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ency STATE QF CALIFORNIA• Environmental Proter�Ag • PETE WILSON, Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> y <br /> 3443 Routier Road, Suite A alga o <br /> Sacramento, CA 95827-3098 . X <br /> PHONE: (916)255-3000 <br /> DOD FAX: (916) 255-3052 DEC 16 1992 <br /> ENVIROiv vIEIUTAL HEALTH <br /> 14 December 1992 <br /> PERMIT/SERVICES <br /> Mr. Abel Haines <br /> Environmental Protection Office <br /> Bldg. S-108, Sharpe Site <br /> Defense Distribution Region West <br /> P. 0. Box 960001 <br /> Stockton, CA 95296-0710 <br /> REMEDIAL WELL-FIELD DESIGN USING THREE DIMENSIONAL GROUND WATER FLOW AND <br /> TRANSPORT MODELING REPORT, DEFENSE DISTRIBUTION REGION WEST (DDRW) , SHARPE, <br /> SAN JOAQUIN COUNTY <br /> We have reviewed the Remedial Well-Field Design Using Three Dimensional Ground <br /> Water Flow and Transport Modeling Report (Modeling Report) for DDRW, Sharpe <br /> submitted on 14 October 1992. We are pleased that Sharpe has produced a three <br /> dimensional (3-D) numerical model for the site and commend Sharpe for the <br /> content of this Report and quality of the modeling effort. We anticipate that <br /> the 3-D model will prove to be a worthwhile investment for the ground water <br /> remedial action. We have provided comments on the Modeling Report which are <br /> contained in the enclosed memorandum. <br /> The 21 October 1992 transmittal letter from Sharpe stated that the regulatory <br /> agencies should evaluate the need for requiring a 3-D model in the future for <br /> other sites. Your suggestion is based on the cost of this modeling effort to <br /> Sharpe ($190,000) and on the assumption that the preliminary extraction <br /> network design, which was based on a less sophisticated model , was adequate. <br /> After reviewing the Modeling Report, we do not concur with your assumption <br /> that the less sophisticated model was adequate, for the following reasons: <br /> 1. Extraction wells were formerly proposed in areas of the aquifer that had <br /> little to no contamination. <br /> 2. Existing extraction wells are now recommended for elimination from the <br /> extraction system. <br /> 3. Proposals for the design of the extraction wells and well field have been <br /> changed. <br /> If a 3-D model had been used initially, then additional monies for another <br /> modeling effort would not have been needed. In addition, the cost of <br /> additional modeling work may be offset when the following points are <br /> considered: <br />