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sic- <br /> _WWW <br /> INTERNATIONAL <br /> 3017 Kilgore Road, <br /> INTERNATIONAL 3017 Kilgore Road,Suite 100 <br /> S E R INCORPORATED Rancho Cordova,CA 95670 <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> February 21, 2007 FEB 2 2 2007 <br /> O Wki'SV ;i UH <br /> Mr. Mike Infurna � <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue, Third Floor '� p• <br /> Stockton, California 95202 <br /> RE: Updated Cross-Section Showing Distribution of Dissolved MtBE Through Time <br /> SECOR Project No.: 77CP.02469.04.1235 <br /> Dear Mr. Infurna: <br /> On behalf of ConocoPhillips, SECOR International Incorporated (SECOR) is forwarding Cross- <br /> section A-A'for the Former 76 Station #4409 and Arco Station#4932 located at the intersection of <br /> EI Dorado Street and Harding Way, in Stockton, California. <br /> The previously prepared cross-section was modified to illustrate dissolved MtBE concentrations <br /> through time. Dissolved MtBE concentrations for selected quarterly events are presented above the <br /> cross-section, and estimated dissolved plume configurations for three time intervals are illustrated <br /> on the cross-section. The significant pattern to note here is the high MtBE concentrations <br /> decreasing with time in up-gradient wells with concurrent change from non-detectable levels to <br /> increasing concentrations in down-gradient wells. Gasoline or diesel has not been stored or <br /> dispensed at the Former 76 Station#4409 site since April 1999,which additionally helps lead to the <br /> perception that the recent increase in MtBE concentrations seen in monitoring wells at the Former <br /> 76 Station #4409 site are from an up-gradient source. <br /> Sincerely, "5\o1�"LGFory�s <br /> / 'Q.SIED)/(S lOCNi. <br /> No.4422 <br /> �*:. •7.24-08 �,�*= <br /> Sean Coyle <br /> Ed Simonis, PG `- s '..• :` �;` <br /> Senior Geologist rq�� Project Manager <br />