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<br />B. Ground Water <br />Ground water occurs to a limited extent in all the sedimentary rocks of <br />Upper Cretaceous age in the region. The only identified strata capable of <br />regionally storing and transmitting water are the Tow Creek, the Trout Creek, <br />and the Twentymile Sandstones, Locally the lenticular and interbedded <br />sandstones of the three coal groups as well as the major coal seams will also <br />store and transmit limited amounts of water. <br />Wells completed in the Mancos Shale generally yield small quantities of water, <br />less than 5 gal/min. The water is predominantly a calcium-bicarbonate type <br />(Brogden and Giles, 1977). Total Dissolved Solids (TDS) concentration ranges <br />from 338 to 2,590 mg/1, and the water may contain concentrations of chloride, <br />fluoride, iron and manganese in excess of U.S. Public Health Service (1962) <br />drinking water standaras (Brogden and Giles, 1977). Although the Mancos Shale <br />contains limited ground water that may be suitable for domestic and stock use, <br />the extensive shales in the upper part of the formation act as relatively <br />impermeable barriers to the subsurface movement of water. The Mancos Shale <br />can be considered as an impermeable, confining layer underlying the Mesaverde <br />Group, and could be classified as an aquiclude. <br />The major bedrock aquifers in the Mesaverde Group occur within the massive, <br />regional sandstone units of the Iles 'and Williams Fork Formations. Wells <br />completed in the Tow Creek Sandstone and Trout Creek Sandstone of the <br />Iles Formation and the Twentymile Sandstone of the Williams Fork Formation are <br />used primarily for domestic and stock purposes, Well yields from these <br />sandstone aquifers are usually less than 10 gal/min (Brogden and Giles, <br />1977). Higher yields generally occur at greater depths where water in the <br />sandstone is under artesian pressure, and where the sandstones have been <br />fractured extensively, Hydraulic conductivity values for fractured sandstones <br />of the Iles and Williams Fork Formations range from 3,7 to 2G feet/day <br />(Brogden and Giles, 1977). <br />Limited ground water also occurs in coal seams and discontinuous, lenticular <br />sandstones within the Mesaverde Group. The permeabilities of these water <br />bearing units are quite low, generally an order of magnitude less than the <br />fractured sandstone aquifers. Ground water within the Iles and Williams Fork <br />Formation is predominantly calcium and sodium-bicarbonate in character. <br />However, water in contact with coals may be calcium sulfate in character and <br />may contain fluoride, iron, manganese, selenium and sulfate in excess of <br />U. S. Public Health Service drinking water standards (Brogden and Giles, <br />1977). TDS concentration of water within the Iles and Williams Fork <br />Formations ranges from 334 to 1,460 mg/1 (Brogden and Giles, 1977), with the <br />water contained in the coals and thin discontinuous sandstones generally being <br />of poorer quality than that from the massive regional sandstone aquifers. <br />Because of the poor quality and limited yield of water-bearing units <br />associated with the coals, use of this water is not significant. <br />At the Seneca II-W Mine, the Wolf Creek coal seam, Wolf Creek/Wadge <br />Interburden, Wadge coal seam and the Williams Fork overburden were examined as <br />potential water bearing strata. The Williams Fork overburden is a term used <br />by Peabody Coal Company to describe the discontinuous, lenticular sandstones <br />overlying the Wadge coal seam. The Division uses the term Wadge overburden to <br />describe these same units throughout this document. <br />- 27- <br />