SITE INFORMATION AND CORRESPONDENCE

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Mr Peter MacNicholl February 21, 2009 Page 7 carbon; which does not appear to be abundant. The lack of studies is not sufficient reason to dismiss the idea before exploring it. 33.GSU suggests obtaining a standardized solution of permanganate/ peroxide, obtaining several duplicate samples from LM74A, and adding different amounts before analyzing for dieldrin. 34.Another treatment strategy would be to ensure immobilization by injecting a water-soluble oil mixed with a detergent to be distributed along the flow path. This would provide a substrate for degradation, and a more effective sorbent than soil particles. 35.Section 9.2 The LUC area should be recalculated to include all parts of the aquifer within which the critical velocity for entrainment of dieldrin is reachable at the maximum pumping rate of an appropriately-designed well in the shallow zone. The 0.1 isopleths are not sufficient. Our preliminary analysis above suggests that a well located 2500 feet downgradient and pumping 10 gpm could remobilize the plume. The section should be revised. 36.Section 9.4 The ROI calculations are incorrect. The plume could most readily be captured by locating the channel and pumping at the downgradient leading edge of the plume, and by injecting at the high end of the plume. This is why having a good conceptual model of the stratigraphy can help design a more effective cleanup with significant cost reductions. The cost estimate appears too high based on ROI numbers that do not reflect the observed behavior of the plume. The section should be revised. 37.New section 9.5 An in-situ treatment alternative based on the concepts outlined above should be discussed and costed out. Pulsed operation to facilitated mixing in the aquifer should be included. The principle of re-occupying the identical flowpaths should be followed. Conclusions and Recommendations: 1. The dieldrin release at this site has many unusual features and does not follow its typical fate and transport mechanisms. Because of this, great care must be taken in the RI to accurately identify what form it is in, how it moves, and what options there are to mitigate it. The RI in its present form does not adequately analyze its probable form, its transport, or remedial alternatives. 2. An alternative conceptual model is offered that is at least consistent with the facts of the release and its extent.