2011-08-09_REVISION - M1981185 (68)

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New Access Road Construction Work Plan Exhibit D — Attachment 1 Water Bars (limited use) Ditches Culvert Debris rack • Install a culver debris rack as designed. The debris rack will be periodically maintained to ensure the inlet is not obstructed. Wildcat Mining Corporation May Day Idaho Mine Complex — 112d Permit Application Revised August, 2011 Exhibit D — Attachment 1 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 95 percent relative compaction per ASTM D1557 -09. 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 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. • 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 %. • 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 D -1 - Sheet C2.00 ); and • 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). • Replace the 24 -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 Attachment U -3 at Table U -8). 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. Page 9 of 15