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May Day and Idaho Mine Complex 112 (d) Permit Application <br />Geologic hazards were considered in evaluating the potential to affect the following: <br />Augmentation Pond: The augmentation pond is the only proposed impoundment for the May <br />Day Idaho Mine Complex. There are no geologic hazards associated with this location and <br />based on the results of the soil testing (Attachment I -2), and the shallowness of the bedrock <br />observed in the field, there are no geologic hazards that will affect this functionality of the <br />augmentation pond. <br />When field access is granted, a geotechnical investigation of the area for the construction of the <br />augmentation pond foundation will be conducted. Geotechnical and hydrogeologic <br />characteristics will be determined prior to finalizing the augmentation pond design and <br />constructability work plan. Material characteristics will be determined to a depth of 10 feet <br />below pond embankments, including strength, hydraulic conductivity, classification (Atterberg <br />limits and grain size distribution), density and moisture content. <br />Slope There are no geologic hazards for slopes greater than 1.5:1 on the May Day Idaho Mine <br />Complex. Any slopes steeper than 1.5:1 will be evaluated for stability. <br />Mav Dav No. 1 Portal and Mill ent collapse and head scarp stabilization: The unconsolidated <br />material located behind and above the existing steel sets at May Day No. 1 portals failed in the <br />first quarter of 2010. Approximately 2,000 cubic yards of unconsolidated material will be <br />removed using an excavator. The material will be temporarily stored on the May Day bench <br />while steel sets are extended into bedrock immediately below the contact of the unconsolidated <br />material and the bedrock. <br />May Day No. 1 and Lamb portal steel set stability analysis: The May Day and Lamb portal steel <br />set stability analysis is presented in Attachment 6.5.1. As shown, soil bearing capacity is the <br />limiting factor in the analyses. For an allowable bearing value of 4,500 pounds per square foot <br />(psf), the steel sets can support up to six feet of compacted soil; for an allowable bearing capacity <br />of 16, 000 psf, up to 20 feet of compacted soil can be supported. The steel sets will be selected <br />to overcome any potential geologic hazards, if identified. <br />0 <br />May Day Idaho Mine Complex 112(d) Permit Application <br />September 21, 2010 <br />2 <br />