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1117 Lone Palm Avenue, Suite B <br /> Modesto, CA 95351 <br /> (: <br /> http-//Y.fww.at-associates.com VYATC <br /> 209.579.2221 <br /> Fax 209.579.2225 <br /> A S 3 4 C I A T E S I N C <br /> November 23, 2004 <br /> 54.27142.0001 <br /> Mr.Nuel C. Henderson <br /> San Joaquin County <br /> Environmental Health Department <br /> 304 E. Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject: Response to San Joaquin Environmental Health Department Correspondence <br /> Regarding Request for Closure for Chapin Brothers Investments, Inc. Property at <br /> 1766 Monte Diablo Avenue, Stockton,California <br /> Dear Mr. Henderson: <br /> ATC Associates Inc. (ATC) has reviewed the San Joaquin County Environmental Health <br /> Department (EHD) correspondence dated October 4, 2004 regarding ATC's Closure Report, <br /> Chapin Brothers Investments, Inc. Property at 1766 Monte Diablo Avenue, Stockton, California, <br /> dated August 10, 2004 for the above referenced site. The following letter contains general and <br /> specific responses by ATC to the EHD's comments stated in their correspondence. <br /> Evaluation of Site Lithology <br /> ATC presented two cross sections in the report. Cross section A-A' is oriented northeast to <br /> southwest and extends a total distance of approximately 250 feet from monitoring well MW2, <br /> located across Monte Diablo Avenue to the north of the site, to soil boring CB3, located <br /> approximately 125 feet to the west of the site. Cross section B-B' is orientated east to west and <br /> extends a total distance of approximately 165 feet from monitoring well MW7, located <br /> approximately 25 feet to the east of the site, to monitoring well MW3, located approximately 55 <br /> feet to the west of the site. It is ATCs opinion that these two cross sections present sufficient <br /> subsurface lithologic detail to determine groundwater flow characteristics. <br /> Discussion of Groundwater Flow and Transport Modeling <br /> ATC has the following comments addressing questions and comments made by the EHD <br /> regarding the groundwater flow and transport model presented in ATC's Closure report. <br /> • A flow model was created using the modular finite-difference ground-water flow model <br /> (MODFLOW) developed by the U.S. Geological Survey (USGS). Once a flow model was <br /> created, a solute transport model was generated using the MT3D model. <br /> environmental 27142\repENORONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />