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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 />system, with water (reverse circulation) being used as the circulation media. Supplemental water, for drilling and
<br />to adjust the density of the drilling medium, may be supplied, as needed, by hauling water from a nearby location
<br />where TCC's holds valid existing water rights. The cuttings will be placed in 115 x 425 x 10 foot, four cell, lined
<br />temporary cuttings pit excavated within the shaft pad adjacent to the shaft excavation. The cuttings pit will be lined
<br />with a nominal 30 -mil PVC flexible membrane liner having a permeability of —10-12 cm/sec.
<br />The cutting head will be rotated from the surface by the drill pipe, which also serves as a conduit to transfer cuttings
<br />from the shaft bottom to the surface collection pit. The drill pipe also serves to suspend the drilling assembly in the
<br />hole and is tensioned to adjust the cutting weight on the head and to keep the drill pipe straight. The cutting head
<br />moves the water from near the center of the head and discharges it at the periphery of the head. This water then flows
<br />down around the cutters and washes the cuttings towards the pick-up pipe in the center of the head. The drill pipe's
<br />upward flow is activated by compressed air injected down the center of the drill pipe. Rock cuttings are moved by the
<br />circulation of the water down the hole, across the shaft bottom and up the drill pipe to the surface collection pit.
<br />Within the collection pit, the rock cuttings are separated or settled out and the water is allowed to drain back or is
<br />pumped back into the hole for re -use. The cuttings volume will be approximately 12,500 cy.
<br />Once the cutter head reaches the coal seam, the cutter head will be disassembled and removed from the A -leg
<br />derrick. Using the same A -leg derrick, the excavated shaft will then be lined to a nominal 6 -foot inside diameter
<br />using a hydrostatic steel liner. The steel liner sections will be pre -fabricated off-site, hauled to the site and field
<br />welded in 30-50 foot joints. The liner will be floated into place. This is accomplished by securing a steel bulkhead
<br />to the bottom joint and leaving the excavated hole full of water while the liner is being lowered into place. By
<br />MRI 1-259 2.05-45.18 11/28/11
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