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"' SHANNON 6 WILSON, INC. <br />•� QEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS <br />October 21, 2009 <br />Revised April 15, 2010 <br />KCCC — Colowyo Coal Company <br />Colowyo Coal Mine <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />Attn: Mr. Tay Tonozzi <br />FLORIDA <br />MISSOURI <br />OREGON <br />WASHINGTON <br />RE: REVISED <br />ADDENDUM NO.3 TO GEOTECHNICAL STUDY FOR EXCESS SPOIL <br />TEMPORARY SPOIL FILL STABILITY <br />SOUTH TAYLOR MINE AREA, COLOWYO MINE <br />MOFFAT AND RIO BLANCO COUNTIES, COLORADO <br />• This document presents our revised Addendum No. 3 to our report "Geotechnical Study, South <br />Taylor Excess Spoil Fills, Rio Tinto Energy America, Colowyo Coal Mine, Job No. 23 -1- <br />01105 -200, dated July 2006. This addendum addresses comments from a review of our reports <br />by the Colorado Division of Reclamation, Mining and Safety (DRMS). With respect to <br />selection of shear strength parameters, stability analysis and recommendations, and comments <br />regarding highwall mining, this revised addendum supercedes the previous Addendum No. 3 <br />.and our 2006 report. <br />The revisions encompassed the following: <br />1 The figures and appendix have been re- designated to be sequential with respect to the <br />2006 report. <br />2 Figure 10 — Temporary Spoil Fill Locations has been revised to match Map 45, TR -81, <br />revised April 7, 2010. <br />3 Figure I I — Analysis Sections has been revised to show the current proposed slopes. <br />The current proposed slopes are about equal to, or slightly flatter than, the slopes on <br />1060 BANNOCK STREET, SUITE 200 <br />DENVER, COLORADO 80204 <br />PHONE 303 ®825 ®3800 <br />FAX 303 ®825 ®3801 <br />—• <br />Exhibit 21, Item 1 Revision Date: 12/06/10 <br />Addendum No. 3- 1 Revision No.: rR -Rl <br />