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Prospect Ditch, Sta. 0 to 15 pg. Exh. 7-14R-31 <br />Prospect Ditch above Sta 15 pg. Exh. 7-14R-25 <br />N. Trib. E. Pit Ditch Sta 0 to 35 pg. Exh. 7-14R-35 <br />N. Trib. E. Pit Ditch above Sta 35 pg. Exh. 7-14R-126/127, and <br />Final East Pit Ditch pg. Exh. 7-14R-120 <br />We also observed that an "intentionally left blank" page Exh. 7-14R-12 was needed, <br />and it is being supplied herewith. <br />Rule 4.05.9-4mpoundments <br />.0-'On the 7 November 2010 "Change Sheet for Permit Revisions, Technical Revisions <br />and Minor Revisions", page 2, Colowyo shows that Pages 7-14H-1 through 53 should be <br />deleted and replaced only with page 7-14H-1. Colowyo is proposing to delete Appendix <br />Exh7-141-1- Generalized Ditch Design Procedures, Permanent Channels, July 2006 in its <br />entirety and replace it with only a cover page denoting the appendix removal. While <br />Colowyo does provide new Exhibit 7, Item 14, Part R- East Pit Reclamation Sequencing <br />and Ditch Designs for Prospect Ditch, North Tributary East Pit Ditch and Final East Pit <br />Ditch, the removal of Appendix Exh7-14H removes all of the generalized ditch designs that <br />were used to design the permanent post-mining drainage channels in the West Pit. <br />Colowyo must retain Appendix Exh7-14H, as it is still required for, at a minimum, the <br />Taylor Tributary Ditch, the Taylor Ditch, the East Taylor Ditch and the West Pit Ditch. <br />Please update the Change Sheet to reflect inclusion of this portion of Exhibit 7. <br />Colowyo's Response: <br />With respect to the inclusion or deletion of Appendix H, that exhibit previously <br />provided a series of generic ditch design charts which spanned the expected flows <br />and gradients of any conceivable ditch design for Colowyo. At the request of <br />CDRMS (Kent Gorham), Colowyo abandoned that approach and deleted Exhibit 7- <br />14H in TR-87. Instead, selection of riprap sizes is now based on case specific <br />SEDCAD modeling, and discussion is provided in the introductory text for each ditch <br />in TR-87. 'The same approach was applied in the recently submitted TR-81 for the <br />four ditches mentioned in this comment. We believe there are no longer any ditches <br />that rely on Exh. 7-14H for riprap sizing. Although it could be re-instated, we <br />recommend that Exh. 7-14H remain deleted to avoid confusion on the current <br />methodology (SEDCAD, OSM/Simons) for selecting riprap sizes. <br />In particular, case specific riprap sizing text based on SEDCAD modeling is now <br />presented in the introductory text in the most recent TR-81 submittal for Taylor <br />Tributary Ditch, Taylor Ditch and East Taylor Ditch. The West Pit Ditch has been <br />deleted from the mine plan under TR-81 as it is no longer needed with the more <br />northerly location of the East Taylor Fill. With respect to the ditches specifically <br />mentioned in this comment, Colowyo believes that is best handled in the review of <br />the recent submittal for TR-81. <br />Colowyo Coal Company, L.P. • 5731 State Highway 13 • Meeker, CO 81641 <br />T + 1 970 824 1578 • F +1 970 824 1598 • http://prospect.riotinto.org/irj/portal