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West Elk Mine <br />The computer program determines the factor of safety for slip circles of varying radii about <br />specified points but does not automatically converge on the minimum factor of safety. In order <br />to minimize cost, a coarse grid was initially established. The grid was then successively <br />refined to converge on the minimum factor of safety. In most cases three to five interactions <br />were required. Stability analysis for SG -1 was performed using a slope stability computer <br />program entitled XSTABL5.105. The program utilizes Bishops and/or Janbus method for <br />circular or non -circular failure. <br />Stability Analysis <br />Various soil states were investigated to determine the most critical condition for each <br />embankment. The unconsolidated undrained condition, the consolidated undrained condition, <br />and the consolidated drained condition were considered for all embankments. In the case of <br />FW -1 and FW -2 (formerly MB -1), for the clay material embankment, the consolidated <br />undrained stability was critical. <br />Both a static analysis and a seismic analysis were performed for each dam embankment. For <br />the static analysis a fully saturated embankment was assumed. The seismic (or dynamic) <br />analyses, assuming the same condition, in combination, are summarized in Exhibit 44. The <br />final run for each analysis is included as a supplement to Exhibit 44. <br />I* Hydrologic Protection During Construction <br />Early in construction, prior to the disturbance of any area for surface construction, <br />sedimentation ponds were constructed, and diversion channels to collect undisturbed surface <br />runoff were constructed to meet specific design requirements. These channels were <br />constructed coincidentally with the initial access road, and divert the runoff away from the <br />disturbed areas. These structures were designed per Exhibit 44. Runoff is released from the <br />sedimentation ponds only after sufficient settlement of suspended solids and satisfaction of the <br />effluent standards has been achieved. Disturbance of the adjacent areas was held to a <br />minimum. The NPDES permits were secured prior to discharging. See Exhibit 7 to this <br />Mining and Reclamation Plan. Construction practices are geared to minimize erosion in all <br />disturbed areas (Exhibit 43). <br />During construction of the ST -4 crushed coal stack -tube and storage area, drainage in the area <br />was diverted into the enlarged MB -3 pond so that the former ponds MB -2 and MB -6 could be <br />dried in preparation for the construction of the coal storage area. <br />Best Management Practices (BMP) were utilized during road construction associated with the <br />Sylvester Gulch Facilities Area (PR07). BMPs were also utilized as the substation was <br />constructed. Prior to the construction of the shafts site benches, a clear -water diversion ditch, <br />designed to handle the peak flow from a 100 -year, 24-hour storm event, was constructed. In <br />. addition, prior to removing vegetation and stripping topsoil at the shafts site benches, sediment <br />pond SG -1 was constructed. The shafts site will naturally drain to the sediment pond, so life - <br />2.05 -37 Rev. 06105,01106,03106,04106& 05/06- PR10; 01/09- MR350; 04/09- TRI16;; 05/09- MR354; 08/09- TR119 <br />