2023-01-05_PERMIT FILE - C1981019 (13)

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RULE 4 PERFORMANCE STANDARDS South Taylor/Lower Wilson – Rule 4, Page 8 Revision Date: 11/23/21 Revision No.: TR-152 Designed terrace ditches will be constructed at approximately 100 foot vertical increments. Terrace ditches will be backsloped to direct runoff against the face to prevent flows from overflowing the edge of the ditch. These terrace ditches will direct surface runoff perpendicular to the face into a permanent drainage channel designed to pass safely the runoff from a 100 year, 24 hour precipitation event. Terrace ditches are shown on Map 12 and design information is provided in Exhibit 7, Item 20, Parts A and B. Reclamation, specifically topsoil replacement, seeding etc. will be implemented consistent with the Section 2.05 of the permit. CONSTRUCTION PLAN All available topsoil will be removed and either stockpiled for later use or direct haul replaced to a reclaimed area. Due to the fact that the valley fill locations are in close proximity to the initial boxcut area means the entire footprint of these fills must be stripped of topsoil. As described in further detail in this submittal under Section 2.05.3(1); “The entire seam sequence from the top overburden through to the bottom G8 seam, which resides in the area of the initial boxcut, will be placed in the valley fill locations; this will allow Colowyo enough spoil room to reach the desired mining depth.” It is anticipated the valley fill drains and associated lateral drains will be constructed as one project during the first two years of operation in the South Taylor operation for practical purposes and as a necessary step in preparation of the area for full scale mining. Channels constructed along the outside of the valley fills (perimeter relief drains) will be built immediately after the logical completion of each terrace ditch across the faces of the fills, which obviously cannot be completed until such a time as the fills themselves develop and are constructed to meet PMT compliance. This activity will be logically sequential in that they will be developed from the bottom up. Colowyo will follow the Shannon & Wilson recommendation for excavation as described in Exhibit 21. A controlled underdrain in accordance with the Shannon & Wilson recommendations will be placed in the natural drainage bottom from the head to the top of the fill, The harder, available sandstones obtained from the mining operation will be selectively handled and placed in at least a 24 foot wide by 8 foot high configuration to serve as the underdrain before covered by spoil material. The natural spoil sorting which will occur by utilizing the thicker lifts recommended by Shannon & Wilson will be sufficient to protect the drain from clogging above the geotextile fabric. Lift thicknesses up to 100 feet thick is acceptable and will be utilized to construct the fill. This method of spoil placement also enhances the construction of a free draining layer of spoil material at the base of the fill. Experience at Colowyo provides evidence that the natural sorting process which occurs while dumping in higher lifts is sufficient to create this drain. Inspection and documentation of this natural sorting is recommended and will be conducted by Colowyo. See the Inspection Plan section for additional details. INSPECTION PLAN During construction of the East Taylor and West Taylor Fills, Colowyo will provide the following information in certified reports as required by Rule 4.09.1(11).