2014-01-16_REVISION - C1996083 (3)

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Page 2 of 3 Pile #2 and are read on a quarterly basis. VWP -06 and -08 are located in the general vicinity of the proposed Drying Area, and continue to show somewhat elevated pore pressures, in the range of 14 to 16 psi. These values stand in sharp contrast to the 1 to 3 psi reported for VWP -05, -09 and -10 which are installed near the toe of the pile. a) Given the fact that pore pressures in the upper portion of Gob Pile #2 have not yet diminished, please expand the stability analysis to address the effects (if any) of the proposed Drying Area on the pile as a whole, using the approved outslope configuration and the current slope of the compacted coal mine waste that will form the base of the Drying Area. Based on previous Buckhorn studies, this may require consideration of a phreatic surface and block -type failure surfaces using total stress analyses and un- drained strength parameters. b) Currently, there are only two functioning VWPs in the upper levels of Gob Pile #2: VWP -06 and -08. Please address any impacts to the Gob Pile #2 VWPs that may occur as a result of constructing the Drying Area, e.g. will either installation be destroyed, or made inaccessible. If any impacts are expected, please provide recommendations regarding any proposed mitigation, such as installation of new VWPs. 3. Buckhorn's Model #1, a 15 -foot pile at 1.5h:1v, results in a Factor of Safety (FoS) of essentially 1.0, which implies that slippage of material down the slope is imminent at all times. While this slope configuration may be acceptable on the sides of the Drying Area, the Division questions whether this is appropriate for the front face of the pile, where a commitment has been made to maintain a 25 -foot buffer. Continual sloughing from the face of the Drying Area pile may encroach on the required 25 -foot buffer between the end dumped material and the face of the pile. If BRL will be placing material at 1.5:1 slopes, the buffer zone will need to be increased to ensure that a minimum of 25 feet will be maintained at all times. Alternatively, the slope of the front face of the Drying Area could be flattened to increase the FoS and reduce the potential for sloughing of material into the buffer zone. Please revise the plan to either increase the pile setback to account for sloughing of material, or flatten the proposed outer face of the Drying Area to achieve an improved FoS. 4. In the Results Discussion section, Buckhorn refers to the long term FoS of 1.5 required by Rule 4.09.1. That rule is specific to disposal of excess spoil. For Coal Mine Waste Banks, Rule 4.10.4(2) applies, which requires a minimum static safety factor of 1.5 (not limited to the "long term" condition). Please revise the Results Discussion paragraph of the December 5, 2013 Buckhorn report to reference Rule 4.10.4(2) rather than 4.09.1. (The Division concurs that the Drying Area itself need not be held to a FoS of 1.5; what is proposed with TR -85 represents a significant improvement in the handling of wet coal mine waste over methods used historically at the site.) 5. Please revise the Table of Contents for Volume IX with the revised page numbering and addition of the December 5, 2013 Buckhorn Geotech analysis proposed in TR -85.