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West Elk Mine <br />2.04 -54 Rev. 06/05- PR10, 03/06- PR10, 04/06- PR10, 09/07- PR12; 05/22- MR462 <br /> <br /> <br />Regional Groundwater Conditions <br /> <br />For the most part, the Mesaverde Formation is dry or the rock units are of such low permeability <br />that they yield insufficient water for sustained use. Even the extensive Rollins Sandstone, a thick <br />basal sandstone immediately above the Mancos Shale, has been found to be highly cemented and a <br />low water producer (an aquitard). Due to its areal extent, the Rollins Sandstone was thought to be a <br />potential aquifer of regional importance, but the Rollins Sandstone has been found to have <br />insufficient yield to sustain groundwater supply wells (Bowie No.1 MRP). In addition, petrographic <br />analysis revealed that the sandstone units within the Rollins Sandstone are depositionally immature <br />and have been designated as a “tight gas sand” by the Colorado Oil and Gas Conservation <br />Commission (Mayo and Associates, 1998 and 1999). <br /> <br />Furthermore, groundwater monitoring wells completed in the Rollins Sandstone do not provide <br />predictable information regarding Rollins Sandstone groundwater conditions, as determined by <br />Mayo and Associates during their investigation of fault-related groundwater inflows from the <br />Rollins Sandstone at West Elk Mine (1998). In that study, and their hydrogeologic study completed <br />in 1999, it was determined that the groundwater systems associated with the Rollins Sandstone are <br />not areally extensive and not in hydrodynamic communication with each other. For these reasons, <br />MCC does not plan to continue monitoring or complete any additional monitoring wells in the <br />Rollins Sandstone. <br /> <br />Most of the stratigraphic members of the Mesaverde Formation above the Rollins Sandstone <br />outcrop within close proximity to West Elk Mine. Up-dip B Seam outcrops occur 0.6 to 4 miles <br />from underground workings. Most workings intercept the B Seam within 2 miles of the up-dip <br />outcrop. Mining areas in the overlying Upper Coal Member have similar distances to the up-dip <br />outcrop. The Lower Coal Member (i.e., B Seam) extends down dip beneath the North Fork of the <br />Gunnison River (North Fork) and does not crop out down-dip in the permit area. Down-dip <br />outcroppings of rock units from the Bowie Sandstone and higher occur along the North Fork and in <br />Sylvester Gulch in the mine permit area. Up-dip outcrops of rocks units associated with mineable <br />coal tend to occur on steep slopes and thus have limited potential for groundwater recharge from the <br />active zone. <br /> <br />The stratigraphic sequence, observed spring locations and topography suggests groundwater <br />recharge is from snowmelt and precipitation and discharges mainly from bedrock and colluvial <br />springs on steeper slopes above the major drainages and is restricted to active zone groundwater <br />systems. A small amount of water infiltrates downward through the bedrock units, while most <br />moves laterally on top of relatively impermeable rock units, discharging where more permeable <br />units outcrop/subcrop. <br /> <br />Sandstone units within the Mesaverde Formation are generally lenticular, regionally discontinuous <br />and are usually highly cemented. In general, the only extensive units are the persistent coal seams, <br />especially the B Seam, and the Rollins Sandstone. The dip of these formations is to the northeast at <br />generally less than 5 degrees.