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to 95 percent of maximum standard Proctor Density. The collection pit is approximately 14 feet deep, is sized to
<br />contain all material excavated from the shaft, and is lined with a PVC membrane liner to minimize infiltration of
<br />any moisture contained in the excavated material. In the event unanticipated groundwater flows are encountered
<br />during shaft sinking operations, portable pumps will be used to continuously dewater the shaft, with discharge to
<br />one of the utility boreholes, which would route the water back into the abandoned underground mine workings, or
<br />to the adjacent ephemeral drainage channel. Facility construction details and configuration are illustrated by Maps
<br />EX16E-M1 and M2; Map EX49A-M2, Shaft Pad Profiles; and Map EX49A-M3, Waste Disposal Pit Profiles, in
<br />Exhibits 16E and 49A. The cuttings pit and associated foundation area were inspected during topsoil stripping;
<br />placement of the liner; and temporary closure, on completion of shaft sinking operations. As -built drawings will be
<br />provided to the CDMG prior to cuttings placement and following temporary closure.
<br />Primary Method of Construction — Conventional Blind Sink Excavation - The 6 -North Mains Ventilation Shaft was
<br />developed by conventional blind sinking excavation. Pre -grouting was not required for conventional blind sinking
<br />operations. A probe -hole was typically carried down the hole and ahead of the shaft as shaft excavation progresses.
<br />Water was grouted off from within the excavated shaft as it was encountered. A shaft collar was excavated to an
<br />approximate 20- to 22 -foot diameter to competent rock at a depth of approximately 20-25 feet. Material from the
<br />collar excavation was placed within waste disposal pit. A surface casing approximately 12-18 feet in diameter
<br />(inside) and large enough to accept the shaft casing and conventional drilling and mucking tools was installed in the
<br />shaft collar. This surface casing is cast -in-place concrete. A nominal 25 by 25 -foot by 4- to 6 -foot thick concrete
<br />pad was poured to accommodate the winches, drilling, mucking and casing equipment, and headframe. Specialized
<br />drilling and mucking equipment in the form of a hoist, headframe, backleg foundation, and muck dumping system
<br />were used to excavate the shaft. An additional concrete pad(s), nominal size of 40 by 100 feet by 2 feet thick, was
<br />placed to accommodate the hoisting winch, transformers, distribution boxes, operator consoles, surrounding
<br />building, and other miscellaneous equipment.
<br />Shaft excavation was completed as a progressive cyclic operation, with each excavation cycle consisting of four
<br />basic operations; drilling, blasting, mucking, and concrete lining. Drilling involved the use of one or more
<br />pneumatic shaft jumbo drills nested in a multiple -deck work stage. Blasting was completed using permissible stick
<br />powder and electric detonators. The blasted shaft materials were mucked using in -shaft pneumatic muckers and a
<br />nominal 3-4 yard hoisting bucket. The shaft cuttings were placed by a wheel -loader in a 14 -foot deep, lined
<br />temporary mine development waste pit excavated within the shaft pad, adjacent to the shaft excavation, as shown
<br />on Maps EX16E-M1 and M2. The cuttings pit is lined with a nominal 30 -mil PVC flexible membrane liner having
<br />a permeability of _10"12 cm/sec. The PVC liner is covered with approximately 6-8 inches of pit -run material to
<br />protect the liner. The shaft concrete lining was placed in nominal 20- to 30 -foot lifts in cycle with the drilling and
<br />mucking operation, using a curb -ring and slip -form assembly. During excavation, the shaft work area was
<br />ventilated using ventilation ducting and a permissible surface fan. Once the blind sink excavation reached the coal
<br />seam, the work stage was removed and disassembled.
<br />The cuttings volume generated by shaft sinking operations is approximately 15,126 cubic yards (22,690 cubic yards
<br />when swelled by 50 percent, based on 20 -foot diameter and 1,300 -foot depth). If drainage of water from the
<br />excavated material resulted in any significant accumulation of water in the cuttings pit, the water was pumped to a
<br />water tanker to maintain essentially dry conditions in the pit. Upon completion of the shaft excavation and concrete
<br />liner installation, any minor water accumulation in the cuttings pit were allowed to dry -out, and the collection pit
<br />and cutting materials were then be covered with previously placed materials from the shaft collar excavation,
<br />graded, and revegetated with a temporary cover. A sign(s) was posted designating the temporary mine
<br />development waste pit. The cuttings and shaft collar excavation materials will be utilized to re -fill the shaft during
<br />eventual reclamation of the facility.
<br />The cement liner serves to isolate the Twentymile Sandstone from the Wadge Overburden. As noted above, a pre -
<br />grout program is not required in a conventional blind sink. A probe -hole is typically carried down the hole as the
<br />shaft is excavated. Water is grouted off from within the excavated shaft as it is encountered. This further assures
<br />that, after final closure, the water in this unit is confined and will not seep down on the inside of the shaft.
<br />Following completion of shaft excavation and cement lining operations, and removal of equipment from the site, an
<br />emergency escape hoist will be installed in the shaft. Hoist installation will involve completion of the following
<br />activities, as illustrated by the design information provided in Exhibit 49N, 6MN Emergency Escape Hoist Design
<br />Drawings:
<br />MRI 1-259 2.05-45.10 11/17/11
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