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ENVIRONMENTAL HEALTH DEPARTMENT <br /> OPOu�N <br /> c <br /> Donna K. Heran, R.E.H.s. SAN JOAQUIN COUNTY <br /> Director <br /> 304 East Weber Avenue,Third Floor Unit Supervisors <br /> Laurie A, Cotulla, R.E.H.S. <br /> �9��FOPN`P • Carl Borgan <br /> Program Manager Stockton,California 95202-2708 Mike HugginsmR.E.H.SHR.D,I. <br /> Telephone: (209)468-3420 Douglas W. Wilson,R.E.H.s. <br /> Fax: (209)464-0138 Margaret Lagorio,R.E.H.S. <br /> Website:Www.s Robert McClellon, R.E.H.S. <br /> jgov.org/ehd/ Jeff Calruesco,R.E. <br /> H.S. <br /> JAMES LL BARTON <br /> CENTRAL VALLEY REGIONAL <br /> 11020 WATER QUALITY CONTROL BOARD <br /> SUN CENTER DRIVE #200 <br /> RANCHO CORDOVA CA 95670 <br /> RE: Case Closure Consideration for <br /> Flag City Chevron <br /> 6421 W. Capitol Ave. <br /> Lodi, California <br /> EHD has reviewed Closure Summary Report—August 2005, Flag City Chevron (CSR), <br /> Prepared by Advanced GeoEnvironmental Inc. (AGE), dated 31 August 20ev and other <br /> technical information for the Flag City Chevron(FCC)site, the New West Shell (NWS) <br /> located at 6327 W.Banner St.,and the Three B's site located at 14749 N. Thornton Road, <br /> to comment on the Case Closure consideration proposed by the Central Valley Regional <br /> Water Quality Control Board(CVRWQCB). Intuitively the site data appears to favor <br /> case closure,but the sensitive groundwater supply for the area, the unauthorized releases <br /> from the New West Shell and Three-B's sites, and proximity of public water supply wells <br /> leads the EHD to a more cautious approach to case closure for this site. EHD is not <br /> comfortable with closing the case without a clear understanding of the MTBE <br /> occurrences in FCC monitoring wells MW-8A and MW-2. At this point, EHD cannot <br /> offer a satisfactory opinion on whether or not the concentration trends in these two wells <br /> indicate a potential threat to the public water supply wells(CSAl and CSA2)toward the <br /> southeast. <br /> Following identification and initial assessment of the MTBE-impact to groundwater in <br /> the FCC area and recognizing the threat it posed to local domestic and public water <br /> supply water wells, a groundwater extraction(GWE)system was operated on the Flag <br /> City Chevron site from November 2000 to August 2004. The GWE system,which <br /> consisted in part of 10 groundwater extraction wells (GWE-1 through GWE-10), had <br /> intermittent or partial operation from April 2000 to November 2000. During full <br /> operation of the GWE system,groundwater elevation contours indicate a depression on <br /> the water table in the extraction area,presumably inducing radial inward flow from all <br /> directions. The inferred groundwater flow direction near MW-2 shifted from easterly to <br /> westerly during the GWE operation, and shifted toward the ESE following termination of <br /> active GWE. A cone of depression was mapped in the extraction area during operation of <br /> the GWE system. <br /> MW-8A, completed in the second water zone, was non-detect(ND)for MTBE from <br /> initial monitoring in May 2000 to December 2001, and has been MTBE-impacted from <br />