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which have a relatively small subsidence potential. The angle of draw of <br />longwall mining activity does not intersect landslide bodies in the area. MCC <br />monitors monuments it has installed on a landslide mass in the mine's surface <br />facilities area. <br />Monument Dam and Minnesota Reservoir - MCC predicts the dam or <br />reservoir will not be subsided by mining because the nearest mining will be <br />800 ft. away in panel E9. The angle of contact between the reservoir is 69 <br />degrees, significantly more than the 20-degree predicted maximum angle of <br />draw in the South of Divide area. MCC has committed to monitoring the <br />angle of draw of panel E9 in order to verify the prediction. MCC predicts that <br />ground vibration (seismicity) created by longwall mining could affect the dam, <br />the reservoir, and the landslide abutting the dam because the static safety <br />factor of the dam has been found to be less than 1.0, as shown in an analysis <br />conducted by MCC's consultant and contained in Exhibit 72 of the permit <br />application. The suspected cause of the relatively low factor of safety is a <br />landslide that underlies the dam's south abutment. Possible effects from <br />mining-induced seismicity are: rockfall into the reservoir; overtopping of the <br />dam by water in the reservoir; catastrophic failure of the dam; flooding, <br />sediment deposition, and erosion downstream from the dam; flood damage to <br />roads, houses and other structures downstream from the dam. MCC has <br />summarized in the permit application the predicted effects of a catastrophic <br />failure of the Monument Dam determined in a Dam Breach Analysis, dated <br />February 8, 1984. Predicted out-of-channel floodwater depths are in the range <br />0.3 to 3.5 ft. in the lower 6 miles of Minnesota Creek. Predicted floodwater <br />velocity is in the range 13 feet per second to 42 feet per second. As many as <br />four houses could suffer shallow flooding, although loss of life would not be <br />expected. Depending on proximity to the creek, houses could suffer structural <br />collapse as a result of foundation erosion. Extensive erosion and resource <br />damage would occur along Minnesota Creek and a sediment bar would <br />probably be deposited in the North Fork of the Gunnison River. In order to <br />mitigate any potential impacts to the dam from mining-induced seismicity, <br />MCC has committed to the following measures (which are set forth in more <br />detail in Section 2.05.6(6) of the permit application): <br />1. Surveying the structures downstream from the dam that could be <br />impacted by dam failure six months prior to longwall mining in the South <br />of Divide area, and incorporating the survey into the permit application as <br />a revision. <br />2. Conducting annual aerial photo surveys of landslides located north and <br />south of the reservoir, <br />3. Installing and periodically surveying monuments on the dam and the <br />north, south, and east edges of the reservoir, <br />4. Monitoring water levels in piezometers installed in the dam, <br />48