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2) Degradation of stream and alluvial water quality due to pumpage of <br />• mine water, and . <br />3) Degradation of stream and alluvial water quality due to seepage from <br />the flooded mine workings. <br />The Eagle No. 9 Mine has development entries extending under the Big Bottom <br />alluvial valley floor. The life of mine plan for the No. 9 Mine calls for <br />extensive room and pillaring underneath the Big Bottom alluvial floor. This <br />development never occurred and the present workings are minimal in area. <br />Subsidence monitoring has shown no significant impacts to the alluvial valley <br />due to this mining. The mine is presently being allowed to flood and <br />reopening of the mine is not permitted in this 5 year term. <br />Other possible hydrologic impacts to surface water quality and quantity are <br />not expected to be significant. Increased runoff and erosion from disturbed <br />areas is controlled by the applicant's runoff and sediment control system. <br />The refuse pile should not have any adverse effects on the hydrologic system <br />in the mine area or adjacent area. The applicant and the Division reached <br />this conclusion about the impacts of the refuse pile for several reasons: <br />1) The pile is designed to reduce its permeability and a toe drain has <br />been constructed to remove water from beneath the pile (minimizing <br />the ground water build up in the pile); <br />2) The sides of the pile will be sloped, top soiled, and revegetated to <br />• reduce the potential for water entering the pile and reducing <br />erosion; and <br />3) Surface water from undisturbed areas will be diverted away from the <br />pile. <br />These factors, in combination with the limited amount of precipitation (14" <br />annually) will tend to limit the amount of acidic, toxic and alkaline leachate <br />generation. The only potential long-term effects are indirect surface water <br />effects. The continued generation of leachate by the coal refuse pile, and <br />the discharge of degraded ground waters from the mines to receiving streams <br />may have a long-term effect on surface water quality, but they are not <br />expected to be significant. <br />In the permit application the applicant has predicted a worst-case estimate of <br />flow from the river to the mines. The equation used was developed by <br />McWhorter (1981) and assumes that the mine is parallel to the river and that <br />coal and the overlying sandstone are in hydrologic connection with the <br />alluvium along the length of mine. The length was calculated assuming that <br />all of the coal and the Middle Sandstone subcrop under the river alluvium is <br />directly contributing to the mine inflow. The total worst-case estimated <br />stream depletion using this equation is 182 gallons per minute (gpm). The <br />mean pumpage rate of the No. 5 Mine in 1985 was 676 gpm and in 1986 was 680 <br />gpm, more than compensating for the estimated stream depletion. Therefore, <br />during mining, any impact to the stream system by depletion occurring from <br />flow into the mine is not projected to occur. <br />• <br />-38- <br />