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ENVIRONMENTAL HEALTWDEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. <br /> :< <br /> Director 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S.Al Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. <br /> Program Manager Douglas W.Wilson,R.E.H.S. <br /> Tele hone: 209 468-3420 <br /> FOR Laurie A.Cotulla,R.E.H.S. h ( ) Robert C�Ilon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 rt M <br /> Mark Barcellos,R.E.H.S. <br /> DENIS L BROWN PR � � ���� <br /> SHELL OIL PRODUST US A <br /> HSE ENVIRONMENTAL SERVICES <br /> 20945 S WILMINGTON AVE <br /> CARSON CA 90810-1039 <br /> RE: Shell Station (former) Site Code: 5050602 <br /> 1267 Country Club Blvd RO#: 062 <br /> Stockton, CA. 95204 SWRCB-CUF#: 018070 <br /> San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Response Letter/Site Investigation Work Plan Addendum (Response <br /> III), dated 06 April 2005, prepared by Cambria Environmental Technology, Inc. <br /> (CETI) on your behalf. <br /> In Response III, CETI recounts the directive/response letter-work plan history of <br /> the site characterization regarding the former waste oil underground storage tank <br /> (WO/UST). EHD is not satisfied with the characterization of the WO/UST <br /> release. Shell and CETI maintain that the WO/UST investigation is adequate <br /> and no further investigation is necessary, but include proposed boring SB-6 to <br /> address EHD concerns. If CETI can demonstrate that the data collected from S- <br /> 3 fully addresses the issue, EHD will reevaluate the results. EHD's concern with <br /> the S-3 data is that the well is 15 to 20 feet from the former WO/UST location in a <br /> very nearly perpendicular cross-gradient direction from the former WO/UST. The <br /> lithologies encountered in the S-3 boring were all fine-grained; sand units that <br /> can serve as significant contaminant migration pathways were not described on <br /> the boring log. <br /> Of course, fine-grained units commonly have lower hydraulic conductivities than <br /> coarse-grained units and normally have a much greater retardation on migration <br /> of many contaminants. The contaminants of concern would have to migrate to S- <br /> 3 at a diffusion and dispersion rate that overcomes the advection rate in the <br /> dominant down-gradient groundwater flow direction to reach S-3. What the S-3 <br /> results do show are the occurrence of 1,2-dichloroethane (1 ,2-DCA) and low <br /> concentrations of nickel and zinc. The 1,2-DCA has not been detected in the <br /> other site wells, although some of the analyses have high detection limits that do <br /> not exclude the possibility that 1,2-DCA may be present. <br />