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Californiategional Water Quality Confol Board ( \ <br /> Linda S.Adams <br /> Central Valley Region _. <br /> Secreiary for Karl E.Longley,SCD,P.E.,Chair Arnold <br /> bnvironmemal Schwartenegger <br /> Protection 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Governor <br /> Phone(916)464-3291 •FAX(916)464-4645 <br /> http://www,waterboads.ca.gov/centra)valley <br /> 3 December 2008 <br /> DESJC, M.BENSON <br /> Defense Distribution Depot San Joaquin <br /> P.O. Box 960001 <br /> Stockton, CA 95296 <br /> DRAFT GROUNDWATER REMEDY ENHANCEMENT CONE PENETROMETER TESTING <br /> AND GROUNDWATER CHARACTERIZATION WORK PLAN, DEFENSE DISTRIBUTION <br /> 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 Draft Groundwater Remedy Enhancement Cone <br /> Penetrometer Testing and Groundwater Characterization Work Plan (Work Plan). URS <br /> Group Inc. prepared the Work Plan on behalf of Defense Logistics Agency Enterprise <br /> Support San Joaquin, California (DESJC) for the Defense Distribution Depot Tracy Site <br /> (DDJC Site), located in Tracy, California. <br /> The purpose of the Work Plan is to utilize cone penetrometer testing (CPT) equipment to <br /> further define the extent of trichloroethene (TCE) and tetrachloroethene (PCE) contamination <br /> on the Annex of the DDJC Site and the offsite area adjacent to the Annex east of Banta <br /> Road. DESJC's objective is to evaluate the potential that there are unknown sources of <br /> TCE or PCE on the Annex or east of the Annex. <br /> Comments <br /> Staff comments are presented below. <br /> 1 . Regional Water Board staff has evaluated the TCE concentration trends in groundwater <br /> monitoring and extraction wells located on the Annex and east of the Annex. I have <br /> attached 14 graphs of these trends to this letter. The Y-axis of each graph represents <br /> TCE concentrations between 0 and 12 micrograms per liter (µg/L). With one exception <br /> explained below, the X-axis of each represents dates of groundwater sample collection <br /> between 1 January 2000 and 1 December 2007. Based on these trends, it appears that <br /> there may have been a source of TCE on or near the Annex in the vicinity of monitoring <br /> wells LM147A and LM 165A. Concentrations in LM147A had ranged from a high of <br /> 8.4 µg/L on 8 March 2000 to 4.0 µg/L on 6 September 2007 (Attachment 1). To date, a <br /> source of TCE to the south-southwest has not been identified. Proposed CPT borings <br /> CP0092 through CP0094 may help to identify such a source. In addition, DESJC should <br /> drill borings east of LM147A. <br /> California Environmental Protection Agency <br /> Qd RecY led Paper <br />