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n' <br /> t <br /> 2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 ){ -`! •'ff t� ' f <br /> (51 0) 663-4100 • FAX (51 0) 663-4141 FF f ,`;t_�1)�y�1 - ,;, GEOMATRIX <br /> September 14, 2000 U 4 9 <br /> Project 6447.005 <br /> Mr. Philip Isorena <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827 <br /> Subject: Response to RWQCB Comments <br /> Draft Site Closure Request, Bruns and Byron Roads Site <br /> Byron, Contra Costa County <br /> Dear Mr. Isorena: <br /> On behalf of Chevron Environmental Management Company (CEMC) and Texaco, <br /> Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter responding to California <br /> Regional Water Quality Control Board, Central Valley Region's (RWQCB) comments to the <br /> draft Site Closure Request, Bruns and Byron Roads Site, dated April 2000. .CEMC and <br /> Texaco requested that the RWQCB review the draft site closure request document regarding <br /> the content, level of detail, and layout provided. The intent of this review was to ensure that <br /> this specific and future site closure requests have sufficient technical and background data for <br /> the RWQCB to support a"low-risk" case closure in accordance with RWQCB draft"Low <br /> Risk Guidelines" and other applicable state resolutions. We appreciate the feedback provided <br /> by RWQCB staff comments dated August 18, 2000. The RWQCB letter included comments <br /> from both yourself and Mr. Eric Becker of the RWQCB's Fresno office. <br /> The RWQCB's comments regarding the Draft Site Closure Request are presented below in <br /> italics, followed by our response. For reference purposes, RWQCB comments have been <br /> designated with letters A through M. <br /> General Comments <br /> A. Human Health Risk Assessment <br /> Chevron used the methodology provided in the human health risk screening evaluation <br /> section of the Preliminary Endangerment Assessment Guidance Manual (PEA; Cal EPA, <br /> 1994) to evaluate risks to a hypothetical future residential receptor. Appendix D provides the <br /> equations, models, and input parameters used to calculate the theoretical lifetime cancer risk <br /> and noncancer hazard index. The evaluation shows that the theoretical lifetime cancer risk <br /> for an adult and child resident is 1x10-7 and a noncancer hazard index for an adult and child <br /> resident of 0.0065. The report states that these values show that the presence of residual <br /> petroleum hydrocarbons in soil at the site does not pose an unacceptable risk to future <br /> Geomatrix Consultants, Inc.. <br /> Engineers, Geologists, and Environmental Scientists <br />