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~ III IIIIIIIIIIIII III ~ STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Depadmenl of Natural Resources 131 3 Sherman 51., Room 215 Denver, Colorado 80203 Phone: (3031 866-3567 FAX: (303) 832-8106 June 5, 1996 Me. Anne Beierle Climax Molybdenum Company P.O. Box 68 Empire, CO 80438 RE: Mine Pill Study, Headersoa Miae, Permit No. N-77-342 Dear He. Beierle: I~~~~ DEPARTMENT OF NATURAL RESOURCES Roy Ramer Governor dames 5. Lochhead Execmive Director Michael B. Long Division Duenor The Division has completed a review the proposed Henderson fill acid drainage work plan, and has developed the following list of comments and concerns: 1. The work plan proposal includes acid-base accounting, British Columbia Research initial testing, and X-ray diffraction. The testing protocol proposed will provide an adequate initial characterization for acid generation potential, however, the Division ie also concerned with the metals generation potential of the Henderson Mine fill. This concern is engendered by the definition of "Acid Hine Drainage" in the Hard Rock/Metal Mininq Rules and Regulations which states that "Acid Mine Drainage" means contamination of water by low pH or heavy metals (emphasis added). Additionally, the Rules and Regulations define "Acid and Toxic Producing Materials" as containing detrimental amounts of acids, bases, or metallic compounds; this definition includes those metals that would not be designated ae heavy metals. It ie the Division•e position that representative samples of Henderson Hine fill should be subjected to appropriate leaching teats to characterize metals generation potential, in addition to the acid-base accounting that ie proposed. The selection criteria for appropriate leaching testa would be based on the physical environment of the fill materials. If the Henderson fill ie subject to contact with meteoric water that rune off the surface of the fill, or meteoric water that infiltrates the fill but percolates quickly to an exit point from the fill, then relatively simple meteoric water rinsing test e, with analysis of the rinsate water quality, would be appropriate. The Nevada Meteoric Water Mobility Test and EPA Method 1312 are examples of these types of testa. If significant saturated zones are present in the fill, rinsing teats would not provide complete characterization, and humidity cell, shake flask, or other appropriate testing with concomitant mineralogical analyses may be necessary. Leachate or rineate water quality analyses must be conducted using analytical methods with detection limits at least as low as the moat restrictive applicable water quality standard. 2. The work plan proposal suggests adoption of an ANP/AGP ratio of two as the boundary between the zone of uncertainty and the potentially non-acid generating field. The rational provided for adoption of this relatively low boundary ie that X-ray diffraction data on mineralogical composition of the fill materials will allow a more accurate description of the acid generating potential of the waste. CMC will have to provide a detailed description of how X-ray diffraction data will be utilized in describing acid generating potential. The Division's concern with the utility of X-ray diffraction data for acid generation prediction is that X-ray diffraction may not identify or quantify mineral species that can have a profound effect on acid generation potential, especially if these species comprise only a small percentage of the whole rock; also, X-ray diffraction will not provide information on potentially toxic trace elements within minerals. Since there is no direct way to interpret either the ANP:AGP ratio method or the difference method for comparing acid production potential with acid