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-u- Description of the Hydrologic Environment (Cont'd) Description of the Ground Water Regime Four categories of potential aquifer~c occur in the Somerset Coal Field. These are: the alluvial and terrace deposr.ts associated with the North Fork of the Gunnison River; the localized, shallow alluvium along creeks tributary to the North Fork; the discontinuous, lenticular sandstones of the upper 19esaverde Formation; and the Rollins sandstone. The most significant occurrence of ground water in the region is associated with the alluvium of the North Fork of the Gunnison River (Figure 4). Significant thicknesses of alluvial sand and gravel between 30 to 80 feet exist along the North Fork. Numerous wells are developed in the alluvium with an average yield of 17.9 gpm. A pumping test conducted by Bear Coal Company on an alluvial well near the site of the proposed Bear No. 3 Pfine yielded values of 806.5 g/d/ft. for transmissivity and 0.2 for storativity. Three water quality analyses were conducted by Bear on the three wells completed in the North Fork alluvium. Two wells exceeded drinking water standards for total dissolved solids, sodium and sulfate. The well located closest to the North Fork (the Bear No. 3 - office well) showed the lowest levels of these constituents. This is due to the dilution of alluvial ground water 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. Two mines in the region draw water from the alluvium of tributaries to the North Fork; the Blue Ribbon Aline dracrs from the alluvium of Hubbard Creek and the Orchard Valley tine draws water from the alluvium of Stevens Culch. Pumping tests conducted by Colorado trestmoreland Incorporated at the Orchard Valley Pline indicate that the Stevens Gulch alluvium could support a pumping rate of 28 gpm. No pumping test was conducted by Blue Ribbon Coal Company at the Blue Ribbon Mine on the alluvium of Hubbard Creek. Terror Creek may have alluvial aquifers that could be developed as water supplies. However, no detailed analysis of this alluvium has been conducted. The Terror Creek alluvium may be used as a source of water at the Morrell Cow Camp to the north of the Orchard Valley Pfin e. Water quality analysis for the Stevens Gulch well water indicates good quality water, with none of the parameters exceeding the recommended drinking water standards. The only treatment necessary is chlorination, as required by the Colorado Department of Health for public drinking water supplies. The water quality for the Hubbard Creek well water is fair to poor and contains total dissolved solids and sodium Levels which exceed secondary water quality standards for drinking water. Occurrences of ground water have been noted in the hfesaverde Formation from 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 area is the laterally continuous Rollins sandstone. The laterally discontinuous lenticular sandstones within the Upper Plesaverde Formation support only localized ground water flows. Recharge to the Rollins sandstone occurs along outcrops and along subcrops beneath the alluvium and in the channels of the North Fork and its tributaries. However, due to the steepness of the topography in the outcrop areas (i.e., sandstones are cliff formers) and the narrowness of the stream valleys, the Rollins sandstone receives little recharge, except in the area under the North Fork of the Gunnison River.