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Colorado River Alluvium <br />The Colorado River alluvium consists of silty sand intermixed with gravel along [he canyon and <br />mine facility site. The alluvium varies between 0 and 60 feet in thickness and has a hydraulic <br />conductivity of 0.01 cm'. The main concern with the alluvial aquifer is [he total dissolved salt <br />(TDS) content that mining contributes to the stream Flow. The diminished quality of water <br />discharged 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 />discharge the mine water (Nos. 001, 002 and 004) and are subject to Colorado Department of <br />Health water quality standards. Potential impacts on alluvial water quality due to mine water <br />discharges were discussed previously in Section II.A. of this document. <br />Strata Overlvine 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 areas where it is recharged 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 discharge occurs primarily as virgin coal seams are mined <br />and drained locally. Discharge 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 stratigraphically below the coal <br />seam to be mined. This unit is comprised of a clean, tan-to-cream sandstone that ranges from <br />89 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 particular leachate generation. The effect of leachate from the Roadside coal <br />processing waste pile on water quality is negligible. Using the worst-case scenario, where all <br />precipitation enters the waste pile, an average of 0.01 cfs would enter the Colorado River via <br />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 />34 <br />