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West Elk Mine <br />4. The landslide feature that is located on and is part of the left (south) abutment will be monitored <br />for movement. MCC will install survey monuments within the landslide on the hill to the south <br />of the dam and within the toe of the landslide. These monuments will be surveyed monthly, <br />when accessible, during the months of February through July when movement due to high soil <br />moisture content would be expected. The monuments will be surveyed once every three months <br />in the period of August to January when soil moisture content is expected to be lower. If a <br />seismic event equal to or greater than the threshold event for the Monument Dam as described <br />below occurs, the monuments will be inspected for movement. The results of the survey will be <br />submitted to CDMG in the semi-annual subsidence report. If movement along the landslide <br />appears to potentially damage the dam itself, CDMG, the Minnesota Reservoir Company, SEO, <br />USFS and other appropriate agencies will be notified by MCC** *immediately***. <br />2)Freguency and Reporting <br />Monument Dam will be surveyed and the monuments on the dam axis monthly when E-Seam longwall <br />mining is occurring within one mile of the dam and the information will be reported semi-annually. If <br />mining is occurring outside the one-mile radius of the dam, the dam monuments will be surveyed on an <br />annual basis. <br />B)Seismic Monitor <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 panel 24. The purpose of installing these <br />stations was to observe the seismic events actually related to mining panels at the West Elk Mine. <br />Monitoring of the four seismographs commenced in June of 2005, and information developed to <br />characterize seismic response from mining activity in the vicinity of the Monument Dam and Minnesota <br />Reservoir. <br />Prior to the commencement of subsidence mining in either the E-seam E-10, E-11, and E12 panels or E-1 <br />and E-2 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 seismometers <br />that will collect seismic data. The accelerometer/seismometer already in place in the area of the <br />Monument Dam will be used as part of this new array. The array will consist of equipment similar to <br />other arrays established in the past by NIOSH in the North Fork Valley to monitor mining induced <br />microseismicity, including those previously established in Sylvester Gulch and over panel 24. This data <br />will be transmitted to data storage devices and to a central location where the data can be monitored on a <br />real-time 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 seismicity. As- <br />built drawings of the location and installation of the devices will be submitted to the Division once they <br />are in place. <br />Monitoring information from the MCC seismic stations and NIOSH and USGS- generated data collected <br />from 1977 through 2005 was used to develop a stability analysis of the Monument Dam by GEI <br />Consultants, Inc of Emde,,Food. Co (Exhibit 72, Material Damage prevention pleasures). This stability <br />analyses indicates the stahi Iity safety factor of the Nlonume;;t :.'a,:; H, its current state is less than 1.0. As <br />indicated in the GEI renni t, the dam was constructed on top of and against a landslide on the dam's left <br />abutment. Accord'!.- to l,e report, the landslide has shoNvn active movement since at least 1985 which <br />has resulted in negative impacts to the integrity of the dam structure. p'iCC recognizes that Monument <br />Dam currently exists in a state of failure since it currently has a static safety factor of less than 1.0. MCC <br />proposes to increase the static safety factor of the dam to 1.5 through the implementation of the measures <br />discussed in a subsequent Section 2.05.6(6)(f)(iv)(A-D), Detailed Description of Mitigating Measures. <br />These measures will include, among other activities, the construction of a stability been and buttress to <br />2.05-167 Revised June 200.1 PRIG, Rev. Uarch 2006; Ala), 2006 PRIO, Nov. 2006TR107.,4prril 2007TR108;Sep. 2007 PR12; Feb. 2008 PR:11