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~ III IIIIIIIIIIIIIIII <br />ROCKY MOUNTAIN CONSULTANTS, INC. <br />Inc <br />Premiere Building <br />825 Delaware Ave.. Suite 500 <br />Longmont. CO 80501 <br />(303) 772-5282 <br />Metro (303) 665-6283 <br />FAX (303) 665-6959 <br />RECEIVEt~ iniTicl, last name)@long.rmcco.com <br />September 6, 2000 <br />Ms. Christina Kamnikar <br />Division of Minerals and Geology <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />SEP 192000 <br />Division at CAinsrols and GaoloAY <br />Re: Stability Analysis for Milliken Pit Application, #M-2000-087 <br />Dear Ms. Kamnikar: <br />Following is our response to your questions about the stability analysis: <br />1. A copy of the requested input file is attached. The analysis was performed using the Bishop <br />method. The input file includes all input parameters for the slope geometry, strength <br />parameters, and the boundaries of randomly generated slip circles. <br />2. Slurry walls are typically three feet thick. The inputted thickness for this analysis was 3.8 <br />feet (refer to coordinates on the attached input file, Soil Type S). <br />3. The site will be dewatered using a combination of in-place wells and/or a one-foot deep <br />perimeter dewatering trench at the toe of the mine slope. The wells could be located <br />anywhere to the interior of the mine slope. Perimeter trenches would be approximately <br />one-foot away from the mine slope. <br />4. The mud lens is commonly encountered in gravel pits along the South Platte River and was <br />shown in site boring logs made by Aggregate Industries, Inc. Soils are classified using the <br />Unified Soil Classification System. The "mud lens" typically classifies as CL, SC and/or SM. <br />The strength parameters inputted are based on our experience and laboratory testing of <br />"mud lens" samples at other sites. <br />5. The irrigation ditch immediately west of the mine supplies water to the site only, and will <br />not be used during mining operations; though the land owners may want to use the ditch <br />after site reclamation. Construction of a slurry wall typically requires a minimum of 20 feet <br />of clearance on the non-mined side of the slurry wall. This clearance allows for trackhoe <br />arm swing and use of desanding equipment. <br />6. Aggregate Industries will use scrapers and dozers to excavate this slope. The minimum <br />setback from the edge of the excavation face to the slurry wall will be 20 feet. The stability <br />analysis assumes the slurry wall is setback 19.6 feet from the top of the excavation slope. <br />• <br />CIVIL AND ENVIRONMENTAL ENGINEERING PLANNING <br />