SITE INFORMATION AND CORRESPONDENCE

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Mr Peter MacNicholl February 21, 2009 Page 5 20.An alternate conceptual model is that the dieldrin is present as nanoparticles. The nanoparticles were formed in the air stripper. GSU suggests that the dieldrin was originally sorbed to PCE, which was commonly used as a carrier. The air stripper removed the PCE, but the dieldrin stayed behind, because it is not strippable. However, dieldrin is basically insoluble in water, and simply precipitated out, but in the turbulent flow regime could not clump, so formed nanoparticles which fell into the water and were swept out into the injection well. Electron microscopy of the filtrate on a porcelain filter would probably bear this out. It is easy to visualize how nanoparticles could be entrained in groundwater and travel in coarse channels, while simultaneously be mechanically filtered out by finer units. GSU is not persuaded that dieldrin is being sorbed or volatilized at all in this form in this environment. The section should be revised. 21.GSU agrees that aquifer properties exert strong control over migration, but disagrees with the way that the site materials are being portrayed. GSU agrees that silts and clays are more layer-like because they were deposited as floodplain and overbank deposits on an alluvial fan, but disagrees that the sand or gravel occurs in either lenses or layers. It is far more likely that sand and gravel represent channel deposits, and thus are long and skinny in the downhill direction of the fan. This characteristic can be discerned in the plume shape, velocity, and direction, as well as the contaminant distribution. The section should be revised. 22. Section 4.1.3 The movement of the plume is not consistent with a retarded species, because the concentration of dieldrin at LM74A is not attenuated. Lack of retardation invalidates the idea that dieldrin is travelling in dissolved phase. The conclusion that retardation will make extraction impractical is invalidated by the observation that pumping remobilized the dieldrin. This argument is simply not supported by the facts. The section should be revised. 23.Section 4.2 No evidence that the dieldrin is colloidal has been presented. Either such evidence should be presented, or the wording changed. 24.Section 4.3 The word lenses should be removed, and the sands and gravels should be described as channels, consistent with the depositional environment. 25.Section 4.3 Characterization as colloids should be proved or removed. 26.Section 4.3. The previous analysis shows that dieldrind did migate in response to hydraulic gradients, and little else except mechanical filtration. The lobe of dieldrin southward is explained by the shape of the injection mound in the