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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 mine <br />to enhance the approved postmining land use; are completely incised, or have a storage <br />capacity no greater than two-acre feet and an embankment no greater than five feet in height. <br />The small impoundments will be inspected on a yearly schedule until removal of the structure <br />or release of the performance bond as directed in rule 4.05.9(]4). The inspections will be <br />performed by a qualified registered professional engineer, or other qualified professional <br />specialist under the direction of a professional engineer, or a qualified person other than, and <br />not under the direction of, a professional engineer. <br />Colowyo successfully demonstrated that failure of the small impoundments would not create <br />a threat to public health and safety or threaten significant environmental harm. A written <br />safety demonstration completed by a professional engineer is located in Exhibit 7, Item 11 in <br />accordance with rule 4.05.9(18)(b). None of the small impoundments act as primary <br />sediment control structure for a particular area; they are all constructed in reclaimed areas of <br />the mine to enhance the approved postmining land use; they are all under two-acre feet. <br />All impoundments will be maintained according to the specifications set forth in this part. <br />Maintenance for impoundments 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 stability <br />• will be removed. <br />Plans for any modification of any sedimentation impoundments or dams will be submitted to <br />the Division, and no modification will begin until approval of the plans have been granted <br />unless such modification is necessary on an emergency basis for public health, safety or the <br />environment would be endangered. <br />4.05.10 Undereround Mine Entry and Access Discharges <br />Colowyo currently conducts surface coal mining exclusively. <br />4.05.1 I Ground Water Protection <br />There are no aquifers or continuous sources of ground water within the stratigraphic section <br />from which the Colowyo Mine mines coal using surface mining techniques. This is also <br />noted in Section 2.04.7. In addition, there are no continuous aquifers of regional extent <br />within the entire Williams Fork Formation in the location of the Colowyo Nline. <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 toxic <br />concentrations of acid forming materials have been found in the overburden, reclaimed <br />slopes or surface and ground water system associated with the Colowyo Mine. <br />\J <br />4.05-9 Revision Date: 6/25/02 <br />Revision No.: TR-55 <br />