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Department of Toxic Substances Control <br /> Maureen F. Gorsen, Director <br /> Linda S.Adams 8800 Cal Center Drive Arnold Schwarzenegger <br /> Agency Secretary Sacramento, California 95826-3200 Governor <br /> Cal/EPA <br /> D��CDD <br /> December 13, 2006 DEC 2 7 2006 <br /> ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <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 GROUNDWATER FATE AND TRANSPORT <br /> MODEL — DEVELOPMENT AND CALIBRATION HANDOUTS, FOR DEFENSE <br /> DISTRIBUTION DEPOT SAN JOAQUIN COUNTY (DDJC), TRACY SITE, TRACY, <br /> CALIFORNIA <br /> Dear Mr. Cloud: <br /> The Department of Toxic Substances Control (DTSC) participated in meetings with <br /> representatives from DDJC and the contractor, URS Corporation, focused on the <br /> development of a 3-dimensional groundwater numerical model (3-D Model) at DDJC- <br /> Tracy. The 3-D Model at DDJC-Tracy was developed as a tool to help analyze capture <br /> zones, optimize the existing groundwater extraction system and help predict cleanup <br /> times for Trichloroethene (TCE), Tetrachloroethene (PCE), and Dieldrin in groundwater. <br /> The 3-D Model will be used in the near future to evaluate the effectiveness of any <br /> extraction well modifications and cleanup times associated with alternative response <br /> actions. <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 during meetings held on August 15, 2006, September 28, 2006, and <br /> November 29, 2006 to ensure the appropriateness of model parameters and to reduce <br /> error between calculated and observed outputs. The August 15, 2006 modeling <br /> meeting focused on the development and calibration of the steady-state groundwater <br />