2020-08-20_REVISION - C1980007 (36)

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yield enough water to function as groundwater supply wells. The West Elk Mine's permeameter tests of the Rollins Sandstone in the permit area found horizontal hydraulic conductivity values in the range 0.0001 ft/day to 0.012 ft/day. The Bowie sandstone, separating the Upper and Lower Coal Members, may produce water locally. Information from mines operating in the Lower Coal Member(i.e., Elk Creek and Bear No. 1 and No. 2 Mines) indicate this formation can yield small flows of water in the area. The unit crops out toward its down-gradient occurrence within the West Elk permit area and there are no seeps or springs emanating from the unit, demonstrating that the unit is dry in some areas. The most significant reliable occurrence of groundwater in the region is the alluvium of the North Fork of the Gunnison River. Significant thicknesses of alluvial sand and gravel between 30 and 80 feet exist along the North Fork. Numerous wells are developed in the alluvium with an average yield of 17.4 gpm. A pumping test conducted by Bear Coal Company on an alluvial well near the site of the Bear No. 3 Mine yielded a value of 806.5 gallons/day/foot for transmissivity. Three water quality analyses were conducted for the Bear No. 3 Mine on three wells completed in the North Fork alluvium. Two wells exceeded drinking water standards for total dissolved solids, sodium and sulfate. The alluvial well nearest the North Fork River channel (the Bear No. 3 office well) showed the lowest levels of these constituents. This is due to the dilution of alluvial groundwater by North Fork River water at this well. Except for areas in the Minnesota Creek Drainage, the alluvium along the lower reaches of tributaries to the North Fork is predominantly thin and confined to discontinuous narrow bands along the stream courses. The deeply incised channels of these tributaries restrict the width of the alluvium, while the stream gradient and the presence of resistant sandstone in the stream channels limit the thickness and downstream extent of the alluvium. Occurrences of groundwater have been noted in the Mesaverde Formation based upon information obtained from drilling, experience in the mines, and from the presence of springs and seeps in the region. This information also indicates that the only potential regional bedrock aquifer in the general area is the laterally continuous Rollins Sandstone. The laterally discontinuous lenticular sandstones within the Upper Mesaverde Formation support only localized groundwater flows. The Rollins Sandstone is recharged in the vicinity of the West Elk Mine by snowmelt and rainfall on outcrops, and in subcrops beneath stream alluvium and in the channels of the North Fork and its tributaries. These 38