Laserfiche WebLink
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 />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. 015/05.01106, 03106, 04106& 05106- FR10: 01109- AIR350: 04109- TRI : 05119- kIR354: 08119- 7R 119