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EA Engineering,Science,and Technology 3841 North Freeway Boulevard,Suite 145 <br /> Sacramento,CA 95634 - <br /> Fax:916-924924 7450 <br /> 7460 <br /> r <br /> 13 December 1996 i <br /> Ms. Marla Guensler <br /> Senior Environmental Engineer <br /> Exxon Company, U.S.A. <br /> P.O.Box 4032 <br /> Concord, California 94524-2632 <br /> Re: Response to Regulatory Comments on the UVB System for Exxon Retail Site 7-3942 <br /> Dear Ms. Guensler: <br /> The intent of this letter is to respond to regulatory review comments on the Groundwater <br /> ' Rcmcdiation System Technical Plan for Former Exxon Retail Site 7-3942, prepared by EA <br /> Eii ineering in October 1996. Two separate sets of comments were; made by Ms. Elizabeth <br /> 1-haycr of the=California Regional Water Quality Control Board (C,RWQCB) Central Valley <br /> Region car_ the installation of a UVB system at.Exxon 7-3.94'2. 'The fist set-ofc:ornmet).ts were- <br /> .mad e-in a:rRWQCB internal memorandum dated.12 November'1996-.and the...second set of <br /> comments were made in a letter to Ms. Margaret Lagorio of the San Joaquin County Public <br /> Healih Services dated 1 S November 1996. The following aesponses address both sets of <br /> Conim.ents. <br /> Comment 1: <br /> ".,. the lateral extent of contamination has not been confirmed to the northwest of the source <br /> area.'" <br /> Response 1: <br /> Comment noted. The intent of the present action is to remediate the on-site plume and to control <br /> further migration. The lateral extent of contamination to the northwest of the source area will be <br /> addressed at a later time. <br /> Comment 2: <br /> "Are the two screened sections of the UVB located in zones of high permeability? 1f not, how <br /> will this affect the circulation zone?" <br /> Response 2: <br /> As shown in the attached as-built construction diagram for the UVB well, both the lower and <br /> upper screen are located within a zone of high permeability, which predominantly consists of <br /> fine-grained silty sand. The UVB system is designed for concurrent extraction and injection <br /> within this zone at a flowrate of 8.8 gpm (2 m3/hr). During development of the UVB well, <br /> extraction flowrates of up to 15 gpm were sustained for each of the two screens. <br />