Laserfiche WebLink
Colluvium removed from the buttress foundation area and not used in buttress construction, in haul <br />roads or for other construction needs, was placed in horizontal windrows orientated generally <br />perpendicular to the face of the waste rock pile within the refuse material to minimize interference <br />with waste rock pile drainage and to minimize potential for negative impact to geotechnical stability. <br />Where beneficial to the stability of the waste rock pile, colluvium may be mixed with wet refuse <br />materials to absorb moisture. The extent of such areas will be kept to a minimum to avoid developing <br />low -permeability zones within the waste rock pile. <br />The buttress was constructed progressively over a three-year period. The initial rock and colluvium <br />buttress foundation was constructed in 2011. The colluvium portion of the buttress was completed in <br />2012. The rock portion of the buttress was completed in 2013. <br />Initial placement of refuse in the disposal area was phased in coordination with buttress construction. <br />With completion of the rock and colluvium buttress, and with adequate modeled long-term slope <br />stability factor of safety as presented in the geotechnical analysis summary, placement of refuse will <br />proceed to the top of No Name Gulch as shown on the permit drawings (Appendix D). Roadways that <br />serve as drainage diversion benches have been and will continue to be established on the waste rock <br />pile slope to control surface water, provide access for operations, maintenance and reclamation, and <br />to enhance the slope stability factor of safety. <br />4.3 Underdrain <br />The underdrain has been designed and will be constructed with adequate capacity to drain and protect <br />the stability of the refuse pile; more specifically, the design meets the alternative underdrain design <br />as provided in Rule 4.10.3(5). <br />The RPEE waste rock pile is situated above the uppermost coal and shale seams. Clearwater drainage <br />diversions will be maintained above the working bench of the waste rock pile to divert surface water <br />away from the waste rock pile. Runoff from the working pad will be drained to the sediment ditches <br />west of the pile. Therefore, the only water that would drain to the underdrain would be percolation <br />through the pile and seeps that may be uncovered in the colluvium under the waste rock pile <br />footprint. <br />20 <br />P:\Mpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />