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West Elk Mine <br /> <br />2.05-119 Rev. 06/05- PR10, 03/06- PR10, 05/06- PR10, 11/060- TR107, 04/07- TR108, 09/07- PR12, 02/08- PR12; 11/10- MR372; 10/20- MR-452; <br /> 12/20- TR149; 12/21- TR150, 1/24-TR152, 2/25-MR486 <br />Dam as described below occurs, the monuments will be inspected for movement. The <br />results of the survey will be submitted to CDRMS in the semi-annual subsidence report. If <br />movement along the landslide appears to potentially damage the dam itself, CDRMS, the <br />Minnesota Reservoir Company, SEO, USFS and other appropriate agencies will be notified <br />by MCC***immediately***. <br />2)Frequency and Reporting <br />Monument Dam will be surveyed and the monuments on the dam axis monthly when E-Seam <br />longwall mining is occurring within one mile of the dam and the information will be reported semi- <br />annually. If mining is occurring outside the one-mile radius of the dam, the dam monuments will <br />be surveyed on an annual basis. <br /> B) Seismic Monitoring <br />In June of 2005, the mine installed one seismic monitoring station in the axis of the Monument <br />Dam, another in Sylvester Gulch, and two more above B seam longwall panel 24. The purpose of <br />installing these stations was to observe the seismic events actually related to mining longwall <br />panels at the West Elk Mine. Monitoring of the four seismographs commenced in June of 2005, <br />and information developed to characterize seismic response from mining activity in the vicinity of <br />the Monument Dam and Minnesota Reservoir. <br />Prior to the commencement of longwall mining in either the E-seam E10, E11, and E12 longwall <br />panels, an array of seismic stations to monitor microseismicity generated by subsidence will be <br />created. This array will consist of at least 4 to 5 strategically placed accelerometers and <br />seismometers that will collect seismic data. The accelerometer/seismometer already in place in <br />the area of the Monument Dam will be used as part of this new array. The array will consist of <br />equipment in cooperation with NIOSH or similar to other arrays established by NIOSH in the <br />North Fork Valley to monitor mining induced microseismicity, including those previously <br />established in Sylvester Gulch and over B seam longwall panel 24. This data will be transmitted <br />to data storage devices and to a central location where the data can be monitored on a real-time <br />basis. The final number, locations and installation of the seismometers and data storage devices <br />will be determined by an expert in the field of collecting and interpreting mining induced <br />seismicity <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 Dam <br />by GEI Consultants, Inc of Englewood, Co (Exhibit 72, Material Damage Prevention Measures). <br />This stability analyses indicated the stability safety factor of the Monument Dam at that time was <br />less than 1.0. In January 2008, MCC completed the reconstruction of Monument Dam increasing <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 included, 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 located <br />on the left abutment of the dam. The construction and implementation of these structures and <br />activities will allow the dam to withstand a seismic event of at least magnitude 2.3 (Richter scale) <br />generating a peak ground acceleration (pga) of 0.16 g. As stated in the GEI report, a maximum <br />seismic event and pga anticipated to be generated by mining in the SOD will be ML 2.3 and 0.06