2011-06-06_REVISION - M1981185 (63)

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Access Road • To the extent practicable vegetative filters will be retained to mitigate potential erosion and sedimentation impacts; • Complete retaining structures as designed Retaining Structures After flatting of the cutslopes has been completed and the desired roadway width established, fill material in the roadway will be removed to expose bedrock. If the bench into bedrock is of sufficient width to reconstruct the fill at an inclination no steeper than 1.5:1, the roadway subgrade will be reestablished so that roadway grades are not steeper than 15 percent. Fill will be free of organic materials and rocks greater than 6 inches in largest dimension have a liquid limit and plasticity index of 35 and 15 respectively and are placed in thin layers, moisture conditioned to near the optimum moisture content and compacted to at least 90 percent relative compaction per ASTM D1557-02. The upper 1 foot of subgrade will be compacted to 95 percent relative compaction. If the bench is not sufficiently wide to construct a fill slope as described above, a retaining structure such as a Hilfiker or Gabion wall will be installed per the manufacturer's recommendations. If both of these approaches are insufficient to establish design roadway widths and grades, excavation on the outboard side of the bedrock bench will commence until a stable rock bench is established on which a fill or retaining wall can be properly constructed. Water Bars (limited use) • Where necessary, create water bars to minimize flow velocities and surface erosion and sedimentation. Water bar separation will range from 100 to 300 feet depending on road grades. When the grades exceed 10% water bars or catchment swales will be constructed on 100 foot centers and 300 foot centers when road grades are equal to or less than 10%. Ditches Maintain an inside V notch bar ditch with a side slope of 1:1 on the inside road cut where the depth is at least one foot deep are capable of conveying the runoff from a 10 year 24 hour storm (Exhibit C-Mine Plan Table C-2 for design calculations). (Attachment A- Sheet C2.00-CLC Associates); • Place riprap in ditches where slopes are in excess of 10%. D50 Riprap of +6 inch must be used were the ditch is subject to erosion (most road ditches will be cut in component bedrock); Culvert • Replace the 36 inch Culvert located beneath the road fill with a new culvert and a debris rack. The culvert is capable of conveying the peak flow from the 100 year 24 hour storm with a peak flow of 20 cfs. (See design calculation presented in the Mine Permit-Exhibit C. The culvert will be extended up gradient to accommodate a sediment trap and to install a flared culvert inlet. Because the close proximity to wetlands, no culvert outlet structures or catch basin will be installed; [Publish Date]