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Mr. Phil Dawson August 26, 2009 Page 5 semi-confined to unconfined as the material above the cone of depression finally finished draining and the cone rate of expansion increased to make up for the loss in flow. Because the early data suggested leaky conditions, it was assumed that leakage would last forever. However, an unconfined aquifer will act leaky until the material above the cone of depression drains. There are several samples of conversion of confined to unconfined conditions during the test at some of the shallower observation wells, as indicated by the observation well hydrograph switching between a smooth and bouncy pattern shown on the attached Figure 3-9 from the Pump Test Report. These same wells over-recovered after the test, which as suggested in the previous paragraph, shows a storage coefficient change during the test, some of which may have been caused by air bubbles trapped in the unsaturated zone. Several years of characterization and monitoring data that confirm plume stability. DLA has concluded that characterization and monitoring data confirm that the plume is stable. Regardless of whether dieldrin is or is not migrating, the pumping tests show that it does migrate when pumped. In the August 13 letter, DLA mentioned the operation of nearby agricultural and DDJC-related pumping wells located outside and deeper than the dieldrin plume. DLA asserts that despite the operation of those wells, located deeper and outside of the northwest corner area, the dieldrin plume has remained stable. However, DLA did not identify these wells or data supporting the assertion. Dieldrin only moves when extraction is in the same zone as the dieldrin, so it is not surprising that pumping a different unit does not affect the plume. Sampling data that show dieldrin is in a filterable form. The aquifer test clearly shows that dieldrin, if present, is readily mobilized by pumping regardless of the form the dieldrin is in. It is also clear from the pumping test that only wells with screens in the same zone as the dieldrin will produce it. This is consistent with the concept that dieldrin mainly travels in the coarser stringers, but that not al; the stringers communicate with one another. Remedial Alternatives DLA maintains that the draft final FS proposes an alternative that addresses the remedial action objectives of protectiveness and compliance with ARARs, and that the data support the conclusion that Alternative 2, Monitoring and ICs, is the appropriate alternative. However, to address the State's concerns, DLA proposes a new alternative: Monitoring and ICs, with a Pump and Treat Contingency.