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RULE 4 PERFORMANCE STANDARDS <br />Hydrology <br />Based on the above, the Colowyo Mine is located on both a topographic and structural high. <br />Thus, these highs cause the mined units of the Colowyo Mine to be above any significant <br />recharge source, e.g., surface water. This is because the bottoms of the pits are at an elevation <br />higher than the elevation of the surface water in the creeks. Only when the units are at an <br />elevation lower than the valleys does any significant recharge occur. Thus, the only source of <br />recharge for the mined units in the pit areas of the Colowyo Mine is precipitation. <br />Precipitation is less than 22 inches (on average) per year. Evaporation rates approach 30 inches <br />per year, with recharge rates in the Goodspring Creek and Taylor Creek basins being less than <br />0.35 inches per year. In addition, any surface water/precipitation on this topographic high has to <br />percolate through the clayey soils, prevalent in the area of the Colowyo Mine, into the underlying <br />bedrock. Any water that recharges the bedrock units tends to accumulate along unit contacts <br />since these tend to be areas of least flow resistance. This is exhibited in the highwall of both pits <br />of the Colowyo Mine, where any discharge is easily seen as issuing primarily from these contacts <br />and has been the case since 1981. <br />Any ground water that has been discharged from the mine highwall has been found to evaporate <br />from the pit floor or be consumed by pit highwall. Past hydrological studies also reveal the <br />mined units tend to have low permeabilities (even the sandstones) and do not allow for large <br />water movement, even if the ground water is present. This is also the case where the ground <br />water is under confined or unconfined conditions (i.e. below the elevation of the valley bottoms). <br />If any ground water does percolate vertically through the discordant geologic units, it encounters <br />a tonstein bed near the base of the Williams Fork Formation. This bed is approximately 150 feet <br />above the top of the Trout Creek Sandstone and is approximately 400 feet below the bottom of <br />the active pits. The tonstein bed has an approximate thickness of 2.5 feet. Permeability tests of <br />this material show it has permeabilities greater than 1x10-10 centimeters per second. Thus, this <br />bed is an effective aquiclude and prevents downward movement of any ground water to the <br />underlying Trout Creek Sandstone. <br />Water Quality <br />The quality of the water in the area of the Colowyo Mine has been rated as poor by the USGS and <br />designated for limited agricultural use. Since USGS testing in 1978, no water quality analysis <br />performed at monitoring points at the Colowyo Mine have shown any significant difference in <br />water quality compared with what the initial USGS work. The water is slightly saline, alkaline <br />and definitely classified as `hard' water. This can be seen in the water quality measurements for <br />total dissolved solids (TDS) and electrical conductivity (eQ. Both TDS and eC exceed the EPA <br />secondary drinking water standards. <br />Since the water is alkaline, the pH is above 7, but rarely exceeding 8.4. Concentrations of heavy <br />metals rarely exceed health limits, as stated in the USGS report. This has also been backed up by <br />the shallow ground water monitoring performed since the Colowyo Mine began operation. <br />Conclusions <br />The Colowyo Mine has no single or multiple continuous geologic units in the mine that contains <br />ground water under unconfined or confined conditions. The only ground water encountered is the <br />Rule 4 Performance Standards 4.05-9 Revision Date: 6/23/08 <br />Revision No.: MR-91