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VEND <br /> -� JUN 2 7 2007 <br /> ENVIRO AIIENT HEALTH <br /> ' <br /> Department of Toxic Substances 115661 CES. <br /> Maureen F. Gorsen, Director <br /> Arnold Schwarzenegger <br /> Linda S.Adams S8800 Cal Center Drive <br /> Sacramento, California 95826-3200 <br /> Agency Secretary <br /> Cal/EPA Governor <br /> June 21, 2007 <br /> Mr. Marshall Cloud <br /> Defense Logistics Agency <br /> Defense Distribution Depot San Joaquin, Tracy Site <br /> Post Office Box 960001 <br /> Stockton, California 95296-0250 <br /> COMMENTS ON THE DRAFT THREE-DIMENSIONAL GROUNDWATER MODEL <br /> REPORT (3-D MODEL), FOR DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN <br /> COUNTY (DDJC), TRACY SITE, TRACY, CALIFORNIA <br /> Dear Mr. Cloud: <br /> The Department of Toxic Substances Control (DTSC) received the subject document on <br /> March 2, 2007. The report presents the development and validation of the two <br /> interconnected groundwater models planning to be used at DDJC-Tracy. The 3-D <br /> Model at DDJC-Tracy was developed as a tool to help analyze capture zones, optimize <br /> the existing groundwater extraction system and help predict cleanup times for <br /> Trichloroethene and Tetrachloroethene in groundwater. The 3-D Model is planned to be <br /> used to evaluate the effectiveness of any extraction well modifications and cleanup <br /> times associated with alternative response actions in the future. <br /> The 3-D Model is comprised of two separate models; the flow model simulating the flow <br /> of groundwater beneath the site and the fate and transport model which simulates how <br /> a contaminant will move within groundwater and predicts the behavior of the <br /> contaminant in the future. <br /> The two groundwater models were developed collaboratively with DTSC's Geological <br /> Services Unit (GSU) during meetings held on August 15, 2006, September 28, 2006, <br /> and November 29, 2006 to ensure the appropriateness of model parameters and to <br /> reduce error between calculated and observed outputs. <br /> The 3-D Model was reviewed by DTSC's GSU which focused its review on the <br /> appropriateness and implementation of the parameters used in the models. DTSC's <br />