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Mine water management <br />91 <br />C. <br />Table 7.3 Dewatering well schedule for Phase 1 of Option 1 mine plan <br />Mining <br />Total <br />Total <br />Description of <br />period <br />number of <br />pumping <br />Dewatering well system <br />wells <br />rate <br />pumping <br />(months from <br />(gpm) <br />start of <br />stripping) <br />-6 to 0 <br />5 <br />50 -75 <br />• Box cut wells (BC -1 to 4) plus pilot well 16B <br />to be brought online six months prior to <br />stripping. <br />0 <br />17 <br />175 -250 <br />e Continue pumping wells BC -1 to 4. <br />• Highwall wells (HW -1 to 5) to be installed <br />and operational by month 0. These wells are <br />to be placed in locations that will not be <br />destroyed by mining. <br />• Sidewall wells (SW -1 to 4) to be installed and <br />operational by month 0. These wells are to <br />be placed in locations that will not be <br />destroyed by mining. <br />• Continue pumping pilot dewatering well 16B. <br />• Advancing wall wells (AW -1 to 3) to be <br />installed and operational by month 0. <br />0 to 6 <br />13 <br />150 to 250 <br />• Wells BC -1 to 4 will continue to be pumped <br />until they are destroyed by mining. They will <br />be filled with gravel to allow them to continue <br />to act as vertical drains. <br />• Continue pumping wells HW -1 to 5. <br />• Continue pumping wells SWA to 4. <br />• Continue pumping wells AW -1 to 3 until they <br />are destroyed by mining. Fill with gravel <br />prior to destruction to convert to vertical <br />drains. <br />6 to 18 <br />15 <br />150 -250 <br />• Add wells HW -4 to 7. <br />• Continue pumping wells HW -1 to 5. <br />• Continue pumping wells SWA to 4. <br />Vertical drains <br />The effectiveness of the dewatering wells to depressurize the units beneath the pit floor <br />is questionable because there are no major permeable coal seams within about 100 ft <br />below the Gb seam, which forms the pit floor. Floor heave may be a problem if <br />excessive pressures exist in the units underlying the pit floor. However, vertical drain <br />holes or shallow wells can be installed in the floor to relieve excess pressures. <br />Piezometers placed at strategic locations beneath the pit floor should be monitored <br />during dewatering operations to determine if vertical drains are needed. <br />2572 -R2 Colowyo Coal Company <br />Water Management Consultants <br />