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I Water Quality Cool Board <br /> CalifornAegiona 01M."Central Valley Region <br /> Linda S.Adams Karl E. Longley, SCD, P.E.,Chair <br /> Secentaryjor Arnold <br /> Environmental PProtectionSchwarzenegger11020 Sun Center Drive 4200,Rancho Cordova,California 95670-6114 Governor <br /> Phone(916)464-3291•FAX(916)464-4645 <br /> http://www.waterboards.ca gov/centralvalley <br /> 24 November 2008 °RECLET` �D <br /> UEC 01 2008 <br /> DESJC, M.BENSON ENVIRONMENT HEALTH <br /> Defense Distribution Depot San Joaquin PERAnIT/SERVICES <br /> P.O. Box 960001 <br /> Stockton, CA 95296 <br /> OU 1 REBOUND TEST AND REMEDIAL ACTION OPTIMIZATION WORK PLAN, <br /> DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN— TRACY, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Regional Water <br /> Board) staff has reviewed the October 2008 Operable Unit 1 Rebound Test and Remedial <br /> Action Optimization Work Plan (Work Plan). URS Group Inc. prepared the Work Plan on <br /> behalf of Defense Logistics Agency Enterprise Support San Joaquin, California (DESJC) for <br /> the Defense Distribution Depot Tracy Site (Site), located in Tracy, California. <br /> In the Work Plan, DESJC proposes to perform a rebound test within Operable Unit 1 at the <br /> Site. DESJC's objectives include evaluation of status and optimization options for the <br /> selected pump and treat remedial action for contaminated OU 1 groundwater. The primary <br /> contaminants of concern (COCs) are trichloroethene (TCE), tetrachloroethene (PCE), and <br /> dieldrin. To achieve these objectives, DESJC proposes to shut down the groundwater <br /> treatment plant and all of the groundwater extraction wells at the Site for 18 months. During <br /> that period they would collect groundwater samples from extraction and monitoring wells for <br /> laboratory chemical analyses of CDCs. DESJC would study the analyses results to <br /> determine what changes in concentrations and distribution of CDCs would occur in the <br /> absence of groundwater extraction. <br /> The Work Plan presents discussions of the following items as rationale for the rebound test: <br /> • COC plume concentrations trends between 2004 and 2007, <br /> • Modeling predictions of long-term COC behavior under both pumping and non-pumping <br /> conditions, <br /> • Migration observations on COC plumes east of Banta Road, outside of groundwater <br /> extraction well influence, <br /> • Groundwater extraction and treatment system cost trend per pound of COCs removed, and <br /> • Dieldrin natural attenuation study conducted in 2007 and feasibility of achieving the dieldrin <br /> aquifer cleanup level (ACL) specified in the Site Record of Decision documents. <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br />