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Stability Analysis <br />See various Buckhorn Geotech and Huddleston Berry Engineering & Testing Stability <br />Evaluations of Proposed Coal Waste Pile No. 3, following this section. <br />Buckhorn Geotech's report dated October 26, 2006 provided a preliminary stability <br />analysis for gob pile #3 based on geotechnical investigation performed by Lambert in <br />2001 and recent field and laboratory experience at gob pile #2. This report concluded <br />the gob pile will be stable at a maximum height of 90' with 3H:1 V side slopes. <br />Buckhorn Geotech's report dated March 29, 2007 revised the previously submitted <br />stability analysis with site specific conditions based on in-depth field testing. This report <br />evaluated numerous gob pile configurations and found various configurations to be <br />considered stable. Please see the report following this section for configuration <br />specifics. The maximum pile height of 115' with 3HAV side slopes would be considered <br />stable. <br />HBET's report dated July 15, 2014 revised the previously submitted stability analyses to <br />steepen the slope angle from 3H:1 V to 2.5H:1 V. The maximum pile height of 122' with <br />2.5H:1 V side slopes is considered stable. <br />The Operator commits to having a qualified third party geotechnical firm perform <br />monitoring and testing. Monitoring will consist of observations of the geotechnical <br />aspects of the construction to determine if any unusual or unexpected conditions are <br />encountered. Testing will include compaction tests and periodic strength tests. Results <br />of the tests and any observed unusual or unexpected conditions will be submitted to the <br />DRMS with the quarterly inspection reports. <br />The quarterly reports will include a summary of instrumentation monitoring on coal mine <br />waste pile #3. The report will include a discussion of the vibrating wire piezometer data <br />to determine if the measured pore pressures are relatively stable and consistent. <br />Up to ten vibrating wire piezometer will be installed at gob pile #3. At this time, five of <br />the proposed vibrating wire piezometers are located either in the active gob drying area, <br />or in the footprint of the west coverfill stockpile. Therefore, only the three piezometers <br />VWP-A, B, & D, located in the center of the pile, are currently accessible and will be <br />installed in 2014. Please see the locations of the vibrating wire piezometers on Figure <br />1. <br />Volume XI <br />TRA 05 - 11 - 09/15 <br />