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Geotechnical Stability Exhibit <br />Exhibit 6.5 <br />Chief Operational Area (Portal) and Reclaimed Drainage Channel: <br />• The Chief Portal was built before 1926. The portal was stabilized in 2009 and the bench <br />leading to the portal was graded to remove debris at the portal entrance. No additional <br />material was removed from the head cut above the adit. There is no sign that stability of <br />the road has been adversely affected by the 2009 Chief Portal scaling activities. A <br />geotechnical work plan is proposed for the Incas Access Road and will be used to <br />determine road stability (Figure 6.5 -2) and whether road and portal construction activities <br />must be implemented to stabilize the structures; <br />• The channel and adjacent disturbed area will be stabilized and reclaimed using BMPs. <br />The drainage channel is designed. (Attachment U-3 and Table U -12) to convey the peak <br />flow from a 100 year, 24 -hour storm event of 87 cubic feet per second (cfs). The channel <br />will be a trapezoid configuration built on a 10 percent slope where the bottom width and <br />channel depth will be 10 feet and 3(H):1(V) side slopes. The flow velocity is estimated <br />to be approximately 7.5 feet per second (fps). The proposed work plan is presented in <br />Attachment D -4. Prior to construction activities, erosion and sedimentation BMPs will <br />be installed which includes: wattles (above and below the construction area), rock check <br />dams, and gabion drop structures. The reclaimed disturbed area will be stabilized by <br />seeding, wattles, jute netting, and appropriately sized rip rap. (See Attachment D -4 and <br />Figure D -1); and <br />• The area disturbed by re- grading the road to the Chief Channel and the Portal will be <br />seeded. The access road will be graded and an inside road ditch with a 1:1 slope <br />configuration will be constructed with ditch rock check dams or cross drains will be <br />placed on approximately 30 foot spacing for the pre- existing roads leading from the La <br />Plata River to May Day No. 1 or May Day No. 3 affected areas. <br />May Day No. 2 Operational Area Reclaimed Drainage Channel: <br />• The channel and adjacent disturbed area will be stabilized and reclaimed. The drainage <br />channel is designed (Attachment U -3, Table U -11) to convey the peak flow from a 100 - <br />year, 24 -hour storm event of 98 cfs. The channel above the proposed culverts will be a <br />trapezoid configuration built on a 5 percent slope where the bottom width of 1.0 foot, a <br />channel depth of 2.0 feet and 3(H):1(V) side slopes. The flow velocity is estimated to be <br />8.8 feet per second (fps). Prior to construction activities, erosion and sedimentation <br />BMPs such as wattles /silt fences (above and below the construction area), and a rock <br />check dam down gradient of the constructed channel and culvert will be installed. The <br />disturbed area will be stabilized by seeding, jute netting, erosion and installing <br />appropriately sized rip rap. The May Day No. 2 reclaimed drainage channel work plan is <br />outlined in Attachment D -3; and <br />• The disturbed area will be graded, and seeded. The Mayday No. 2 portal will be installed <br />with a gate capable of being locked. The portal will remain open in the event the portal <br />will be utilized in the future for ventilation and or future mining and closed during final <br />reclamation. <br />Wildcat Mining Corporation <br />May Day Idaho Mine Complex — 112d Permit Application <br />Revised August 2011 <br />Geotechnical Stability Exhibit 6.5 <br />Page 7 of 11 <br />