2011-02-02_REVISION - C1981019 - Laserfiche WebLink

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Rule 4.05.4- Stream Channel Diversions and Stream Channel Reconstruction 4. The narrative on revised page Exh.7-14R-3 discusses the use and design of temporary ditches to divert runoff from spoil and reclaimed areas to the unreclaimed East Pit. These temporary ditches result in areas that are excluded from producing runoff in the SEDCAD modeling for the Prospect Pond. The text narrative references Figure Exh. 7- 14R-7 and states that the ditches are "short term in nature and will be removed as reclamation progresses." Figure Exh.7-14R-7 shows one of the ditches extending a significant distance northeast into previously reclaimed areas. Please explain in more detail in the narrative on revised page Exh.7-14R-3 how and when these ditches will be constructed and used and when each ditch will be removed or reclaimed. Colowyo's Response: After conferring with the Division is was decided that this comment was superfluous, as these additions were made in the text of Exh. 7-14 R-4. 5. Currently approved permit page Exh.7-14D2 (revised 25 July 2006, TR-63) shows the approved design information for the Final East Pit Ditch and the Prospect Ditch permanent channels. Proposed SEDCAD design runs for the 10-year, 24-hour storm event for the Prospect Pond result in new design information for the Final East Pit Ditch and Prospect Ditch that would appear to supersede the currently approved information on page Exh.7- 14D2. Please review the designs for the Final East Pit Ditch and the Prospect Ditch and submit new permanent channel design information that is consistent with the SEDCAD modeling submitted with Technical Revision 87 for these two ditches. Colowyo's Response: The ditch design information for the Final East Pit Ditch and the Prospect Ditch, which were formerly described in Exh. 7-14D but pursuant to TR-87 are now described in Exh. 7-14R, appear in the new rows dealing with Exh. 7-14R at the bottom of Table 1 on pages 7-14-5 through 7-14-7 of the introductory text of Exhibit 7, Item 14. The specific design data for the two ditches in Comment No. 5 appears on the final page of that table, that is, page Exh. 7-14-7, along with ditch design data for the North Tributary East Pit Ditch which also is described in the new appendix Exh. 7-14-R. While the critical flow conditions for these ditches are all included in the SEDCAD modeling, locating them requires a detailed and comprehensive study of the networking, and is further complicated by the fact that several modeling time frames were examined (2010, 2012 and 2017). As discussed on page Exh. 7-14R-2, it was found that the critical time frame for some of the ditch reaches was 2010 while for others it was 2017. To aid in review of the submittal, the flows, channel slopes, and rip-rap sizing requirements that appear in the new Exh. 7-14R rows of Exhibit 7, Item 14 Table 1 "Summary of Ditch and Channel Design Parameters" can be found on the following pages of the SEDCAD modeling that was included in TR-87 in Exh. 7-14R: Colowyo Coal Company, L.P. - 5731 State Highway 13 - Meeker, CO 81641 T + 1 970 824 1578 - F +1 970 824 1598 - http://prospect.riotinto.org/irj/portal