2009-12-30_GENERAL DOCUMENTS - C1982056

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shaft; and fan, fan shroud, mechanical building, and silencer, for the ventilation exhaust shaft. Average thickness for the reinforced concrete pads will be 2 feet, and the pads will be a maximum of 4,050 square feet. Specialized blind drilling equipment consisting of A- leg derricks, drive motors, and drill- string handling components will be installed on the shaft pads and used to drill the pilot holes and, complete shaft drilling. Nominal 17.5 -inch pilot holes will be drilled for each shaft to an approximate depth of 1,360 feet and surveyed to determine vertical shaft deviation and location underground for mine entry tie -ins. The pilot holes will then be reamed to a nominal diameter of 7.5- 8.0 feet to accommodate the final steel liner. The reaming technique utilizes an inverted disc cutter equipped hemispherical raise -bore head, to cut the rock. During the drilling of the pilot holes and the 7.5 -8.0 -foot diameter excavation, all cuttings will be removed from the excavation using an airlift system, with water (reverse circulation) being used as the circulation media. Supplemental water, for drilling and to adjust the density of the drilling medium, may be supplied, as needed, by hauling water from a nearby location where TCC's holds valid existing water rights. The cuttings will be placed in 115 x 425 x 10 foot, four cell, lined temporary cuttings pit excavated within the shaft pad adjacent to the shaft excavation. The cuttings pit will be lined with a nominal 30 -mil PVC flexible membrane liner having a permeability of - -10 -12 cm /sec. The cutting head will be rotated from the surface by the drill pipe, which also serves as a conduit to transfer cuttings from the shaft bottom to the surface collection pit. The drill pipe also serves to suspend the drilling assembly in the hole and is tensioned to adjust the cutting weight on the head and to keep the drill pipe straight. The cutting head moves the water from near the center of the head and discharges it at the periphery of the head. This water then flows down around the cutters and washes the cuttings towards the pick- up pipe in the center of the head. The drill pipe's upward flow is activated by compressed air injected down the center of the drill pipe. Rock cuttings are moved by the circulation of the water down the hole, across the shaft bottom and up the drill pipe to the surface collection pit. Within the collection pit, the rock cuttings are separated or settled out and the water is allowed to drain back or is pumped back into the hole for re -use. The cuttings volume will be approximately 12,500 cy. Once the cutter head reaches the coal seam, the cutter head will be disassembled and removed from the A -leg derrick. Using the same A -leg derrick, the excavated shaft will then be lined to a nominal 6 -foot inside diameter using a hydrostatic steel liner. The steel liner sections will be pre- fabricated off -site, hauled to the site and field welded in 30 -50 foot joints. The liner will be floated into place. This is accomplished by securing a steel bulkhead to the bottom joint and leaving the excavated hole full of water while the liner is being lowered into place. By calculating the buoyancy of the liner, and adding water to the capped liner column, as needed, the liner is easily and safely lowered into position. Once the liner is in place, a nominal 9 -inch thick grout seal will be pumped between the strata and liner. The grouted steel liner will serve to isolate the Twentymile Sandstone from the Wadge Overburden. As previously noted, TCC plans to pressure grout the Twentymile Sandstone to minimize seepage to the shaft. This will help assure that, after final closure, groundwater from this unit will be confined and not seep down the inside of the shaft. Upon completion of shaft drilling and steel liner installation for both shafts, the cuttings pit will be dewatered. Excess water will be hauled to the Area 1 Pit, and the remainder will be allowed to evaporate. After dewatering the cuttings pit and allowing the cuttings to consolidate and dry -out, the collection pit and cutting materials will be covered with stockpiled materials from the shaft collar excavation, graded and revegetated with a temporary cover. A sign(s) will be posted designating the temporary mine development waste pit. The cuttings and shaft collar excavation materials will be utilized to re -fill the shafts during eventual reclamation of the shaft installation.