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Broken Arrow Investments, LLC Derr Pit, File No. M-2008-017, TR-01 Adequacy Review - 02 Comment Responses <br />12/7/10 <br />-2- <br />vertical mining face would need to be <br />reclamation cost estimate to include <br />justification for omitting this cost. <br />graded to a 3HAV. Please revise the <br />grading for Phases 2-4 or provide <br />Response: <br />The reclamation cost estimate has been revised to include costs for grading. <br />6.4.19 Exhibit S - Permanent Man-made Structures <br />4. The Division has reviewed the Applicant's Slope Stability Analysis. Please <br />respond to the Division's comments in the attached document and make any <br />necessary changes to the applicable exhibits. <br />Response: <br />The type of equipment used for wet mining will include excavators initially to reach a <br />depth of 15 feet to 18 feet and a dragline for the remaining depths down to the <br />maximum depth of 85 feet. The attached slope stability results were revised for Case <br />4A only since the resulting factors of safety were nearly the same and the material <br />properties for each case are the same. The loading for the dragline when lifting a full <br />load for a section cut through the dragline with the tracks parallel to the crest of the <br />slope is 2,100 pounds per square foot for each track (track width is 5 feet). The <br />loading is more uniform than that of a HS-20 loading however the results of the slope <br />stability model are similar. The resulting static condition safety factors of 1.43 and <br />1. 60, for wet mining and dewatered conditions respectively, are above the SEO <br />minimum requirement of 1.25 for an embankment during construction. The resulting <br />pseudo-static condition safety factors of 1.16 and 1.41, for wet mining and dewatered <br />conditions respectively, are above the minimum requirement of 1.0 for an <br />embankment subject to earthquake loading. It should be noted that this slope <br />stability model shall be used only for determining that a failure of the slope would <br />remain within the final mining limit and within the subject property boundary. This <br />slope stability model shall not be used to determine how close the operator can set <br />equipment to the edge of the interim wet mining limit. The operator is responsible for <br />operating the equipment in a safe manner per MSHA and per the equipment <br />operations manual. <br />Thank you for your consideration of the responses we are providing and the revised exhibits for <br />the technical revision request. Please feel free to contact me with any questions or comments. <br />Sincerely, <br /> <br />J.C. York, P.E. <br />J&T Consulting, Inc. <br />cc: Broken Arrow Investments, LLC <br />V 1400 W 122nd Avenue - Suite 120 - Westminster CO 80234 - Ph: 303-457-0735 - Fax: 303-920-0343