SITE INFORMATION AND CORRESPONDENCE

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Mr. Maurice Benson - 2 - 21 January 2011 Defense Logistics Agency In 2009, DLA scheduled Warehouse 10 for demolition. At that time, the Army Corp of Engineers and DLA conducted investigations of contamination in soil and groundwater beneath the building. Based on the extent of contamination discovered in these investigations, DLA began evaluation of additional remedial alternatives to the currently established alternatives in the Comprehensive ROD. DLA completed the Final SWMU 20 FS in 2010. The SWMU 20 FS evaluated seven alternative remedies for cleanup of soil contamination beneath Warehouse 10, and selected SVE, enhanced with pneumatic fracturing, as the remedy for soil cleanup after building demolition. Central Valley Water Board staff concurred with this remedy. Furthermore, we concurred with documenting this remedy change in an ESD. Area 1/Building 237, SWMU 1/Areas 2 and 3, and SWMU 20 Cleanup Standards Sections 9.6.5 and 9.7.5.10 of the Comprehensive ROD require that the following three cleanup standards for trichloroethene (TCE) and tetra chloroethene (PCE) be met to achieve vadose zone cleanup at Area 1/Building 237, SWMU 1/Areas 2 and 3, and SWMU 20: 1. The concentrations of TCE and PCE (TCE only at SWMU 20) present in soil gas are equal to or less than the cleanup standard; 2. It is demonstrated that the remaining TCE and PCE can no longer cause leachate concentrations to exceed the aquifer cleanup standards; and 3. TCE and PCE have been removed to the extent technically and economically feasible. This evaluation will include, at a minimum, the following factors: a. The total cost and duration of continued operation of the SVE system until aquifer cleanup standards are met. b. The total cost and duration of continued groundwater treatment to meet aquifer cleanup standards. In the Draft ESD, DLA proposes to change the Comprehensive ROD so that achievement of only one of these three standards is required to complete a cleanup. Central Valley Water Board staff disagrees; if DLA believes that alternative, less stringent numeric standards are protective at a specific site, DLA must present supporting evidence that constituents of concern (COCs) remaining in soil vapor are not a threat at that specific site; if DLA determines that the COCs at a specific site are technically and economically not feasible, a Technical Impracticability Wavier must be applied for and granted for that specific site. Furthermore, Central Valley Water Board staff finds that the three criteria for achievement of cleanup were based on threat to groundwater quality and were not based on threat to indoor air. DLA must include this exposure pathway in any evaluation of alternative cleanup standards. California Environmental Protection Agency co Recycled Paper