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STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />COLORADO <br />Denver, Colorado 80203 <br />D I V I S [ O N O F <br />F <br />Phone: (303) 866 -3567 <br />RECLAMATION <br />FAX: (303)832 -$10b <br />INTEROFFICE MEMORANDUM <br />MINING — <br />SSAFETY <br />Date: <br />21 February 2014 <br />Go a oHickenlooper <br />To: <br />Susan L. Burgmaier, Lead Specialist <br />Mike King <br />Executive Director <br />From: <br />Marcia L. Talvitie, P.E. 11W <br />Loretta E. Pineda <br />Director <br />Subject: <br />Bowie No. 2 Mine — Permit No. C -1996 -083 <br />TR -85 — CMWDA #2 Drying Area <br />Geotechnical Adequacy Review No. 2 <br />Bowie Resources, LLC (BRL), through the office of J.E. Stover and Associates, has submitted a response <br />to the Division's preliminary adequacy review of the TR -85 application. In addition to a cover letter, <br />BRL's package includes revised pages 12, 13, 14, 14a, 19, and Figure 1, all from Volume IX. A response <br />letter from Buckhorn Geotech, dated 04- Feb -2014, has also been provided. <br />I have reviewed BRL's response package; some issues remain to be addressed. The adequacy items I <br />listed in my 09- Jan -2014 review memo to you have been renumbered below to correspond to those <br />used in the Division's 16- Jan -2014 adequacy review sent to BRL. <br />Adequacy Comments <br />1. Buckhorn has responded that a compacted coal mine waste wet density of 104.6 pcf will be <br />used for stability analyses. This item has been addressed. <br />2. MILT 01/09: The second bullet of Buckhorn's Assumptions section reads, "No phreatic surface <br />was modeled in either the gob or native material which is consistent with our analyses of pile #2 <br />to date." The Division's review of Buckhorn's earlier CMWDA #2 analyses found that the 22 -Sep- <br />2008 study did consider a phreatic surface based on pore pressure measurements and also <br />conducted a sensitivity analysis using an increased phreatic surface. In that study, block failure <br />as well as circular failure was considered. <br />Buckhorn's Summary of Instrumentation Monitoring for the 3rd Quarter 2013 includes data for a <br />series of Vibrating Wire Piezometers (VWPs) that have been installed in CMWDA #2 and are read <br />on a quarterly basis. VWP -06 and -08 are located in the general vicinity of the proposed Drying <br />Area, and continue to show somewhat elevated pore pressures, in the range of 14 to 16 psi. <br />These values stand in sharp contrast to the 1 to 3 psi reported for VWP -05, -09 and -10 which <br />are installed near the toe of the pile. <br />a) MLT 01/09: Given the fact that pore pressures in the upper portion of CMWDA #2 have <br />not yet diminished, please expand the stability analysis to address the effects (if any) of <br />the proposed Drying Area on the pile as a whole, using the approved outslope <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines <br />