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Mine water management <br />0 <br />Table 7.5 Dewatering well schedule for Option 2 mine plan <br />95 <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 />3 <br />30 -45 <br />• North side wells used for water supply <br />0 to 2 <br />6 <br />60 -90 <br />• Additional north side wells used for water <br />supply <br />2 to 6 <br />12 <br />90 -150 <br />• Continue to pump north side water supply <br />wells <br />• Install about 6 wells on the advancing face <br />(rows 1 and 2 are combined) for first three <br />rows of wells <br />• Plug wells over interval below the pit floor <br />prior to placing spoil over them to prevent <br />continued upward flow into spoil pile <br />6 to 20 <br />16 <br />150 -250 <br />• Continue to pump north side water supply <br />wells <br />• Add additional rows of about 10 dewatering <br />wells for rows 4 and higher <br />• Plug wells over interval below the pit floor <br />prior to placing spoil over them to prevent <br />continued upward flow into spoil pile <br />Under the Option 2 mine plan, it is assumed that dewatering wells will be installed on the <br />north side of the ultimate mine footprint during stripping as shown in Figure 7.3. These <br />wells will be used to provide water supply to the mine. The wells are optional and could <br />be eliminated if other water supply sources are available. Since these wells can be <br />pumped for many years, they will also provide significant depressurization on the north <br />side of the mine footprint well in advance of any mining. As a result, it may be possible <br />to reduce the number of dewatering wells needed in the northern portion of the mine <br />footprint. <br />Prior to placing spoil material over dewatering wells that have been mined through, they <br />should be sealed to reduce upward seepage into the spoil material. Sealing may be <br />best accomplished by grouting wells prior to mining through them. <br />t <br />2572 -R2 <br />Colowyo Coal Company <br />Water Management Consultants <br />