2009-12-30_GENERAL DOCUMENTS - C1982056

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The collection pit will consist of four cells covering an area of approximately 130 x 520 feet, with a depth of approximately 10 feet, and is sized to contain all drilling fluids and cuttings from both shafts (total capacity of approximately 12,500 cubic yards). Facility construction details and configuration are illustrated by the design drawings provided in Exhibit 49R. The cuttings pit and associated foundation area will be inspected during soil material stripping, placement of the liner, and temporary closure, on completion of shaft boring operations. As -built certifications will be provided to the DRMS prior to cuttings placement and following temporary closure. In general, the shaft pad is designed and configured to balance cuts and fills, and minimize any need for borrow material or handling of excess cut material. Prior to drilling the pilot hole for each shaft, a maximum 17.5 -inch diameter exploration borehole will be drilled to a depth of approximately 1,360 feet to verify geologic and hydrologic conditions for the shaft site. Any excess water from the exploration borehole will be routed to the previously constructed cuttings pit. The exploration borehole will be completed with a 12 -inch diameter steel casing, an 8 -inch and two, 2.5 inch diameter pipes will be installed within the casing, and the annulus will be grouted between the borehole and casing. It is anticipated that the 8 -inch pipe will be used as a nitrogen injection borehole, and the two 2.5 -inch pipes for communication lines. The exploration borehole will provide information on site ground water conditions, however, in the event unanticipated ground water flows are encountered, they would occur during drilling of the pilot holes 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. The substation area will be constructed at the same time as the shaft pad, as previously discussed. The substation area will be a 50 x 100 foot gravel- surfaced pad. Pole- or pad - mounted transformers and switch -gear will be installed on the pad, and a grounding field will be established under the near edge of the shaft pad during construction. If transformer pads are utilized, a maximum of three 20 x 20 foot pads would be constructed. The substation area will be enclosed by a chain -link security fence with locked gate, to limit access. A 69KV powerline will be extended up to 3,000 feet to the new substation from the existing Yampa Valley Electric Association line to the northeast. Installation of this line will require placement of approximately 12 -16 new power poles. Primary 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 (6.25 ") holes, approximately 600 -800 feet deep around the perimeter each shaft will be considered and undertaken, as needed, to limit groundwater flows between the shaft and the formations. Individual grout holes will be drilled, and a cement grout pumped under pressure into each borehole before completing the next hole, to seal any wet zones encountered. Each borehole will 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, approximately 10 -foot diameter shaft collars will be excavated for each shaft to competent rock, at a depth of approximately 40 feet. Material from the collar excavation will be placed within and on either end of the cuttings pit. Surface casing approximately 8 feet in diameter (inside) and large enough to accept the shaft casing and drilling tools will be installed in each shaft collar. This surface casing will be either steel casing grouted in -place or cast -in -place concrete. Maximum 18 -inch diameter auger holes will be drilled into competent rock and reinforced concrete piers will be poured to anchor the shaft pads and any other significant structures. It is anticipated that up to 40 anchor piers may be required. Two concrete pads, either "T" shaped or rectangular, will be poured to accommodate the drilling and casing equipment; emergency escape hoist, and shaft heater, for the ventilation intake