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the Upper and Lower Coal Members of the Mesaverde Formation. <br /> The Rollins Sandstone has been considered an aquifer of regional <br /> importance, because of its areal extent and potential yielding <br /> capability. However, available data indicate that the Rollins is a <br /> marginal aquifer in terms of yield and water quality. One pumping <br /> test conducted on the Rollins sandstone in the vicinity of the mine <br /> indicates that the formation was capable of producing only <br /> .approximately 3 gpm. This is further documented in the vicinity of <br /> the Orchard Valley Mine where it is reported that drill holes which <br /> penetrated the Rollins Sandstone had an insufficient yield to sustain <br /> groundwater supply wells. <br /> In the Jumbo Mountain area, the Rollins Sandstone appears to be <br /> hydraulically isolated. To the south and west, the Rollins Sandstone <br /> outcrops in the form of cliffs; and to the north and northeast, it <br /> discharges into the North Fork of the Gunnison River. In the Jumbo <br /> Mountain area, the average interburden thickness between the B Seam <br /> and the Rollins Sandstone is 150 feet. <br /> The latter massive sandstone separating the Upper and Lower Coal <br /> Members may locally produce water. However, information from <br /> mines operating in the Lower Coal Member (i.e., Somerset and Bear <br /> No. 1 and No. 2 Mines) demonstrate that there is a lack of water in <br /> this member. This is evidenced by the dryness of the Bear Mine and <br /> the lack of springs associated with this unit. <br /> The most significant occurrence of ground water in the region is <br /> associated with the alluvium of the North Fork of the Gunnison River. <br /> Significant thicknesses of alluvial sand and gravel between 30 and <br /> 80 feet exist along the North Fork. Numerous wells are developed in <br /> the alluvium with an average yield of 17.4 gpm. A pumping test <br /> conducted by Bear Coal Company on an alluvial well near the site of <br /> the Bear No. 3 Mine yielded a value of 806.5 gallons/day/foot for <br /> transmissivity. <br /> Three water quality analyses were conducted for the Bear No. 3 Mine <br /> on three wells completed in the North Fork alluvium. Two wells <br /> exceeded drinking water standards for total dissolved solids, sodium <br /> and sulfate. The well located closest to the North Fork (the Bear <br /> No. 3 - office well) showed the lowest levels of these constituents. <br /> This is due to the dilution of alluvial ground water by North Fork <br /> River water at this well. <br /> Except for areas in the Minnesota Creek Drainage, the alluvium along <br /> the lower reaches of tributaries to the North Fork is predominantly <br /> thin and confined to discontinuous narrow bands along the stream <br /> courses. The deeply incised channels of these tributaries restrict the <br /> 25 <br />