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Chevron/UPRR - 4 - 12 June 2007 <br /> TAOC Tracy Pump Station RA <br /> Geomatrix comments/clarification- <br /> "As presented in the comment letter, OEHHA calculated the exposure point concentrations <br /> and the estimated risks and hazards for a future outdoor industrial worker based on the <br /> combined data set of surface and subsurface soil. The results of OEHHA's evaluation and <br /> recalculation demonstrated that there is no significant risk/hazard to chemicals detected in <br /> soil." <br /> Regional Water Board response: <br /> No comment. <br /> 3. OEHHA HHRA comment: <br /> Ambient air modeling. "Geomatrix modified the volatilization factor equation shown in the U.S. <br /> EPA Soil Screening Guidance to derive the emission rates. I was not able to verify the <br /> modified equation due to lack of details regarding the modification in the report." <br /> Geomatrix comments/clarification: <br /> "There are a couple of typos embedded within the text of Appendix B... " <br /> Regional Water Board response.- <br /> Geomatrix <br /> esponse:Geomatrix corrected the conversion factor formula and included the revised equation in the <br /> April 2007 response letter. The original emission rate value was unchanged as previously <br /> presented. <br /> SUMMARY <br /> Based on Geomatrix's comments to OEHHA's HHRA review and our 16 January 2007 <br /> comments, topics needing clarification have been adequately addressed and no further <br /> investigation and/or characterization is required. <br /> According to the field investigative data and information, coupled with OEHHA's findings and <br /> Geomatrix's response to comments, and with the provision that the information provided was <br /> accurate and representative of site conditions, Chevron/UPRR may prepare a request of no <br /> further action determination. Chevron/UPRR's request should be in accordance with Central <br /> Valley Regional Water Quality Control Board's 16 April 2004 update to Appendix B of the Tri- <br /> Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of <br /> Underground Tank Sites— No Further Action Requests, Section 6.5 NFAR for Cases <br /> Exceeding Water Quality Objectives. <br /> If existing, additional, or previously unidentified chemical constituents at the site cause or <br /> threaten to cause pollution or nuisance or are found to pose a threat to public health or water <br /> quality, then 1) nothing in this determination is intended or shall be construed to limit or <br />