PERMFILE47451

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 51 Lower Refuse Pile
• Media Type: D
• Archive: Yes

Mountain Coal Company, L.L.C. Exhibit 51
West Elk Mine ~ Lower Refuse Pile
• 5.6.2 Parameter Selection
A brief description of the criteria used in the PCSTABL~ program to evaluate the (actors of safety for the
reconfieured LRP desien are as follows:
Reconfigured LRP Geometry: The LRP stability analysis incorporates the slope geometry of the
three profiles identified in the Critical Section paragraph. -
Groundwater: Groundwater levels are assumed to be located at the coal refuse natural slope
interface. Groundwater has been noted at this interface during previous drilling programs of the
LRP. The slope stability analysis assumes a low to no groundwater level in all models.
Note: Recent water level monitoring (monitoring conducted April 26, 1996) of the piezometers
located around the perimeter of the coal refuse pile indicates wound water levels at 30 to 39 feet
below the foundation of the coal refuse pile. Upstream monitoring (top of the coal refuse pile)
indicates no groundwater a[ [he interface between the refuse coal and the existing slope.
Subsequently, we assume that if low eroundw•ater levels are indicated at the base of the coal
refuse pile, and dry conditions are indicated near the top of the coal refuse pile then the
possibility that a perched sroundwater table existing within the coal refuse pile is highly
unlikely. Data to verify this fact, are found in Iv1CC's AHRs.
Soil Streneth Properties: Two coal refuse apes were used in the model. The title '`initial coal
refuse" is defined as the first waste coal placed in the foundation of the present coal refuse pile.
The inherent shear strength parameters of the initial coal refuse was determined by previous
laboratory testing conducted in 1983. For the Phase V addition to the existing coal refuse pile, a
sensitivity-style analysis of the shear strength parameters was performed on the "current coal
refuse". The current coal refuse strength parameters are based on recent laboratory soil testing
presented in Appendix K and previous triaxial shear tests taken at the initial stages of LRP
development. They are as follows:
Initial Coal Refuse: Coal refuse placed on the LRP during the initial stages of development, cohesion
288.0 psf, internal fiction angle 30.0 degrees, moist unit welsh[ 80.0 pcf, saturated unit weight 90.0 pcf.
Current Coal Refuse (sensitivity analysis):
• Coal refuse having 7.6 % fines. cohesion 1100 psf, intemal friction angle 35.0°, moist unit weight
58.0 pcf, saturated unit weight 68.0 pcf.
• Coal refuse having 10.0 ;% fines. cohesion 0.0 psf, internal friction angle 39.0°, moist unit weigh[
58.0 pcf, saturated unit weisht 68.0 pcf.
• Coal refuse having 20.0 % fines. cohesion 300 psf, internal friction angle 39.0°, moist unit weight
58.0 pcf, saturated unit weisht 68.0 pcf.
• Coal refuse having 30.0 ;% fines. cohesion 1100 psf, intemal friction angle 36.5°, moist unit weight
X8.0 pcf, saturated unit weight 68.0 pcf.
The input information for the analyses includes slope geometry, groundwater conditions. soil strengths.
and loading conditions.

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