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GEOMATRIX Mr.Robert D.Mihalovich Chevron Environmental Management Company October 4,2001 Page 3 Exposure pathways considered in this screening evaluation include incidental ingestion of soil, dermal exposure with soil,and inhalation of volatile emissions from volatile organic compounds (VOCs)or inhalation of fugitive dust emissions from non-VOCs. Evaluations of the potential impact of chemicals in groundwater varies with site-specific conditions (Cal- EPA, 1999). According to the property owner,groundwater underlying the property is cur- rently extracted from an existing on-site well for non-potable use(for sinks and toilets only), but not for drinking water(personal communication between Mr.Mihalovich and Mr. Pombo, 2001). Bottled water.is provided to workers at the site for drinking.water. The property owner ' also.indicated that the existing on-site well will be destroyed once the facility is connected to the City municipal supply water. Therefore, under current land use,groundwater beneath the site is not used as a potable supply. Similarly,under future land use conditions,it is unlikely that a groundwater production well would be installed at the site for drinking water. Based on this information,potential exposures,associated with domestic uses of groundwater are not complete under a hypothetical residential scenario. However,for the purpose of this screen- ing evaluation, shallow groundwater underlying the site was evaluated as both a potential source and as not a potential source of drinking water. If shallow groundwater underlying the site is a source of drinking water,potential exposures to chemicals in water include ingestion, dermal, and inhalation of VOCs released from tap water used indoors. Conversely,if shallow groundwater is not a source of drinking water,these pathways are incomplete. Regulatory agencies such as Cal-EPA and U.S.EPA have defined an acceptable level of risk in similar though slightly different ways. The U.S.EPA considers 1x10'to 1x10 to be the target range for acceptable risks at sites where remediation is considered(U.S.EPA 1990). Estimates of lifetime excess cancer risk associated with exposure to chemicals of less than one-in-one-million(1x10-6) are considered to be so low as to not warrant any further investi- gation or analysis (U.S. EPA, 1990), Within the State of California, Cal-EPA also tends to work within the same target range for acceptable risks. For example,pursuant to the Califor- nia Safe Drinking.Water&Toxic Enforcement Act of 1986,the Office of Environmental Health Hazard Assessment(OEHRA)has established a no significant risk level at 1x10"5. In addition,many air management districts consider 1x10'5 to be an acceptable risk level for managing air emissions.under the Toxics Hot Spots program. For chemicals that are classified as noncarcinogens, a hazard quotient less than or equal to 1 indicates that the predicted expo- sure to that chemical should not result in an adverse noncarcinogenic health effect(U.S. EPA, 1989). Incorporating the May and October 2000 analytical data, a summary of the theoretical excess lifetime cancer risk and the nonca.ncer hazard index for future adult and child resident is dis- cussed below and in Table 3. Supporting risk calculations are presented in Attachment 2 i through 5. All detected constituents, except for TPH measurements,in soil and groundwater were evaluated. TPH results were not directly evaluated as prescribed in the PEA. The tox- icity of these petroleum mixtures is best described by the aggregated toxicity of key individ- ual constituents in the-mixture, such as BTEX or PAHs (Cal-EPA, 1999).