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INTEROFFICE MEMORANDUM <br />Date: 02 July 2014 <br />To: Susan L. Burgmaier, Lead Specialist <br />From: Marcia L. Talvitie, P.E. <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. 3 — Engineering and Geotechnical <br />I have conducted a review of the TR -84 adequacy response dated 12- Jun -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 01/07 and 03/06/2014 adequacy comments that had yet to be satisfactorily addressed are <br />repeated below. For ease of comparison, the numbering used in the Division's adequacy <br />review letters to BRL is provided in parentheses, in bold font (XX). My new comments are <br />italicized. <br />Volume XI: <br />Note: In the Jun -2014 response, the earlier TR -84 analyses prepared by Buckhorn were <br />replaced by a June 11, 2014 "Stability Evaluation — Gob Pile #3" prepared by Huddleston- <br />Berry Engineering & Testing, LLC (HBET). <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 4t" 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 />Please address the requirements of 4.10.4(2) (minimum static FoS of 1.5) for this <br />proposed reconfiguration of CMWDA #3. Based on previous stability analyses <br />