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predicted to not exceed 5,000 mg/l. The leachate samples at Trapper have remained in <br />the range of 1,100 to 4,100 mg/1. <br />Leachate quality predicted by batch leaching tests - Batch leaching tests performed <br />by the applicant indicated that the metallic constituents in coal spoil at Trapper which <br />are most likely to form a leachate are manganese, molybdenum, and vanadium (section <br />4.8.2.5 of permit application). As of 1997, high levels of manganese have been <br />detected in samples from three of the four wells on Trapper that monitor water quality <br />in spoils-filled pits (wells GD-3, GD-5, GD-7, and GF-11) [Appendix W of permit <br />application]. Molybdenum and vanadium have not been detected in samples from the <br />four wells. <br />Leachate migration - The leachate that saturates the spoil in a back-filled pit flows <br />through the spoil to the lowest point in the pit (the north end) where it accumulates <br />against the un-mined low-wall of the pit. As the leachate accumulates, it creates a <br />saturated zone in the spoil against the low-wall. Leachate from this saturated zone then <br />discharges into any permeable bedrock units in the low-wall whose hydraulic head is <br />less than the head in the saturated zone. This discharge results in a leachate plume <br />extending out into the bedrock. The Division predicts leachate plumes have formed or <br />will form in Johnson, Pyeatt, and Flume gulches (Hydrology Notes map in Technical <br />Revision 90). If the water quality of the leachate is worse than the native ground water <br />quality, the leachate degrades the ground water. If the saturated zone in the spoil <br />builds up high enough, the leachate overtops the lip of the pit and flows out onto the <br />ground surface as a spoil spring. The only major aquifer that would be in the flow path <br />of an advancing subsurface plume of leachate at Trapper is the Third White Sandstone. <br />Page 4-226a of the permit application explains that if leachate were to flow beyond the <br />permit area, two bedrock wells (W-624-74 and 80998) could be affected. <br />Duration of leachate formation and migration - Rainwater, snowmelt, and ground <br />water will infiltrate the spoil perpetually. Leachate will continue to be generated in the <br />spoil until the infiltrating waters are no longer coming in contact with minerals in the <br />spoil that can react with the water. Over time, the amount of this contact between the <br />water and the minerals diminishes as the flowing water chemically removes minerals <br />from the spoil, resulting in a network of channels in the spoil. Eventually the mineral <br />supply in the spoil will be exhausted, and the leachate quality will approximate the pre- <br />mining ground water quality. The amount of time necessary for the mineral supply to <br />become exhausted is predicted to be on the order of a few hundred years. <br />Leachate formation from buried ash - The permit's restrictions on waste placement <br />were designed to limit the amount of subsurface water that comes into contact with <br />buried ash. The restrictions require ash to be buried above the predicted subsurface <br />saturation elevation (section 4.3.4.6 of permit application). Almost all of the waste ash <br />material will be coal combustion ash and sludge from the Craig power plant. The main <br />elemental components of the combustion wastes are: barium, calcium, iron, <br />magnesium, potassium, silicon, and titanium. Adequate ground water monitoring is in <br />Trapper Mine 23 July 25, 2008