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West Elk Mine <br />As-built drawings of the location and installation of the devices will be submitted to the Division <br />once they are in place. <br />Monitoring information from the MCC seismic stations and NIOSH and USGS- generated data <br />collected from 1977 through 2005 was used to develop a stability analysis of the Monument <br />Dam by GEI Consultants, Inc of Englewood, Co (Exhibit 72, Material Damage Prevention <br />Measures). This stability analyses indicates the stability safety factor of the Monument Dam in <br />its current state is less than 1.0. As indicated in the GEI report, the dam was constructed on top <br />of and against a landslide on the dam's left abutment. According to the report, the landslide has <br />shown active movement since at least 1985 which has resulted in negative impacts to the <br />integrity of the dam structure. MCC recognizes that Monument Dam currently exists in a state <br />of failure since it currently has a static safety factor of less than 1.0. MCC proposes to increase <br />the static safety factor of the dam to 1.5 through the implementation of the measures discussed in <br />a subsequent Section 2.05.6(6)(f)(iv)(A-D), Detailed Description of Mitigating Measures. These <br />measures will include, among other activities, the construction of a stability berm and buttress to <br />reduce the risk of movement of the dam itself and damage due to movement of the landslide <br />located on the left abutment of the dam. The construction and implementation of these structures <br />and activities will allow the dam to withstand a seismic event of at least magnitude 2.3 (Richter <br />scale) generating a peak ground acceleration (pga) of 0.16 g. As stated in the GEI report, a <br />maximum seismic event and pga anticipated to be generated by mining in the SOD will be ML <br />2.3 and 0.06 g, respectively. <br />The data collected will be used to determine the future need and best locations for seismic <br />• monitoring stations in the SOD area. <br />1)Seismic Notification and Results o(MonitorinP <br />In the event that seismic monitoring indicates the seismic pazameter (0.16 g) of the stability <br />analysis for the Monument Dam has been exceeded by mining events, MCC will, within two <br />days, measure the survey monuments (provided weather conditions allow fmding and measuring <br />the monuments), evaluate the condition of the dam, and provide an electronic or verbal report to <br />the CDMG of the survey. If the changes appeaz to compromise the integrity of the dam or <br />reservoir, the Division, the Minnesota Reservoir Company, SEO, USFS, and other appropriate <br />agencies will be notified by MCC *~"~immediately'~*'~. Arrangements will be made with the <br />Division, the irrigation company, and the SEO to inspect the dam and reservoir as soon as <br />possible if damages due to mining activities are found. Mitigation will be implemented to repair <br />damages to the dam or reservoir basin. A report of the event, inspection, and any mitigation <br />requirements will be submitted to the Division within 3 months of the event. <br />2)Freguency of Seismic Monitoring <br />Quarterly reports will be generated from the above monitoring and a copy delivered to the <br />CDMG and USFS within a month following the end of the quarter. This monitoring will <br />continue until mining is completed in longwall panels E-1, E-2, and E-3 and E-9 through E-12 or <br />as long is as necessary to determine the impacts, if any, of microseismicity generated by MCC <br />subsidence mining of the SOD on Monument Dam. <br />n <br />U <br />2.05-168 Revised June 2005 PRlO, Rev. March 2006; May 2006 PR/0 <br />