2014-01-16_REVISION - C1996083 (2)

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Page 5 of 8 Please provide calculations or a Sedcad run for the 100 -yr event on Drainage Area D. (Rules 2.05.3(4)(a)(ii) and 4.10.3) 31. The proposed revision materials indicate that Watershed H will be enlarged, as shown on Map 20, and new designs for Ditches H1 and H2 are provided. There does not appear to be a revised design for Culvert H1 in the submittal. Please provide a revised design for Culvert H1, to reflect the proposed increased acreage of Watershed H. (Rule 2.05.3(4)(a)(ii)) 32. Buckhorn's analysis determines that the pile configuration proposed under TR -84 will provide a long -term static Factor of Safety (FoS) of 1.5, in accordance with Rule 4.09.1. The report text does not specifically address Rule 4.10.4(2), which requires coal mine waste banks to have a minimum static FoS of 1.5 (not limited to the "long- term" condition). Previous studies prepared by Buckhorn for the Bowie No. 2 Mine (for TR -44, TR -45, TR -56, TR -64, etc.) have considered the effects of pore pressure, and evaluated total stress, not only effective stress when determining the critical FoS. The TR -45 Buckhorn analysis dated 29- Mar -2007 evaluated a number of pile geometries, as tabulated on Page 14 of that report. For "Cross Section A ", the 2nd and 4t" entries give Total Stress Analysis FoS of 1.46 and 1.44, respectively, for block failure. (The 2nd entry, 2.5h:1V, with a pile height of 100', is very similar to what is now being proposed.) Please address the requirements of 4.10.4(2) (minimum static FoS of 1.5) for this proposed reconfiguration of Gob Pile #3. Based on previous stability analyses performed, this will include a consideration of the dissipation of pore pressures, if any, as the coal mine waste is dewatered, over time. 33. Section 6.0 of the TR -45 (29- Mar -2007) Buckhorn report provides a list of seven recommendations "to fulfill assumptions made in our evaluation and to ensure an adequate safety margin for the gob pile ". Item 6 states, in part: "Gob must be placed at, or slightly below its optimum moisture content. Gob placed significantly above the optimum moisture content likely will not achieve adequate compaction or undrained shear strength." Item 7 follows with, "We also recommend implementation of a moisture content specification allowing moisture contents no greater than 4% above the optimum moisture content." There does not appear to be a commitment by BRL in the text portion of Volume XI to implement the moisture content recommendation. Coal Mine Waste Bank reports are submitted by BRL on a quarterly basis. Included are the results of any compaction tests conducted on coal mine waste placed during the quarter. The Division observes that the moisture contents (MC) for approximately 25% of the tests exceed the optimum MC by more than 4 %. For the first three quarters of 2013, the MC averages 2.2% greater than optimum. (These numbers reflect a significant improvement over 2012 results, when the average MC was 4% above optimum, and 40% of the tests were >4% above optimum.) Even with MCs that are slightly high, BRL has been successful in achieving the minimum recommended 90% compaction level 97% of the time in 2013. Please review the Recommendations made by Buckhorn in 2007, in light of the coal mine waste compaction and moisture content results obtained, to date. The Rules specify only that compaction must be achieved, and do not specifically address the moisture content of the coal mine waste. It is unclear whether Buckhorn's MC recommendations constitute a permit requirement, as they are not repeated in the permit text. Clarifying language in the "Placement and Compaction" portion of the permit would be beneficial. Also,