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West Elk Mi»e Gravity Seaaration of Solids -Because an extremely long detention time was required to treat mine water to achieve compliance discharges (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. I 1 Chemical Treatment -Two options were evaluated for chemical treattnent; 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. Flows from the mine vary as pumps in the mine cycle on and off as sumps fill and empty, and/or a precipitation event occurs. This option was also labor and maintenance intensive, requiring handling of bulky containers, and electrical and piping maintenance in several remote locations on the mine site. Physical Treatment -Five alternatives were evaluated. One alternative was unsuccessful, because it was ineffective in removing the small particle-sized suspended solids. A Multi- media filtering pilot plant was unable to handle higher flows, nor capture the small particles (98 % of the suspended solids were < 10 microns) in the dirty thine water. Scalping (cyclones) and ponding the coarse material was evaluated, however, even through the specific gravity of the suspended clay was 1.82, the fines were small enough to travel with the water and would not separate in the cyclones without chemical addition to coagulate the solids. The solids also needed to be more concentrated and consolidated (i.e., in a filter press) for economic disposal. A thickener/clarifier with chemical and sand addition was also evaluated. The process could treat the entire volume of mine water, or scalped portions, and delivered consistent results. On the downside, the process required X10 percent solids in the feed and the system required two chemical elements and sand, increasing the maintenance and overall costs. Centrifugal separators were evaluated, however, power consumption and the problems that plagued the cyclone alternative (described above), also contributed to [he centrifugal separator ineffectiveness. Dissolved air flotation (DAF) was considered, but because of sparging (external air source), large bubbles occurred with chemical addition and caused foaming (similar to a washing machine that has been overloaded with soap), and therefore did not effectively float clays and silicates. Induced air floatation (IAF) with a single chearical 2.05-185 Revised Jun. /995 PR06; Revised Nov. 19987880: //98 PR08