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RULE 4 PERFORMANCE STANDARDS <br />The Division granted Colowyo a waiver to the requirements of 4.05.9(17) for small impoundments. The <br />waiver applies only to impoundments which are not the primary sediment control structure for a particular <br />area; are constructed in reclaimed areas of the mine to enhance the approved postmining land use; are <br />completely incised, or have a storage capacity no greater than two-acre feet and an embankment no <br />greater than five 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 4.05.9(14). The <br />inspections will be performed by a qualified registered professional engineer, or other qualified <br />professional 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 a threat to <br />public health and safety or threaten significant environmental harm. A written safety demonstration <br />completed by a professional engineer is located in Exhibit 7, Item 11 in accordance with rule <br />4.05.9(18)(b). None of the small impoundments act as primary sediment control structure for a particular <br />area; they are all constructed in reclaimed areas of the mine to enhance the approved postmining land use; <br />they are all under two-acre feet. <br />All impoundments will be maintained according to the specifications set forth in this part. Maintenance <br />for impoundments may include mowing and cutting of excess vegetative growth for the purpose of <br />facilitating inspections and repairs and will include keeping ditches, culverts, spillways, and other outflow <br />structures free of debris. All combustible material, other than mulch or other material needed for erosion <br />control and surface stability will be removed. <br />Plans for any modification of any sedimentation impoundments or dams will be submitted to the <br />Division, and no modification will begin until approval of the plans have been granted unless such <br />modification is necessary on an emergency basis for public health, safety or the environment would be <br />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 section from which <br />the Colowyo Mine mines coal using surface mining techniques. This is also noted in Section 2.04.7. In <br />addition, there are no continuous aquifers of regional extent within the entire Williams Fork Formation in <br />the location of the Colowyo Mine. Occasionally, a minimal amount of water is found under perched <br />conditions in 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 slopes or surface <br />and ground water system associated with the Colowyo Mine. <br />4.05.12 Protection of Groundwater Recharge Capacity <br />The reclamation plan as described in 2.05.4 will return the disturbed lands to approximately the pre- <br />mining condition; therefore, ground water recharge capacity is expected to approximate the premining <br />condition. Also, because of the minimal existence of ground water in the mining area, the mining <br />operation and subsequent reclamation should have no adverse effect on the existing ground water <br />recharge capacities. <br />Rule 4 Performance Standards 4.05-7 Revision Date: 6/23/08 <br />Revision No.: MR-91