2010-03-11_REVISION - C1981019 - Laserfiche WebLink

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analyses shall be performed in accordance with 2.05.3(6)(b), (c) and (d) to determine the size of the rock toe buttresses and keyway cuts". Paragraph (10) contains no language that would limit these requirements to "final" slopes. Since the temporary fill outslope proposed for the East Taylor valley fill is 2.5h: Iv, which is steeper than 2.8h: Iv, please address the keyway cut/rock toe buttress requirements of Rule 4.09.1(10), revising the October 2009 study and permit documents as appropriate. 25. A bedrock buttress is depicted at the southeastern toe of Section D-D' in the October 2009 Shannon and Wilson Study and on Map 45. The mass was incorporated into the stability analysis for this section, but no dimensions are presented on the height, slope, and length of this structure. Please modify the October 2009 Shannon and Wilson Study to include the design details, and modify the plan and D-D' cross-sectional views of Map 45 to include the location and dimensions of the bedrock toe buttress. Rule 4.14 - Backfilling and Grading 26. With the approval of Permit Revision 02, the Division approved a variance from AOC for steep slope mining for the South Taylor Pit. This variance allowed a decrease in the elevation of the backfilled areas as well as a decrease in the slopes of the associated backfilled areas. The overall post-mining topography kept the pre-mining watershed boundaries intact. With the submittal of TR-81, Colowyo has proposed to increase the amount of permanent, out-of-pit spoil by approximately 10 million cubic yards AND decrease the swell factor. This will lead to a further overall decrease in the post-mining topography of the South Taylor Pit by more than six feet, on average, over the entire pit area of approximately 960 acres. Rule 4.14.2(d) states that "(b)ox cut spoil or initial cut spoil may not be permanently disposed of outside of the mined area unless the applicant demonstrates that such material is not required to achieve approximate original contour of the area in accordance with Rule 4.09.1" (emphasis added). While the Division did approve the currently approved permanent, out-of-pit spoil piles in PR-02, with TR-81 Colowyo is requesting the Division to approve a further variance (decrease) in AOC, although such a variance is not specifically requested in the revision. Based on the Division's review of the currently approved Map 19B - Post-Mining Topography-South Taylor Area and the proposed Map 19B, there do not appear to be any changes to the post-mining topography in the South Taylor Pit. The only changes noted on the proposed Map 19B are to the East and West Taylor Fills. Pursuant to Rule 4.09.2(d), please provide the Division with documentation and justification why the additional 10 million cubic yards of material proposed for the South Taylor Fills will not be needed to meet AOC. The Division cannot make a finding to approve further decreasing the final topography of the South Taylor Pit by an average of five feet (up to 17 feet with the change in swell), over the entire pit area while approving an increase in the volumes of the East and West Taylor permanent fills. 27. In question 3 the Division details the decrease.in the amount of available spoil material due to the decrease in the swell factor from 20% to 15%. Since a majority of the South Taylor Operation will be a truck/shovel operation, this decrease will be amplified as mining progresses from the box-cut area to the east. The Division believes that this