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FILE COPY <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Donna K.Heran,R.E.H.S. Unit Supervisors <br /> 304 East Weber Avenue Third Floor Carl Borgman,'R.E.H.S. <br /> Nc of Director ' Mike Huggins,R.E.H.S.,R.D.I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> 'FOR Laurie A.Cotulla,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Mark Bareellos,R.E.H.S. <br /> JIM PARKINSON APR O 2 2003 <br /> PARKINSON'S ARCO <br /> 3250 W HAMMER LANE <br /> STOCKTON CA 95209 <br /> RE: Parkinson's ARCO SITE CODE 2224 <br /> 3250 W Hammer Lane RO: 709 <br /> Stockton, CA 95209 <br /> San Joaquin County Environmental Health Department (EHD)has reviewed Additional <br /> Assessment and Interim Remediation Report, dated 8 November 2002, and First Quarter <br /> 2003 Groundwater Monitoring Report, dated 3 February 2003, submitted on your behalf <br /> by Shaw Environmental, Inc. (Shaw). Based upon these results, the extent of impacted <br /> groundwater does not appear to have been fully delineated down gradient; nor has the <br /> vertical extent of impacted groundwater been demonstrated. A laterally continuous, <br /> significant aquitard at 54 feet below ground surface (bgs) seems unlikely when less than <br /> two feet of clay were recovered from it in a sand section more than 43 feet thick. <br /> EHD suggests that you consider conducting a Cone Penetration Test (CPT)1 investigation <br /> to aid the development of a hydrogeological model of the site. Information obtained <br /> from the CPT investigation may help determine the need for additional groundwater <br /> monitoring wells and aid selection of advantageous monitoring well locations and design. <br /> A site conceptual model (SCM) should be prepared for this site. The SCM should <br /> include the following: <br /> 1. Local and regional plan view maps showing location of sources, extent of <br /> contamination(i.e., an interpretive drawing-not merely a plot of laboratory <br /> results), direction and rate of groundwater flow, and locations of receptors. <br /> I <br /> "Receptors" include,but are not limited to, all-supply wells within 2000 feet of <br /> the source area; <br /> 2. Cross-sections showing subsurface geologic features, depth of groundwater,man- <br /> made conduits, monitoring well construction, and an interpretive drawing of the <br /> vertical extent of soil contamination; <br /> I <br />