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w <br /> n <br /> ENVIROiVMENTAL HEALTwDEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.H rector R.E.H.S. <br /> • � )t< 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> Director <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,.R.E.H.S.,R.D.I. <br /> • c P • Program Manager Douglas Wilson, . <br /> 9C�FORS S. <br /> Laurie A.Cotulla,R.E.H.S. Telephone: (209) 468-3420 Margarett n <br /> Lagoo,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> MICHAEL KARVELOT <br /> QUIK STOP MARKETS INC JUN 14 2006 <br /> 4567 ENTERPRISE STREET <br /> FREMONT CA 94538 <br /> RE: Quik Stop Market No. 132 <br /> 3555 West Hammer Lane <br /> Stockton, California 95209 <br /> ATC Associates Inc. (ATC)has recommended that the above-referenced site be considered for closure. <br /> San Joaquin County Environmental Health Department(EHD)has reviewed historical data dating back <br /> to 1990 as well as current data to get an understanding of current site conditions. During this process it <br /> became apparent that a site conceptual model (SCM) that incorporates findings from the last sixteen <br /> years is needed to evaluate present site conditions. The general purposes for an SCM are to <br /> demonstrate where the contaminants came from, where they are at the present time, how they move <br /> through the subsurface, how they will respond to changes in the groundwater flow characteristics or to <br /> potential remediation efforts, what the contaminants' ultimate environmental fate will be, and to help <br /> evaluate the risk posed by the contaminants to groundwater supplies and sensitive receptors. In <br /> addition, the SCM may demonstrate data gaps, thereby illustrating where additional investigation may <br /> be needed. To be sure that the SCM will adequately address the assessment, remediation and, <br /> ultimately, final closure requirements for this site, please include the following, as appropriate, in the <br /> SCM: <br /> • Local and regional plan view maps showing locations of sources, boring and monitoring well <br /> locations, lines of cross section, extent of contaminants in each media (i.e., an interpretive <br /> drawing—not merely a plot of laboratory results),direction and rate of groundwater flow,and <br /> receptor locations,including water supply wells within 2,000 feet of the site; <br /> • Cross sections showing subsurface geological features, depth to groundwater, man-made <br /> conduits, monitoring well construction and the interpreted vertical extent of soil and <br /> groundwater contamination; <br /> • Cross-plots of key chemical concentrations verses time for representative wells that <br /> demonstrate significant contaminant concentration trends; <br /> • Summary tables of contaminant concentrations in the different media; <br /> • Rose diagram showing directions of dominant groundwater flow; <br /> • Well and boring logs (including construction/screening); and <br /> • Narrative description of the SCM that describes controls on contaminant distribution; <br /> contaminant migration mechanisms, pathways and rates; plume disposition over time; and <br /> sorbed and dissolved contaminant masses. <br />