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The Division granted Colowyo a waiver to the requirements of 4.05.9(17) for small <br />impoundments. The waiver applies only to impoundments which are not the primary <br />sediment control structure for a particular area; are constructed in reclaimed areas of the <br />mine to enhance the approved postmining land use; are completely incised, or have a <br />storage capacity no greater than two-acre feet and an embankment no greater than five <br />feet in height. The small impoundments will be inspected on a yearly schedule until <br />removal of the structure or release of the performance bond as directed in rule <br />4.05.9(14). The inspections will be performed by a qualified registered professional <br />engineer, or other qualified professional specialist under the direction of a professional <br />engineer, or a qualified person other than, and not under the direction of, a professional <br />engineer. <br />Colowyo successfully demonstrated that failure of the small impoundments would not <br />create a threat to public health and safety or threaten significant environmental harm. A <br />written safety demonstration completed by a professional engineer is located in Exhibit <br />7, Item 11 in accordance with rule 4.05.9(18)(b). None of the small impoundments act <br />as the primary sediment control structure for a particular area; they are all constructed in <br />reclaimed areas of the mine to enhance the approved postmining land use; they are all <br />under two-acre feet. <br />All impoundments will be maintained according to the specifications set forth in this part. <br />Maintenance for impouhdments may include mowing and cutting of excess vegetative <br />growth for the purpose of facilitating inspections and repairs and will include keeping <br />ditches, culverts, spillways, and other outflow structures free of debris. All combustible <br />material, other than mulch or other material needed for erosion control and surface <br />stability will be removed. <br />Plans for any modification of any sedimentation impoundments or dams will be <br />submitted to the Division, and no modification will begin until approval of the plans have <br />been granted unless such modification is necessary on an emergency basis for public <br />health, safety or the environment would be endangered. <br />4.05.10 Underground Mine Entry and Access Discharges <br />Colowyo currently conducts surface coal mining exclusively. <br />4.05.11 Ground Water Protection <br />There are no aquifers or continuous sources of ground water within the stratigraphic <br />section from which the Colowyo Mine mines coal using surface mining techniques. This <br />is also noted in Section 2.04.7. In addition, there are no continuous aquifers of regional <br />extent within the entire Williams Fork Formation in the location of the Colowyo Mine. <br />Occasionally, a minimal amount of water is found under perched conditions in <br />noncontiguous lenticular sandstones and in fractured coal under the sandstones. No <br />toxic concentrations of acid forming materials have been found in the overburden, <br />reclaimed slopes or surface and ground water system associated with the Colowyo <br />Mine. <br />4.05-9 <br />June 25, 2002 <br />TR-55 <br />CF 4.1.2.6 <br />