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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
<br />approximately 10 feet, and is sized to contain all drilling fluids and cuttings from both shafts (total capacity of
<br />approximately 12,500 cubic yards). Facility construction details and configuration are illustrated by the design
<br />drawings provided in Exhibit 49R. The cuttings pit and associated foundation area will be inspected during soil
<br />material stripping, placement of the liner, and temporary closure, on completion of shaft boring operations. As-
<br />built certifications will be provided to the DRMS prior to cuttings placement and following temporary closure. In
<br />general, the shaft pad is designed and configured to balance cuts and fills, and minimize any need for borrow
<br />material or handling of excess cut material.
<br />Prior to drilling the pilot hole for each shaft, a maximum 17.5 -inch diameter exploration borehole will be drilled to
<br />a depth of approximately 1,360 feet to verify geologic and hydrologic conditions for the shaft site. Any excess
<br />water from the exploration borehole will be routed to the previously constructed cuttings pit. The exploration
<br />borehole will be completed with a 12 -inch diameter steel casing, an 8 -inch and two, 2.5 inch diameter pipes will be
<br />installed within the casing, and the annulus will be grouted between the borehole and casing. It is anticipated that
<br />the 8 -inch pipe will be used as a nitrogen injection borehole, and the two 2.5 -inch pipes for communication lines.
<br />The exploration borehole will provide information on site ground water conditions, however, in the event
<br />unanticipated ground water flows are encountered, they would occur during drilling of the pilot holes when the
<br />collection pit would have significant excess capacity. The combination of excess capacity and flow controls should
<br />be adequate to prevent any off -site discharge.
<br />The substation area will be constructed at the same time as the shaft pad, as previously discussed. The substation area
<br />will be a 50 x 100 foot gravel- surfaced pad. Pole- or pad - mounted transformers and switch -gear will be installed on
<br />the pad, and a grounding field will be established under the near edge of the shaft pad during construction. If
<br />transformer pads are utilized, a maximum of three 20 x 20 foot pads would be constructed. The substation area will
<br />be enclosed by a chain -link security fence with locked gate, to limit access. A 69KV powerline will be extended up to
<br />3,000 feet to the new substation from the existing Yampa Valley Electric Association line to the northeast.
<br />Installation of this line will require placement of approximately 12 -16 new powerpoles.
<br />Primary Method of Construction — Blind Drilling _Prior to the beginning of the blind drilling process, a pressurized
<br />pre -grout operation utilizing up to ten small diameter (6.25 ") holes, approximately 600 -800 feet deep around the
<br />perimeter each shaft will be considered and undertaken, as needed, to limit groundwater flows between the shaft and
<br />the formations. Individual grout holes will be drilled, and a cement grout pumped under pressure into each borehole
<br />before completing the next hole, to seal any wet zones encountered. Each borehole will be filled with grout and
<br />allowed to set -up, effectively sealing the borehole and any fractures or voids in the grouted formation(s). Any surface
<br />casing extending above ground surface will be cut -off flush with, or below, natural ground level.
<br />If needed, and once the pre -grout operation is completed, approximately 10 -foot diameter shaft collars will be
<br />excavated for each shaft to competent rock, at a depth of approximately 40 feet. Material from the collar
<br />excavation will be placed within and on either end of the cuttings pit. Surface casing approximately 8 feet in
<br />diameter (inside) and large enough to accept the shaft casing and drilling tools will be installed in each shaft collar.
<br />This surface casing will be either steel casing grouted in -place or cast -in -place concrete. Maximum 18 -inch
<br />diameter auger holes will be drilled into competent rock and reinforced concrete piers will be poured to anchor the
<br />shaft pads and any other significant structures. It is anticipated that up to 40 anchor piers may be required. Two
<br />concrete pads, either "T" shaped or rectangular, will be poured to accommodate the drilling and casing equipment;
<br />emergency escape hoist, and shaft heater, for the ventilation intake shaft; and fan, fan shroud, mechanical building,
<br />and silencer, for the ventilation exhaust shaft. Average thickness for the reinforced concrete pads will be 2 feet,
<br />and the pads will be a maximum of 4,050 square feet. Specialized blind drilling equipment consisting of A -leg
<br />derricks, drive motors, and drill -string handling components will be installed on the shaft pads and used to drill the
<br />pilot holes and, complete shaft drilling.
<br />Nominal 17.5 -inch pilot holes will be drilled for each shaft to an approximate depth of 1,360 feet and surveyed to
<br />determine vertical shaft deviation and location underground for mine entry tie -ins. The pilot holes will then be
<br />reamed to a nominal diameter of 7.5 -8.0 feet to accommodate the final steel liner. The reaming technique utilizes
<br />an inverted disc cutter equipped hemispherical raise -bore head, to cut the rock. During the drilling of the pilot
<br />holes and the 7.5 -8.0 -foot diameter excavation, all cuttings will be removed from the excavation using an airlift
<br />MR10 -249 2.05-45.17 11 /01 /10
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