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CaliforniSegional Water Quality Condkl Board <br /> l\- Central Valley Region <br /> vs, f <br /> Karl E.Longley,RD,P.E.,Chair ' '- <br /> Linda S.Adams 11020 Sun Center Drive 4200.Rancho Cordova.California 95670-6114 Arnold <br /> Secremn for Phone(916)464-3291 •FAX(916)464-4645 Schwaraenegger <br /> EnvironmenmlGovemor <br /> Protection hup://www.waterboards.ca.gov/centralvalley <br /> 4 March 2009 <br /> DESJC, M.BENSON MAR 0 <br /> Defense Distribution Depot San Joaquin 6 2009 <br /> P.O. Box 960001 ENVIRONMENT' EALTH <br /> Stockton, CA 95296 PERMIT/SERVICES <br /> REVIEW OF DRAFT NORTHWESTERN CORNER DIELDRIN PLUME FEASIBILITY STUDY <br /> REPORT FOR DEFENSE LOGISTICS AGENCY, DEFENSE DISTRIBUTION DEPOT SAN <br /> JOAQUIN— TRACY SITE <br /> California Regional Water Quality Control Board, Central Valley Region (Regional Water <br /> Board) staff has reviewed the Defense Distribution Deport (DDJC) Draft Northwestern Corner <br /> Dieldrin Plume Feasibility Study Report(Draft FS), dated 21 November 2008. The Draft FS <br /> was prepared by URS Corporation on behalf of Defense Logistics Agency Enterprise Support <br /> San Joaquin, California (DESJC) for the DDJC Tracy site. <br /> The Draft FS evaluates alternatives for response actions to address the presence of dieldrin in <br /> groundwater beneath the northwest corner (NWC) area of the Tracy site. The dieldrin in the <br /> NWC is outside of the capture zone of existing groundwater treatment systems on the site. <br /> Three assessment efforts are described in the Appendixes of the Draft FS, not yet presented <br /> in any investigation reporting documents. Appendix A presents new groundwater sampling <br /> results and monitoring well installation activities associated with the NWC dieldrin plume; <br /> Appendix B presents the draft results of two groundwater pumping tests performed within the <br /> NWC over a period of 30 days in September and October 2008; Appendix C is a newly <br /> completed draft human health risk assessment of dieldrin in groundwater beneath the NWC. <br /> This review letter begins by presenting comments on the reports in the Appendixes and <br /> finishes with comments on the Draft FS. <br /> Dieldrin Sampling Comments <br /> Appendix A of the Draft FS presents the November 2008 Draft Dieldrin Groundwater Sampling <br /> Results and Well Installation Report (Draft Sampling Report), prepared by URS. The Draft <br /> Sampling Report concludes that dieldrin beneath the NWC occurs in the Upper and Middle <br /> Hydrogeologic Zones. Regional Water Board staff concurs. The Draft Sampling Report also <br /> concludes that the dieldrin is not dissolved in groundwater, is primarily found in fine-grained silt <br /> and clay layers, but not coarse-grained layers, and is immobile. These conclusions are not <br /> supported by the monitoring data. The monitoring data do appear to support the conclusion <br /> that dieldrin has not migrated significantly between the time of the 1998 CPT sampling events <br /> conducted by RUST Environmental and recent CPT sampling events conducted by URS. <br /> However, the CPT events and the groundwater monitoring well data show that the dieldrin <br /> plume did expand up to approximately 600 feet between the time of injection and the 1998 <br /> events. Therefore, dieldrin is mobile. If it were not, dieldrin would not be present in monitoring <br /> wells and CPT samples at such distant locations from the injection wells. <br /> California Environmental Protection Agency <br /> QC Re, rled Pnper - <br />