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A#� GEOMATRIX Appendix C presents the equations,models, and input parameters used to calculate the theoretical lifetime cancer risk and noncancer hazard index from exposure to petroleum constituents detected in soil and groundwater on this site;all input assumptions were based on conservative default parameters provided in the PEA. As shown in Appendix C, the theoretical lifetime cancer risk for an adult and child resident is 1x10;this value is at the lower end of the acceptable risk range of 1x10 to 1x10'4 used by Cal-EPA and U.S.EPA for sites where remediation is considered(CCR Division 4.5,Title 22§67500.15 and U.S.EPA, 1990). The noncancer hazard index for an adult and child resident is 0.37;this value is less than 1,indicating that the predicted exposure to petroleum constituents detected on the site should not result in an adverse noncarcinogenic health effect(U.S.. EPA, 1989). Therefore,based on this evaluation,the presence of residual petroleum constituents in soil and groundwater at the site does not pose an unacceptable human health risk to hypothetical future residents at the site,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. 6.0 CONCLUSIONS AND RECONIMENDATIONS Data collected during Us investigation indicate that the lateral and vertical extent of petroleum hydrocarbon-affected soil on the subject property has been defined. Toluene,ethylbenzene,xylenes, and several PAHs were detected at low concentrations in the four soil samples affected by residual petroleum. Low concentrations of two PAHs were detected in the grab groundwater sample collected beneath the affected soil;no BTEX or MTBE were detected. The potential health risk posed by the residual petroleum constituents detected in soil and groundwater at the site was evaluated based on the methodology presented in the Human Health Screening Evaluation of the PEA. This evaluation indicates that exposure to residual petroleum constituents in soil and groundwater should not pose an unacceptable risk to hypothetical future on- site adult and child 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. \\SF3MEPTDATAOC SAFE\50005\5650\POMBOWOM-SOML W.TXT.DOC 5