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<br /> <br /> <br /> 37 C1981-041 RN7 findings <br /> <br />Four hydrologic units have been identified as aquifers that may be effected by the <br />mining operation. These are: Colorado River alluvium, strata overl ying the Cameo <br />coal seams, Cameo coal seams, and the Rollins sandstone unit. Each of these will be <br />addressed below as to the mines' probable hydrologic impact. <br /> <br />Colorado River Alluvium <br /> <br />The Colorado River alluvium consists of silty sand intermixed with gravel along the <br />canyon and mine facility site. The alluvium varies between 0 and 60 feet in thickness <br />and has a hydraulic conductivity of 0.01 cm2. The main concern with the alluvial <br />aquifer is the total dissolved salt (TDS) content that mining contributes to the stream <br />flow. The diminished quality of water discharged from the mine due to salt and <br />sediment loading is improved somewhat by allowing the water to settle out the solids. <br />The discharged mine water is given sufficient time to allow gravity to settle the solids <br />before discharge occurs to the Colorado River. Three NPDES points discharged the <br />mine water during active operations (Nos. 001, 002 and 004) and were subject to <br />Colorado Department of Health water quality standards. Discharge Sites 001 and 004 <br />have been inactivated since operations ceased. Outfall 002 has been retained as a <br />back-up system for the South Mine, with new Outfall 016 now operating as the <br />primary mine-water discharge site. Potential impacts on alluvial water quality due to <br />mine water discharges were discussed previously in Section B.II.A. of this document. <br /> <br />Strata Overlying the Cameo Coal Seams <br /> <br />The unit directly overlying the Cameo coal seams consists of interbedded sandstones <br />and shales of discontinuous lateral extent. Consequently, the stratigraphy indicates <br />that the entire sequence of strata overlying the coal zone in the permit area behaves as <br />a single hydraulic unit which contains only localized perched aquifers in areas where <br />it is recharged by the river. Groundwater moves slowly through and between <br />interconnected sandstone and shale lenses and beds. <br /> <br />The Cameo Coal Seam <br /> <br />The third water bearing zone is the Cameo coal seam. Water quality is poor and <br />quantity is insufficient for beneficial use. Water discharge occurs primarily as virgin <br />coal seams are mined and drained locally. Discharge rates vary over time, indicating <br />that saturated zones may be discontinuous over the permit area. <br /> <br />Rollins Sandstone <br /> <br />The fourth water bearing zone is the Rollins sandstone, which is stratigraphically <br />below the coal seam to be mined. This unit is comprised of a clean, tan -to-cream <br />sandstone that ranges from 89 to 114 feet thick throughout the permit area. Due to <br />the extreme depth (from 50 to 1900 feet below surface) and location of the mining <br />operation, it is believed that no damaging effect to the hydrologic properties of the