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_22_ <br />~~ ~~ <br />Ground water within the Iles and Williams Fork formations of the Mesa Verde <br />Group is predominantly calcium and sodium-bicarbonate types. However, water <br />in contact with coals is a calcium sulfate type and can contain fluoride, <br />iron, manganese, selenium and sulfate concentrations in excess of U.S. Public <br />Health Service drinking water standards (Brogden and Giles, 1977). Dissolved <br />solids concentration of water within the Iles and Williams fork Formations <br />ranges from 334 to 1,460 mg/1 (Brogden and Giles, 1977), with the water <br />contained in the coals and thin discontinuous sandstones generally being of <br />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, and the depth of drilling; the ground water in the <br />coals and the thin discontinuous sandstones are currently not used for <br />agricultural or domestic purposes. The potential future use of this ground <br />water for this purposes is low. Ground water for the coals and the thin <br />sandstones do inflow into the underground working and the open pits. These <br />inflow waters are used by the mining operations for cooling, dust suppression, <br />fire protection, and other industrial uses. <br />Limited ground water yields have been obtained from the Lewis Shale but use of <br />water from this unit is considered insignificant in the Big and Round Bottom <br />Synclinal Basins. Where the Lewis Shale is present in the ground water study <br />area, (the Big and Round Bottom Synclinal Basins), it acts as an impermeable <br />confining layer creating artesian conditions within the underlying aquifers of <br />the Mesaverde Group. <br />The Yampa River alluvium and the Williams Fork River alluvium both contain <br />alluvial ground water. These alluvial water bearing units may store and <br />release water used by the overlying vegetation, and may sustain a component of <br />baseflow to the associated river systems. These alluvial units may provide <br />recharge to rock aquifers and also are recharged by rock aquifers within the <br />ground water study area. <br />Empire Energy Corporation has analyzed the quantity and quality of ground <br />water in the alluvium of the Yampa River and Williams Fork River. Previous <br />Williams Fork alluvium tests conducted for the Empire Energy were suspect and <br />Empire Energy Corporation reran the tests. The results of the rerun tests are <br />contained in Appendix III-3a. Given the relatively thin saturated thickness <br />(5 to 6 feet) and low well yields (less than 1 gpm) these wells were slug <br />tested and analyzed by the Bower and Rice method, 1976. Low transmissivity <br />values of between 36 to 130 gpd/ft and low permeability values of between 5.5 <br />and 24 gpd/ft2 were obtained for the Williams Fork alluvium. Slug test <br />analyzed by the Bower and Rice method and pumping tests were run on the Big <br />Bottom alluvium. Transmissivity values and 'permeability values obtained for <br />the Big Bottom alluvium were low; transmissivities ranged between 57 and 3100 <br />gpd/ft and averaged 900 gpd/ft; permeabilities ranged between 12 and 440 <br />gpd/ft2 and averaged 120 gpd/ft2. These tests indicate that the alluvial <br />bodies of the Williams Fork and Yampa Rivers are poor aquifers in the general <br />area. <br />