ARCHIVED REPORTS_RESULTS OF THE UPDATED HUMAN HEALTH RISK SCREENING EVALUATION

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Ms. Dink Mather March 14, 2000 Page 3 • 4. Geomatrix reports petroleum related hydrocarbons at depths from 8.5 to 12.5 feet bgs. Earth Systems Consultants reports petroleum related constituents down to 15 feet bgs. Borings EB-7 and EB-9 are in close proximity to GMX-7 and GMX-6 respectively. However, the results of the soil analysis are dissimilar. Can these data be explained? The lateral ex- tent of the contamination appears to be adequately addressed. 5. The grab groundwater sample was not analyzed for TPH gas or diesel yet it was analyzed for BTEX and PAHs. Please explain the logic of this decision. 6. Geomatrix uses the environmental data from Earth Systems Consultants in the risk assess- ment yet the data is not provided in the data summary provided in Appendix B. If the data are to be used in the risk assessment, copies should be included in the Appendix for HERD's review. The Earth Systems data are clearly the highest reported detections at the property. 7. HERD reproduced the risk calculations. The hazard index was less than 0.4 and the theo- retical excess cancer risk was approximately 1 x 10-6. Both of these risk levels are at or be- low acceptable risk ranges. Conclusions and Recommendations There are several discrepancies in the document that need to be addressed. The issue of the location of the former Mohawk Gas Station and its contribution to site contamination versus the • former Old Valley Pipeline requires clarification. HERD recommends that Figure 2 and the text revised appropriately. The vertical extent of contamination within the two "plumes" requires clarification. HERD recommends that the analytical data supporting the Earth Systems investi= gation be included in Appendix B. HERD recommends that the qualitative OVA data presented in the Boring Logs are included in the text to explain the vertical extent of petroleum related hy- drocarbon contamination. The residual levels of petroleum-related hydrocarbons in the soils at the site are below levels that would constitute an unacceptable risk to human health and the environment as evidenced by a cancer risk of less than 1 x 10-6 and a hazard index of less than 1.0. Once the document is appropriately revised, HERD can support a request for no further action for the property. Please contact me at [(916) 327-2510] or e-mail at dberry@dtsc.ca.gov if you have any ques- tions regarding the evaluation of the above document. Reviewed by: Stephen DiZio, Ph.D. Senior Toxicologist, HERD •