2008-01-11_PERMIT FILE - C1982056A (2)

Home Browse Search

A typical road drainage ditch design is provided in Figure 2 of Exhibit 8X, prepazed by Water & Earth Technologies, Inc, August 2004. Two culverts are required to intercept and transfer flow from the runoff ditches to limit runoff velocities in the ditches to less than or equal to 3.75 feet per second (fps). This systems approach assures that the ditches remain stable with no channel scour or degradation during peak • flow events. All drainage calculations and documentation for the shaft pad, sedimentation pond, and access road are provided in Exhibit 8X, and drainage structures are shown on Map 24 (Sheet 3 of 3). Construction of the ventilation shaft access road involved topsoil recovery and stockpiling, installation of required drainage structures, 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. Following topsoil removal, the exposed sub-grade was scarified to a depth of approximately 12-inches and re-compacted to 95 percent of maximum standard Proctor Density (ASTM D698), with random density testing to verify compaction. Road construction required minimal -cut and limited fill, so the actual road disturbance azea averaged approximately35 feet wide. Cut slopes were established at a maximum of 1,SH:I V and fill slopes were graded to 2Ha V or less, with all disturbed slopes stabilized by seeding with the topsoil stockpile stabilization seed mixture. The access road top surface is approximately 24 feet wide and is graded and crowned to promote effective drainage. For permitting purposes, a road disturbance corridor 100 feet wide has been defined as encompassing all project-related activities, including road construction and topsoil stockpiling. Preparation of the ventilation shaft pad involved topsoil recovery and stockpiling, installation of the required drainage structures and sediment pond, gading and compaction to establish a level pad working area, excavation of a temporary underground mine development waste disposal pit for surface collar material and conventional excavation of the shaft, haulage or stockpiling of the excavated borrow material, and placement of gravel surfacing material to control dust and sediment from the pad area. Excavated borrow material from the collection pit was used to construct the embankment of the waste disposal pit, which was constructed in 8 to I2 inch lifts, compacted to 95 percent of maximum standard • Proctor Density. The collection pit is approximately 14 feet deep, is sized to contain all material excavated from the shaft, and is lined with a PVC membrane liner to minimize infiltration of any moisture contained in the excavated material.. In the event unanticipated groundwater flows aze encountered during shaft sinking operations, portable pumps will be used to continuously dewater the shaft, with discharge to one of the utility boreholes, which would route the water back into the abandoned underground mine workings, or to the adjacent ephemeral drainage channel, Facility construction details and configuration are illustrated by Maps EX16E-MI and M2; Map EX49A-M2, Shaft Pad Profiles; and Map EX49A-M3, Waste Disposal Pit Profiles, in Exhibits 16E and 49A. The cuttings pit and associated foundation area were inspected during topsoil stripping; placement of the liner; and temporary closure, on completion of shaft sinking operations. As-built drawings will be provided to the CDMG prior to cuttings placement and following temporary closure. Primary Method of Construction -Conventional Blind Sink Excavation The 6-North Mains Ventilation Shaft was developed by conventional blind sinking excavation. Pre- grouting was not required for conventional blind sinking operations. A probe-hole was typically carried down the hole and ahead of the shaft as shaft excavation progresses, Water was grouted off from within the excavated shaft as it was encountered. A shaft collar was excavated to an approximate ZO- to 22-foot diameter to competent rock at a depth of approximately 20-ZS feet. Material from the collar excavation was placed within waste disposal pit. A surface casing approximately 12-18 feet in diameter (inside) and large enough to accept the shaft casing and conventional drilling and mucking tools was installed in the shaft collar. This surface casing is cast- in-place concrete. A nominal 25 by 25-foot by 4- to 6-foot thick concrete pad was poured to accommodate the winches, drilling, mucking and casing equipment, and headframe. Specialized drilling and mucking equipment in the form of a hoist, headframe, backleg foundation, and muck dumping system MR06-218 2.05-45.6c 07/26/07