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41 <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> :f <br /> Robert Schneider,Chair <br /> Terry Tamminen Arnold Schwarzenegger <br /> Secretary for Sacramento Main Office Governor <br /> Environmental Internet Address: http://www.swrcb.ca.gov/rwgcb5 <br /> Protection 11020 Sun Center Drive hone(916 Rancho <br /> Cordova,CA 95670-61RE /�HVED <br /> 22 November 2004 NOY 2 3 2004 <br /> Mr.John Fray Mr. Jay Allen ENVIRONMENT HEALTH <br /> Union Oil Company of California Stone Brothers Management Company PERMIT/SERVICES <br /> 276 Tank Farm Road. 1024 W.Robinhood Dr. <br /> P.O. Box 1069 Stockton, CA 95207 <br /> San Luis Obispo, CA 93406 <br /> REPORT REVIEW, CLEANUP AND ABATEMENT ORDER (CAO)NO. 5-00-707, <br /> FORMER UNOCAL STATION#5098 AT 5606 PACIFICA VENUE,AND <br /> FORMER MONTGOMERY WARDS AUTO SERVICE AT 5400 PACIFIC AVENUE,STOC%TON, <br /> SANJOAQUIN COUNTY, <br /> I reviewed the 15November 2004 Geochemical Evaluation Regarding Potential Chromium Mobilization During <br /> Ozone Treatment(Report), submitted by ENSR International (ENSR)on behalf of Unocal. The Report provides <br /> an evaluation of site-specific geochemistry of groundwater and soil sample results,to determine whether leaching <br /> of metals or other effects detrimental to water quality in the aquifer may occur during in-situ ozone injection. <br /> The Report states Chromium 6+was not detected in soil or groundwater samples, although total Chromium was <br /> detected in soil at 16 mg/kg. The Report adds that while Chromium can be oxidized to Chromate (H2CrO4, <br /> mineral form of Chromium 6+)by ozone, "...Absorption to oxyhydroxide minerals will control chromate <br /> groundwater levels. How ozone treatment enhances or decreases this adsorption process cannot be predicted <br /> from the available information. After ozone treatment is finished, it is expected that chromium groundwater <br /> levels will return to their pre-treatment state, that is no detectable chromium, as the aquifer redox returns to its <br /> pre-treatment state." The Report recommends conducting the bench scale testing(BST)to provide the <br /> additional information needed to determine whether Iron (Fe2 ) and sulfide minerals are present and will react <br /> with Chromium to produce Chromate. <br /> The Report provides an interesting, in-depth discussion of aquifer geochemistry as related to in-situ ozone <br /> injection and similar in-situ oxidation technologies. The Report meets the requirements for a GE Report,per my <br /> Letter of 4 October 2004. The Letter also required submittal of a Workplan by 15 November 2004,to conduct <br /> the BST, if so recommended in the Report. In a phone conversation on 19 November 2004, ENSR requested an <br /> extension until 29 November 2004 for the BST Workplan. If the BST Workplan is submitted by <br /> 29 November 2004,I will not recommend action for non-compliance to the Notice of Violation(NOV)for <br /> CAO No. 5-00-707 issued on 18 June 2004. You may call me at(916)464-4615 for questions or additional <br /> information. <br /> ,'� <br /> /JAMES L. BARTON,R.G. <br /> Engineering Geologist <br /> cc: Mr.Mark Owens,UST Cleanup Fund, SWRCB, Sacramento <br /> Mr. Mike Infuma, San Joaquin County Environmental Health Division, Stockton <br /> Ms. Jill Tracy, Esq.,UNOCAL,Brea <br /> Mr.Ben Heningburg, ENSR International, Sacramento <br /> Mr. Gary Hall, GHH Engineering, Inc,Auburn, CA <br /> California Environmental Protection Agency <br /> ped Recycled Paper <br />