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RULE 4 PERFORMANCE STANDARDS <br /> mom. .+Pa.^a-c^,�u.-.ui.�-.a&a;a-m9as,�..r:�."iv..t q,,a•�en. sa , ,. _, .>.,M.,.z. ..,,..x. .. .... ... ,xxPoOt. ;'s, m`e <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 /> 4.05.13 Surface and Groundwater Monitoring <br /> The current monitoring program can be found in Section 4.05.13 in Volume 15. <br /> 4.05.14 Transfer of Wells <br /> Colowyo does not plan to transfer any monitoring wells to water wells. <br /> 4.05.15 Water Rights and Replacement <br /> Colowyo, if necessary, will replace the water supply of any owner of interest in real estate who <br /> obtains all or part of a supply of water for domestic, agricultural, industrial or other legitimate use <br /> from an underground or surface source where the water supply has been affected by the mining <br /> operation. <br /> Rule 4 Performance Standards 4-17 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />