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Interoffice Memorandum <br /> <br />through both temporary and permanent sections of the fill. Since the additional load of the proposed temporary excess <br />spoil fill has potential effects on the long-term stability of the currently approved permanent excess spoil pile, the <br />Division believes that Rule 4.09.1(7), regarding long-term static safety factor of 1.5, is applicable for this situation. <br />However, after further review, the Division finds that Colowyo has satisfied these rules by showing a long-term static <br />safety factor in excess of 1.8 using average test values attained from field samples. No additional comments are needed. <br />2) DRMS: Shannon &Wilson’s analysis does not address the fact that some of the proposed excess spoil would overlay <br />an area of highwall mining. Please address the potential impact of the additional load from the proposed excess spoil fill <br />on the excavated sections from highwall mining as well as the integrity of the proposed excess spoil fill. <br />Colowyo: In Exhibit 21, Item 1, Addendum No. 3-6, potential highwall mining impacts have been presented and approved <br />by the Division previously. Colowyo believes this section of the report addressing highwall mining in the vicinity of the <br />proposed spoil pile adequately addresses potential impacts from previously preformed highwall mining below the <br />permanent West Taylor Fill. <br />DRMS: Potential impacts on excess spoil piles from previously performed highwall mining have been adequately <br />addressed in Exhibit 21, Item 1, Addendum No. 3-6. No additional comments are needed. <br />This concludes my comments regarding Shannon & Wilson, Inc.’s (S&W) Addendum No. 4 as part of Colowyo’s proposed <br />TR-98. If you have any questions, feel free to contact me. <br />Sincerely, <br />Zach Trujillo <br /> <br />