Laserfiche WebLink
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 this <br /> member. This is evidenced by the dryness of the Bear Mine and the <br /> lack of springs associated with this unit. <br /> The most significant reliable occurrence of groundwater 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 No. 3 <br /> - office well) showed the lowest levels of these constituents. This is <br /> due to the dilution of alluvial groundwater by North Fork River water <br /> 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 thin <br /> and confined to discontinuous narrow bands along the stream courses. <br /> The deeply incised channels of these tributaries restrict the width of the <br /> alluvium, while the stream gradient and the presence of resistant <br /> sandstone in the stream channels limit the thickness and downstream <br /> extent of the alluvium. <br /> Occurrences of groundwater have been noted in the Mesaverde <br /> Formation based upon information obtained from drilling, experience in <br /> the mines, and from the presence of springs and seeps in the region. <br /> This information also indicates that the only potential regional bedrock <br /> aquifer in the general area is the laterally continuous Rollins Sandstone. <br /> The laterally discontinuous lenticular sandstones within the Upper <br /> Mesaverde Formation support only localized groundwater Flows. <br /> 31 <br />