2011-04-18_REVISION - M1981185 (20)

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Response to CN-01 Preliminary Adequacy Issues for a 112(d) Application 6.5 Geotechnical Stability construction and constructability criteria. Material characteristics to be determine to a depth not to exceed 15 feet will include grain size (if possible), hydraulic conductivity, Atterberg limits, density, and moisture content The live storage pond area will be constructed below ground surface where the dead storage area will not extend more than five feet above ground surface. Therefore the concern for dam failure through a constructed berm is not probable La Plata River Bridge The La Plata River Bridge is designed to support an AASHTO truck loading of 15 tons (Attachment E). The bridge is approximately 36 feet long, and 11 feet wide supported by four 12 x 12 beams. The bridge supports are on approximately 33 foot centers. The bridge will be upgraded to support an AASHTO truck loading of 25 tons (Sakura, 2009) where construction activities will be limited to reinforcing the bridge deck with steel 1-beams and installing pedestal supports. (2) On a site-specific basis, an Applicant is required to provide engineering stability analyses for proposed final reclaimed slopes, highwalls, waste piles, embankments and ore leach facilities. An Applicant may also be required to provide engineering stability analyses for certain slope configurations as they will occur during operations, including but not limited to embankments and ore leach facilities. Information for slope stability analyses may include, but is not limited to, slope angles and configurations, compaction and density, physical characteristics of earthen materials, pore pressure information, slope height, post-placement use of site and information on structures or facilities that could be adversely affected by slope failure. Geotechnical slope stability observations were conducted for the following features: • Bench stabilitv including rock storage areas (Mav Dav_No. 1, May Day No. 2, Lamb and the Idaho augmentation pond rock storage area; o Existing mine benches were constructed in the early 1900's with no signs of failure or instability. The angle of repose of the benches range from 30 to 35 degrees where the natural slopes range from 1.5 to 2 (horizontal) to 1 (vertical). Since the proposed benches and waste rock disposal/storage areas to be constructed are similar to the run of mine rock (D50>4 inch) to be mined in the future, bench and waste rock slopes of 1.5 to 1 will be used as design criteria. Augmentation pond (if necessary) foundation o Prior to constructing the augmentation pond, Wildcat Mining Corporation will drill geotechnical foundation borings to determine pond foundation geotechnical characteristics. Data obtained from the assessment will be utilized to finalize pond construction criteria and to determine the best method and equipment to excavate, transport and dispose the excavated material and to determine the best methods to line and stabilize the cut slopes of the structure. May Day Idaho Mine Complex 112(d) Permit Application Revised: April 14, 2011 3