2013-03-19_REVISION - M1981185 - Laserfiche WebLink

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Phase 2 Scope of Work After work within the LDG has been completed, as outlined above, construction will proceed to stabilizing the highwall and the access road immediately above the existing portal and repair of the existing manway exit from the mine. A geotechnical stability report was completed on March 16, 2013 by Wildcat Mining Corporation that gives recommendations on how to stabilize the highwall. Geotechnical Investicration: The Rule 6.5 Geotechnical Stability Report — Chief Portal, dated March 16, 2013, prepared by Wildcat Minning Corporation (the Geotechnical Stability Report) was completed by J. Erich Rauber, PE to provide recommendations to stabilize the highwall above the Chief Portal. The full Geotechnical Stability Report can be found in Appendix D. The subsurface investigation included excavating five test pits, two on the bench in front of the portal and three along the existing access road to May Day 3, and performing moisture content, Atterberg Limits and compaction tests on samples taken from each of the test pits. Based on this analysis, the Geotechnical Stability Report made the following recommendations for the reconstruction of the highwall in Section 5.0 — Recommendations: • Loose fill and debris should be removed from the highwall area and a buttress should be constructed to establish a pad on which the portal improvements can be supported. A typical detail of the buttress can be found in the Appendix of the Geotechnical Stability Report. • The finished slope of the highwall shall not exceed 1.5:1. • Fill materials should be free of organic material with the largest particle sizes less than six inches. Fill should be placed in layers of eight inches or less, moisture conditioned and compacted. Additional recommendations were provided for the repair of the portal entrance and repair of the Portal Access Road. Construction of Improvements: Reconstruction of the highwall will start with the removal of trees, vegetation, debris and loose dirt and rock from the collapsed area above the portal. The trees, vegetation and debris will be hauled off -site and disposed of in a landfill. The loose dirt and rock will be stockpiled with the material removed from the LDG on May Day 3. Once the highwall has been cleared, the Contractor will reconstruct the slope to meet the design prepared in Figure 8 — Highwall Grading Plan (see Appendix C) and the recommendations of the Geotechnical Stability Report. The portal opening will need to be extended as part of the reconstruction of the highwall because the proposed slope will completely cover the existing opening. To extend this emergency exit, a 66 -inch pipe will be installed at a 11% slope from the proposed retaining wall to a point that catches inside the existing opening. A plan and profile of this design has been provided in Figure 9 — Chief Portal Plan & Profile. The portal access road and the existing access road above the Chief Portal will need to be stabilized after the grading of the highwall has been completed. The alignment and elevations of both of these access roads will remain the same, but both roads will need to be scarified, moisture treated and compacted to meet the recommendations of the Geotechnical Stability Report. The contractor will need to place erosion control measures (BMP's) on the proposed improvements as work is completed. Slopes will need to be stabilized with seeding and mulching or hydromulch with a tackifier. All disturbed slopes steeper than 3:1 shall also have erosion control blankets to prevent Chief Portal Work Plan Page 4 P• \Wmcduc \dwg \Eng \Final Drawings \DRMS TRs \b - Chief Portal TR \Chief Portal Work Plan -Rev1 doc