ARCHIVED REPORTS_REPORT OF ADDITIONAL SOIL AND GROUNDWATER INVESTIGATION

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groundwater was conservatively used as the representative concentration. This GEONSATRik ' evaluation indicates that exposure to residual petroleum constituents present in soil and groundwater should not pose an unacceptable health risk to hypothetical future on-site residents under the conditions evaluated. In addition,based on the conservative nature of ' the PEA evaluation,the presence of residual petroleum constituents in soil and groundwater should also not pose an unacceptable human health risk to future commercial and construction workers at the site. In an April 27,2000 letter, DTSC ' stated that the analytical data were adequate in both quantity and quality and the residual levels of petroleum-related hydrocarbons in soils are below levels that would constitute an unacceptable risk to human health and the environment. ' Results from the investigations summarized in this report do not affect the findings of the previous human health screening evaluation. Three analytes were detected in ' groundwater that had not been detected when the risk assessment was performed(toluene at 0.7µg/1,xylenes at 1.5 µg/1,and phenanthrene at 0.2µg/1). None of these constituents are carcinogens and,therefore,the calculated theoretical excess cancer risk has not changed. Geomatrix included these three constituents in a recalculation of the noncancer hazard index. Because these constituents have nominal non-cancer effects at the concentrations detected,the newly calculated hazard index remained unchanged at 0.65, ' indicating that the potential exposure to petroleum at the site should not result in an adverse non-carcinogenic health effect(U.S.EPA, 1989). ,. Based on these findings,this site conforms with RWQCB's criteria to be classified and closed as a low risk site. 1