FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Human Health Screening Evaluation US Can—Welty Road March 19,2012 Ci=bulk soil concentration of contaminant i (chemical concentration in soil, mg/kg x [10-6 kg/mg]) The above equation is valid for calculating Ei only if the soil concentration of a VOC is less than or equal to the soil saturation concentration for the VOC. SAIC compared the maximum detected soil concentrations of the VOCs listed above to soil saturation concentrations provided in Table 19 (Emission Rate for VOCs), based on Equation 2.5 (as modified per Item 3 of the Errata Sheet) and parameters presented in the PEA Guidance Manual. The maximum soil concentrations are all below the respective soil saturation concentrations. Soil/Water Partition Coefficient SAIC used the soil/water partition coefficient(Kd) of a chemical in the calculation of Ei (Table 20)using the following equation(PEA Guidance Manual, Figure 2.5): Kd=Koc x foc Where: Kd= soil/water partition coefficient, cm 3/g (or L-water/kg-soil) Koc =organic carbon partition coefficient, L/kg or cm3/g foc= fraction of organic carbon (default=0.02) 3.5 EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION FOR INDOOR SUBSURFACE VAPOR INTRUSION SAIC used the Screening-Level Model for Groundwater Contamination, Version 3.0; 04/03 (screening-level model; DTSC and Cal/EPA, 2009), to evaluate human health risks and hazards from subsurface vapor intrusion into buildings as recommended in the Vapor Intrusion Guidance. The model was developed by the EPA, and has been modified by the Human and Ecological Risk Division of the DTSC to incorporate human health criteria specific to California. The model incorporates health-protective, default exposure parameters and site-specific parameters promulgated by the DTSC and EPA that represent the Reasonable Maximum Exposure for health hazards and health risks. SAIC calculated chronic cancer and non-cancer impacts for an adult assuming an exposure duration of 30 years. The tables used and presented by the screening-level model are provided as Appendix E. The exposure parameters and site-specific parameters incorporated into the screening-level model are provided in Table 21. SAIC selected the maximum detected on-site groundwater concentration as the EPC for each COPC. Incremental lifetime cancer risks were calculated for potential residential adult receptors. The EPC (Table 7) was used to estimate risks and hazards. SAIC estimated cancer risks as the incremental probability of an exposed individual developing cancer over a lifetime as a result of exposure to a potential carcinogenic constituent(i.e., incremental lifetime cancer risk; EPA, 1989). The potential cancer health risks for each individual chemical were summed to estimate an overall cancer risk for the receptor. Likewise, SAIC calculated non-cancer health hazards for potential residential adult receptors. Hazards were estimated by comparing estimated potential doses to an acceptable reference-dose 10 5A 1C