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I <br /> ENSR International <br /> Old Placerville Road <br /> .� LITY Suite 210 <br />' Sacramento,CA 95827-2508 <br /> January 31, 2005 FEB 0 2 2005 (916)362 7100 <br /> FAX (916)362-8100 <br /> ENVIRONMENT HEALTH WWensrcom <br /> PERMIT/SERVICES <br /> Mr James L Barton <br /> Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670-6114 <br /> IRE Ozone Spar9 ing Bench Scale Testing Results Report <br /> Former Unocal facility No. 5098 <br /> 5400 and 5606 Pacific Avenue, Stockton, Califomia <br /> Cleanup and Abatement Order (CAO) No 5-00-707 <br /> Dear Mr Barton <br /> On behalf of Union Oil Company of California (Unocal), ENSR Corporation (ENSR) is providing <br /> the enclosed January 27, 2005 report titled, Evaluation of Ozone for the Destruction of Petroleum <br /> Hydrocarbons in Soil and Groundwater prepared by ENSR's subconsultant, Prima Environmental <br /> (Pnma) The report documents the recently performed bench scale testing (BST) of soil and <br /> groundwater from the former Unocal facility No 5098 located at 5400 and 5606 Pacific Avenue, <br /> Stockton, California The BST was performed consistent with a request from the Regional Water <br /> Quality Control Board (RWQCB) in its November 22, 2004 letter and the BST workplan included in <br /> ENSRs November 29, 2004 Addendum to the Geochemical Evaluation Regarding Potential <br /> I Chromium Mobilization During Ozone Treatment The RWQCB approved the BST workplan in a <br /> letter dated November 30, 2004 (Attachment A) <br /> During the BST, hexavalent chromium (Cr VI) was generated by ozonation of soil and <br /> groundwater The concentration of Cr VI after the ozone sparging test reached 73 micrograms <br /> per liter The subsequent Cr VI fate analysis performed by Prima, indicates that non-ozone <br /> treated soil can reduce the Cr VI, however, in the laboratory setting a 68% reduction took two <br /> days As a result of the magnitude of Cr VI formed, ENSR recommends evaluating additional <br /> alternatives that will not pose a threat to groundwater quality In its November 29, 2004 letter <br /> referenced above, the RWQCB requested that a recommended altemative to ozone sparging, if <br /> Inecessary, be completed by January 31, 2005 ENSR received the results of the BST on <br /> I <br /> i <br /> J Trojects106940 5098-2931Woriongtorrespondenoe15098 013105 Cvr Ltr to RWQCB doc <br /> Ce er�rahn� ", �ed,s of Ex�a!ientce ,i Envro�vnian,al S-ivicec <br />