2020-05-07_PERMIT FILE - C1981010A

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3.3.3 East Panel Landslide Geotechnical Evaluation An East Panel landslide occurred on October 8, 2006. A geotechnical evaluation program was designed by Agapito Associates Inc. (AAI). This program was designed to determine the slide plane and to determine parameters for future development of G and K pit. This program also included sites in Z dip pit. Ten sites were completed with varying combinations of inclinometers, piezometers and surface benchmarks. Surface benchmarks are used to monitor changes in down -dip displacements over time. Data retrieved from inclinometers is deflection of casing as a function of depth below the collar. Plats are developed of deflection versus depth. Piezometers are used to monitor water levels. The monitoring was performed in accordance with the recommendations of Agapito Associates Inc. as described below: • Once per month during the dry season. • Once per week during the wet months of spring (April -May) and fall (September - October). • Once per day after major precipitation (rainstorm) events > 0.50 inches for 3 — 4 days transitioning to weekly for 1 — 2 weeks and back to a normal schedule thereafter. In September of 2008, the required monitoring frequency was reduced (by AAI) to the guidelines shown below: • Once per month • Once per week for two weeks following a major rainstorm event (> 0.5 inches) In October of 2009, the original monitoring program was replaced with a state-of-the-art program that was developed in conjunction with the MSHA ground control plan at that time. The monitoring plan was developed with the assistance of AN and Applied Geomechanics. Each station is continuously monitored with an automatic data acquisition system. The acquisition system shares power and telemetry with the GPS system via Intuicom radios. These radios transmit data through repeater stations to the Trapper Mine office. As of the end of 2015, mining operations have progressed to the point in the landslide area that all of the slide displaced overburden has been mined through and is being actively backfilled and graded. The remaining stations will be utilized into the near future to observe spoil and pit endwall stability. Landslide monitoring will no longer be necessary in the future and semi- annual reporting to DRMS will be discontinued. This is in compliance with the current MSHA ground control plan for Trapper Mine. 3-27a Revision: -rl` ` //s Approved: