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<br />Williams Fork Mines Prepared by: R. Reilley M.S. GISP <br />C1981044 5 November 2018 <br /> <br /> <br /> 7 <br />even higher proportion of the water used is for irrigation of grasslands and hay fields. <br /> <br />Aquifer Stratigraphy. Within the general vicinity of the Williams Fork Mines, ground water exists in both <br />bedrock and alluvial aquifers. Significant bedrock aquifers are (listed in ascending stratigraphic order) the <br />Trout Creek, Middle, Twentymile, and White Sandstones. The Middle, Twentymile and White Sandstones are <br />in the Williams Fork Formation; the Trout Creek Sandstone is the uppermost member of the underlying Iles <br />Formation. The main alluvial aquifers in the area are associated with the Yampa and Williams Fork Rivers. <br />The alluvial aquifers probably contribute to baseflow of the rivers during dry periods. Coal seams, <br />discontinuous sandstones, and siltstones and smaller alluvial bodies in the area of the mine are also water- <br />bearing, but contain insufficient quantities of water to be considered significant aquifers. <br /> <br />Ground Water Use. The Trout Creek Sandstone, the Twentymile Sandstone, and the White Sandstone are <br />bedrock aquifers currently being used for ground water supplies in the general vicinity of the Williams Fork <br />Mines. The Middle Sandstone is not currently used as a ground water supply in the vicinity. The alluvial bodies <br />associated with the Yampa River and Williams Fork River contain limited ground water and are not considered <br />major aquifers in the general area. Alluvial bodies along the Yampa River up- and downstream of the general <br />area, however, are significant sources of ground water. High yield irrigation and municipal water supply wells <br />are completed in the Yampa River alluvium in those areas. Also, the Yampa River alluvium outside the vicinity <br />is widely used as a source of domestic and livestock watering. Within the vicinity, alluvial ground water is not <br />a significant source of water put to beneficial use. Ground water from the coals and thin sandstones are not <br />considered aquifers, but they flow into the underground workings and the mine uses them for cooling, dust <br />suppression, fire protection, and other industrial uses. <br /> <br />Ground Water Recharge, Discharge, and Flow. The sandstone aquifers in the Big Bottom Synclinal Basin <br />are recharged at their subcrops beneath the stream/alluvial systems of the Yampa and Williams Fork Rivers, <br />and at their outcrops in upland areas. From a recharge area, flow would be generally northward, downdip <br />toward the axis of the Big Bottom syncline. Faults may provide conduits of flow for ground water wherever a <br />fault is not sealed with fine-grained gouge material. <br /> <br />Ground Water Hydraulics. The sandstone aquifers are under atmospheric pressure (water table conditions) <br />near their recharge areas and under hydrostatic pressure (artesian conditions) within the structural basins or at <br />discharge points. Hydrostatic pressures in the sandstone aquifers increase with depth and are at a maximum in <br />the axial areas of the Big and Round Bottom Synclines. Artesian conditions are developed in aquifers which <br />are confined by overlying and underlying strata with low permeabilities. Several of the wells drilled into the <br />bedrock aquifers within the study area exhibit artesian flows at the surface. The operator conducted aquifer <br />tests to determine the hydraulic properties of the aquifers (see permit application). <br /> <br />Bedrock Ground Water Quality. Ground water in the Trout Creek Sandstone and Williams Fork Formation <br />is predominantly calcium and sodium bicarbonate types. Water in contact with coals is a calcium sulfate type <br />and can contain fluoride, iron, manganese, selenium, and sulfate concentrations in excess of U.S. Public Health <br />Service drinking water standards, with the water contained in the coals and thin discontinuous sandstones <br />generally being of poorer quality than that from the massive regional sandstone aquifers. <br /> <br />Alluvial Ground Water Occurrence. The Yampa River alluvium and the Williams Fork River alluvium both <br />contain alluvial ground water. These alluvial water-bearing units may store and release water used by the <br />overlying vegetation, and may sustain a component of baseflow to the associated river systems. These alluvial <br />units may provide recharge to rock aquifers and also are recharged by rock aquifers within the ground water <br />study area. <br />Alluvial Ground Water Quality. Alluvial water quality is variable, depending on the underlying rock and