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STATE OF DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 Phone: (303) 8fi(r3567 FAX: (303) 832.8106 ~~~ ~~~ COLORADO DIVISION O F MINiSRALS GEOLOGY SAFETY•sCIENCE INTEROFFICE MEMORANDUM Bill Owens Governor Russell George Executive DirecTOr December 21, 2005 Rona)a w, catwny / ~ Division Director \ J ( / Natursl Resource Trustee To: , ,, Wally Erickson Z~Z~~I~rH~/1 From: ~ Harry Posey ! V RE: Potential for release of acid-toxic substances from proposed gravel operation, Jack Clark Jr.; Upper Animas Sand and Gravel Pit; San Juan County; M-2005-065. The proposed gravel pit area may be a site of tailings deposition from the upstream Eureka mining district. The following comments presume, for discussion sake, that tailings do indeed exist in the target area, and presumes that such tailings have the potential to generate acid and release metals, much like the pre-law tailings at Howardsville Mill area and elsewhere in the upper Animas basin. Tailings residing above the water table are most susceptible to acid generation (and metals release) because oxygen is readily available. Periodic wetting and drying generates acid in sulfidic tails. In turn, the acid dissolves local minerals and may evaporate to form soluble metals salts, which are released quickly when re-saturated by rain or snowmelt. Tailings stored below the low water level can contact only the oxygen that is dissolved in the ground water, an amount that is miniscule relative to oxygen in air. Hence, the generation and release of sulfuric acid and dissolved metal from the weathering of sulfide minerals in saturated tailings would be trivial, and environmentally trenign. The amount of soluble salts released from a single locale -from tailings in the proposed gravel pit area, far instance -can be compared with salts from those same tailings spread regionally (on roads for instance). Metal salts released from road beds during rain or snowmelt would be diluted broadly whereas those released from a single site would be more concentrated in metals and acid and therefore more problematic to aquatic life. I find no compelling reason to conduct studies to determine the abundance or manner of occurrence of tailings in the proposed gravel pit. There is little evidence supporting the notion that mining a sulfide tailings-bearing gravel, which admittedly would generate acid and could release dissolved metals, would cause problems worse than those already potentially caused at the site (if tailings are indeed present). Moreover, assuming tailings are present, it would be more environmentally beneficial to spread out those tailings regionally, as on roadbeds, and take advantage of the dilution that would follow from the more regional rather than local distribution. Considering only the acid-generating and metals release potential of mining the gravel vs leaving it in place, I find no convincing reason to deny the proposed operation. Other issues, however, must be considered separately. cc: Bruce Humphries ~~ Office of Office of Colorado Mined Land Rxlamation Active and InaRive Mines Geological Survey