2010-03-11_REVISION - C1981019 - Laserfiche WebLink

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19. A review of the proposed cross-sections provided on Maps 20, 20A and 20B show the following changes: a. Map 20, Section B-B' - TR-81 is proposing a change from Station 15000 to 17000 - lowering the post-mining topography (PMT) by up to 180 feet. b. Map 20A, Section E-E' - TR-81 is proposing a change from Station 15500 to 18000+, lowering the PMT by up to 180 feet. c. Map 20B, Section A-A' - The PMT in the eastern (right-hand) portion of this section is below the pre-mine elevations, but higher in the west. d. Map 20B, Section B-B' - The extent and steepness of the permanent valley (West) fill (Station 0+00 to 20+), are dramatically different that what was previously proposed and approved. e. Map 20B, Section C-C' - The extent and steepness of the permanent valley (East) fill have changed only slightly with TR-81, as has the PMT. However, the PMT (proposed and previously approved) is more than 200 feet lower in elevation than the pre-mining topography was. f. Map 20B, Section D-D' - The PMT from Station 40+00 to 82+00 is substantially higher than what existed pre-mining (no change proposed with TR-81). This configuration (increasing the backfill elevation above the mined-out area) seems preferable to increasing the size of valley fills. g. Map 20B, Section E-E' - The PMT across the pit is up to 200 lower lower than the pre-mining topography. No changes are proposed with TR-81. These decreases in the currently approved post-mining topography are exactly what the Division is concerned about with Colowyo's proposal to increase the volume in the South Taylor Fills by 10.3 million cubic yards. This concern has addressed in several of the TR-81 adequacy questions (questions 2, 3, 26 and 27). Please review the currently approved post-mining topography map, Map 19B, as well as their respective cross- sections, Maps 20, 20A and 20B, and explain how the changes discussed above are acceptable within Colowyo's currently approved variance from AOC for steep slope mining for the South Taylor Pit and explain how these changes meet the definition of AOC. 20. The final configuration for the East Taylor Fill, as shown on Map 41A - Watershed Boundaries for Hydrologic Modeling, shows that the upper (southern) portion of the fill will be a large, flat area. This flat area will cover approximately 110 acres. Pursuant to Rule 4.09.2(7), please describe how Colowyo plans to divert the runoff from this large, flat area of the pile into stabilized ditches which will safely pass the 100-year, 24-hour storm event. Please include this description in the text under Rule 4.09 - Disposal of Excess Spoil, which begins on Page 20 (South Taylor/Lower Wilson-Rule 4, Page 20) in Volume 12. 21. The final configuration for the West Taylor Fill, as shown on Map 41A - Watershed Boundaries for Hydrologic Modeling, shows that the middle portion of the fill will be a