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Section 780.21(c) Continued. <br />Revised 11/20/80 <br />be no lowering of water levels in private wells in the mine plan <br />and adjacent area, because there are no wells which produce water <br />from the coal aquifer, as discussed in Section 779.15. <br />The maximum decline of water levels in the coal aquifer was esti- <br />mated using the "line-sink" equation for constant discharge to a <br />linear drain given in Lohman (1972), p. 40: <br />s = (720) 2 T D(u)q <br />Qb x <br />Where: s = drawdown at distance x from the drain. <br />Qb = constant discharge to the drain per linear <br /> foot. <br />x = ~istan£e ffrom the <br />on <br />n eet drain to point of observa- <br /> i <br />, <br />. <br />T = transmissivity, in feet sq uared per foot per <br /> day. <br />D(u)q = drain function for constant discharge (Lohman, <br /> 1977). <br />The above equation is based on the following assumptions: the <br />aquifer is homogeneous, isotropic, and of semi-infinite areal <br />extent (bounded on one side only by the drain), the discharging <br />drain completely penetrates the aquifer, the aquifer is bounded <br />above and below by impermeable strata, the flow is laminar and <br />unidimensional, the release of water from storage is instantaneous <br />and in proportion to the decline in head, and the drain discharges <br />at a constant rate. The maxlmum dewatering rates previously calcu- <br />lated for each mining unit were used in the above equation. Values <br />of maximum drawdown were calculated for distances of 100, 500, <br />1,000, and 2,000 feet from active pit as 75.5, 15.1, 7.5, and 3.8 <br />feet, respectively. Water level decline is not expected to be <br />measureable more than one mile from the mine plan area. This <br />simulation represents the worst case projection of water level <br />decline in the adjacent area. <br />780-114 as <br />