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May Day and Idaho Mine Complex 112 (d) Permit Application <br />• Mayay No. 2 Operational Area Reclaimed Drainage Channel: <br />o The channel and adjacent disturbed area will be stabilized and reclaimed. The <br />drainage channel is designed (Table 6.5 -2) to convey the peak flow from a 100 <br />year 24 hour storm event of 98 cfs. The channel will be a trapezoid configuration <br />built on a 5 percent slope where the bottom width of 1.0 foot and channel depth <br />will be 2.0 feet and 3(H):l(V) side slopes. The flow velocity is estimated to be <br />8.8 feet per second (fps). Prior to construction activities erosion and <br />sedimentation BMPs will be installed which will include straw /silt fences bales <br />(above and below the construction area), a rock check dam down gradient of the <br />structure, the disturbed area will be stabilized by seeding, jute netting and <br />appropriately sized rip rap. <br />o The disturbed area will be graded, and seeded. Approximately 250 cubic yards <br />are required to stabilize the access to reclaim the Little Deadwood Gulch channel, <br />and close the Mayday No. 2 Portal. <br />• La Plata River Bridsze <br />• La Plata River bridge is currently designed to support an AASHTO truck loading <br />of 15 tons (Attachment 6.5.5). As the Access Road will have a rating of 18 tons, <br />the bridge requires to be upgraded. In order to consider a safety factor, the bridge <br />will be upgraded to support an AASHTO truck loading of 25 tons (Sakura, 2009). <br />Construction activities will be limited to reinforcing the bridge deck with steel I- <br />beams and installing pedestal supports. As build bridge drawings will be <br />prepared and submitted 45 days after the bridge has been upgraded. <br />• The bridge is 36 feet long, 11 feet wide with four 12 "x12" beams. The bridge <br />supports are approximately 33 feet on center. The bridge is capable of supporting <br />an AASHTO truck loading type H15 -44 which is 6,000 pounds on the front axle <br />and 24,000 pounds on the rear axle spaced 14 feet on center. <br />(3) On the basis of our observations and engineering analyses, we conclude that there are no <br />areas adjacent to the permit area where potential off -site stability impacts could occur. <br />There are no geologic structures or earthen facilities that have the potential to impact <br />offset locations. The closest adjacent properties considered in the assessment include the <br />area parallel to the access road from 4 +40 to 6 +20 (Sakura Road Design Drawings Sheet <br />6 of 16) which was evaluated in connection with the new access road. The private owner <br />property boundary is approximately 80 feet from the new access road cut slope and if the <br />road cut failed (which is highly unlikely) where a final 3:1 slope was created, the land <br />slide head cut would be approximately 40 to 45 feet from the private landowner's <br />property boundary. Recent geotechnical assessments described in Sections 6.5.1 and <br />6.5.2 indicate that the current and final cut slopes are stable. <br />• <br />May Day Idaho Mine Complex 112(d) Permit Application <br />September 21, 2010 <br />