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RULE 4 PERFORMANCE STANDARDS <br /> <br />Collom – Rule 4, Page 15 Revision Date: 6/20/22 <br /> Revision No.: TR-154 <br />mine topography shown on Map 19C. The final configuration of the fill is designed to minimize erosion. <br />The final outslope will not exceed 3h:1v. A geotechnical evaluation of the stability of the permanent out <br />of pit excess overburden is provided in Volume 20 Exhibt 23, Item 3. <br /> <br />Two terrace ditches will be constructed on the face of the Little Collom Valley Fill. Please refer to <br />Volume 18B Exhibit 7, Iem 23, Part I for the location and design configuration of the terrace ditches. <br />Both terrace ditches will be backsloped to direct runoff against the face to prevent flows from <br />overflowing the edge of the ditch. These terrace ditches will direct surface runoff perpendicular to the <br />face into a permanent drainage channel designed to pass safely the runoff from a 100-year, 24 hour <br />precipitation event. <br />CONSTRUCTION PLAN <br />All available topsoil will be removed for the Little Collom Valley Fill and either stockpiled for later use <br />or direct hauled to a reclaimed area. <br />The Little Collom Valley Fill drain has been constructed to the design configuations (not locations) <br />presented in Volume 20 Exhibit 23, Item 1. Given the smaller footprint of the temporary and final out of <br />pit stockpile materials than is shown in Volume 20 Exhibit 23, Item 1, Figure 4.09-1 presents the adjusted <br />location of the constructed rock drain and the as constructed dimensions of the drain under the Little <br />Collom Valley Fill. The rock drain was constructed as follows. <br />Prior to overburden placement, an 820 feet long by 24 feet wide rock drain was constructed. This rock <br />drain was constructed from large sandstone rock sorted on-site from existing excess spoil areas, and the <br />sorted rock was placed with loaders and dozers. Once the rock drain was completed, excess spoil was <br />placed over the rock drain, rising in approximately 50-foot-high lifts until reaching a final height of 130 <br />feet above the valley floor at the north edge of the rock drain. <br />North of the constructed rock drain, natural dump sorting was used to create the remaining excess spoil <br />rock drain. When material is placed at heights over 100 feet, the larger boulders and rock roll down the <br />slope effectively sorting the material and making a natural drain at the toe of the spoil. This method has <br />been implmented at Colowyo for many years and is further described in Volume 20 Exhibit 23 Item 1 <br />report. This report states in Section 8.2, β€œIn our opinion, a drain extending the full distance from the <br />downstream toe to the upstream toe is not required, particularly for a temporary spoil fill. Our experience <br />and observations indicate that the spoil and placement methods at Colowyo produce a relatively free <br />draining layer at the base of each lift of spoil.” Once a suitable height that allowed for natural dump <br />sorting was achieved, the Little Collom Valley Fill construction progressed towards the northern limits of <br />its overall footprint. <br />INSPECTION PLAN <br />During construction of the Little Collom Valley Fill, Colowyo will provide certified reports as required <br />by Rule 4.09.1(11). Inspections will be conducted at quarterly during the construction period, final <br />grading, and revegetation. <br /> <br />Each inspection report will be provided to the Division within two weeks after the end of each quarter of <br />the year, and the report will be certified by a professional engineer. Each report will certify that the fill <br />has been constructed as specified in the minimum design approved by the Division. The reports will <br />include a description of any appearances of instability, structural weakness and other hazardous <br />conditions observed during the inspection.