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<br />Slope Stability Analysis <br />of the <br />Sediment Pond Embankments in the PR-05 Amendment Area <br />New Horizon 2 Mine <br />by: Greg Lewicki, P.E. <br />January 12, 2000 <br />1.General Pond Information <br />The purpose of this report is to demonstrate that all the sediment ponds at the New Horizon 2 <br />Mine will be permanently stable and the embankments will have minimum long-term safety <br />factor of 1.3. <br />As of the PR-05 Amendment, the New Horizon 2 Mine will have 7 sediment ponds, numbered <br />• from Ponds 007 through 013. Ponds 007 and 008 are within the original permit area and ponds <br />009 through 013 are within the year 2000 amendment area. All of the existing and future ponds <br />have embankments have the following characteristics: <br />- that are no higher than 10.0 feet measured from the original ground at the center of the <br />embankment to the top. Some.ponds have some incised storage volume. <br />- top width of at least 10.0 feet. <br />- sideslopes of 2.5H:1.OV on both the outer and inner slopes. <br />-high compaction due to the material and equipment available on site. <br />- a principal spillway pipe and an emergency spillway cutout in the dam. <br />Across-section of the typical pond is shown on Drawing 1 of this report. In the amendment area <br />ponds, a keyway will be dug at the bottom center of the embankment for added stability, <br />although this keyway will not be assumed in the analysis to be conservative. Also, the cross- <br />section used for the analysis shows adownward-sloping original ground surface away from the <br />embankment. This is conservative since all the ponds except for Pond 010 have a mild original <br />ground surface. <br />2. Foundation and Embankment Material Characteristics <br />By examining the pond locations and the soils map, it is apparent that the material for <br />embankment cdnstruction will be either two types: <br />• 1) Those subsoils with coarse fragments (soil unified classification types GC or GM). These are <br />soils 986, 98C, 98D, 98G or 98H as shown on the soil inventory map of the permit. Table 1 on <br />REVISED MARCH zoos Attachment 2.05.3(3)-15-1 <br />