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RULE 4 PERFORMANCE STANDARDS <br />If any ground water does percolate vertically through the discordant geologic units, it <br />encounters a tonstein bed near the base of the Williams Fork Formation. This bed is <br />approximately 150 feet above the top of the Trout Creek Sandstone and is approximately <br />400 feet below the bottom of the active pits. The tonstein bed has an approximate thickness <br />of 2.5 feet. Permeability tests of this material show it has permeabilities greater than 1x10- <br />10 centimeters per second. Thus, this bed is an effective aquiclude and prevents downward <br />movement of any ground water to the 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 <br />USGS and designated for limited agricultural use. Since USGS testing in 1978, no water <br />quality analysis performed at monitoring points at the Colowyo Mine have shown any <br />significant difference in water quality compared with what the initial USGS work. The <br />water is slightly saline, alkaline and definitely classified as `hard' water. This can be seen <br />in the water quality measurements for total dissolved solids (TDS) and electrical <br />conductivity (eC). Both TDS and eC exceed the EPA secondary drinking water standards. <br />Since the water is alkaline, the pH is above 7, but rarely exceeding 8.4. Concentrations of <br />heavy metals rarely exceed health limits, as stated in the USGS report. This has also been <br />backed up by the shallow ground water monitoring performed since the Colowyo Mine <br />began operation. <br />Conclusions <br />The Colowyo Mine has no single or multiple continuous geologic units in the mine that <br />contains ground water under unconfined or confined conditions. The only ground water <br />encountered is the discontinuous perched pockets of ground water. This lack of ground <br />water, except for discontinuous perched ground water pockets, encountered during mining <br />precludes the necessity to monitor ground water on a ridge top. <br />Rule 4 Performance Standards 4-17 Revision Date: 5/25/18 <br />Revision No.: RN -07 <br />