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t <br /> Department of Toxic Substances Control <br /> Maureen F. Gorsen, Director <br /> Alan C. Lloyd, Ph.D. 8800 Cal Center Drive '-1 1•/dk�o chwarzenegger <br /> Agency Secretary Sacramento, California 95826-3200 Governor <br /> Cal/EPA 'i! it 9, 5 2006 <br /> ENVIRUNMENT HEALTH <br /> July 20, 2006 PERMIT/SERVICES <br /> Mr. Marshall Cloud <br /> Defense Logistics Agency <br /> Defense Distribution Depot San Joaquin, Sharpe Site <br /> Post Office Box 960001 <br /> Stockton, California 95296-0250 <br /> COMMENTS ON THE DRAFT THREE DIMENSIONAL GROUND WATER MODEL <br /> REPORT, FOR DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN COUNTY (DDJC), <br /> SHARPE SITE, LATHROP, CALIFORNIA <br /> Dear Mr. Cloud: <br /> The Department of Toxic Substances Control (DTSC) received the above-mentioned <br /> report on June 2, 2006. The report discusses the development and verification of a <br /> three-dimensional numerical ground water (3D Model) model for the DDJC-Sharpe site. <br /> The ground water model was developed as a tool to help analyze capture zones, <br /> optimize the existing extraction system and help predict cleanup times for <br /> Trichloroethene and Tetrachloroethene in ground water. DDJC-Sharpe plans to use the <br /> 3D Model to evaluate the effectiveness of any extraction well modifications and cleanup <br /> times associated with proposed alternative response actions. <br /> The 3-D Model actually is comprised of two separate models: the flow model simulating <br /> the flow of ground water beneath the site, and the fate and transport model, which <br /> simulates how a contaminant will move within ground water and predicts the behavior of <br /> the contaminant into the future. Both models were developed collaboratively with <br /> DTSC's Geological Services Unit to ensure the appropriateness of model parameters. <br /> DTSC has reviewed the report and has the following comments: <br /> Specific Comments <br /> 1.) Figure 3-5, Ground Water Extraction System Well Locations; The figure is <br /> missing extraction wells (EWs) EWCC3, EWNA8, EWNB6, EWNCS, EWNA4, <br /> and EWNA6 and should be revised to include these extraction wells. <br /> 2.) Page 2-1, section 2.1.0.4, fifth sentence; The "deep sumps" are previously <br /> described as "catch basins" in the Final May 2006 DDJC-Sharpe Site P-5A <br />