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I When coal excavation begins (Figure 5), ground water movement in the coal <br />seam ie intersected and ground water flows relatively easily into the mine <br />cavity. Ae a result of the lowering of pressure caused by the mine. the <br />1 piezometrie surface drops toward the mine cavity. Water in the mine <br />cavity is no longer under pressure. as i[ was in the u~ined coal. and it <br />cannot flow uphill towards the mine portal. Water inflow then tends to <br />accumulate in the mine and dewatering becomes necessary. Water withdrawn <br />I from the mine and consumptively used is water which would otherwise have <br />been discharged to the surface water system (Figure 6). <br />$ffeet of !lining on se~lin Creek basin <br />I Mine inflows have been calculated to be 142.5 acre-feet per year. based <br />upon discharge records for 1985. For future mining. it is estimated that <br />mine inflow may reach a maximum of 213.2 acre-feet per year. when the mine <br />I is enlarged to the proposed area show on Figure 2. The estimate of <br />future iaflowa to the mine was calculated using tradi[ioaal ground water <br />1 flow equations. Input to the equation include the ground water gradient <br />in the area. estimated permeability. and the expected maximum disturbed <br />I area of the mine. Presently. the impact of the mine on the regional <br />ground water system is limited to a very short distance from the mine. <br />Although the water level fluctuations are not conclusive. rater level <br />fluctuations in observation wells indicate that the impact of the mine is <br />limited to no more than approximately 1000 feet from the mine. <br />Observation wells completed adjacent to or above the seams being mined <br />show limited interference from the mine suggesting the limited <br />interference. This means that the mining operation is diverting rater <br />from storage in the ground water system and intercepting very little rater <br />that. under undisturbed conditions, would have been discharged to the <br />surface system. The historic base flow to Pevlin Creek and Magpie Creek <br />I from the zones being mined prior to mining has been estimated to be <br />approximately 17.7 acre-feet per year. <br />-28- <br />