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58 <br />1 A permanent depression in the piezometric surface will exist: in the ~~e <br />C vicinity of the flooded mine workings. This depression wili exist because <br />1 of the high permeability region of the mine and not because of any continued <br />discharge from the aquifer. The magnitude of the depression will not be <br />large, but may extend to a distance (measured from the center of the mine) <br />equal to 4 times the equivalent radius of the mine. <br />The water passing through the flooded mine will be of modified quality <br />1 relative to that in the undisturbed coal seam for a period of time. The <br />difference between the quality of the current discharge from the i111en <br />Mine and that for well LA 221A may be indicative of the change that can be <br />] anticipated, although the small difference is within the range of variation <br />observed. The water of modified quality wilt spread in a plume downgradient <br />1 of the mine. Based on structural contours of the coal seam, water passing <br />J through the flooded mine will move in a northeasterly direction. The theory <br />1 of flow through a region of modified permeability predicts that the plume <br />of modified water quality may spread to a maximum total width of about 4 <br />timesthe equivalent radius of the mine: The period of tlme over which <br />waters passing through the flooded workings will continue to pick up dis- <br />solved species in addition to those already present is difficult to even <br />estimate. It is anticipated that soluble materials will be readily flushed, <br />but flow rates will be very slow, causing the flushing action to persist <br />! aver a long time period. <br />Stream And Near Surface Ground Paters <br />Our best estimate of the effective vertical permeability of the over- <br />burden is 0_ 00021 ft/d as determined oreviousiv in ehis rappei_g wer- <br />ing the piezometric surface to the roof of the mine, mining beneath the <br />valley could cause the vertical hydraulic gradient to be a maximum of unity. <br />In this cast, the vertical discharge per unit area is equal to the effective <br />i <br />pemeability in the vertical direction (i.e., 0.00021 ft/d). The width. <br />measured normal to the axis of the valley, of saturated alluvium is conserva- <br />i <br />1 lively estimated to average 350 ft. in the vicinity of the Maxwell t4ine. <br />The distance between the east and west ends of the study area is 6(100 ft. <br />which yields a horizontal surface area of saturated alluvium equal to <br />