2012-11-28_REVISION - M1995030 - Laserfiche WebLink

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LARRY E. O'BRIAN FOUNDER STEVAN L. O'BRIAN PRESIDENT C,1 ✓/ Ei)viroI)n)eI)t, Iqc. November 27, 2012 Mr. Michael A. Cunningham Division of Reclamation, Mining & Safety 1313 Sherman St., Suite 215 Denver, CO 80203 Dear Michael: RE: McAtee Construction Co. ,/ Green Bros Pit No. 2 - M- 1995 -030 adequacy review response #2 On behalf of my client McAtee Construction Company, I am responding to your November 13, 2012 adequacy review letter. Have included your review points that needed to be addressed in the order nresent in "oilY the answers will be in the same document for easy reference. 6.4.4 Exhibit D - Mining Plan 7985 VANCE DRIVE, SUITE 205A ARVADA, COLORADO 80003 303 - 423 -7297 FAX 303 - 423 -7599 RECEIVED Nnv ?8 2012 DIVISION OF RECLAMATION MINING AND SAFETY 1. The Applicant has stated the natural angle of repose of the pit walls will be 2.5H:1 V. Please describe the basis for this assumption or otherwise demonstrate to the Division that the pit walls will adhere to a 2.5H: 1V grade during mining. Also, describe how the Operator will verify that the mine face is maintained at 2.5H: 1V for the proposed wet mining operation. This was not an assumption the information comes from the dredge operator who had mined sand from the South Platte River from North Platte to Ft Morgan. McAtee's production records show that only 1 to 3% of the material passes the 200 screen. Meaning the material lacks cohesiveness and had little or no plasticity. Once mining has opened enough lake area so the dredge is working off the mine floor and the working face slopes are uniform we measure it to confirm the actual slope rate. We believe there is adequate time to determine the actual slope rate as it will be a number of years before mining approaches a structure. Most likely we would use a boat and electronic sonar to chart the slopes. It is found that the slopes are steeper then the esti- mated rate then the sloping setback will be adjusted to leave adequate material to complete the 3:1 sloping as approved. 2. Please provide the Division with a typical cross section which shows the slope of the mining face during active operations. The cross section should depict the point of maximum disturbance when the top of the mine siope reaches the mining line. In addition, include the 25' offset and the permit boundary line.