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_22_ <br />is isolated into separate narrow alluvial bodies by water gaps formed by <br />the resistant sandstone strata. The alluvial yround water is <br />predominantly a calcium, sodium, meynesium bicarbonate type. The total <br />dissolved solids concentration is about 350 mg/1. Alluvial ground water <br />is utilized by Coal Creek Mine for domestic and industrial uses. The <br />alluvial ground water discharges to Dutch, Coal, Bear and Porcupine <br />Creeks. This ground water discharye produces base flows in the creeks <br />duriny low flow periods. The alluvium is recharged directly from the <br />streams duriny snowmelt and during precipitation events. <br />The unconsolidated landslide deposits have the potential to support <br />spring and seep flows in the Coal Basin Drainage. During spring <br />snowmelt, these deposits recharge. The ground water migrates to the toe <br />of the slides and discharges as intermittent springs and seeps. <br />Tne major regional bedrock aquifers in the general area of the mines are <br />the Cozette sandstone, Rollins sandstone, the Middle sandstone, and the <br />Upper sandstone members of the Mesaverde Group; and the Wasatch <br />Formation-Ohio Creek Conglomerate. <br />The regional sandstone aquifers of the Mesaverde Group are thick, fine to <br />medium-grained, calcium carbonate cemented, quartzitic sandstones. As <br />aquifers, they have low to moderate permeabilities and transmissivities. <br />At the North Thompson Creek ihines, the only regional sandstone to have <br />aquifer tests performed on it was the Upper sandstone member, which <br />yielded a transmissivity value of 1700 gpd/ft. This value may be high <br />due to fracture permeability. The Rollins, Cozette, and Middle <br />sandstones, where fractured, should have similar transmissivities. The <br />water quality analyses of the Upper sandstone member yield values for pH <br />of 7.5 to B. O, and TDS of 1262 mg/1. <br />No wells are drawing water from the sandstones of the Mesaverde Group in <br />the general area. However, ground water mine inflows from the Williams <br />Fork Formation are utilized by the mines. This water is used in mining <br />within the North Thompson Creek Mines, and used outside of the mines for <br />a sanitary supply, for dust suppression, for equipment washdown and in <br />the washplant, A portion of this mine inflow water may be tributary to <br />both North and Middle Thompson Creeks. A small percentage of the inflow <br />waters within the Sunlight and Coal Basin mines are used within the <br />mines. The majority of the mine waters from these two mines are <br />discharged to the surface. <br />The coal seams of the Williams Fork Formation are not aquifers, since the <br />coals are tight and have insufficient primary porosity to transmit <br />water. Ground water movement within the brittle coals is dependent on <br />secondary porosity and is localized in fracture and fault zones. The <br />highest occurrence of ground water in the coal seams is found in areas <br />adjacent to and/or under streams. This occurrence is due to the <br />combination of a good source of recharge water and a well developed <br />fracture system associated with stream valleys in the area. <br />