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1 • • ' GEOMATRIX 1 was conducted based on the methodologies presented in the Human Health Screening Evalua- tion section of the PEA Guidance Manual(PEA; Cal-EPA, 1999). The PEA evaluation con- sists of a compilation of methods, models, and assumptions commonly used by California and United States Environmental Protection Agencies (Cal-EPA and U.S. EPA) to quantify human health risk and hazard at a site. The PEA evaluation is intended to provide conservative esti- mates of the theoretical lifetime excess cancer risk and noncancer hazard index based on reasonable maximum exposure in a residential setting. The PEA methodology was used to evaluate a hypothetical future residential receptor as a conservative measure; this evaluation would over-estimate potential risks posed by the residual petroleum to commercial or construc- tion workers. Exposure pathways considered in this evaluation include inhalation of volatile organic chemicals from soil and groundwater; inhalation of airborne dust from soil; ingestion of soil and groundwater; and dermal contact with soil and groundwater. For purposes of this evaluation, all equations and default input assumptions provided in the PEA were used. Total petroleum hydrocarbons (TPH) quantified as crude oil (TPHc),toluene, xylene, ethylben- zene, and select polynuclear aromatic hydrocarbons (PAHs)were detected in soil samples col- lected from the site. TPH quantified as gasoline(TPHg), TPH quantified as diesel (TPHd), toluene, xylene, ethylbenzene, and select PAHs were detected in groundwater samples. For purposes of this evaluation, all detected chemicals in soil and groundwater were quantitatively evaluated; the maximum detected concentration for each chemical was conservatively used as the representative concentration. It should be noted, however, that TPH measurements were not directly included in this evaluation, as prescribed in the PEA. The toxicity of these petro- leum mixtures is best described by the aggregated toxicity of key individual chemicals in the ' mixture, such as benzene, toluene, ethylbenzene, and xylenes(BTEX) and PAHs (Cal-EPA, 1999). According to the National Contingency Plan, lifetime excess cancer risks at or below 1 x 10-6 are generally acceptable(U.S. EPA, 1990a and 1990b). Risks above 1x104 are considered unac- ceptable, while a risk between 1x104 and 1x10-6 are within the target range for acceptable risks. Depending upon site-specific exposures and conditions, risk management measures are consid- ered when the risks are within the target range of acceptable risks. For noncarcinogenic health effects, a hazard index (HI) of I or less is considered to be an acceptable level (U.S. EPA, 1990a and 1990b). ' The theoretical lifetime excess cancer risk for an adult and child resident at the site is 1x10"6; ' this value is equivalent to the acceptable target risk of 1x10'6. It should be noted that the I1Dm—Salk\6000s\6447.007IiRA\Swland FRA.dm 3