SITE INFORMATION AND CORRESPONDENCE

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C. Dean Hubbard 0 October 13, 2006 Page 10 11. App. C, Summary Risk Characterization: Off Site Resident—Geomatrix calculated the Total Hazard Index by adding the calculated hazard index for adult to the calculated hazard index for child. This is not supported from a toxicological point of view. Instead, the hazard index for the child should be used as Total Hazard Index for off-site resident. A summary of my hazard and risk calculations is provided in the table below. Summary of Non Cancer Hazard Indices and Excess Lifetime Cancer Risks per Scenario As recalculated by the OEHHA Scenario Hazard Index Excess Lifetime Cancer Risk Industrial Worker 2.8E-02 2.9E-06 Construction Worker 1.9E-01 8.9E-07 Off-Site Resident 7.3E-09 2.2E-10 My calculations resulted in lower estimates of non-cancer hazard indices and excess lifetime cancer risks. Only the excess lifetime cancer risk for industrial worker resulted above the de minimis risk of 1.0E-06. However, Geomatrix combined the pathways for outdoor industrial worker and indoor industrial worker. The outdoor industrial worker should not be exposed to inhalation of VOCs indoors. The indoor industrial worker should not be exposed to soil ingestion and dermal contact with soil. Also,his/her exposure to particles indoors should be lower than the exposure of his/her counterpart working outside. As a result, the risk and hazard of each type industrial worker is expected to be lower than the combined one. The ambient air concentrations obtained above may overestimate the risk/hazard since, contrary to what is expected, they are higher than the calculated indoor air concentrations, resulting in higher risk and hazard. However the above calculated hazard and risk do not consider groundwater contamination or soil contamination below 10 ft bgs. Ecological Risk Assessment 12. The consideration of potential risk to ecosystems was found on p. 1, section 1.1 Objective: "Based on the nature and location of the site in a developed area of Tracy, it is expected that human health concerns will override ecological concerns. Thus consideration of potential effects to ecological receptors was not performed as part of this assessment. " This rather minimal evaluation may or may not provide you with adequate information to make an informed decision about ecological concerns. Editorial Comment 1. Appendix A shows the ProUCL outputs for all chemicals of interest. However, all titles in Appendix Al read Benzo(a)anthracene, and in Appendix A-2 Acenaphthene.