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0 <br />2 <br />• <br />The effective vertical permeability of the overburden materials is small <br />and vertical leakage to the mine from the surface and near surface waters <br />in the valley is estimated to be less than 3 gpm in the absence of subsidence. <br />This small quantity of flow will have a negligible effect on the quality, <br />quantity, and levels of water in the valley. <br />During active mining, the drawdown of the piezometric surface will ex- <br />tend outward from the mine possibly as far as 15,000 ft., measured from the <br />center of the mine. Recovery of the piezometric surface to the post-mining <br />steady state levels will occur over approximately 80 years, beginning with <br />the cessation of mining. Most of that time period is required to flood the <br />mine workings. The post-mining distribution of piezometric head is expected <br />to exhibit a permanent depression in the vicinity of the mine due to the <br />essentially infinite permeability of the workings. The post-mining quality <br />of ground water passing out of the flooded mine probably will be slightly reduced <br />relative to the undisturbed ground water. Based on the dip of the coal seam, <br />the plume of water of modified quality will move toward the northeast <br />at a very slow rate. <br />The discharge of mine waters to the stream constitutes a small, temporary <br />change in the local hydrologic regime, both with respect to quantity and <br />quality. No permanent modifications of the recharge or discharge of ground <br />water are expected. The post-mining pattern of flow in the vicinity of the <br />mine will be modified relative to the pre-mining condition insofar as there <br />will remain a "permanent" concentration of flow tines around the flooded <br />mine workings. <br /> <br />I <br />i <br />