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1(d). Amended Exhibits 12-2 and 20-2 were amended as requested. Item Resolved. <br />2. Operation plan narrative on amended page 6 was revised as requested. Item <br />Resolved. <br />Tab 12 text was amended as requested to clarify that various roads and ponds <br />depicted on Exhibit 20-2 are "proposed" as permanent and that required <br />demonstrations will be made to allow for approval of such roads and ponds as <br />permanent structures by the end of 2008. Item Resolved. <br />4. Requested clarificafion was provided regarding delineation of 180 day backfilling <br />and grading variance areas. Item Resolved. <br />The outdated exhibits were withdrawn as requested and associated text was <br />properly amended. Topsoil stockpiles are depicted on amended Exhibits 12-2 and <br />13-2. Item Resolved. <br />6. On the revised PMT map (Exhibit 20-2), the short steep segment associated with <br />the PM-2 valley headwall (noted in the Division's previous adequacy letter) is not <br />apparent; the slope over the same 200 foot segment is approximately 30%. The <br />steepest final reclamation slopes depicted on the amended PMT map appear to be <br />approximately 40% (final highwall slopes in the Sage Creek/Wolf Creek Block, <br />and in the Pond 017 watershed). The 40% maximum slope corresponds to the <br />worst case slope specified in the stability analysis provided in the amended <br />application. <br />However, we are concerned that the stability analysis does not apply to all the <br />actual field site conditions. Specifically, soil strength parameters for the stability <br />analysis were determined from tests on remolded samples compacted to 99% <br />maximum dry density or 105.5 pounds per cubic foot (pcf). Field densities (page <br />1 of the report) ranged from 91.5 to 112 pcf. Thus the analysis might be valid for <br />an average of field conditions, but does not identify factors of safety for the areas <br />of lower (in-place) soil densities. <br />The response indicates that some soil field densities were as low as 91.5 <br />pounds per cubic foot (pcf). Lower densities often result in lower soil <br />strengths. Please supplement the MHW Pit Backfill Stability Technical <br />Memo IIW Mine Area Routt County, Colorado of March 2005 (stability <br />report) with information on factors of safety determined for backfill placed <br />at a dry density of 91.5 pounds per cubic foot. <br />The above request applies to the situation where the backfill has already <br />been placed. For areas of planned future backfill placement, the stability <br />analysis report should include an identification of the compaction test <br />procedure used, and include the associated density versus moisture curve. <br />4 <br />