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• As stated above, mine drainage to the Trapper pRs has not been as large as expected. Inflow to pits has <br />however been large enough to require continuous mine dewatering in spec pits. Continuous dewa- <br />tering we{Is are installed in Derringer and Flintlock pits with the intent of gradually pumping pit water and <br />consequently reducing the erosion potential in surtace drainage downstream. Continuous dewatering <br />wells may be installed in Ashmore, Flintlock and Gaftling pits if necessary during permit term 1998-2002. <br />Historicaly, the northern end of the Ashmore Pit produces the most water, and was normally pumped <br />18-20 hours after it had been open for approximatery one week. A large pump is used to remove the <br />water and the quantity of water pumped indicates the average yield from the aquifer is in the range of 70 <br />gpm. Dertinger Pit is dry in the southern portion but normally yields water at the northern end. Pumpage <br />from Derringer pR is estimated at less than 10 gpm for an average yield. The bulk of the water <br />accumulation in Enfiekt pit is from the diversion of surface water (spoils and roads) into the pR. <br />Drawdown in the coal aquifers will be large adjacent to the open pits. The gradient of the piezometric <br />surtace should be steep in the coal aquifers, because they contain low transmissivities. A large percent- <br />age of the water yield to a pit is from the non-confining portion of the aquifer. The aquifer will be in <br />unwnfined conditions near the pit and therefore, mainly the unconfined properties govern drainage to the <br />pR and drewdowns from that drainage. Drewdowns near the Ashmore Pit are probably in a few tens of <br />feet at 1,000 feet from the pR wall after a year or more. The rate of mine movement reduces the quantity <br />of time an area will be impacted by the mine drainage. Drawdowns of a very few feet are not expected to <br />extend beyond one mile of the pit walls by 1985. The following calculations were used. <br />Drawdown calculation near Ashmore Pit <br />For: Drawdown estimate at one year and 1,000 feet from pit. <br />Transmissivity (T) = 250 gaUday/ft <br />• Specific yield (S) = 0.01 <br />Distance from pk's edge (r) = 1,000 ft <br />Time since start of pumping =385 days <br />• <br />P~ -~I <br />4225 <br />R9iaY 1 ;s 199 <br />