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<br /> <br /> <br /> 38 C1981-041 RN7 findings <br />Rollins will occur. To date, there has been no significant impact on this unit. <br /> <br />Additional issues that affect the hydrology of the site include waste pile impact on <br />groundwater supplies, in particular leachate generation. The effect of leachate from <br />the Roadside coal processing waste pile (RSRDA) on water quality is negligible. <br />Using the worst-case scenario, where all precipitation enters the waste pile, an average <br />of 0.01 cfs would enter the Colorado River via alluvium percolation. This would have <br />the effect of raising the total dissolved solids content of the Colorado River by 0.01 <br />percent. There is no evidence that leachate from the pile has ever reached or affected <br />the Colorado River. <br /> <br />The two other refuse piles, CRDA Nos. 1 and 2, located across the Colorado River <br />from the facility area, have more hydrologic control due to geographic and structural <br />features. All leachate, should it occur, is routed to sediment ponds. CRDA No. 1, in <br />addition, has a series of rock underdrains that would channel the leachate to the <br />sediment pond directly. Since neither CRDA-1 nor CRDA-2 are underlain by <br />alluvium, the area provides a more stable environment for leachate detection and <br />minimization. During the period of active use, minor intermittent seepage was <br />observed from the rock underdrains beneath CRDA-1, and from widely scattered seep <br />areas on the CRDA-1 and CRDA-2 bench outslopes. <br /> <br />Groundwater Quantity <br /> <br />Possible hydrologic impacts on groundwater quantity by the underground mining <br />operation include: <br /> <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 /> <br />Groundwater Quantity: Effect due to Subsidence <br /> <br />Groundwater quantity will initially be affected due to subsidence activity in the Rapid <br />Creek basin. The effect will be temporary in nature and provide no material damage <br />to downstream users. To quote from the Brooks study of 1986 on the operation's <br />potential impact to the area, "Mining coal in the Mesaverde Group temporarily will <br />dewater the rock adjacent to the underground mine. This rock will become rubblized <br />and increase the permeability of the rock thus increasing the flow of groundwater into <br />the area." Inflow in the mine is expected to increase as a result with a secondary effect <br />of lowering the potentiometric surface temporarily. Water levels should return to <br />pre-mining levels after the underground mine is sealed, with saturation occurring after <br />several years. The mine utilized limited extraction methods in the Cottonwood and <br />Rapid Creek areas. <br /> <br />Past monitoring of the alluvium of Rapid and Cottonwood Creeks has not detected <br />any significant depletion of alluvial water in either creek system, and no significant