2010-06-04_PERMIT FILE - C1982056A (9)

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Following topsoil removal, required drainage and sediment control structures were constructed or installed. These structures include designed culverts for the road crossing of Fish Creek (see Exhibit 8R, Fish Creek Culvert Design, NW Mains Ventilation Shaft) and road crossings of smaller ephemeral drainage channels; a temporary diversion ditch around the upgradient perimeter of the shaft pad; runoff collection ditches for the pad area topsoil stockpiles; a downgradient containment berm, and discharge control structure (sump and rock check -dam) at the downgradient limit of the shaft pad. The drainage from the shaft pad is addressed under a Small Area Exemption (SAE), as it is relatively small (approximately 1.8 acres), and encompasses gravel- surfaced and/or reclaimed areas. The access road follows relatively level terrain and is gravel- surfaced, so access road drainage control requirements are minimal. To address high -flow flooding in the area of the Fish Creek road crossing, TCC installed four 24 -inch relief culverts above the natural flow channel to pass flood flows safely under the road. The existing primary culvert is designed to safely pass the design flows, and all culverts are covered with a minimum of 1.0 foot of compacted fill. All drainage calculations and documentation are provided in Exhibit 8S, the SAE demonstration is provided later in this section, and the drainage structures are shown on Map 24. The SAE demonstration includes ditch sizing for the upland diversion and road ditches. The access road into the shaft pad crosses Fish Creek, and TCC placed "Buffer Zone" signs at the boundary of the stream crossing disturbance. Except for the disturbance associated with the stream crossing, no further activity is planned within the Buffer Zone boundary. Construction of the ventilation shaft access road involved topsoil recovery and stockpiling, installation of required drainage structures, scarification and re- compaction of surface materials, placement of geotextile in selected areas, and placement and compaction of approximately 8 inches of pit -run gravel and 3 inches of road -base material. The access road surface is approximately 22 feet wide and is graded and crowned to promote effective drainage. Road construction required minimal cut, and limited fills in the area of the Fish Creek drainage crossing. Fill slopes were graded to 3H:1 V and stabilized by seeding with the topsoil stockpile stabilization seed mixture. Preparation of the ventilation shaft pad involved topsoil recovery and stockpiling, installation of required drainage structures, grading and compaction to establish a level pad working area, excavation of mud pits for drilling of the shaft pilot hole, temporary stockpiling of the excavated material, and placement of gravel surfacing material to control dust and sediment from the pad area. Mud pits were approximately 20 x 20 x 8 feet, and were sized to contain all drilling fluids. In the event unanticipated ground water flow is encountered during shaft boring, there was provision to enlarge or add pits to handle the increased flows. The ventilation shaft pilot hole was drilled using a reverse circulation drill -rig to drill a 14 -inch nominal diameter pilot hole from the surface to a depth of approximately 1,450 feet. The shaft collar area was excavated to a depth of approximately 20 -foot, a collar - liner, consisting of steel ring -beams and liner -plate was placed, and the annulus between the liner and the collar excavation cemented. A temporary head -frame was erected on the shaft collar structure, over the pilot hole, to support and handle the shaft boring equipment. The shaft boring drive -unit was installed on the shaft collar structure in preparation for shaft boring operations. During drilling, drilling fluids were generally re- circulated from the excavated mud pits, which served as temporary fluid reservoirs. Shaft boring and casing of the approximate 20 -foot diameter ventilation shaft were conducted as separate operations. A surface- mounted drive unit was used to turn a rotary cutting head attached to a shaft extending from the surface through the pilot hole, and a hoist on the temporary headframe was used to maintain continuous upward pressure on the cutter head. As boring progressed, the cuttings were dropped down the shaft bore and are recovered, transported, and placed in mined -out areas underground. An alternative to transporting the cuttings to mined -out areas was included, which involved slurrying them into the EMD sump. For this option, an underground line would be installed and the cuttings slurried to the EMD and pumped behind the seals in 7 -, 9- or 10- Right. Any underground development waste cuttings not placed underground were transported to the surface via the existing conveyance system and stored south and east of the Area 1 Pit. The overall cuttings volume was approximately 21,000 CY (16,862 CY swelled by 25 percent). Any excess cuttings discharged from the existing rock belt, where they were loaded into trucks and hauled to the previously approved overburden storage area (see Map 24 for locations). This overburden storage area is in a previously disturbed area and within TCC's existing sediment control system. The overburden storage area is TR09 -66 2.05 -45.1 02/17/09