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INTEROFFICE MEMORANDUM <br />Date: 06 March 2014 <br />To: Susan L. Burgmaier, Lead Specialist <br />From: Marcia L. Talvitie, P.E. ` W--R <br />Subject: Bowie No. 2 Mine — Permit No. C -1996 -083 <br />TR -84— Reconfigure Coal Mine Waste Disposal Area No. 3 (Gob Pile #3) <br />Adequacy Review No. 2 — Engineering and Geotechnical <br />I have conducted a review of the TR -84 adequacy response dated 07- Feb -2014 and submitted <br />by J. E. Stover and Associates (Stover) on behalf of the operator, Bowie Resources, LLC (BRL). <br />TR -84 proposes to increase the capacity of Coal Mine Waste Disposal Area No. 3 (CMWDA #3) <br />by steepening the slopes of the pile to 2.5h:1v (the permit approves currently slopes of 3h:1v). <br />My original 07- Jan -2014 adequacy comments are repeated below. For ease of comparison, the <br />numbering used in the 16- Jan -2014 letter to BRL is provided in parentheses, in bold font (XX). <br />have created two new adequacy items at the end of the Volume XI section. <br />Volume XI: <br />The adequacy response package included revised Vol. IX pages xvi, 2, 3, 4, 5, and 9; a letter <br />from Buckhorn dated Jan. 28, 2104 (typo); and Figure 1. Rather than placing a series of <br />stability analysis letters into the permit for this revision, a single, comprehensive document <br />should be prepared which thoroughly addresses the final approved configuration of <br />CMWDA #3 (a similar request has been made for TR -85). <br />1 (32) MLT 01/07: Buckhorn's analysis determines that the pile configuration proposed under <br />TR -84 will provide a long -term static Factor of Safety (FoS) of 1.5, in accordance with <br />Rule 4.09.1. The report text does not specifically address Rule 4.10.4(2), which requires <br />CMW banks to have a minimum static FoS of 1.5 (not limited to the "long- term" <br />condition). Previous studies prepared by Buckhorn for the Bowie No. 2 Mine (for TR -44, <br />TR -45, TR -56, TR -64, etc.) have considered the effects of pore pressure, and evaluated <br />total stress, not only effective stress when determining the critical FoS. The TR -45 <br />Buckhorn analysis dated 29- Mar -2007 evaluated a number of pile geometries, as <br />tabulated on Page 14 of that report. For "Cross Section A ", the 2nd and 4th entries give <br />Total Stress Analysis FoSs of 1.46 and 1.44, respectively, for block failure. (The 2nd entry, <br />2.5h:1V, with a pile height of 100', is very similar to what is now being proposed.) <br />