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Four hydrologic units have been identified as aquifers that may be effected by the mining <br />operation. These aze: Colorado River alluvium, strata overlying the Cameo coal seams, Cameo <br />coal seams, and the Rollins sandstone unit. Each of these will be addressed below as to the <br />mines' probable hydrologic impact. <br />Colorado River Alluvium <br />The Colorado River alluvium consists of silty sand intermixed with gravel along the canyon and <br />mine facility site. The alluvium vanes between 0 and 60 feet in thickness and has a hydraulic <br />conductivity of 0.01 cmz. The main concern with the alluvial aquifer is the total dissolved salt <br />(TDS) content that mining contributes to the stream flow. The diminished quality of water <br />dischazged from the mine due to salt and sediment loading is improved somewhat by allowing <br />the water to settle out the solids. The discharged mine water is given sufficient time to allow <br />gravity to settle the solids before discharge occurs to the Colorado River. Three NPDES points <br />discharged the mine water during active operations (Nos. 001, 002 and 004) and were subject to <br />Colorado Department of Health water quality standards. Dischazge Sites 001 and 004 have been <br />inactivated since operations ceased. Outfa11002 has been retained as a back-up system for the <br />South Mine, with new Outfall 016 now operating as the primary mine-water dischazge site. <br />Potential impacts on alluvial water quality due to mine water dischazges were discussed <br />previously in Section II.A. of this document. <br />Strata Overlying the Cameo Coal Seams <br />The unit directly overlying the Cameo coal seams consists of interbedded sandstones and shales <br />of discontinuous lateral extent. Consequently, the stratigraphy indicates that the entire sequence <br />of strata overlying the coal zone in the permit area behaves as a single hydraulic unit which <br />contains only localized perched aquifers in azeas where it is rechazged by the river. Groundwater <br />moves slowly through and between interconnected sandstone and shale lenses and beds. <br />The Cameo Coal Seam <br />The third water bearing zone is the Cameo coal seam. Water quality is poor and quantity is <br />insufficient for beneficial use. Water dischazge occurs primarily as virgin coal seams aze mined <br />and drained locally. Dischazge rates vary over time, indicating that saturated zones may be <br />discontinuous over the permit area. <br />Rollins Sandstone <br />The fourth water bearing zone is the Rollins sandstone, which is stratigraphicallybelnw the coal <br />seam to be mined. This unit is comprised of a clean, tan-to-cream sandstone that ranges from 89 <br />to 114 feet thick throughout the permit area. Due to the extreme depth (from 50 to 1900 feet <br />below 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 particulaz 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 />33 <br />