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Mountain Coal Company, L.L.C. Exhibit 51 <br />West Elk Mine ~ Lower Refuse Pile <br />implies that the slope is marginally stable for the cross-se:•ion ^rofiles. r,at:ve clay bedrock material <br />• strengths, groundwater levels, and the slope conditions. <br />The reconfigured LRP was desiened to have a minimum factor of safety of I.~ and 1.0 for an earthquake <br />loading factor. A factor of safen• of l.~ is the minimum level of safety required by the CDMG for slopes <br />utilizing coal refuse. <br />5.6.1 Critical Sections <br />Three profiles from the reconfigured Phase V were modeled for the slope stability analysis (see Fieure 3 <br />in Appendix K). All three profiles are located in the same critical locations as previously identified in <br />Section 5.5. The physical conditions for each profile are as follows: <br />• Profile One bisects the northwest comer of the LRP. The critical feature in this profile is a <br />sediment control pond located at the base of the coal refuse slope. <br />• Profile Two bisects the northern slope of the LRP. The critical feature in this profile is the <br />location of Highway 133 located at the base of the coal refuse slope. <br />• Profile Three is located in the central portion of the eastern slope of the LRP. The critical feature <br />in this profile is the location of the WEM haul/access road located at the base of the coal refuse <br />slope. <br />5.6.1.1 Sensitivity Analysis of Critical Sections <br />•. The purpose of the sensitivity-style analysis is to account for possible changes in the slope stability <br />factors of safety in response to the changing physical properties of the current coal refuse being <br />generated by the West Elk Mine. The current coal refuse is very granular with very few non-coal (Clay <br />or silt) fine grain components. The sensitivity-style analysis examines the cohesion and internal friction <br />angles of four coal refuse samples having varying percentages of crushed coal fines (coal dust passing <br />[he # 200 sieve). The purpose of varying the percentage of coal fines was to determine if the factors of <br />safety would change by increasing the amount of coal fines created by mechanical compaction. <br />To develop the parameters for the sensitivity-style analysis, coal refuse was collected (so as to represent <br />current conditions) from two test pits near the active fill wedge on the coal refuse pile. The refuse coal <br />was randomly selected by MCC personnel retrieving a sample with the use of a backhoe bucket. To <br />maintain quality assurance-quality control (QA/QC), three fiveeallon sample containers of coal refuse <br />and roof spar (sandstone and shale) were taken for labatory testing. Each five gallon sample container <br />represents a typical load of coal refuse deposited on to the coal refuse pile. <br />Labatory testing consisted of running the coal refuse samples through a series of sieves to determine <br />grain size. A sieve analysis of the five eallon sample containers indicate that the current coal refuse has <br />approximately 7.6 % coal fines (particle sizes passive the # 200 sieve). For the sensitivity-style analysis, <br />crushed coal was added to the #'_00 sieve to vied samples containing 10 %, 20 % and 30% fines by total <br />weight for submittal for direct shears. Once again, to maintain QA/QC. each recompacted coal refuse <br />sample that was direct shear tested used the same set-up testing parameters. The only variable changing <br />in each test was the amount of fines contained within the sample. A complete review of the laboratory <br />testing can be found in Appendix K. <br />~~ <br />:_...v- <br />