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<br /> <br />a•ctansive]y dis`urhed in '4ir.~ 1 and Eckman Park. Due *_o the use of draglines <br />in the mining operation t:~e spoils ~nateriai generally becomes Finer in size <br />towards the top of the spoils pile;. <br />2. Ground Water <br />ATthough ground water occurs in all the sedimentary rocks within the <br />Twentymile Park Basin, the only identified strata capable of regionally <br />storing and transmitting ground water are the Tow Creek, Trout Creek and <br />Twentymile Sandstones, and the lenticular and interbedded sandstones of the <br />three coal groups. <br />'Hells completed in the Mancos Shale generally yield less than 5 gpm, of <br />predominantly calcium-bicarbonate type water (Brodgen and Giles, 1977), Total <br />dissolved solids (TDS) concentrations range from 338 to 2,590 mg/1. The water <br />may contain concentrations of chloride, fluoride, iron and manganese in excess <br />of U. S. Public Health Service (1962) drinking water standards (Brodgen and <br />Giles, 1977). The Mancos Shale contains limited ground water that may be <br />suitable for domestic and stock use. Extensive shales in the upper part of <br />the formation act as relatively impermeable barriers to ground water flow, <br />therefore, the Mancos Shale is considered to be a confining layer underlying <br />the Mesaverde Group. <br />The massive, regional sandstone units of the Iles and Williams Fork Formation <br />are the primary bedrock aquifers in the Twentymile Park Basin. Wells <br />completed in the Taw Creek Sandstone, Trout Creek Sandstone and the •Twentymile <br />Sandstone are used primarily for domestic and stock watering purposes. These <br />sandstone aquifers produce generally less than 10 gpm (Brodgen and Giles, <br />1977). Higher yields of up to 100 gpm occur often at greater depths where <br />water in the sandstone is under artesian pressure or where the sandstones have <br />been fractured extensively. Hydraulic conductivity values for fractured <br />sandstones of the Iles and Williams Fork Formations range from 3.7 to 26 <br />feet/day (Brodgen and Giles, 1977). <br />The Trout Creek Sandstone provides recharge to alluvial aquifers and base <br />flows to Trout Creek and its tributaries. This sandstone is an important <br />regional bedrock aquifer within the Twentymile Park Basin. Water from the <br />Trout Creek Sandstone is a sodium bicarbonate type that has TDS concentrations <br />of approximately 900 mg/1, Hydraulic conductivities of the Trout Creek <br />Sandstone range from 0,1 to 1.2 ft/day. This water is used for industrial <br />(mining), domestic, and irrigation purposes. <br />The Trout Creek sandstone and overlying Wadge coal seam are separated by 150 <br />to 300 feet of interbedded shales, siltstones, sandstones and coals within the <br />basin. This interbedded unit acts as semi-confining layer above the artesian <br />Trout Creek sandstone aquifer. <br />The coal seams of the Mesaverde Group and associated discontinuous, lenticular <br />sandstones contain limited ground water. Twentymile Park mines are extracting <br />the Wolf Creek, Wadge and Lennox seams, and are consequently interrupting the <br />hydrologic regimes of these coals, Ground water within the Iles and Williams <br />Fork Formation is predominantly a calcium-and sodium-bicarbonate type. Water <br />in contact with coals, however, :nay ~e a calcium sulfate type and may contain <br />'."i <br />