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occurs or has the potential to occur due to mining or reclamation activities. Rule <br /> 1.1 (13) defines "Designated Chemicals" as "...toxic or acidic chemicals used <br /> within the permit area in extractive metallurgical processing, the use of which, at <br /> certain concentrations, represents a potential threat to human health, property or <br /> the environment." <br /> Henderson does not question its status as a DMO. However, the determination <br /> by the DMG that HDS constitutes a "designated chemical' as defined in Rule 1.1 <br /> (13) and regulated in Rule 6.4 (19) is questionable given how it is produced and <br /> its characterization. <br /> To better understand how HDS is produced, a process flowsheet is included in <br /> Appendix B. Briefly, mine waters from the Henderson Mine and the Urad site are <br /> consolidated and treated with enough slaked lime to raise the water to pH 9+. <br /> Water is then passed through an agitated mix tank, an agitated lime reactor tank, <br /> an agitated flocculation tank, and a clarifier to precipitate metals and solids and <br /> produce discharge water meeting CDPES limitations (with the addition of sulfuric <br /> acid to adjust the final pH). Sludge is recycled as a part of the treatment <br /> process. Sludge density ranges from 35 percent to 50 percent (Figure 1). When <br /> discharged to the drying beds, HDS has a pH in excess of 9.0. <br /> Recent research into the stability of water treatment sludge indicates that HDS <br /> produced from alkaline precipitation systems is very stable at the typical alkaline <br /> pH. Studies of alkaline sludge produced from treatment of acidic mine waters at <br /> the Climax Mine site (Ford, et al. 1998a; Ford et al. 1998b) "...indicate that there <br /> is little potential for dissolution of metal-bearing phases under neutral to alkaline <br /> conditions." Copies of these publications are included in Appendix C. <br /> Afftit <br /> 3 <br /> June 23.1999 <br /> TR.tlac <br />