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C-1981-019 TR-81 <br />14 July 2010 <br />AR#2 - mlt <br />Page 4 of 6 <br />This observation was made in comparing the original TR-81 Map 20B with the currently- <br />approved Map 20B (via PR-02 in May 2007). <br />d) Map 20B, Section B-B' - The extent and steepness of the permanent valley (West) fill <br />(Station 0+00 to 20+), are dramatically different that what was previously proposed and <br />approved. <br />The Division agrees with Colowyo's response. <br />e) Map 20B, Section C-C' - The extent and steepness of the permanent valley (East) fill have <br />changed only slightly with TR-81, as has the PMT. However, the PMT (proposed and <br />previously approved) is more than 200' lower in elevation than the pre-mining topo was. <br />As with item c), above, this observation was made in comparing the TR-81 submittal with <br />the Map 20B approved under PR-02. The Division was not mistakenly addressing South <br />Taylor sections. <br />f) Map 20B, Section D-D' - The PMT from Station 40+00 to 82+00 is substantially higher than <br />what existed pre-mining (no change proposed with TR-81). This configuration (increasing <br />the backfill elevation above the mined-out area) seems preferable to increasing the size of <br />valley fills. <br />This is a moot point. <br />g) Map 20B, Section E-E' - The PMT across the pit is up to 200' lower than the pre-mining <br />topo. No changes are proposed with TR-81. <br />Please refer to the Division's comments for items c) and e), above. <br />2.?) The original Jul-2006 S&W Study concluded that no rock toe buttresses or key-way cuts are <br />required for the South Taylor valley fills. Section 4.09.1(10) requires that, "where the slope in <br />the disposal area is steeper than 2.8h:1v... keyway cuts or rock toe buttresses shall be <br />constructed to stabilize the fill. Where the toe of the spoil rests on a downslope, stability <br />analyses shall be performed in accordance with 2.05.3(6)(b), (c) and (d) to determine the size of <br />the rock toe buttresses and keyway cuts. Paragraph (10) contains no language that would limit <br />these requirements to "final" slopes. The temporary fill outslope proposed for the East Taylor <br />valley fill is 2.5h: Iv, which is steeper than 2.8h:ly. Please address the keyway cut / rock toe <br />buttress requirements of Rule 4.09.1(10), revising the Oct-2009 study and permit documents as <br />appropriate. <br />As Colowyo states, this item was addressed in April 2010 correspondence between Marcia L. <br />Talvitie, P.E. and Colowyo. Rock toe buttresses or keyways are not required at this location. <br />This item is resolved; no additional response is required. <br />25(9) . A bedrock buttress is depicted at the southeastern toe of Section D-D' in the Oct-2009 S&W <br />Study and on Map 45. The mass was incorporated into the stability analysis for this section, but <br />no dimensions are presented on the height, slope, and length of this structure. Please modify the <br />Oct-2009 S&W Study to include the design details, and modify the plan and D-D' cross-sectional <br />views of Map 45 to include the location and dimensions of the bedrock toe buttress. <br />Colowyo has responded that because the toe buttress is existing ground, and not a buttress, no <br />change has been made as a result of the Division's question. The Division's question may <br />have been confusing. What the Division intended to ask was whether certain dimensions of