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

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central soil stockpile areas as shown on the design drawings in Exhibit 49R. Natural vegetative materials (mulch) incorporated into the soil, and seeding with the topsoil stockpile stabilization seed mixture identified on page 2.05- 121, will stabilize the stockpiled soil materials. • Following soil removal, required drainage and sediment control structures will be constructed or installed. In order to minimize potential environmental and aesthetic impacts, surface drainage will be handled by a downslope drainage collection ditch; a culvert crossing where this ditch intersects the light -use road; Alternative Sediment Controls (ASC's) for the substation and soil stockpile; a partially incised two -cell sedimentation pond downgradient of the pad area; and a discharge control structure (rock check dam) and transition ditch at the outlet of the second sedimentation pond cell. TCC will apply for a modification to its existing CPDS Discharge Permit to include the new discharge point. The limited road drainage will be handled by a designed road ditch. In addition, the pad and light -use road will be gravel- surfaced to minimize erosion and sediment loss, other disturbed areas (including topsoil stockpiles) will be stabilized with erosion control fabric and temporary vegetation, and any structures will be painted in neutral earth -tone colors to blend with the natural surroundings. The light -use road will run along the contour of the low ridge at a relatively flat gradient, and will be gravel - surfaced, so road drainage control requirements are minimal. A typical road drainage ditch design is provided in Figure 2 of Exhibit 8DD, prepared by Water & Earth Technologies, Inc. The only culvert that will be required will be at the point where the light -use road crosses the downslope drainage collection ditch. All drainage calculations and documentation are provided in Exhibit 8DD. Construction of the ventilation shaft light -use road will involve soil recovery and stockpiling, installation of required drainage structure, scarification and re- compaction of surface materials, and placement and compaction of approximately 8 inches of pit -run gravel and 3 inches of suitable road -base material. The road surface will be approximately 24 feet wide, and will be graded and crowned to promote effective drainage. Road construction will require minimal cut and limited fill, so the actual road disturbance area will average approximately 30 feet in width. Cut slopes will be established at a maximum of 1.5H:1 V 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 50 feet wide has been defined as encompassing all project - related activities, including road construction and soil recovery and handling. Preparation of the ventilation shaft pad and substation area will involve installation of required drainage structures, soil material recovery and stockpiling, excavation and lining of a collection pit for blind drilling of the shaft pilot hole and shafts, placement and compaction of fill material (from cuttings pit excavation) to establish level pad working areas, haulage or stockpiling of any excess excavation material, and placement of gravel surfacing material to control dust and sediment from the pad areas. 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 TR09 -70 2.05-45.16 11/16/09