2013-04-10_PERMIT FILE - C1981019 (85)

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RULE 4 PERFORMANCE STANDARDS regional practices on similar rangelands. Since the source of water is surface runoff from revegetated areas the quality of the water will meet the requirements of the intended use. The post- mining impoundments have slopes of 3h:ly or less to provide easy access to both livestock and wildlife. These impoundments and any associated ditches, while intended to be permanent, will be classified as temporary until the requirements of Rule 4.05.9 are met. Prior to construction, all designs are submitted to the Division. A copy of the as -built design information will be submitted after construction for inclusion into Exhibit 7, Item 23. In addition, sedimentation ponds that are subsequently approved as part of the post- mining land use, as shown on the hydrology Map 4113, will remain as permanent impoundments after the requirements of Rule 4.05.9 have been met. Please refer to Section 4.05.6 for additional information regarding compliance with Rule 4.05.9(7)(a thru e). All embankments, impoundments, and associated structures will be revegetated if construction materials are conducive to plant growth. If not, rock or gravel will be used on the embankments. The quarterly routine inspections of these structures will be conducted as required by Rule 4.05.9(17) if and until a waiver is granted to allow for annual inspections of these structures in the future. As per Rule 4.05.9(14) requirements, inspections performed during and after construction of these structures will be performed by a qualified registered professional engineer or other qualified professional specialist under the direction of a professional engineer. The inspections will be made regularly during construction, at completion of construction, and at least annually (quarterly until such a time as annual inspections are requested from granted by DRMS) until removal of the structure or release of the performance bond. The qualified registered professional engineer shall provide the Division with a certified report that the impoundment has been constructed and /or maintained as designed, and in accordance with the approved plan and the applicable regulations. As per Rule 4.05.9(15), certified inspection reports shall include discussion of: 1) Any appearance of erosion, instability, structural weakness or other hazardous conditions; 2) Existing and required monitoring procedures and instrumentation; 3) The depth and elevation of any impounded waters at the time of the certified report; 4) Existing storage capacity of the impoundment; and 5) Any other aspects of the structure affecting stability, or requiring maintenance. Colowyo will maintain a copy of each certified report at the mine site. Colowyo successfully demonstrated that failure of small impoundments would not create a threat to public health and safety or threaten significant environmental harm. A written safety demonstration completed by a professional engineer is located in Exhibit 7, Item 11 of the existing permit document in accordance with rule 4.05.9(18)(b). None of the small post- mining impoundments act as primary sediment control structure for a particular area; they are all constructed in reclaimed areas of the mine to enhance the approved postmining land use; they are all under two -acre feet. All impoundments will be maintained according to the specifications set forth in this part. Maintenance for impoundments may include (if necessary) mowing and cutting of excess vegetative growth for the purpose of facilitating inspections and repairs including keeping ditches, culverts, spillways, and other outflow structures free of debris. All combustible material, other than mulch or other material needed for erosion control and surface stability (vegetative growth) will be removed. Collom — Rule 4, Page l l Revision Date: 9/28/11 Revision No.: PR -03