ARCHIVED REPORTS HUMAN HEALTH SCREENING EVALUATION

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Human Health Screening Evaluation Surland Homes—Bridle Creek February 12,2009 0.1. This level of hazard is below a hazard index of 1, and therefore indicates an acceptable non- cancer health hazard for exposures to on-site soils for a construction worker. 7. UNCERTAINTIES Section 7 presents a discussion of the uncertainties in the evaluation of human health cancer risk and non-cancer health hazard performed during this HHSE. Site-specific conditions that contribute most significantly to the uncertainty of the risk and hazard estimates are identified and discussed. Two site characterization studies were conducted at this site in 1998199 and 2007. A total of 23 soil samples from 15 soil borings were collected for analysis. The soil samples collected in 1998 were not analyzed for PAHs for the purpose of supporting the development of an HHSE; consequently, low detection limits were not specified for PAHs. Detection limits in these samples ranged from 0.005 to 0.25 mg/kg. The characterization study conducted in 2007 ' specifically included the collection of on-site soil and groundwater samples to support the development of this HHSE. Data of adequate analytical quality (e.g., low detection limits) were collected from seven borings at depths ranging from 1 foot bgs to 12 feet bgs to support this HHSE. Detection limits in the boring samples ranged from 0.0003 to 0.033 mg/kg. This HHSE was performed at the request of the DTSC after adequate characterization of the site. As the site was well characterized during two site characterization studies, uncertainties in this HHSE were reduced to an acceptable level. The on-site soil impacts are believed to be well- characterized; therefore, EPCs were evaluated as the UCL of the mean soil concentration for each COPC evaluated in this HHSE. The UCL is a conservative estimate of the mean concentration, and is unlikely to lead to underestimation of exposure concentrations. CEMC prepared a letter documenting metals concentrations in soil associated with historical crude-oil sites. This letter noted that the presence of crude-oil affected soil did not impact the metals concentrations in soil. Thus, this HHSE over-represents the risks associated with metals at the site, as metals which are likely naturally occurring are included in the overall assessment of cancer risk and non-cancer health hazard. On-site exposures and potential resulting risks and hazards were estimated in this HHSE using algorithms developed by the DTSC, which were based on EPA and DTSC guidance and methodology. The equations evaluated exposures to soils by dermal, oral, and inhalation exposure routes using health protective, conservative reasonable maximum exposure parameters. Cancer and non-cancer toxicity values promulgated by Cal/EPA Office of Environmental Health Hazard Assessment and EPA (IRIS) were also used to quantitatively estimate potential risk and hazards. Therefore, it is unlikely that the risks and hazards estimated during the development of this HHSE are significantly underestimated. In fact, considering the conservative and health- protective assumptions used to develop this HHSE, it is likely that the actual on-site potential ' future risks and hazards will be much lower than those discussed in this HHSE. 8. ECOLOGICAL SCREENING EVALUATION SAIC queried the California Natural Diversity Database (CNDDB), maintained by the California Department of Fish and Game, to search for threatened, endangered, or sensitive species in the 13 From Science fo Solutions 1