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+ SECOR www.secor.com <br /> INTERNATIONAL 3017 Kilgore Road,Suite 100 <br /> Rancho <br /> S E C O R INCORPORATED 6-61 0400 Cordova, <br /> EA 95670 <br /> g <br /> 916-861-0430 FAX <br /> December 21, 2004 <br /> IRECENED <br /> Ms. Vicki McCartney DEC 2 2 2004 <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue, Third Floor ENVIRONMENT HEALTH <br /> Stockton, California 95202-2708 PERMIT/SERVICES <br /> RE: Response to Regulatory Letter <br /> Chevron Service Station 9-1452 <br /> 334 East Main Street <br /> Ripon, California <br /> SECOR Project No.: 77CH.91452.06.0170 <br /> Dear Ms. McCartney: <br /> SECOR International Incorporated (SECOR), on behalf of Chevron Environmental <br /> Management Company (Chevron), has prepared this letter to respond to the San Joaquin <br /> County Environmental Health (County) letter dated November 18, 2004 (Attachment 1), for <br /> the above-referenced site. In addition, this letter has been prepared to document our <br /> telephone discussion on December 16, 2004. <br /> In your letter, the County requested that a work plan for an ozone sparging pilot test be <br /> submitted by December 17, 2004. However, SECOR and Chevron no longer consider <br /> ozone sparging a feasible alternative. The underground storage tank (UST) complex is <br /> located in close proximity to the apparent source area. Ozone is an oxidizer and could <br /> compromise the integrity of the USTs. <br /> As we discussed during our phone conversation on December 16, 2004, the original intent <br /> of batch groundwater extraction with the vacuum truck was to mitigate dissolved <br /> concentrations of methyl tertiary butyl ether (MtBE) in the vicinity of the USTs. However, <br /> dissolved concentrations continued to increase indicating a possible residual non aqueous <br /> phase liquid (NAPE) source. On December 15, 2004, Chevron's remedial system review <br /> team (RSRT), recommended that SECOR perform additional soil investigation to define the <br /> lateral and vertical extent of the possible NAPL source. In addition, RSRT has <br /> recommended that soil vapor extraction (SVE) be implemented to mitigate impacts from this <br /> possible source. <br /> Therefore, prior to January 21, 2005, SECOR will prepare and submit a work plan to <br /> perform an additional soil investigation. Based on the results of the investigation, a <br /> possible SVE pilot test will be performed to assist the design of an SVE system. In the <br /> interim, SECOR will continue the use of weekly batch extraction. <br /> l <br /> County Letter 12-6-04.docl:\Chevron\91452\Correspondence\2004\County Letter 12-6-04.doc <br />