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The two other refuse piles, CRDA Nos. I and 2, located across the Colorado River from the <br />facility area, have more hydrologic control due to geographic and structural features. All <br />leachate, should it occur, is routed to sediment ponds. CRDA No. I, in addition, has a series of <br />rock underdrains that would channel [he leachate [o the sediment pond directly. Since boat <br />CRDA No. I and No. 2 are no[ underlain by alluvium, the area provides a more stable <br />environment for leachate detection and minimization. <br />Groundwater Quantity <br />Possible hydrologic impacts on groundwater quantity by the underground mining operation <br />include: <br />1. The effect of subsidence and the related dewatering of the area, and <br />2. The effect of additional water added to the Colorado alluvial system from mine <br />inflow being discharged through the mine and to the surface. <br />Groundwater Otiantitv: Effect due to Subsidence <br />Groundwater quantity will initially be affected due to subsidence activity in the Rapid Creek <br />basin. The effect will be temporary in nature and provide no material damage to downstream <br />users. To quote from the Brooks study of 1986 on the operation's potential impact to the area, <br />"Mining coal in the Mesaverde Group temporarily will dewater the rock adjacent to the <br />underground mine. This rock will become rubblized and increase the permeability of the rock <br />thus increasing the flow of groundwater into the area." Inflow in the mine is expected to <br />increase as a result with a secondary effect of lowering the potentiomettic surface temporarily. <br />Water levels should return to pre-mining levels after the underground mine is sealed, with <br />saturation occurring after several years. The mine is utilizing limited extraction methods in the <br />Cottonwood and Rapid Creek areas. <br />Past monitoring of the alluvium of Rapid and Cottonwood Creeks has not detected any <br />significant depletion of alluvial water in either creek system. With continued limited coal <br />extraction and water monitoring, no depletion of alluvial water is anticipated during the next <br />permit term. <br />There is no beneficial use of the groundwater in the mine permit area or vicinity. Mine inflow <br />quantity is documented in the Annual Hydrology Report. It has been demonstrated that most of <br />the mine inflow waters originate in the new faces of virgin coal seams. As these seams are <br />mined, the coal seam aquifer is dewatered. New areas of the mine have a higher inflow rate than <br />older, developed ones, which dry out after the area has been developed. Additional water <br />originates from the Mesaverde sandstone lenses as they are dewatered by mining activity <br />combined with subsidence. <br />The operator has committed to a mitigation contingency plan for downstream users should they <br />be effected by subsidence. <br />35 <br />