2011-08-09_REVISION - C1981019 (10)

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• • RULE 4 PERFORMANCE STANDARDS bedrock. The recharge rates in the Good Spring Creek and Taylor Creek basins are estimated to be 0.35 inches per year, based on past studies. Any water that does recharge the bedrock units tends to accumulate along unit contacts since these tend to be zones of least flow resistance. This was and is exhibited in the highwall of both pits of the Colowyo Mine, where any discharge is seen as issuing primarily from these contacts and has been the case since 1981. Any ground water that has been discharged from the mine highwall has been found to evaporate from the pit floor or be consumed by down slope (usually northern) pit highwall. Past hydrological studies also reveal the current mined units tend to have low permeabilities (even the sandstones) and do not allow for large water movement, even if the ground water is present. This is the situation whether ground water is under unconfined or confined conditions. The projected bottom of the current South Taylor pit will be at an elevation higher than the majority of the coal seams mined in the West Pit, where only perched water has been encountered in the last 14 years. The only source of water via recharge for the mined units in the South Taylor pit is precipitation and the storage ponds that were used for cattle and sheep watering. Therefore, no monitoring of a continuous non - perched aquifer is possible, even if the beds of the Williams Fork formation were continuous over a large area. The same geologic setting is also found in the proposed Collom mining area. The southern portion of the proposed permit area has the top portion of the Iles formation and the bottom of the Williams Fork formation exposed above Wilson Creek. Drilling in this area down to the TCSS revealed dry conditions and long term monitoring of a TCSS monitoring well revealed no water. Thus in the Collom permit area, like at the active Colowyo mining area, there is no up- gradient bedrock ground water in a continuous aquifer, which can monitored down gradient of the proposed mining area. If any ground water does percolate vertically through the discordant geologic units, it encounters a tonstein bed near the base of the Williams Fork Formation. This bed is approximately 150 feet above the top of the Trout Creek Sandstone and is approximately 400 feet below the bottom of the active pits. The tonstein bed has an approximate thickness of 2.5 feet. Permeability tests of this material show it has permeabilities greater than 1x10 -10 centimeters per second. Thus, this bed is an effective aquiclude and prevents downward movement of any ground water to the underlying Trout Creek Sandstone. The monitoring of deep ground water above and below any mined area or proposed mine area is not possible. With no significant recharge of the Williams Fork formation from the south (up- dip), no ground water can be transmitted down gradient through a continuous unit, which could then be monitored. Valley Fill Ground Water As seen on the topographic maps of the Colowyo permit area (previously submitted to the DRMS), there are numerous valleys crossing the property. These valleys trend in a south to north direction following the topographic slope. These valleys include (from east to west): • Good Spring Creek, and its tributary, West Fork Good Spring Creek • Taylor Creek • Wilson Creek • Jubb Creek and its tributaries, East Fork and West Fork of Jubb Creek • Little Collom Gulch • Collom Gulch Collom — Rule 4, Page 19 Revision Date: 8/5/11 Revision No.: PR -03