SITE INFORMATION AND CORRESPONDENCE

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GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company May 9, 2002 Page 5 contaminants at a site or multiple pathways of exposure." The 10-6 risk level is the point of departure. Acceptable risk levels are generally between 10-4 and 10-6 however the actual level of acceptable risk is a site-specific risk management decision. Therefore, in conformation with the NCP, 1x10-6 is the point of departure for acceptable risk in the health risk assessment. All discussions with respect to "acceptable"levels of risk in the HRA should be based on this point of departure. Comment noted. 7. Attachment 2,page 10, of the updated risk evaluation only includes equations for calculation of risk due to inhalation exposures ofgroundwater. Although the report appears not to include all the exposure pathways,HERD verified that all exposure pathways were included in the calculated risk values. Specifically, the risk table results do include risks due to oral and dermal exposures ofgroundwater. In addition,page 17 of Attachment 2, includes the risk for inhalation, oral and dermal groundwater exposures. Comment noted. 8. Using the maximum detected concentrations, as in Attachment 2, the screening level risk evaluation identified total risks to residential receptors of 3x10-6 with the potential future groundwater exposure contributing a risk of 2x10-6 and potential soil exposure contributing a risk of 1x10-6 The total hazard index was 0.4. No response required. 9. The most appropriate means of applying the data is using the 95% UCL soil concentration and the maximum detected groundwater concentration. HERD compiled this information by drawing from Attachment 4 for soil and Attachment 2 for groundwater. The resulting screening level risk evaluation identified total risks to residential receptors of 2x10-6 with potential future groundwater exposure contributing a risk of 2x10-, and potential soil exposure contributing a risk of 2x10-� The total hazard index was 0.1. No response required. CONCLUSIONS HERD evaluated the October 2, 2001 "Results of the Updated Human Health Screening Risk Evaluation,Pombo Property(San Joaquin County APN 232-170-07), 1755 West 11th Street, Tracy, California." Using the 95% UCL soil concentration and the maximum detected groundwater concentration, the total screening level risk to residential receptors is of 2x10-6 with potential future groundwater exposure contributing a risk of 2x10-6 and potential soil exposure contributing a risk of 2x10- The total hazard index is less than ].