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discontinuous over the permit area. <br />Rollins Sandstone <br />The fourth water bearing zone is the Rollins sandstone, which is stratigraphically below the coal <br />seam to be mined. This unit is comprised of a clean, tan -to -cream sandstone that ranges from 89 to <br />114 feet thick throughout the permit area. Due to the extreme depth (from 50 to 1900 feet below <br />surface) and location of the mining operation, it is believed that no damaging effect to the <br />hydrologic properties of the Rollins will occur. To date, there has been no significant impact on <br />this unit. <br />Additional issues that affect the hydrology of the site include waste pile impact on groundwater <br />supplies, in particular leachate generation. The effect of leachate from the Roadside coal <br />processing waste pile (RSRDA) on water quality is negligible. Using the worst -case scenario, <br />where all precipitation enters the waste pile, an average of 0.01 cfs would enter the Colorado River <br />via alluvium percolation. This would have the effect of raising the total dissolved solids content of <br />the Colorado River by 0.01 percent. There is no evidence that leachate from the pile has ever <br />reached or affected the Colorado River. <br />The two other refuse piles, CRDA Nos. 1 and 2, located across the Colorado River from the facility <br />area, have more hydrologic control due to geographic and structural features. All leachate, should it <br />occur, is routed to sediment ponds. CRDA No. 1, in addition, has a series of rock underdrains that <br />would channel the leachate to the sediment pond directly. Since neither CRDA -1 nor CRDA -2 are <br />underlain by alluvium, the area provides a more stable environment for leachate detection and <br />minimization. During the period of active use, minor intermittent seepage was observed from the <br />rock underdrains beneath CRDA -1, and from widely scattered seep areas on the CRDA -1 and <br />CRDA -2 bench outslopes. <br />Groundwater Quantity <br />Possible hydrologic impacts on groundwater quantity by the underground mining operation 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 inflow <br />being discharged 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 has *in. <br />The effect will be temporary in nature and provide no material damage to downstream users. To <br />quote from the Brooks study of 1986 on the operation's potential impact to the area, "Mining coal <br />in the Mesaverde Group temporarily will dewater the rock adjacent to the underground mine. This <br />rock will become rubblized and increase the permeability of the rock thus increasing the flow of <br />groundwater into the area." Inflow in the mine is expected to increase as a result with a secondary <br />effect of lowering the potentiometric surface temporarily. Water levels should return to pre - mining <br />levels after the underground mine is sealed, with saturation occurring after several years. The mine <br />utilized limited extraction methods in the Cottonwood and Rapid Creek areas. <br />32 <br />