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Z, <br />r. Rob Zuber <br />my 7.2014 <br />Page 3 <br />Design Depth = 0.75(maximum depth) + 0.25(minimum depth) <br />�sue 4: Please elaborate on the rational, for this assumption or provide a source for this <br />equation. <br />Response: The source for determining a Design Depth of Cover is a formula from a <br />presentation by Zipf, R.K. (2005) entitled "Ground Control Design for Highwall Mining', SME <br />Annual Meeting, Preprint 05 -82, pp.7, to define what an average overburden Depth of Cover is <br />��hen the overburden cover varies over a highwall mining panel. <br />Furthermore. the Mine Safety and Health Administration (MSHA) has required that this formula <br />be used to determine a single value for the Design Depth of Cover for each individual Highwall <br />Miner Panel. The Design Depth of Cover value is then used in conjunction with highest mining <br />height anticipated to be mined in each individual Panel to determine the Web and Barrier Pillar <br />dimensions for each Panel. <br />Also included with this adequacy response package are the revised materials and a <br />change of index sheet to ease incorporation into the permit document. If you should have any <br />additional questions or concerns, please feel free to contact "Tony "Tennyson at (303) 254 -1232. <br />Sincerely, <br />Barbara A. Walz <br />Senior Vice President` <br />Policy & Compliance/ <br />Chief Compliance Officer <br />BAW:TT:pvt <br />Enclosure <br />cc: Kurtis Blunt (via email) <br />Chris Gilbreath (via email) <br />Tony Tennyson (via email) <br />AN EQUAL OPPORTUNITY / AFFIRMATIVE ACTION EMPLOYER <br />A T mdi,tonr Ener;;v'C q,erttn e t <br />