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Susan Burgmaier <br />C- 1996 -083 TR -84 PAR <br />07- Jan -2014 <br />Page 3 of 5 <br />this modification, BRL has submitted a new Stability Analysis, prepared by Buckhom Geotech <br />and dated 15- Oct -2013. The new analysis incorporates updated Material Properties for the coal <br />mine waste and the native foundation material. The new properties (Mohr - Coulomb phi and unit <br />weight) for the CMW reflect additional testing that has been performed on material from the coal <br />preparation plant. <br />1. Buckhom's analysis determines that the pile configuration proposed under TR -84 will <br />provide a long -term static Factor of Safety (FoS) of 1.5, in accordance with Rule 4.09.1. <br />The report text does not specifically address Rule 4.10.4(2), which requires CMW banks <br />to have a minimum static FoS of 1.5 (not limited to the "long- term" condition). Previous <br />studies prepared by Buckhorn for the Bowie No. 2 Mine (for TR -44, TR-45, TR -56, TR- <br />64, etc.) have considered the effects of pore pressure, and evaluated total stress, not only <br />effective stress when determining the critical FoS. The TR -45 Buckhorn analysis dated <br />29- Mar -2007 evaluated a number of vile geometries, as tabulated on Page 14 of that <br />report. For "Cross Section A ", the 2" and 41h entries give Total Stress Analysis FoS of <br />1.46 and 1.44, respectively, for block failure. (The 2 "d entry, 2.5h:1 V, with a pile height <br />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 43. Based on previous stability analyses <br />performed, this will include a consideration of the dissipation of pore pressures, if any, as <br />the CMW is dewatered, over time. <br />2. Section 6.0 of the TR -45 (29- Mar -2007) Buckhorn report provides a list of seven <br />recommendations "to fulfill assumptions made in our evaluation and to ensure an <br />adequate safety margin for the gob pile ". Item 6 states, in part: "Gob must be placed at, <br />or slightly below its optimum moisture content. Gob placed significantly above the <br />optimum moisture content likely will not achieve adequate compaction or undrained <br />shear strength." Item 7 follows with, "We also recommend implementation of a moisture <br />content specification allowing moisture contents no greater than 4% above the optimum <br />moisture content." There does not appear to be a commitment by BRL in the text portion <br />of Volume XI to implement the moisture content recommendation. <br />Coal Mine Waste Bank reports are submitted by BRL on a quarterly basis. Included are <br />the results of any compaction tests conducted on CMW placed during the quarter. The <br />Division observes that the moisture contents (MC) for approximately 25% of the tests <br />exceed the optimum MC by more than 4 %. For the first three quarters of 2013, the MC <br />averages 2.2% greater than optimum. (These numbers reflect a significant improvement <br />over 2012 results, when the average MC was 4% above optimum, and 40% of the tests <br />were >4% above optimum.) Even. with MCs that are slightly high, BRL has been <br />successful in achieving the minimum recommended 90% compaction level 97% of the <br />time in 2013. <br />Please review the Recommendations made by Buckhorn in 2007, in light of the CMW <br />compaction and moisture content results obtained, to date. The Rules specify only that <br />compaction must be achieved, and do not specifically address the moisture content of the <br />CMW. It is unclear whether Buckhorn's MC recommendations constitute a permit <br />