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The upper coal aquifer is defined as the region between the second and fourth <br />coal seam, a distance which ranges from thirty (30) to thirty-five (35) feet. <br />Baseline information documented transmissivity values of 0.18 gpd/ft to 5.2 <br />gpd/ft and a storage capacity of 0.01. This calcium sulfate water has iron, <br />lead and sulfate concentrations in excess of standards for use by livestock. <br />Conductivity levels ranges from 9.65 to 1.800 mmhos/cm and the pH is neutral <br />(7). <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 Twentymile Park <br />Basin. Where the Lewis Shale is present in the area, it acts as an <br />impermeable confining layer creating artesian conditions within the underlying <br />aquifers of the Mesaverde Group. <br />The highest reported well yields of ground water aquifers in the basin can be <br />obtained from the unconsolidated alluvial deposits of the Yampa River and its <br />tributaries. Well yields range from 5 gal/min along the upper tributaries to <br />as much as 900 gal/min along the Yampa (Brogden and Giles, 1977). The <br />principal use of water from the alluvial aquifers is for domestic and stock <br />watering purposes; however, permeabilities are sufficient in some areas to <br />support long-term, high-yield wells for municipal and industrial needs and <br />irrigation, particularly in the Yampa River alluvium. Water quality is <br />variable, depending on the underlying rock and source of alluvial material. <br />Dissolved solids concentrations range from 82 to 2,970 mg/1 and the water may <br />contain concentrations of arsenic, iron, manganese, nitrate, selenium, and <br />sulfate in excess of U. S. Public Health Service Drinking Water Standards <br />(Brogden and Giles, 1977). <br />Alluvial aquifers in Hayden Gulch are both narrow and shallow. The alluvial <br />aquifers receive a majority of their recharge from the stream primarily in the <br />spring and early summer when snowmelt and surface water is abundant and when <br />transpiration by vegetation and evaporation is at a minimum. <br />Ground water flow in the Upper Yampa River Basin is controlled by the geologic <br />structure, stratigraphy and geomorphology of the general area. The flows of <br />ground water in the rock aquifers are controlled by the structural folding and <br />faulting and stratigraphy while the flows of ground water in the alluvial <br />aquifers are controlled by the geomorphology of the stream valleys and surface <br />water flows. <br />The lenticular and interbedded sandstones associated with the coal bearing <br />zones develop only localized discontinuous aquifers. Movement of ground water <br />within these sandstones is usually localized, with the flows of water from the <br />recharge to the discharge area occurring within a short distance. Some <br />limited regional movement of ground water may occur if there is <br />intercommunication between the sandstones. <br />The recharge, discharge and movement of ground water within the alluvial <br />aquifers are controlled by: 1) the gradient of the rock channel into which <br />the alluvium has been deposited, 2) the width of the alluvial deposit, 3) the <br />thickness of the alluvial body, 4) the permeability of the alluvial deposit, <br />-15- <br />j .. <br />