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Ground Water Hydrology <br />The stratigraphy and geologic structure within the Twentymile Park Synclinal Basin control the <br />ground water flow within the permit and adjacent areas. There are three regional bedrock <br />aquifers within the permit and adjacent areas of the Foidel Creek underground mine. These <br />aquifers are the Trout Creek sandstone, the Twentymile sandstone, and the Wadge/Wolf Creek <br />coal-overburden/interburden zones. All three aquifers exhibit artesian conditions in central <br />portions of Twentymile Park Basin. Ground water in the Twentymile Park Basin is not suitable <br />for most domestic uses. Use of groundwater in the general area is restricted to livestock <br />watering, irrigation and limited domestic use (PAP, page 2.04-24) . <br />The geologic structure created by folding and faulting within the Twentymile Park Synclinal <br />Basin affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the <br />direction of ground water flow in the bedrock aquifers is down dip toward the center of the <br />Twentymile Park Basin. Faults in the area produce localized fracture zones within the rock <br />strata. These zones of increased permeability increase the potential for vertical and horizontal <br />movement of ground water within the rock strata. However, experience to date in the Foidel <br />Creek Mine shows little to no inflow along the fault zones at the level of the Wadge coal seam. <br />Some inflows were encountered in 9 Right and 6 Right gateroads as they were developed into the <br />Eastern Mining District. These inflows appeared to be localized, and tapered off over time. <br />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/1. This aquifer is occasionally used for domestic needs. <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 />Local Climate <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 />Soils <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 />Foidel Creek Mine 12 February 25, 2016 <br />