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1.0 Introduction and Background <br />This report summarizes actions taken to stabilize a slide area along Haul Road HR -1, presents <br />information for the addition of slope stability monitoring devices (mirrors, inclinometers, and <br />piezometers) for the haul road area and for the Refuse Pile Expansion East (RPEE) buttress and <br />refuse pile, and presents revisions to the RPEE drainage plan and sediment ditch. This report has <br />been prepared to present information regarding these items and support a technical revision (TR - <br />128). <br />1.1 Background <br />Construction of a coal mine waste bank, known as the Refuse Pile Expansion East (RPEE) was <br />permitted in early 2010. Mountain Coal Company began construction of the RPEE buttress in the <br />summer of 2010. Phase IA of the buttress was completed in early 2012, at which time the Colorado <br />Division of Reclamation Mining and Safety (CDRMS) approved use of the new facility for mine <br />refuse placement. The RPEE waste bank area preparation construction included placement of a rock <br />buttress at the toe of the proposed waste bank, clearwater diversions, sediment ditches, and haul road <br />construction. <br />An area along the lower reach on Haul Road HR -1 from the Refuse Pile Expansion (RPE) to the <br />RPEE began to slump in spring 2011. The area was investigated and repaired during the 2011 <br />construction season. A secondary slump occurred in December 2011 and was repaired in early 2012. <br />The approximate limits of the two slumps, combined, are shown on Figure 1. <br />The slump repair needed to be completed quickly to allow start of operation of the RPEE. As such, <br />excavation of the slump, investigation of subsurface conditions, and design of drains needed to be <br />done on a compressed schedule, sometimes concurrently with each other. This document provides a <br />description of the investigation and the drains that were designed for the stabilization effort, and <br />evaluates the completed slope repair construction. <br />A monitoring plan, including mirrors, inclinometers, and piezometers, was proposed in the original <br />RPEE permit design approved in Technical Revision TR -120. Implementation of the first <br />components of the monitoring plan is proposed since the initial phase of buttress construction has <br />been completed and refuse placement has started as approved in Minor Revision MR -383. The haul <br />road slump area will also be monitored to confirm the effectiveness of the repairs. The specific <br />instruments and data to be collected are presented in this report. <br />P:\Mpls\06 CO\26\06261003 Haul Road Slide Repair\WorkFiles\Report\MCC—Slump_Repair-Instrumentation-Drain Rev 2012-12-12.docx 1 <br />