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1 <br />1 <br />' When coal excavation begins (Figure 5). ground water movement in the coal <br />seam is 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 />' piezometric surface drops toward the mine cavity. Water in the mine <br />cavity ie no longer under pressure. as it 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 Water withdrawn 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 />' from the mine and consumptively used ie water which would otherwise have <br />been discharged to the surface water system (Figure 6). <br />t Bffect of Mining on Newlin Creek Basin <br />t 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 />is enlarged to the proposed area ahovn on Figure 2. The estimate of <br />future inflows to the mine was calculated using traditional 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 />area of the mine. Presently. the impact of the mine on the regional <br />ground water system ie limited to a very short distance from the mine. <br />' Although the water level fluctuations are not conclusive. water level <br />fluctuations in observation wells indicate that the impact of the mine ie <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 water <br />from storage in the ground water system and intercepting very little water <br />' that. under undisturbed conditions. would have been discharged to the <br />surface system. The historic base flow to Newlin Creek and Magpie Creek <br />from the zones being mined prior to mining has been estimated to be <br />approximately 17.7 acre-feet per year. <br />-28- <br />