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INTEROFFICE MEMORANDUM <br />Date: 06 December 2012 <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 -75 (Coal Mine Waste Disposal Area No. 4 As -Built Plans) <br />2"d Adequacy Review — Engineering /Geotechnical <br />I have conducted a review of the TR -75 adequacy response materials submitted by J.E. Stover <br />and Associates (Stover) on behalf of Bowie Resources, LLC (BRL) on Dec. 3, 2012. <br />Specifically, I have focused on the Buckhorn Geotech, Inc. (Buckhorn) memo dated November <br />20, 2012, which addresses my original adequacy comment related to Rule 4.10.4. <br />My October examination of the as -built topography provided with the TR -75 application <br />indicated that portions of CMWDA #4 were constructed with steeper slopes than what was <br />approved in the original design for the pile. On an attached map, I identified areas of the slope <br />that appeared to be between 2.0 H:1 V and 2.5 H:1 V, and other areas that were steeper than 2.0 <br />H:1 V. <br />Buckhorn has conducted a revised As -Built Stability Analysis, and determined that slopes as <br />steep as 2.0 H. I V will provide the required Minimum Factor of Safety of]. 5. However, in the <br />Conclusions section of*the memo, Buckhorn recommends, "that the areas highlighted in the <br />DRMS letter of October 31, 2012 be surveyed to confirm the slopes in those areas. Any areas <br />steeper than 2.0 H. •I V should be re- graded to achieve a slope with a minimum F.S. of 1.5 as <br />required " <br />I recommend that TR -75 not be approved until BRL has taken the actions recommended by <br />Buckhorn, i.e., survey the steeper portions of the pile to identify and re -grade any segments <br />steeper than 2.0 H.I V, in order to achieve the required factor of safety. This work should be <br />accomplished prior to the placement of cover material across those areas. <br />Please let me know if you have any questions. <br />cc: Sandy Brown, DRMS <br />