2016-06-08_PERMIT FILE - C1982056A

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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 an upslope drainage diversion ditch; a culvert crossing where this ditch intersects an existing natural drainage and crosses under the light -use road; and a interceptor ditch and rock -lined sump (Alternative Sediment Controls (ASC's)) on the downslope side of the pad. All drainage calculations and documentation are provided in Exhibit 49Y. Once the pad is constructed, surface runoff from the pad will be limited by placement of gravel surfacing material, and any limited surface drainage from the pad will flow to the cuttings pit. As a limited disturbance area, the pad, ditches, and ASC's will function under a Small Area Exemption to assure effective runoff and sediment control. Road drainage will be minimized by placement of gravel surfacing. Other disturbed areas (including topsoil stockpiles and pad outslopes) will be stabilized with temporary vegetation, and any structures will be painted in neutral earth - tone colors to blend with the natural surroundings. Construction of the ventilation shaft light -use road will involve soil recovery and stockpiling, installation of a 30 - inch CMP culvert, 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. For permitting purposes, a road disturbance corridor 40 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 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, placement and compaction of fill material (from cuttings pit excavation and site grading) to establish level pad working areas, and placement of gravel surfacing material to control dust and sediment from the pad area.. 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. The cuttings pit will be a single cell approximately 70 x 100 feet, and approximately 8 feet deep, and is sized to contain all drilling fluids and cuttings from the shaft (total capacity of approximately 1,700 cubic yards). Facility construction details and configuration are illustrated by the design drawings provided in Exhibit 49Y. 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 DBMS prior to cuttings placement and following temporary closure. A 69KV distribution line will be extended approximately 1,000 feet to the new ventilation shaft pad from the existing Fish Creek Water Treatment Facility Substation. Because the new pad is adjacent to the powerline feeding this substation, the distribution line can be hung on the existing poles, requiring only two additional poles and pad - mounted transformer at the pad location. Primary Method of Construction — Blind Drilling — The potential exists to complete either one 48 -inch shaft or two 30 -inch shafts. Prior to blind drilling, a shaft collar(s), up to 8 -foot in diameter will be excavated to competent rock, at a depth of approximately 60 feet. Material from the collar excavation will be placed within and on either end of the cuttings pit. Surface casing up to 7 feet in diameter (inside) and large enough to accept the shaft casing and drilling tools will be installed in the shaft collar(s). This surface casing will be either steel casing grouted in- place or cast -in-place concrete. Maximum 18 -inch diameter auger holes will be advanced into competent material, and reinforced concrete piers will be poured to anchor the shaft pads and any other significant structures. It is anticipated that up to 10 anchor piers may be required. A "T" shaped concrete pad will be poured to accommodate the drilling and casing equipment for the ventilation intake shaft. Average thickness for the reinforced concrete pad will be 2 feet, and the pad will be a maximum of 770 square feet. Specialized blind drilling equipment consisting of an A -leg derrick, drive motor, and drill -string handling components will be installed on the shaft pad and used to drill the pilot hole(s) and, complete shaft drilling. MR14-283 2.05-45.23 10/30/14