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EbkENSR Intemational <br /> 10411 Old Placerville Road <br /> Suite 210 <br /> Sacramento,CA 95827-2508 <br /> (916)362-7100 <br /> ,�IECIEg <br /> FAX 362-8100 <br /> Id�U1 IrII ,lensr.com <br /> November 15, 2004 <br /> NOV 1 7 2004 <br /> ENVIRONMENT HEALTH <br /> Mr. James Barton PERMIT/SERVICES <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670 <br /> RE: Geochemical Evaluation <br /> Regarding Potential Chromium <br /> Mobilization During Ozone Treatment <br /> Dear Mr. Barton: <br /> On behalf of Union Oil Company (Unocal) of California, ENSR Corporation (ENSR) has prepared <br /> the attached geochemical evaluation regarding potential chromium mobilization during ozone <br /> treatment at the Former Unocal Station No. 5098 at 5606 Pacific Avenue, and Former <br /> Montgomery Wards Auto Service located at 5400 Pacific Avenue, Stockton California (Former <br /> Unocal Facility). The location of the site is shown in Figure 1 and site features are illustrated in <br /> Figure 2. The California Regional Water Quality Control Board, Central Valley Region (RWQCB) <br /> requested this geochemical evaluation in a letter dated, October 4, 2004. A copy of the letter is <br /> included in Attachment A. The attached geochemical evaluation is based primarily on analytical <br /> results from water and soil samples collected at the Former Unocal Facility in September and <br /> October, 2004 and is being submitted to meet the November 15, 2004 deadline stated in ENSRs <br /> Work Plan to Evaluate Potential SVE/AS System Enhancements and Additional Well Installation <br /> within the Deeper Aquifer Units, dated November 2, 2004. The geochemical evaluation was <br /> prepared by Dr. Carol R Johnson, ENSR, and Mr. Arthur Taddeo, ENSR. Dr. Johnson holds a <br /> bachelors degree in Chemistry from the University of California, San Diego and a Ph.D. in <br /> Agricultural and Environmental Chemistry from the University of California, Davis. She also <br /> worked as a post-doctoral associate with Dr. Phil Gschwend in the Civil and Environmental <br /> Engineering Department at the Massachusetts Institute of Technology. Her research there <br /> focused on manipulating aquifer geochemistry to facilitate chromium remediation. She has <br /> worked for ENSR for five years completing numerous projects involving the geochemistry of <br /> metals in groundwater, as well as the environmental chemistry of other inorganic and organic <br /> compounds. Mr. Taddeo holds a bachelors degree in Microbiology and a Masters in Chemistry <br /> and has 23 years of experience in site investigation and remediation. <br /> The interpretations contained in this geochemical evaluation represent our professional opinions <br /> based on information currently available. As new information about the site becomes available, <br /> the opinions expressed in this geochemical evaluation may require revision. <br /> If you have any questions regarding this geochemical evaluation, please contact Ben Heningburg, <br /> Celebrating 35 Years of Excellence in Environmental Services <br />