ARCHIVED REPORTS_HUMAN HEALTH SCREENING EVALUATION 2012

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1 Human Health Screening Evaluation ' US Can—Welty Road March 19,2012 The Central Valley RWQCB is satisfied that the Site soil characterization dataset adequately describes site conditions; therefore, an exposure point concentration(EPC) was calculated as the upper confidence limit(UCL) of the mean soil concentration for each of the COPCs. SAIC used an EPA statistical software program, ProUCL Version 4.00.05, to analyze the datasets provided in Tables 1 and 2. All COPCs had a high number of non-detect results. Therefore, as recommended in the ProUCL User's Guide, nonparametric statistical methods were used to develop the EPCs where appropriate. Kaplan-Meier nonparametric estimation methods were deemed most appropriate for data sets with multiple detection limits, as recommended in the User's Guide (EPA, 2010). In addition, it may not be possible to calculate a UCL when the detection frequency is very low(less than 4 to 5 percent). In these cases, the ' User's Guide recommends using the sample median or sample mode as the EPC. SAIC used the sample median in this HHSE to represent the EPC for benzene, dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene (Table 6). 3.2 GROUNDWATER IMPACTS AND EXPOSURE CONCENTRATIONS 1 SAIC conducted site investigations that indicated the Site groundwater is affected by TPH, BTEX, and PAHs. The area of crude-oil affected groundwater is depicted on Figure 2. SAIC used all groundwater analytical data from site investigations to evaluate chemical exposures to a potential resident from subsurface vapor intrusion. Groundwater analytical data from the previous investigations at the Site are included as Appendix C. SAIC used the analytical data for 35 groundwater samples from 35 borings and monitoring wells to evaluate cancer risks and non-cancer hazards from exposure to BTEX and PAHs. Three locations were cone penetrometer test borings with separate depth-discrete groundwater samples at each location. Only results from the shallowest groundwater sample interval was used for evaluation of vapor intrusion. A summary of the analytical results for BTEX and PAHs for groundwater samples collected at the Site are provided in Tables 4 and 5, respectively. SAIC considered all volatile analytes detected in at least one groundwater sample as COPCs in ' groundwater. Benzene, ethylbenzene, xylenes, acenaphthene, benzo(b)fluoranthene, chrysene, fluorene, methylnaphthalenes, naphthalene, and pyrene are considered COPCs in groundwater for the Site, and were evaluated quantitatively in this HHSE (Table 7). SAIC conservatively estimated EPCs as the maximum detected concentration for each of the COPCs in groundwater, as recommended in the Vapor Intrusion Guidance. ' 3.3 TOXICITY VALUES SAIC used toxicological information(toxicity values)to quantitatively estimate potential health impacts for COPCs. Cancer potency factors (slope factors)were used to estimate potential ' cancer risks. Reference doses were used to estimate non-cancer health hazards. As presented in the PEA Guidance Manual, the hierarchy of sources for toxicity values was as follows: • California Cancer Potency Factors and Chronic Reference Exposure Levels (Cal/EPA Office of Environmental Health and Hazard Assessment [OEHHA], 2011a,2011b); and • EPA Integrated Risk Information System (IRIS; EPA, 2011). Slope factors used in this HHSE are provided in Table 8, and non-carcinogenic toxicity criteria (chronic reference doses) are provided in Table 9. 5 SAIL