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Human Health Screening Evaluation Former Vernalis Pump Station September 2,2010 Therefore, nonparametric statistical methods were used to develop the EPCs where appropriate as recommended in the ProUCL User's Guide (EPA, 2009). Kaplan-Meier nonparametric estimation methods were deemed most appropriate for data sets with multiple detection limits, as recommended by Singh et al. (EPA, 2009). It may not be possible to calculate a UCL when the detection frequency is very low (less than 4 to 5 percent). Singh et al. recommend using the sample median or sample mode as the EPC in these cases. Ethylbenzene, acenaphthene, benzo(k)fluoranthene, dibenz(a,h)anthracene, and fluorene were each detected in only one of 67 samples; this corresponds to a detection frequency of 1.5 percent. SAIC-Benham used the sample median to represent the EPC for these compounds. Naphthalene was detected in only two of 67 samples; this corresponds to a detection frequency of 3 percent. While this detection frequency is below the levels recommended in the ProUCL User's Guide, SAIC-Benham used the calculated UCL of 1.1 milligrams per kilogram (mg/kg), rather than the sample median of 0.005 mg/kg, to ensure that the human health risk estimates are conservative and health protective. The likely result is an overestimation of human health risk for residential exposure. SAIC-Benham calculated the UCL of the mean soil concentration using all soil samples collected between 0 and 10 feet bgs. The total number of soil samples analyzed, the total number of samples with detectable concentrations, and the EPCs for all soil COPCs evaluated in this HHSE are provided in Table 6. 4. TOXICITY VALUES SAIC-Benham used toxicological information(toxicity values)to quantitatively estimate potential future 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 Hazard Assessment [OEHHA], 2010a, 2010b). • EPA Integrated Risk Information System(IRIS; EPA, 2010). Slope factors used in this HHSE are provided in Table 7. Non-cancer toxicity criteria(chronic reference doses)used in this HHSE are provided in Table 8. 5. EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION SAIC-Benham estimated the potential residential exposures to chemicals in on-site soils by oral, dermal, and inhalation routes using algorithms presented in the PEA Guidance Manual. These algorithms incorporate health-protective, default exposure parameters promulgated by the DTSC and EPA that represent the reasonable maximum exposure for health hazards and health risks. 5 �a The Benham Companies,LLC ,..frt j`® A Wholly Owned Subsidiary From&mxe to Solanoss