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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> �.•_,�'•.oG Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. <br /> .A Third Floor <br /> N: Director Mike Huggins,R.E.H.S.,R.D.I. <br /> ,Al OlsenR.E.H.S. Stockton, California 95202-2708 <br /> �:•• Douglas W.Nilson,R.E.H.S. <br /> �... = Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> 9�'F 6' Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. <br /> OCT 0 4 2004 <br /> MR RUSSEL CHAPIN <br /> CHAPIN BROTHERS, INC <br /> 1203 N CARLTON AVE <br /> STOCKTON CA 95203 <br /> RE: CHAPIN BROTHERS Site Code: 0850 <br /> 1766 MONTE DIABLO AVENUE <br /> STOCKTON, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Closure <br /> Report(CR), prepared by ATC Associates, Inc. (ATC)for the above-referenced site. <br /> The CR has nine main sections: Introduction, Hydrogeologic Setting, Background, <br /> Existing Conditions, Model of Groundwater Plume, Groundwater Receptor Survey, <br /> Evaluation of Low Risk Criteria, Conclusions /Recommendations, and References. The <br /> heart of the report consists of ATC's hydrogeological model and the fate and transport <br /> model for dissolved contaminants that ATC interprets to justify a recommendation for an <br /> immediate site closure with no further monitoring. After careful review of the CR and <br /> consultation with the Central Valley Regional Water Quality Control Board (CVRWQCB) <br /> representative, Mr. Jim Barton, EHD cannot concur with this recommendation for <br /> reasons presented in detail below, but in brief, EHD believes the models presented are <br /> not adequate to characterize the plume dynamics or to predict future plume behavior <br /> following cessation of the groundwater extraction program. Also, the report and models <br /> do not provide adequate information to evaluate the effectiveness of the current pump- <br /> and-treat groundwater remediation system, so EHD cannot approve termination of its <br /> operation at this time. Following discussion of the report, EHD provides suggestions to <br /> improve and test the models. <br /> The first three sections of the report in general are adequately presented, although there <br /> is no discussion of hydrologic units and how they control ground water movement, flow <br /> direction, and the combined effect on contaminant migration. In fact, the distribution of <br /> dissolved contaminants is utilized to infer a predominant flow direction (southwest) used <br /> for modeling that is oblique or counter to the flow direction inferred from ground water <br /> elevation isocontour maps (northeast to southeast) since 1994 with no explanation for <br /> the apparently conflicting flow direction indicators. <br /> The Existing Conditions section consists of two subsections, the first discussing the <br /> distribution of contaminants in soil and the second discussing the distribution of <br /> contaminants in ground water. <br />