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1/ <br /> `- Department of Toxic Substances Control <br /> Alan C. Lloyd,Ph.D. 8800 Cal Center Drive Arnold Schwa¢enegger <br /> Agency Secretary Sacramento, California 95826-3200 Governor <br /> Cal/EPA - ^ OWED <br /> November 19, 2007 u fNOV 2 1 2007 <br /> ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Mr. Marshall Cloud <br /> Remedial Project Manager <br /> Defense Distribution Depot—Tracy Site <br /> Post Office Box 960001 <br /> Tracy, California 93727-0525 <br /> RECOMMENDATION FOR PATH FORWARD FOR NORTHWEST CORNER <br /> DIELDRIN GROUNDWATER REMEDY AND REMEDY-IN-PLACE GOAL: DEFENSE <br /> DISTRIBUTION DEPOT SAN JOAQUIN (DDJC) — TRACY SITE, TRACY, CALIFORNIA <br /> Dear Mr. Cloud: <br /> On October 29, 2007, the Department of Toxic Substances Control (DTSC) and <br /> Regional Water Quality Control Board met with the United States Environmental <br /> Protection Agency (U.S. EPA), by phone to discuss our response to DDJC's <br /> August 22, 2007 letter requesting input on a Dieldrin Remedy for Operable Unit 1 <br /> (OU-1). During the call, the agencies identified what we believe to be the most effective <br /> path forward for selecting a final remedy for dieldrin contamination in the Northwest <br /> Corner (NWC) plume and, at the same time, accomplishing the final Remedy-in-Place <br /> goal for DDJC Tracy. The agencies recommend focusing on remedy selection for the <br /> NWC dieldrin plume, rather than Operable Unit wide. <br /> This recommendation is based on the following: 1) The regulatory agencies will not <br /> entertain an increase in the Aquifer Cleanup Level previously selected, 2) the Sanitary <br /> Sewage Lagoon (SSL) Plume currently has an operating remedy which will have <br /> recurring effectiveness evaluations during, at a minimum, five-year reviews, and 3) the <br /> groundwater conceptual site model for the NWC dieldrin plume is sufficiently different <br /> from the conceptual site model for the SSL plume that direct correlations in response <br /> to pumping may be limited. <br /> DDJC Tracy's August 22, 2007 letter requests input on the use of the U.S. EPA's <br /> technical impracticability guidance for evaluating remedies for dieldrin in OU-1 in lieu <br /> of a formal feasibility study. Comments recently provided by the Regional Water <br /> Quality Control Board recommends DDJC Tracy prepare a `focused' feasibility study <br /> 0 Printed on Recycled Paper <br />