2008-03-21_PERMIT FILE - C1980007A (46)

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West Elk Mine the colloidal particles. The colloids are clay particles with 95 percent of the particles smaller than five microns and 35 percent smaller than two microns. The chemical flocculents/polymers that had historically been effective did not work on this colloid. After extensive testing by MCC, consultants and chemical suppliers, MCC determined that conventional alum in heavy doses would be the most practical means for meeting the necessary TSS limits. There are significant drawbacks to alum applications in this situation. First, substantial quantities of alum aze required. For example, with MB-1 and MB-2R at capacity, approximately 4,000 pounds of alum per week per pond were necessary. The chemical is corrosive and applying it to the sedimentation ponds is difficult and costly (MCC has rented a "hydroseeder" truck to spray on liquid alum). An even larger concern is the enormous quantity of "floc" that is generated by the alum additions. MCC recognizes that it will be necessary to remove the alum floc that has accumulated in the sedimentation ponds, on a more frequent basis, and this will require a major expenditure each time. Continuing to apply alum in the current manner on a long-term basis is not feasible. MCC investigated and evaluated numerous water treatment systems to identify effective, reliable, long-term alternatives for the reduction of TSS. Four technology categories were evaluated; gravity sepazation of solids, batch treating of ponds, chemical treatment, and physical treatment. The technology categories evaluated aze summarized below: Gravity Seaaration of Solids • Because an extremely long detention time was required to treat mine water to achieve compliance dischazges (up to several weeks), this treatment technology was determined to be infeasible. Batch Treating of Ponds This TSS treatment technology was determined to be infeasible for the following reasons: Runoff from precipitation events cannot be prevented from entering an already treated pond, so adding chemicals to treat the runoff could increase the potential for chemically overdosing the pond. Also, due to the more frequent filling of the ponds, and thus constant settling of solids, the sediment storage volumes would be filled faster, displacing water storage volumes. As a result, expensive sediment clean-out of lined ponds would be more frequent, increasing the potential for damage to the liners and creating high repair and/or replacement costs. Chemical Treatment Two options were evaluated for chemical treatment; both temporary and permanent treatment systems. A temporary treatment system was determined to be infeasible, because gravity feeding chemicals caused dosages to be irregular and difficult to maintain. To ensure proper treatment, constant attention would be required for chemical adjustment. Also, chemicals aze often cold temperature sensitive and would not flow properly from the dispenser during the winter. Surface applications of alum worked well, however, the applications were expensive and would not work . if the ponds were frozen. A permanent chemical treatment system was evaluated and was not successful alone, as the system required a mechanical feed of chemical into a constant flow. 2.05-114 Revised November 1004 PRl 0; Rev. March 2006; Rev. May 1006 PRlO