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Ground Water Use. The Trout Creek Sandstone, the Twentymile Sandstone, and the White <br />Sandstone are bedrock aquifers currently being used for ground water supplies in the general <br />vicinity of the Williams Fork Mines. The Middle Sandstone is not currently used as a ground <br />water supply in the vicinity. The alluvial bodies associated with the Yampa River and Williams <br />Fork River contain limited ground water and are not considered major aquifers in the general <br />area. Alluvial bodies along the Yampa River up- and downstream of the general area, however, <br />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 <br />outside the vicinity is widely used as a source of domestic and livestock watering. Within the <br />vicinity, alluvial ground water is not a significant source of water put to beneficial use. Ground <br />water from the coals and thin sandstones are not considered aquifers, but they flow into the <br />underground workings and the mine uses them for cooling, dust suppression, fire protection, and <br />other industrial uses. <br />Ground Water Recharge, Discharge, and Flow. The sandstone aquifers in the Big Bottom <br />Synclinal Basin are recharged at their subcrops beneath the stream /alluvial systems of the Yampa <br />and Williams Fork Rivers, and at their outcrops in upland areas. From a recharge area, flow <br />would be generally northward, downdip toward the axis of the Big Bottom syncline. Faults may <br />provide conduits of flow for ground water wherever a fault is not sealed with fine - grained gouge <br />material. <br />Ground Water Hydraulics. The sandstone aquifers are under atmospheric pressure (water table <br />conditions) near their recharge areas and under hydrostatic pressure (artesian conditions) within <br />the structural basins or at discharge points. Hydrostatic pressures in the sandstone aquifers <br />increase with depth and are at a maximum in the axial areas of the Big and Round Bottom <br />Synclines. Artesian conditions are developed in aquifers which are confined by overlying and <br />underlying strata with low permeabilities. Several of the wells drilled into the bedrock aquifers <br />within the study area exhibit artesian flows at the surface. The operator conducted aquifer tests to <br />determine the hydraulic properties of the aquifers (see permit application). <br />Bedrock Ground Water Quality. Ground water in the Trout Creek Sandstone and Williams Fork <br />Formation is predominantly calcium and sodium bicarbonate types. Water in contact with coals <br />is a calcium sulfate type and can contain fluoride, iron, manganese, selenium, and sulfate <br />concentrations in excess of U.S. Public Health Service drinking water standards, with the water <br />contained in the coals and thin discontinuous sandstones generally being of poorer quality than <br />that from the massive regional sandstone aquifers. <br />Alluvial Ground Water Occurrence. The Yampa River alluvium and the Williams Fork River <br />alluvium both contain 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 baseflow to the <br />associated river systems. These alluvial units may provide recharge to rock aquifers and also are <br />recharged by rock aquifers within the ground water study area. <br />Alluvial Ground Water Quality. Alluvial water quality is variable, depending on the underlying <br />rock and source of alluvial material. Ground water from the Yampa River alluvium is primarily <br />sodium sulfate type. Dissolved solids average 4,586 mg /l with a maximum measure of 8,810 <br />mg/l. Ground water for the Williams Fork alluvium is primarily of the sodium bicarbonate type. <br />Williams Fork Mines 8 Permit Renewal 06 <br />C- 1981 -044 December 8, 2014 <br />