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May Day and Idaho Mine Complex 112 (d) Permit Application <br />New Access Road -road stability including g ut slope: The construction work plan including <br />IN erosion and sedimentation BMPs are summarized in Attachment 6.5.2. The New Access Road <br />(Sakura, 2009) has been designed to carry loads up to 18 tons with a safety factor of 1.5. The <br />safety factor for the cribbed section is estimated to be 2 (Attachment 6.5.3). In addition, <br />recommendations resulting from a geotechnical evaluation of access road stability performed in <br />May 2010 (Attachment 6.5.4) have been incorporated into the road construction work plan. No <br />potential road construction geologic hazards have been identified that have not been mitigated. <br />Embankments These are discussed with respect to the Augmentation Pond (above). <br />Hi hg_ walls Highwalls will be reclaimed to slopes that are less steep that 2:1. Potential geologic <br />hazards will be evaluated once site access is granted and a final determination will be provided to <br />the DRMS. <br />Waste Piles the following mined rock storage areas were evaluated: <br />Bench stability including rock storage areas (May Day No. 1 May Day No. 2, Lamb, and the <br />Idaho augmentation pond rock storage area: Instability has not been noted based on the fact that <br />the Idaho, Lamb and May Day mine benches and rock storage areas were constructed in the early <br />1900's, and have remained intact to date. No geologic hazards have been identified that would <br />affect any of these present rock storage locations. Future bench and storage areas will be limited <br />to existing configurations and in any event no outslopes will be steeper than 1.5(H):I(V) <br />(horizontal:vertical) without additional geotechnical analysis. Drainage (surface and subsurface) <br />control design will be incorporated into all structures and appropriate BMPs will be adopted to <br />mitigate offsite erosion and sedimentation including diversion ditches, sedimentation traps, rock <br />drains and rock berms to minimize any potential impacts as discussed in the Storm Water <br />Management Plan (Exhibit T). Future benches and rock storage areas are located where ponds or <br />material saturation are minimized or nonexistent. <br />(2) Geotechnical slope stability assessments were conducted for the following features: <br />Bench stabilitv including rock storage areas, Ma Day No. 1, May Day No. 2, and Lamb <br />Operational Areas: Existing mine benches were created in the early 1900's with no signs <br />of failure or instability. In the future, stable rock storage areas will be constructed where <br />the backfilled material will be placed without compaction. The angle of repose of the <br />benches range from 30 to 35 degrees where the natural slopes range from 1.5 to 2 <br />(horizontal) to 1 (vertical). Since the proposed benches and waste rock disposal /storage <br />areas to be constructed are similar to the rock (D50 >4 inch) to be mined in the future <br />operating and reclaimed bench and waste rock slopes of 1.5 (H) to 1(V) will be used as <br />design criteria. Approximately 4,500 cubic yards will be disposed at the Lamb with <br />outslopes of 1.5(H);1(V), approximately 3,500 cu yards will be used from the existing <br />bench to reclaim the May Day No. 1 bench and portal. <br />• <br />May Day Idaho Mine Complex 112(d) Permit Application <br />September 21, 2010 <br />3 <br />