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Ground water Hydrology <br />Description of the Ground Water Regime <br />Several categories of potential aquifers occur in the <br />Somerset coal field. These are: 1) the alluvial and terrace <br />deposits associated with the North Fork of the Gunnison <br />River; 2) the localized, shallow alluvium along creeks <br />tributary to the North Fork; 3) the discontinuous, <br />lenticular and laminar sandstones of the Mesa Verde <br />Formation; 4) the Rollins sandstone; 5) the coal seam; and <br />6) shallow colluvial surficial deposits. <br />The most significant occurrence of ground water in the <br />region is associated with the alluvium of the North Fork of <br />the Gunnison River. Significant thicknesses of alluvial <br />sand and gravel between 30 to 80 feet exist along the North <br />Fork. Numerous wells are developed in the alluvium with an <br />average yield of 17.4 gpm. A pumping test conducted by Bear <br />Coal Company on an alluvial well near the site of Bear No. 3 <br />Mine yielded a value of 806.5 g/d/ft for transmissivity and <br />.02 for storativity. <br />Three water quality analyses were conducted for the Bear No. <br />3 on three wells completed in the North Fork alluvium. Two <br />wells exceeded drinking water standards for total dissolved <br />solids, sodium and sulfate. The well located closest to the <br />North fork (the Bear No. 3 - office well) showed the lowest <br />levels of these constituents. This is due to the dilution <br />of alluvial ground water by North Fork River water at this <br />well. <br />Except for areas in the Minnesota Creek Drainage, the <br />alluvium along the lower reaches of tributaries to the North <br />Fork is predominantly thin and confined to discontinuous <br />narrow bands along the stream courses. The deeply incised <br />channels of these tributaries restrict the width of the <br />alluvium, while the stream gradient and the presence of <br />resistant sandstone in the stream channels limit the <br />thickness and downstream extent of the alluvium. <br />Two mines in the region draw water from the alluvium of <br />tributaries to the North Fork, the Blue Ribbon Mine draws <br />from the alluvium of Hubbard Creek and the Orchard Valley <br />Mine draws water from the alluvium of Steven Gulch. Pumping <br />tests conducted by Colorado Westmoreland Incorporated at the <br />Orchard valley mine indicate that the Stevens Gulch alluvium <br />could support a pumping rate of 28 gpm. The Bear Mine and <br />Terror Creek Loadout use some water drawn from wells <br />completed in the alluvium along the North Fork of the <br />Gunnison River. The Sear Mine pumps on the average of 2 <br />acre feet a year for use in the mine. The water quality of <br />7 <br />