2010-03-11_REVISION - C1981019 - Laserfiche WebLink

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reclamation at Colowyo are proposed in TR-81 (mainly the quantity and location of the temporary overburden stockpiles in the South Taylor Pit area, which is a large cost in the current estimate), the Division will not be able to propose a decision on the revision until the revised cost estimate is approved. Colowyo will need to submit the cost estimate for the changes that may be approved with this revision. Because the Division has a number of adequacy questions associated with TR-81, we defer the cost estimate until the issues are near resolution. Rule 4.05.4 - Stream Channel Reconstruction 10. Colowyo has proposed to modify several permanent post-mining drainage channels that will either divert water around or off of the East and West Taylor Fills. These drainage channels are the West Taylor West Tributary Ditch, the West Taylor East Tributary Ditch, the East Taylor West Tributary Ditch and the East Taylor East Tributary Ditch. Colowyo has provided SEDCAD modeling for these channels using the 10-year, 24-hour storm event. These channels are specifically designed to divert water off of and away from the fill. Pursuant to Rule 4.09.2(7), which states, in part, that surface water "... shall be diverted away from the fill and into stabilized diversion channels designed to pass safely the runoff from a 100-year, 24-hour precipitation event... (and) runoff from the fill surface shall be diverted to stabilized channels off the fill which will safely pass the runoff from a 100 year, 24-hour precipitation event..." Please resubmit the SEDCAD modeling for the West Taylor West Tributary Ditch, West Taylor East Tributary Ditch, East Taylor West Tributary Ditch and East Taylor East Tributary Ditch using the 100-year, 24-hour storm event as required by Rule 4.09.2(7). 11. Diversion of runoff off of the face of the fill resulting from the 100-year, 24-hour storm event is required pursuant to Rule 4.09.2(7). Colowyo has proposed two ditches to accomplish this for the East Taylor Fill. These two ditches are the East Taylor West Tributary Ditch and the East Taylor East Tributary Ditch. These ditches, however, do not extend the entire length of the East Taylor Fill and, therefore, do not convey all of the runoff off of or around the fill. Pursuant to Rule 4.09.2(7), please lengthen the East Taylor West Tributary Ditch and the East Taylor East Tributary Ditch to the beginning point (south) of the East Taylor Fill so they adequately divert water off of and around the East Taylor Fill. 12. As shown on Map 41A - Watershed Boundaries for Hydrological Modeling and Map 45 - South Taylor Fill, Colowyo proposes the use of terrace ditches both in the backfill above the West Taylor Fill and on both the East and West Taylor Fills to divert runoff off of and around the fills. Pursuant to Rule 4.09.2(7) these ditches must be properly sized and constructed to carry the runoff from a 100-year, 24-hour storm event. Colowyo does provide general design information for the terrace ditches in Exhibit 7, Item 20, Part G (in Volume 13). The introductory text of the exhibit states that "(a) series of terrace ditches will be constructed across the face of the permanent fills..." Based on the above referenced maps, Colowyo is also proposing additional terrace ditches above and on the West Taylor Fill that must be sized for the 100-year, 24-hour storm event as well. Please amend the text in Exhibit 7, Item 20, Part G to include a discussion of the terrace