2011-09-30_PERMIT FILE - C1980007A

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Exhibit No. 82, TR 127 Refuse Pile Expansion East Mountain Coal Company, LLC • West Elk Mine Addendum No. 1 October 3. 2011 The refuse pile is situated above the uppermost coal and shale seams. Clearwater drainage diversions will be maintained above the working bench of the refuse pile to divert surface water away from the refuse pile. Runoff from the working pad will be drained to the sediment ditches east and west of the pile. Therefore, the only water that would drain to the underdrain would be minor percolation through the pile and seeps that may be uncovered in the colluvium under the refuse pile footprint. Little water percolation or migration is expected through the refuse pile. The HELP model predicts a peak daily discharge of less than five cubic feet per day, or approximately 0.003 gallons per minute (gpm). HELP model results are summarized in Table 4. The refuse pile foundation surface is higher than groundwater found in the site investigation (see boring logs, Appendix A, and slope stability model Figures 2 -1 through 2 -6), and a canyon to the south cuts off groundwater flow upgradient of the refuse pile location at elevations higher than the base of the refuse pile (see Figure 1 -2). As a result, any seeps that are encountered in the • construction of the refuse pile would be the result of local hydrologic conditions. Seepage rates and quantities would be low as they would need to be fed from local infiltration of rain or snow. Based on these observations, a design flow rate of 10 gpm has been selected for the design of the • underdrain. Underdrain slope, materials used to construct the underdrain, and cross - section area must be considered in designing an underdrain that is appropriately sized for the design flow rate. The average slope of the native thalweg from the rock buttress to the upper end of the refuse pile is about 29 %. Drainage rock for underdrain construction is specified to consist of stones ranging in size from 6 inches to 30 inches nominal diameter. A transmissivity value of 0.1 cm /sec has been assumed for the drainage rock. Based on these values, an underdrain with nominal cross - sectional dimensions of 14 feet wide by 4 feet deep provides a capacity of approximately 24 gpm, resulting in a factor of safety of 2.4 when compared to the assumed flow rate of 10 gpm that may drain to the underdrain. Filter rock will be placed over the drainage rock. The filter rock zone will extend a minimum of 4 feet beyond the lateral limits on each side of the underdrain. Woven geotextile will be placed below and along the sides of the underdrain, and under the full extent of the filter rock on either side of the underdrain. Woven geotextile also will be placed over the top P:\Mpls \06 CO\26 \06261003 RPE E. Permit Mod Support\WorkFiles\Permit Application \Text\Exhibit 82 RPEE design 2011 -10 -03 TR 127 Addendum l.doc Vii