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• be 2.4 acre-feet. This water requirement is 100 percent consumptively used. Future consumptive use will be <br />the same as present consumptive use since the azea of surface disturbance will not change. <br />Evaporation From Ponds <br />There are a maximum of two ponds proposed for the Northfield Mine property with an assumed total surface <br />area of one acre. Table 3 presents the estimate of annual pond evaporation. The water lost to evaporation is a <br />consumptive use and is equal to approximately 3.1 acre-feet per year from the two ponds. The rate of <br />evaporation is higher during the summer months than during the winter months, with approximately 90 percent <br />of the loss occurring from May through October. Since the surface areas of the ponds will not increase in the <br />future, consumptive use will not change. <br />Total Consumptive Use <br />Total monthly water requirements do not change greatly through the year but are slightly higher in the warmer <br />months because of increased evaporation from ponds and the need for outside dust suppression. Projections <br />• for the monthly consumptive uses are shown in Table 3. The total annual consumptive use by the mine is <br />projected to be 30.1 acre-feet. <br />DESCRIPTION OF RELATIONSHIP OF MINE WATER USAGE WITH SURFACE FLOWS <br />The mine azea is located almost entirely within the Chandler Creek drainage. As described previously, water <br />levels in the observation wells represent a potentiometric surface, as represented in Figure 6. Since ground <br />water movement is in the direction of decreasing potentiometric levels, ground water movement in the mine <br />site azea is to the north-northeast, somewhat parallel to drainages in the Chandler Creek basin. <br />When coal excavation begins, ground water movement in the coal seam is intersected and ground water flows <br />into the mine cavity. As a result of the lowering of pressure caused by the mine, the potentiometric surface <br />drops toward the mine cavity. Water inflow then tends to accumulate in the mine and dewatering becomes <br />necessary. Water withdrawn from the mine and consumptively used is water which would otherwise have been <br />discharged into the surface water system. <br />• -19- <br />