SITE INFORMATION AND CORRESPONDENCE

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Mr. Phil Dawson August 26, 2009 Page 6 The State maintains that the draft final FS and the alternative presented in DLA's August 13, 2009 letter are not supported by the site-specific data showing the technical and economic feasibility of the pump and treat remedy. Also, the alternatives proposed by DLA are not in compliance with ARARs because the . requirements of State Water Resources Control Board (SWRCB) Resolution 92-49 have not been met. Puma and Treat Remedy, The State's position is that the number of extraction wells DLA believes would be required to implement the pump and treat remedy is excessive as stated in its July 1, 2009 letter. Many of the 78 wells proposed on Figure 9-2 of the feasibility study are in places where dieldrin has not been detected. DLA's consultant has designed for an aquifer that is homogenous and isotropic, and appears to assume the distribution of dieldrin is uniform. The State considers that the injected water contaminated with dieldrin migrated along preferential pathways, and the highest concentrations are located in these pathways. Furthermore, the State believes that pumping in particular should be done at the locations of interconnected stream channels that were intersected by the old injection wells. The aquifer tests clearly showed that the cones of depression were elongated southwest to northeast, which matches the general depositional setting of stream channels on the site alluvial fan. The aquifer tests also indicated that the radius of influence is longer along the depositional axis, and so a network of about a dozen wells, biased to areas of high concentrations, and aligned along northeast trending flow lines centered on the injection wells, would likely retrieve most of the mobile dieldrin. Compliance with ARARs. In order to address dieldrin, the April 1998 Site-Wide Comprehensive Record of Decision modified the remedy for groundwater that had been selected in the August 1993 Operable Unit No. 1 Record of Decision (ROD). The selected remedy is groundwater extraction and treatment because it meets the following ARARs concerning groundwater protection documented in the site-wide ROD: • SWRCB Resolution No. 68-16 • SWRCB Resolution No. 92-49 (as amended 21 April 1994 and 2 October 1996) The institutional controls remedy does not comply with the ARARs. The State asserts that the pump and treat remedy is technically and economically feasible and should be implemented in accordance with the April 1998 ROD. If, after reasonable efforts to achieve the ROD cleanup level with pump and treat, and data from performance monitoring demonstrate that pump and treat is not technically or economically