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Fork of the Gunnison River; 2) the localized, shallow alluvium along <br />creeks tributary to the North Fork; 3) the discontinuous, lenticular and <br />laminar sandstones of the Mesaverde Formation; 4) the Rollins <br />Sandstone; 5) the coal seam; 6) shallow colluvial surficial deposits; and <br />7) fracture zones in bedrock. <br />The most continuous sandstone aquifers of any significance in the <br />region are the Rollins Sandstone and the massive sandstone separating <br />the Upper and Lower Coal Members of the Mesaverde Formation. The <br />Rollins Sandstone has been considered an aquifer of regional <br />importance because of its areal extent and potential yielding capability. <br />However, available data indicate that the Rollins is a marginal aquifer <br />in terms of yield and water quality. One pumping test conducted on the <br />Rollins sandstone in the vicinity of the mine indicates that the formation <br />was capable of producing only approximately 3 gpm. This is further <br />documented in the vicinity of the Orchard Valley Mine (now the Bowie <br />No. 1 Mine) where it is reported that drill holes which penetrated the <br />Rollins Sandstone had an insufficient yield to sustain groundwater <br />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 massive sandstone separating the Upper and Lower Coal Members <br />may locally produce water. However, information from mines that <br />operated in the Lower Coal Member (i.e., Somerset and Bear No. 1 <br />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 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 />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 />29 <br />