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The Twentymile sandstone is separated from the underlying Wadge coal-overburden aquifer by <br />up to 700 feet of impermeable shale within the permit and adjacent areas. The underlying <br />700-foot shale and the overlying shales and siltstones of the upper Williams Fork Formation and <br />the Lewis Shale Formations produce the confined artesian conditions within the Twentymile <br />sandstone aquifer. To the northeast, the Twentymile sandstone recharges the alluvial aquifer and <br />provides base flow to the tributaries of Trout Creek down gradient of the mine. Salts in the <br />Twentymile sandstone waters are predominantly sodium bicarbonate and result in TDS levels of <br />150 mg/l. This aquifer is occasionally used for domestic needs. <br /> <br />The alluvium of Trout Creek and its tributaries is an important source of ground water. The <br />alluvial bodies are used as water supplies, provide sub-irrigation to vegetation, and supply base <br />flow to the streams. The alluvial bodies are recharged by both the streams and the bedrock <br />aquifers. <br /> <br />Local Climate <br /> <br />The local climate is semi-arid with a mean annual precipitation of 14.6 inches. Approximately <br />45 percent of this precipitation occurs during the growing season of April through September. <br />High temperatures generally range from 70-80°F in the summer months to below freezing in the <br />winter months. Normally, a significant snowpack resides on the ground for 4-5 months during <br />the winter. <br /> <br />Soils <br /> <br />Two broadly classified soil complexes exist within the permit area. These are Typic <br />Paleoborolls - Borollic Camborthids and Argic Cryoborolls- Cryic Paleoborolls. However, prior <br />to mining, the Typic Paleoborolls - Borollic Camborthids soils covered the disturbed area. They <br />occur primarily on uplands and are formed in materials weathered in place from soft shale. <br />These clayey soils are moderately deep to deep, well drained and usually contain less than 35 <br />percent rock fragments. Permeability is low, shrink/swell potential is high and potential frost <br />action is moderate to high. These soils are used for rangeland, non-irrigated cropland, and <br />irrigated hay and pastureland. <br /> <br />Vegetation <br /> <br />The permit area is situated below a western spruce/fir forest within both a mountain <br />mahogany/scrub oak complex and a sagebrush steppe vegetation zone. The lower portions of <br />Twentymile Park were historically dominated by low sagebrush community which has since <br />given way to cultivated vegetation types and other agricultural practices. Somewhat higher <br />elevations are dominated by big sagebrush or mountain shrub communities. The highest <br />elevations and/or steep north facing slopes surrounding Twentymile Park are dominated by <br />aspen, mountain shrub, and occasionally, spruce/fir communities. <br /> <br />Within the permit area, existing vegetation is comprised of seven plant communities consisting <br />of aspen, mountain shrub, sagebrush, sagebrush/meadow, pasture, cropland, and meadow. Of <br />these, only four may be disturbed by surface facilities: sagebrush, sagebrush/meadow, pasture, <br />and cropland. <br /> <br /> <br />10 <br /> <br /> Foidel Creek MineOctober 8, 2013 <br /> <br />