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2 <br />completed in the Yampa River alluvium in those aeeas. Also, the Yampa River alluvium outside <br />the vicinity is widely used as a source of domestic and livestock watering. Within the vicinity, <br />alluvial ground water is not a significant source of water put to beneficial use. Ground water <br />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 ayuifers in the Big Bottom <br />Synclinal Basin are rechazged at their subcrops beneath the stream alluvial systems of the Yampa <br />and W illiams Fork Rivers, and at their outcrops in upland areas. From a rechazge 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 tine-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 dschazge points. Hydrostatic pressures in the sandstone aquifers <br />increase with depth and are at a maximum in the axial areas of the Big a~ad Round Bottom <br />Synclines. Artesian conditions are developed in aquifers which aze 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 [he Trout Creek Sandstone and Wi]]iams For;; <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 standazds, 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 aze <br />rechazged 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/1 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 />Total dissolved solids average 1,009 milligrams per liter (mg/1) with a maximum measured <br />value of 1,510 mg/1. Maximum primary and secondary drinking water standards are exceeded in <br />both aquifers for many parameters including barium, cadmium, chloride, chromium, pH, sulfate, <br />and selenium. In addition, average concentration values for chloride, total dissolved solids, iron, <br />lead, manganese, and sulfate exceed EPA primary and secondary stand.azds. <br />9 <br />