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where all precipitation enters the waste pile, an average of 0.01 cfs would enter the Colorado <br />River via alluvium percolation. This would have the effect of raising the total dissolved solids <br />content of the Colorado River by 0.01 percent. There is no evidence that leachate from the pile <br />has ever reached or affected the Colorado River. <br />The two other refuse piles, CRDA Nos. 1 and 2, located across the Colorado River from the <br />facility area, have more hydrologic control due to geographic and stmctural features. All <br />leachate, should it occur, is routed to sediment ponds. CRDA No. 1, in addition, has a series of <br />rock underdrains that would channel the leachate to the sediment pond directly. Since neither <br />CRDA-1 nor CRDA-2 are underlain by alluvium, the area provides a more stable environment <br />for leachate detection and minimization. During the period of active use, minor intermittent <br />seepage was observed from the rock underdrains beneath CRDA-1, and from widely scattered <br />seep aeeas on the CRDA-1 and CRDA-2 bench outslopes. <br />Groundwater Ouantity <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 dischazged through the mine and to the surface. <br />Groundwater Quantity: 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 azea, <br />"Mining coal in the Mesaverde Group temporarily will dewater the rock adjacent to the <br />underground mine. This rock will become mbblized and increase the permeability of the rock <br />thus increasing the flow of groundwater into the azea." Inflow in the mine is expected to <br />increase as a result with a secondary effect of lowering the potentiometric 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 utilized limited exttaction 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, and no significant depletion is <br />anticipated. <br />There is no beneficial use of the groundwater in the mine permit azea or vicinity. Mine inflow <br />quantity has been documented in past Annual Hydrology Reports. It has been demonstrated that <br />most of the mine inflow waters originate in the new faces of virgin coal seams. As these seams <br />aze mined, the coal seam aquifer is dewatered. New aeeas of the mine have a higher inflow rate <br />than older, developed ones, which dry out after the azea has been developed. Additional water <br />originates from the Mesaverde sandstone lenses as they are dewatered by mining activity <br />combined with subsidence. <br />34 <br />