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material excavated from the well bores are described using standard the soil classification system and <br />a general geologic description. Downhole geophysical surveys including gamma and neutron logs <br />should be performed to provide stratigraphic and hydro-stratigraphic correlation. <br />Development Rock Pile Chemistry <br />MWMP testing and microprobe analysis of development rock samples collected from trenches show <br />that this material contains elevated amounts of several elements of concern, and also that there is the <br />potential for the generation of leachate containing elevated concentrations of these same elements. <br />A water balance model and an UNSAT H computer model both indicated that it would be unlikely <br />that any leachate generated by infiltration on the development rock piles would enter the <br />groundwater and that the development rock piles should remain unsaturated. <br />The predictions made by these models will require confirmation through the drilling of a well <br />through the dump and completed at the interface of bedrock and overlying unconsolidated material. <br />The well should be screened at the base of-the-material overlying bedrock; but we recommend a <br />sump of about two to three feet to facilitate collection and sampling of water. If any bottom hole <br />water is encountered it should be sampled and characterized (see Table 1). This well should be left <br />open for at least one year, if not longer, so that seasonal variations in saturation, if any, can be <br />observed. Because of this, the well should be placed in a location that will not interfere with <br />operations in the short term. Please ensure that the material excavated from the well bore at this <br />location (and for the other monitoring wells) is described using the standard soil classification system <br />and a general geologic description. <br />Little is known about what wind or surface-water borne sediment transport away from the <br />development rock piles has occurred in the past. A geochemical survey of surface sediments which <br />incorporates biased sampling toward preferential transport directions caused by topography and <br />prevailing winds is needed. We suggest mapping a maximal extent with a gamma detector, with <br />limited screening for arsenic and cadmium and establishing baseline chemistry for native soil <br />material (see Table 2) in the vicinity of the Topaz mine. <br />We appreciate Denison's patience as we move towards completing our analysis. We will work with <br />you to expedite the clearance of any work needed to gather the information identified in this letter. If <br />you have any technical questions about what we have proposed, please contact James Blair at (970) <br />882-6862. <br />Sincerely, <br />mie Sellar-Baker <br />Associate Manager <br />CC: Phil Buck, Denison <br />Bob Oswald,,DRMS <br />Files <br />2 of 4