SITE INFORMATION AND CORRESPONDENCE

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Mr. Maurice Benson - 2 - 1 July 2009 Defense Logistics Agency Background In March 1991, DDJC started an interim pump and treat system for removal of trichloroethene (TCE) and tetrachloroethene (PCE) in groundwater. The treated effluent was discharged to three injection wells located in the northwest corner (NWC) area of the Tracy depot, outside of the TCE and PCE plume areas. Approximately 572,000 gallons were injected into these wells for 9 days in October 1991, but was shutdown due to design problems. The system was restarted in November 1992 and discharged approximately 5,173,000 gallons of treated effluent into the injection wells before it was shutdown again in February 1993 due to plugging of the wells. The treated effluent, discharged to the injection wells between March 1991 and February 1993, contained dieldrin that had leaked into groundwater from the sewage lagoons and industrial waste lagoons located southeast of the NWC area. As a result, a dieldrin plume was created in the NWC area of the depot. In June of 1991, a Federal Facilities Agreement was finalized for the site and in August 1993 a Record of Decision (ROD) for Operable Unit 1 (OU1) was finalized. The ROD established pump and treat as the remedy for TCE and PCE in groundwater. Although dieldrin was identified in the ROD as a Chemical of Concern in groundwater, it was stated to be occurring sporadically. Later in the February 1998 Site-Wide Comprehensive Record of Decision, groundwater pump and treat was selected as the remedy for dieldrin in groundwater at the Tracy site. In November 2000, DLA submitted the OU1 Pesticide Extraction and Treatment System Remedial Design (3096) document. That document presented plans for dieldrin- contaminated groundwater pumping from extraction wells located adjacent to the wastewater lagoons, in the Tracy Depot Annex, and in the NWC area. Also, the pesticide design specified carbon adsorption vessels for treatment of effluent from extraction wells containing dieldrin before pumping to one of the two existing treatment plants for TCE and PCE removal. In addition, the document presented plans for conveyance piping from the extraction wells to the treatment plants. In May 2002, DLA submitted the OU1 Pesticide Extraction and Treatment System Remedial Design (100%) document. That document did not include the proposed wells and piping in the NWC area because data gaps remained. No explanation was given for why these data gaps, which were identified in the 30% document, were not closed before completion of the 100% document. To date, DLA has not implemented the pump and treat remedy for removal of dieldrin injected into the NWC area groundwater. However, as a means of closing the pesticide design document data gaps, DLA submitted the Draft Northwestern Comer Dieldrin Plume Feasibility Study Report (Draft FS) dated 21 November 2008. The Draft F5 evaluated alternatives for response actions to address the presence of dieldrin in groundwater beneath the NWC area. An Appendix of the Draft FS presented draft results of two groundwater pumping tests performed within the NWC area over a period of 30 days in September and October 2008. Based on the pumping tests, DLA concludes that dieldrin removal by pumping is not effective. The State concludes that the pumping tests present evidence to the contrary.