2008-01-11_PERMIT FILE - C1982056A (2)

Home Browse Search

Road construction requires minimal cut and limited fill, so the actual road disturbance area will average approximately 35 feet wide. Cut slopes will be established at a maximum of 1.SH:1V and fill slopes will be graded to 2H:1 V or less, with all disturbed slopes to be stabilized by seeding with the topsoil stockpile stabilization seed mixture. For permitting purposes, a road disturbance corridor 100 feet wide has been . defined as encompassing all project-related activities, including road construction and topsoil stockpiling/windrowing. Preparation of the ventilation shaft pad will involve topsoil recovery and stockpiling, installation of required drainage structures, grading and compaction to establish a level pad working area, excavation of a collection pit for blind drilling of the shaft pilot hole and shaft, haulage or stockpiling of the excavated borrow material, and placement of gravel surfacing material to control dust and sediment from the pad area. Excavated borrow material from the collection pit will be hauled to the nearby Fish Creek Loadout for use in final reclamation. The collection pit will be approximately 100 x 200 x 10 feet and is sized to contain all drilling fluids and cuttings. In the event unanticipated ground water flows are encountered, they would occur during drilling of the pilot hole when the collection pit would have significant excess capacity. The combination of excess capacity and flow controls should be adequate to prevent any off-site discharge. Facility construction details and configuration are illustrated by Maps 15-50 and 1 W-50 in Exhibits 16C and 16D. The cuttings pit and associated foundation area will be inspected during topsoil stripping, placement of the liner, and temporary closure, on completion of shaft boring operations. As- built certification will be provided to the CDMG prior to cuttings placement and following temporary closure. Primarv Method of Construction -Blind Drilling: Prior to the beginning of the blind drilling process, a pressurized pre-grout operation utilizing up to ten small diameter (2") holes, up to approximately 400 feet deep around the shaft perimeter will be considered and undertaken, as needed, to limit groundwater flows between the shaft and the formations. Individual grout holes would be drilled and a cement grout would be pumped under pressure into each borehole before completing the next hole, to seal any wet zones encountered. Each borehole would be filled with grout and allowed to set-up, effectively sealing the borehole and any fractures or voids in the grouted formation(s). Any surface casing extending above ground surface will be cut-off flush with or below natural ground level. If needed and once the pre-grout operation is completed, a shaft collar will be excavated to an approximate 10-foot diameter to competent rock at a depth of approximately 10-15 feet. Material from the collar excavation will be placed within and on one end of the cuttings pit. A surface casing approximately 8 feet in diameter (inside) and large enough to accept the shaft casing and drilling tools will be installed in the shaft collar. This surface casing will be either steel casing grouted in-place or cast-in-place concrete. A 48 by 24 foot concrete T-shaped pad will then be poured to accommodate the drilling and casing equipment. Specialized blind drilling equipment in the form of an A-leg derrick will be used to drill the pilot hole and excavate the shaft. A nominal 17-1/2-inch pilot hole will then be drilled to an approximate depth of 1,000 feet and surveyed to determine vertical shaft deviation and location underground for mine entry tie-ins. The pilot hole will then be reamed to a nominal diameter of 7.5 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 hole and the 7.5' diameter excavation, all cuttings will be removed from the excavation using an airlift system, with water (reverse circulation) being the circulation media. Supplemental water, for drilling and to adjust the density of the drilling medium, may be supplied, as needed, by a small portable pump drawing from Fish Creek under TCC's existing water rights. The cuttings will be placed in a 200 x 100 x 10 foot, lined temporary mine development waste pit excavated • within the shaft pad adjacent to the shaft excavation, as shown on Map 1W. The cuttings pit will be lined with a nominal 30-mil PVC flexible membrane liner having a permeability of ~10"12 cm/sec. MR07-225 2.05 - 45.5 11/13/07