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Human Health Screening Evaluation <br /> US Can—Welty Road March 19,2012 <br /> Ci=bulk soil concentration of contaminant i (chemical concentration in soil, <br /> Mg/kg x [10-6 kg/mg]) <br /> The above equation is valid for calculating Ei only if the soil concentration of a VOC is less than , <br /> or equal to the soil saturation concentration for the VOC. SAIC compared the maximum <br /> detected soil concentrations of the VOCs listed above to soil saturation concentrations provided <br /> in Table 19 (Emission Rate for VOCs), based on Equation 2.5 (as modified per Item 3 of the <br /> Errata Sheet) and parameters presented in the PEA Guidance Manual. The maximum soil <br /> concentrations are all below the respective soil saturation concentrations. <br /> SoiUWater Partition Coefficient <br /> SAIC used the soil/water partition coefficient(Kd)of a chemical in the calculation of Ei (Table <br /> 20)using the following equation(PEA Guidance Manual, Figure 2.5): <br /> Kd =Kocxfoc <br /> Where: <br /> Kd= soil/water partition coefficient, cm 3/g(or L-water/kg-soil) <br /> Koc=organic carbon partition coefficient, L/kg or cm 3/g , <br /> foc=fraction of organic carbon(default=0.02) <br /> 3.5 EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION FOR <br /> INDOOR SUBSURFACE VAPOR INTRUSION <br /> SAIC used the Screening-Level Model for Groundwater Contamination,Version 3.0; 04/03 ' <br /> (screening-level model; DTSC and Cal/EPA, 2009),to evaluate human health risks and hazards <br /> from subsurface vapor intrusion into buildings as recommended in the Vapor Intrusion <br /> Guidance. The model was developed by the EPA, and has been modified by the Human and <br /> Ecological Risk Division of the DTSC to incorporate human health criteria specific to California. <br /> The model incorporates health-protective, default exposure parameters and site-specific <br /> parameters promulgated by the DTSC and EPA that represent the Reasonable Maximum <br /> Exposure for health hazards and health risks. <br /> SAIC calculated chronic cancer and non-cancer impacts for an adult assuming an exposure <br /> duration of 30 years. The tables used and presented by the screening-level model are provided as <br /> Appendix E. The exposure parameters and site-specific parameters incorporated into the <br /> screening-level model are provided in Table 21. <br /> SAIC selected the maximum detected on-site groundwater concentration as the EPC for each <br /> COPC. Incremental lifetime cancer risks were calculated for potential residential adult receptors. ' <br /> The EPC (Table 7)was used to estimate risks and hazards. <br /> SAIC estimated cancer risks as the incremental probability of an exposed individual developing <br /> cancer over a lifetime as a result of exposure to a potential carcinogenic constituent(i.e., <br /> incremental lifetime cancer risk; EPA, 1989). The potential cancer health risks for each <br /> individual chemical were summed to estimate an overall cancer risk for the receptor. <br /> Likewise, SAIC calculated non-cancer health hazards for potential residential adult receptors. , <br /> Hazards were estimated by comparing estimated potential doses to an acceptable reference-dose <br /> 10 <br /> SAIC <br /> i <br />