2007-07-30_GENERAL DOCUMENTS - C1981041

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I contains only localized perched aquifers in areas where it is recharged by the river. Groundwater moves slowily through and between interconnected sandstone and shale lenses and beds. The Cameol Coal Seam ~II'. I' The third water bearing zone is the Cameo coal seam. Water quality is poor and quantity is insufficient~for beneficial use. Water discharge occurs primarily as vvgin coal seams are mined and drained locally. Discharge rates vary over time, indicatinglthat saturated zones may be discontinuous over the permit area. I Rollins Sandstone ~ ~, i„ The fourth water bearing zone is the Rollins sandstone, which is stratigraphically below the coal seam to be mined. This unit is comprised of a clean, tan-to-cream sandstone that ranges from 89 to 114 feet thick throughout the permit area. Due to the extreme depth (from 50 to 1900 feet below surface) and location ofthe mining operation, it is believed that no damaging effect to the hydrologic properties of the Rollins will occur. To date, there has been no significant impact on this unit. Additional issues that affect the hydrology of the site include waste pile impact on groundwater supplies, in particular leachate generation. The effect of leachate from the Roadside coal processing waste pile (RSRDA) on water quality is negligible.. Using the worst-case scenario, where all precipitation enters the waste pile, an average of 0.01 iifs would enter the Colorado River via alluvium percolation. This would have the effect of raiging the total dissolved solids content of the Colorado River by 0.01 percent. There is no evidence that leachate from the pile has ever reached or affected the Colorado River. The two other refuse piles, CRDA Nos. 1 and 2, located across the Colorado River from the facility area, have more hydrologic control due to geographic,,and structural features. All leachate, should it occur, is routed to sediment ponds. CRDA No.. l , in addition, has a series of rock underdrains that would channel the leachate to the sediment pond directly. Since neither CRDA-1 nor CRDA-2 are underlain by alluvium, the azea provides a more stable environment for leachate, detection and minimization. During the period of aLtive use, minor intermittent seepage was observed from the rock underdrains beneath CRDA ~1, and from widely scattered seep areas on the CRDA-I and CRDA-2 bench outslopes. Groundwater Ouantiri Possible hydrologic impacts on groundwater quantity by the underground mining operation include: 1. The effect of subsidence and the related dewatering o1'the area, and 2. The effect of additional water added to the Colorad~i alluvial system from mine inflow being discharged through the mine and to the surface. i Groundwater Ouantiri: Effect due to Subsidence Groundwater quantity will initially be affected due to subsidenc9 activity in the Rapid Creek basin. The effect will be temporary in nature and provide no material damage to downstream users. To quote from the Brooks study of 1986 on the operation's potential impact to the area, Penni[ Revision No. 3 July 30, 2007 Permit No. C-1981-041 Page 32