2007-11-16_GENERAL DOCUMENTS - C1981041 (3)

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2. Surface water runoff from disturbed areas on the mine site passes through sediment ponds, with the exception of the small areas discussed in Section C.II. A. of this document. Discharges from these ponds have historically met effluent limits in the mines' CDPS permit except for discharges related to severe storm events. Effects on water quality due to disturbed-area runoff have been and should continue to be insignificant. Groundwater Groundwater Quality Four hydrologic units have been identified as aquifers that may be effected by the mining operation. These are: Colorado River alluvium, strata overlying the Cameo coal seams, Cameo coal seams, and the Rollins sandstone unit. Each of these will be addressed below as to the mines' probable hydrologic impact. Colorado River Alluvium The Colorado River alluvium consists of silty sand intermixed with gravel along the canyon and mine facility site. The alluvium varies between 0 and 60 feet in thickness and has a hydraulic conductivity of 0.01 cm2. The main concern with the alluvial aquifer is the total dissolved salt (TDS) content that mining contributes to the stream flow. The diminished quality of water discharged from the mine due to salt and sediment loading is improved somewhat by allowing the water to settle out the solids. The discharged mine water is given sufficient time to allow gravity to settle the solids before discharge occurs to the Colorado River. Three NPDES points discharged the mine water during active operations (Nos. 001, 002 and 004) and were subject to Colorado Department of Health water quality standards. Discharge Sites 001 and 004 have been inactivated since operations ceased. Outfall 002 has been retained as a back-up system for the South Mine, with new Outfall 016 now operating as the primary mine-water discharge site. Potential impacts on alluvial water quality due to mine water discharges were discussed previously in Section BALA. of this document. Strata Overlying the Cameo Coal Seams The unit directly overlying the Cameo coal seams consists of interbedded sandstones and shales of discontinuous lateral extent. Consequently, the stratigraphy indicates that the entire sequence of strata overlying the coal zone in the permit area behaves as a single hydraulic unit which contains only localized perched aquifers in areas where it is recharged by the river. Groundwater moves slowly through and between interconnected sandstone and shale lenses and beds. The Cameo Coal Seam 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 virgin coal seams are mined and drained locally. Discharge rates vary over time, indicating that saturated zones may be discontinuous over the permit area. Rollins Sandstone Permit Renewal No. 5 32 November 16, 2007