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- Nood, Y)EPARTMENT <br /> ENVIRONMENTAL HEALTH <br /> aA "'' SAN JOAQUIN COUNTY <br /> /16._�.,oG unit Supervisors <br /> 2 !—°°g'—" :1, Donna K.Heran,R.E.H.S. Carl Sorgman,R.E.H.S. <br /> 304 East Weber Avenue, Third Floor <br /> m < DirectorMike Hugoins,R.E.H.S.,R.D.I. <br /> ' AI Olsen,R.E.H.S. Stockton, California 95202-2108 Douglas W.Wilson,R.E.H.S. <br /> • �.. �Pa Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> q�ikoa�' Robert McClellon,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-01.38 <br /> Program Manager stark Barcellos,R.E.H.S. <br /> CRAIG OGATA MAY 0 3 2004 <br /> DIRECTOR OF FACILITIES MANAGEMENT <br /> SAN JOAQUIN COUNTY PUBLIC WORKS <br /> 1722 EAST SCOTTS AVENUE <br /> STOCKTON CA 95205-6240 <br /> RE: San Joaquin County Courthouse SITE CODE 1285 <br /> 222 East Weber Avenue RO: 11 <br /> Stockton, CA 95202 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the data submitted <br /> for the July 2002 through December 2003 quarterly groundwater monitoring events, soil and <br /> groundwater analytical results from three soil borings, boring lithologies, and the well receptor <br /> survey report prepared by Ramage Environmental pursuant to consideration of the site for <br /> regulatory closure. EHD has concerns regarding the high concentrations of benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX), gasoline, and methyl tertiary-butyl ether (MTBE) <br /> currently found in groundwater sampled from monitoring well MW-1. Benzene is reported at <br /> 1900 micrograms per liter (µg/l..), well above the California Environmental Protection Agency <br /> Regional Water Quality Control Board Central Valley Region maximum contaminant level <br /> (MCL)of 1 µg/L. <br /> Additional information is needed to evaluate the site closure request. Please prepare a site <br /> conceptual model (SCM) to use as a tool for closure consideration. The general purposes for an <br /> SCM are to demonstrate where the contaminants came from, where they are at the present time, <br /> how they move through the subsurface, how they will respond to changes in the groundwater <br /> flow characteristics or to potential remediation efforts, what the contaminants' ultimate <br /> environmental fate will be, and to help evaluate the risk posed by the contaminants. to <br /> groundwater supplies and sensitive receptors. In addition, the SCM may demonstrate data gaps, <br /> thereby illustrating where additional investigation may be needed. To be sure that the SCM will <br /> adequately address the assessment, and final closure requirements for this site, please include the <br /> following, as appropriate, in the SCM: <br /> • Local and regional plan view maps with sources, boring and monitoring well locations, <br /> lines of cross section, extent of contaminants in each media, direction and rate of <br /> groundwater flow, and receptor locations 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 />