2 dated from 5/21197 to 10/12/01 <br /> 3 Groundwater sampling events used for well MW-2A dated from 7125195 to 10/12/01 <br /> 1 <br /> Screening-level calculations using site-specific parameters were again performed using the <br /> GWSCREEN XLS spreadsheet tool The incremental cancer risk for benzene (8 5E-7) using <br /> site-specific parameters is less than both the "guideline"preliminary remediation risk goal of <br /> I <br />' San Joaquin County GW Monitoring Report2(Appendix D)v 2 4 12/27/2001 <br />