2010-03-29_REVISION - C1981019 (3)

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32. Colowyo submitted its proposed post-mining topography as Map 19C. The Division preliminarily reviewed the proposed PMT and has the following comments. Although a review of the PMT is not a completeness issue, the designs for the post- mining drainage channels required by Rule 4.05.4 will require an acceptable PMT. As such, the Division has the following comments. a. On the premining topography Map (Map 1813) there is an unnamed drainage in Section 26 that connects with Collom Gulch. Based on the topography, this drainage continues into Sections 35 and 2 (to the south), basically along profile A- A'. This drainage, however, is not highlighted as such on the premining topography map past Section 26. Additionally, this drainage has been removed from the post-mining topography. The removal of this drainage leaves a large area of reclamation that will have uncontrolled sheet flow over it. Please redesign the post-mining topography to replace this drainage. Colowyo Response: The post-mining topography has been redesigned to show the unnamed drainage in section 35 and section 2 similar to the pre-mine topography drainage in this area. With the above changes in the Postmining topography, Map 19C has been included with this submittal. Also Map 20C is being resubmitted because the post- mining profiles changed. b. In the far northeast corner of Section 35 (basically on the "B" of profile B-B') there is an extremely steep portion of the reconstructed Little Collom Gulch drainage (approximately a 1:1 slope). There are other portions of the reconstructed Little Collom Gulch drainage that appear to be virtually flat. Please fix these portions of the Little Collom Gulch drainage to ensure a stable landform. Colowyo Response: The post-mining topography has been redesigned in the far northeast corner of section 35 in the Little Collom Gulch drainage. A profile of the Little Collom drainage was built through the entire drainage from the North Postmining Tie-In to the South Postmining Tie-In. All steep portions of the post-mining topography that appeared on the profile were redesigned to ensure a stable landform. c. The areas to the east and west of the Little Collom Gulch drainage that will be flowing into it (basically along profile lines B-B' and F-F) appear to be too steep to remain stable (approximately 40% slopes). Please review this portion of the post-mining topography and revise as necessary. Colowyo Response: The post-mining topography has been redesigned on the areas East and West of the Little Collom drainage. Cross sections were made through the entire drainage on 500 foot intervals from the North Postmining Tie-In to the South Postmining Tie-In. All sections were reviewed and any identified slopes steeper than 311:1 V were redesigned. Colowyo Mine C-1981-019 page 13 of 16 25 March 2010 Permit Revision 03 - Collom Permit Expansion