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May Day & Idaho Mill Complex - General Portal Repair Comments Page 2 March 11, 2011 made on page 2, referenced in Item 1 above. Please clarify the applicant's certainty as to whether geologic hazards exist or not relative to highwalls and portals. Also, see Item 7 below. 4. Page 3, Bench Stability: The last paragraph states "Existing mine benches were created in the early 1900's with no signs of failure or instability." The Division is concerned that if footings for the proposed steel sets are constructed on top of historic fill, that additional settling may occur due to the increased load and potentially compromising the safe operation of the mill. Please provide either a demonstration of the stability of the historic fill (if structures are to be founded on it) or avoid placing structural supports on any historic fill. Also, see Item 6 below. Exhibit E, Reclamation Plan: 5. On page 3 of Exhibit E, Reclamation Plan, last paragraph states, "With the exception of the bench out slopes and the portal face (1.5H:1V), slopes will be reclaimed to 2(H):1(V) or to slopes no steeper than the existing topography where the natural slopes are estimated to be I (H): I (V). Where possible, slopes will be graded to approximate original contour." Please provide clarification of where 1H:1V slopes are proposed. Attachment 6.5.1, Lamb and Matey No. 1 Steel Set Geotechnical Stability Assessment: 6. The copy of design calculations presented in Attachment 6.5.1 are difficult to make out all the numbers and nomenclature due to poor quality and the interference of the grid lines on the paper. However, the legible portions of the calculations appear adequate for a preliminary design. The Division will require specifications for the structural steel, rebar, pipe supports, concrete, shotcrete, all thread and all associated hardware. The assumed soil bearing capacity (4,500 psf) appears acceptable if the soil is similar to a gravel or gravel-sand mixture. The Division will require a demonstration that this is indeed the case. The calculations do not appear to include a factor of safety for the footing. Due to the mill housed inside the portal, the steel set footings should have a factor of safety equal to at least 3.0. The potential for geologic hazards (see Item 7) may necessitate a higher factor of safety. The final design shall include as a minimum, evaluation of axial, bending, shear, and buckling of the supports in uniform and nonuniform loading and support conditions. The maximum steel stress shall not exceed 0.6 times the steel yield strength (fy). A safety factor appropriate for the level of uncertainty and the nature of the construction shall be applied. Prior to construction, the Applicant will be required to submit design drawings and specifications that address the following: a. Shop drawings of the portals, including as a minimum the limits of proposed excavations and geometries of portal excavations in both plan view and in cross- section. b. Detailed description of the procedures, equipment, and methods proposed to conduct the portal excavations, including as a minimum: excavation sequence for the shaft and portals; schedule of operations; methods of loosening rock; spoil removal system; and personnel and equipment access. c. Detailed shop drawings and descriptions of the procedures and methods proposed to provide Ground Support, including as a minimum: Ground Support erection scheme; Ground Support element descriptions, sizes, spacings, and strengths; and mAmin\tc1\m-1981-185 maydayidaho\portalcomments_meml lmarl l.docx