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RULE 4 PERFORMANCE STANDARDS <br /> «: a•e.,aws.aa+r, :at..%A'#'rok..4 F.aK4.0Y6. ^.04,#^4Ht$ts4t ro'lN kg:a 4':.rY, .:`R '.'yv e>l+w•w..,fir. .a =a.^'tati✓,. <br /> Syncline, located approximately 0.5 miles north of the north edge of the reclaimed East <br /> Pit,trends west-northwest(approximately N60°W)with a slight dip in the axis to the west- <br /> northwest. The Collom Syncline is sub-parallel to the Axial Anticline on the north and the <br /> Danforth Hills Anticline on the south. The Collom Syncline is asymmetrical, with the <br /> north flank of the syncline steeply dipping (200-40°) to the south-southwest. The south <br /> flank dips to the north-northeast at around 10°±5°. The Colowyo Mine is located on the <br /> south flank of the Collom Syncline. Therefore,based on the geologic structure of the area, <br /> the coal seams and non-coal beds of the Colowyo Mine dip to the north-northeast at <br /> approximately 10°. The southern portion of the Colowyo Mine is located on a structural <br /> high, an unnamed anticline, which is an offshoot of the Danforth Hills anticline. <br /> Topographically,the mine is located on a topographic high, bordered on the east and west <br /> by deeply incised valleys. These valleys are Good Spring Creek and Wilson Creek, on the <br /> east and west respectively. The valleys slope from south to north, similar to the <br /> topographic slope at Colowyo Mine. The topography in the area of the Colowyo Mine <br /> ranges from 8000 feet on the south to 7150 feet on the north. The valleys have elevation <br /> ranges from approximately 7100 feet on the south to 6550 feet on the north. On the south, <br /> south of the Section 16 mine area,the topography drops off into the West Fork Good Spring <br /> Creek, a small tributary to Good Spring Creek. <br /> Hydrology <br /> Based on the above, the Colowyo Mine is located on both a topographic and structural <br /> high. Thus, these highs cause the mined units of the Colowyo Mine to be above any <br /> significant recharge source, e.g., surface water. This is because the bottoms of the pits are <br /> at an elevation higher than the elevation of the surface water in the creeks. Only when the <br /> units are at an elevation lower than the valleys does any significant recharge occur. Thus, <br /> the only source of recharge for the mined units in the pit areas of the Colowyo Mine is <br /> precipitation. <br /> Precipitation is less than 22 inches (on average) per year. Evaporation rates approach 30 <br /> inches per year,with recharge rates in the Goodspring Creek and Taylor Creek basins being <br /> less than 0.35 inches per year. In addition, any surface water/precipitation on this <br /> topographic high has to percolate through the clayey soils, prevalent in the area of the <br /> Colowyo Mine, into the underlying bedrock. Any water that recharges the bedrock units <br /> tends to accumulate along unit contacts since these tend to be areas of least flow resistance. <br /> This is exhibited in the highwall of both pits of the Colowyo Mine, where any discharge is <br /> easily seen as issuing primarily from these contacts and has been the case since 1981. <br /> Any ground water that has been discharged from the mine highwall has been found to <br /> evaporate from the pit floor or be consumed by pit highwall. Past hydrological studies also <br /> reveal the mined units tend to have low permeabilities (even the sandstones) and do not <br /> allow for large water movement, even if the ground water is present. This is also the case <br /> where the ground water is under confined or unconfined conditions(i.e.below the elevation <br /> of the valley bottoms). <br /> Rule 4 Performance Standards 4-16 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />