2014-04-25_PERMIT FILE - C1982056A (3)

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The drilled pier retaining structure would consist of 40 to 45 drilled circular reinforced- concrete piers extending at least 10 feet into the bedrock, and 2 feet above the ground surface. Each pier would be 2 feet in diameter and approximately 45 to 50 feet long. The piers would be aligned and spaced to create a "fence- line" structure along the slope to stabilize the slope, and prevent further downslope movement. Regrading of the slope would occur following completion of pier placement, with the regarded slope tying into the pier retaining structure. Pier design and placement are detailed in the NWCC Report provided in Exhibit 25AA, Loadout Slope Stabilization. Geotechnical Investization - Sandstone Cliff MitiEation Measures (MR95 -117) Twentymile Coal Company will conduct a geotechnical investigation of the proposed construction sites for mitigation measures to be utilized to protect County Road 27 from hazards associated with rockfall potential beneath the Twentymile Sandstone. Detailed designs and a technical revision application for construction of the specific mitigation measures are presented as TR -19 (see Exhibit 7F). The geotechnical investigation for the proposed measures entails the drilling of five (5) shallow holes. Four (4) of the proposed drilling locations are located north of County Road 27 at locations within areas proposed for disturbance by construction of the sandstone cliff mitigation measures. For purposes of the mitigation measures design study, County Road 27 in this vicinity was divided into several zones (see Exhibit 7F). The drill sites located within proposed mitigation measure construction areas are located in zones 1, 3, 4, and 5. One additional proposed drill site is located south of County Road 27 in zone 2. This site is intended to provide information for the construction a portion of rerouted County Road 27 and is also within an area proposed for disturbance. Drilling will be conducted with a self - leveling track - mounted portable drilling rig (CME 45 mounted on Bombardier Snow Cat). Four inch (4 ") diameter continuous flight power augers will be utilized. Drill holes will be driven approximately 10 to 15 feet with core samples obtained as necessary to evaluate construction requirements for the proposed mitigation measure structures. No drilling fluids will be utilized in association with the rig and no structures or preliminary site preparation work will be necessary to support the drilling effort. All five sites are located in areas of previously undisturbed native topsoil. Drilling is estimated to take approximately one day although holes will be left open for two to three days to evaluate the potential presence of groundwater. No topsoil salvaging operations are proposed in association with the drilling program as drilling will not result in any adverse impacts to the topsoil resource. All drill sites are located in areas to be further disturbed during construction the sandstone cliff mitigation measures. Topsoil will be salvaged as appropriate during the initial construction phase of the mitigation measure project. The track mounted equipment utilized for the geotechnical investigation will produce minimal disturbance in traveling over undisturbed ground and drilling for short durations. Particular care will be taken to access the sites during a period when dry ground conditions are prevalent. To the extent possible, cuttings generated during the drilling process will be returned to the drill holes prior to abandonment to minimize potential sediment transport from each site. In the event an aquifer is intercepted during drilling at any site, the affected drill hole will be sealed using a grout plug in the aquifer zone and then will be backfilled to the surface with cuttings. In the event formation water is encountered during drilling and liberated on the surface, silt fences will be erected as secondary sediment control measures to minimize the transport of sediment off site. Construction of the mitigation measures is anticipated to commence during the summer of 1995. In the event construction initiates on schedule, permanent sediment control measures and topsoil salvage operations as detailed in the technical revision application for this project will be completed. In the event construction is significantly delayed, the associated geotechnical investigation drill sites will be evaluated and appropriate temporary sediment control measures will be implemented as necessary to ensure off -site sediment transport is controlled. Water System Water for the surface facilities and the mine is supplied by two water systems. The first source is TCC well No. 1 which is a 407 foot deep well. Well water is pumped into a 10,000 gallon surge tank and a centrifugal pump delivers MR 12 -262 2.05 -49 05/14/12