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Limited ground water also occurs in coal seams and <br />discontinuous, lenticular sandstones within the Mesaverde <br />Group. The permeabilities of these water bearing units are <br />quite low, generally an order of magnitude less than the <br />fractured sandstone aquifers. Ground water within the Iles and <br />Williams Fork Formation is predominantly calcium and <br />sodium-bicarbonate in character; however, water in contact with <br />coals may be calcium sulfate in character and may contain <br />fluoride, iron, manganese, selenium and sulfate in excess of <br />U.S. Public Health Service drinking water standards (Brogden <br />and Giles, 19771. TDS concentration of water within the Iles <br />and Williams Fork Formations ranges from 334 to 1,460 mg/1 <br />(Brogden and Giles, 1977), with the water contained in the <br />coals and thin discontinuous sandstones generally being of <br />poorer quality than the water from the massive regional <br />sandstone aquifers. Because of the poor quality and limited <br />yield of water-bearing units associated with the coals, use of <br />this water is not significant in the Twentymile Park Basin. <br />At Energy Mine No. 3, ground water occurs within the Wadge Coal <br />Seam (which is the seam being mined) and the overlying <br />discontinuous, lenticular sandstones of the Middle Coal Group. <br />These locally water bearing units are collectively termed the <br />Wadge overburden aquifer by CYCC. The Division also utilizes <br />this name when describing these units later in this section of <br />this findings document. ' <br />Limited ground water yields have been obtained from the <br />Lewis Shale but use of water from this unit is considered <br />insignificant in the Twentymile Park Basin. Where the <br />Lewis Shale is present in the area, it acts as an impermeable <br />confining layer creating artesian conditions within the <br />underlying aquifers of the Mesaverde Group. <br />The highest reported well yields of ground water aquifers in <br />the basin can be obtained from the unconsolidated alluvial <br />deposits of the Yampa River and its tributaries. Well yields <br />range from 5 gal/min, to as much as 900 gal/min (Brogden and <br />Giles, 19771. The principal use of water from the alluvial <br />aquifers is for domestic and stock watering purooses; however, <br />permeabilities are sufficient in some areas to support long <br />term, high yield wells for municipal and industrial needs and <br />irrigation, particularly in the Yampa River alluvium. Water <br />quality is variable, depending on the underlying rock and <br />source of alluvial material. TDS concentration ranges from <br />82 to 2,970 mg/1, and the water may contain concentrations of <br />arsenic, iron, manganese, nitrate, selenium, and sulfate in <br />excess of U.W. Public Health Service Drinking Water Standards <br />(Brogden and Giles, 19771. <br />-20- <br />