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2 <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 /> i <br /> mine will be modified relative to the pre-mining condition insofar as there <br /> will remain a "permanent" concentration of flow lines around the flooded <br /> 1' mine workings. <br /> �i <br />