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Mountain Coaf Company, L.LC. Exhibit 51 <br />West Elk Mine ~ Lower Refuse Pile <br />• It is estimated that the above assumptions incorporates conservativeminimum safety factor of 100. <br />5.4.2.2 Leachate Estimate Performed for Phase V <br />A computer simulation was performed to investigate probable leachate production within the lower <br />refuse pile sr.d cemoare with existine underdrain capacity. Results indicate existing underdrains should <br />accommodate the LRP as modified, including ?H:I V sideslopes on the north and east, and an ultimate <br />peak elevation of 6330 feet. <br />The simulation was performed using the Hydrologic Evaluation of Landfill Performance (HELP), <br />version 3.01 computer model developed by the U.S. Army Corps of En,ineers Waterways Experiment <br />Station, in Vicksburg, MS. The model accepts weather, soil, and design data and computes surface <br />storage, snowmelt. runoff, infiltration. evapotranspiration, vegetative growth, soil moisture storage, <br />lateral subsurface drainage, unsaturated vertical drainage, and leakage through soils. Average monthly <br />precipitation and temperature data from a monitorine station one mile southwest of Paonia, Colorado, were <br />used for the simulation. The HELP program was developed to conduct water balance analyses of <br />landfills. cover systems. and solid waste disposal and containment facilities, such as the LRP. <br />Two simulations were performed: I) using existine LRP conditions to compare with observed leachate <br />flow; and 2) using the modified final (i.e., with reclaimed 2H:1 V sideslopes) LRP physical parameters. <br />Underdrain Flow computed estimates are as follows: <br />• Existing LRP conditions peak daily leachate flow - 1.8 gallons per day <br />• Existing LRP conditions average annual leachate flow - 38.7 gallons per year <br />• Final LRP configuration peak daily leachate flow - 2.9 gallons per day <br />• Final LRP configuration average annual leachate flow - 38.5 gallons per year <br />The HELP model simulation results are included in Appendix H. The existing LRP results correlate well <br />with observed underdrain flow. The model indicates that the existing 4-ft x 3-ft rock underdrains <br />(Section S.4.S). designed to carry 4b gpm, are more than adequate for conveying expected leachate <br />production. <br />5.4.3 Leachate Testing Results <br />Four separate leachate tests were conducted on refuse samples since August 198. These samples provided <br />a representative range of refuse variation. The tests were conducted by mixing a one to one ratio by weigh[ <br />of refuse material and distilled water and allowing the mixture to equilibrate for approximately 24 hours. <br />The liquid was then decanted from [he mixture and analyzed. The laboratory reports are provided in <br />Appendix H. <br />The pH of the leachate is approximately9.0, indicating little possibility for generation of acid leachate. The <br />pH of the leachate is consistent with the results of nvo solids analyses of the refuse material showing low <br />pyritic sulfur content in the ranging from .08%to .?7%. <br />Sodium accounts for over 30% of the dissolved solids leached from the refuse materials. Sodium <br />concentrations in the leachate ranged from'_1 ~ to SSO mgll with corresponding sodium absorption ratios <br />• (SARs) of ?_-68. These SARs are approximately 30 times lower than the calculated allowable leachate <br />SAR which, after mixing with river flow, will meet the North Fork in-stream standard (ISS) SAR of 3. The <br />16 <br />