1981-11-13_PERMIT FILE - C1981013 (28)

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24 represent the permeability of an approximately 2 ft. thick fracture zone P P Y PP Y and is on the order of 10,000 times greater than the permeability measured on core plugs (Table 1 ). The storage coefficients shown in Table 2 are typical values for thin, well confined aquifers. No bedrock pumping tests were conducted at the Allen Mine and there i is , therefore, no direct way to compare coal seam permabilities at the two locations. However, it is possible to mathematically estimate inflows to the Maxwell Mine using the hydraulic properties discussed above and, by comparing with measured inflows at the Allen, establish some insight to the relative magnitudes of the controlling hydraulic properties at the two sites. Mathematical Estimate of Maxwell Mine Inflows The plan-view geometry of the Maxwell Mine will be complex, both during and after mining, and the changing geometry will affect the inflows to the mine. However, the advance of the mine and the precise geometry at a particular time consitute second-order considerations; the length of peri- meter separating the mine workings from the undisturbed ground being the most important aspect. A simple model whereby the total inflow is calcu- lated as the product of the length of perimeter and the inflow at points on the perimeter, obtained by assuming planar flow normal to the perimeter, retains the effects of first order importance. Flow to the mine is derived from storage in the water-bearing zones and is transmitted to the mine primarily through the undisturbed coal seam. Figure 6 is a schematic representation of the flow to the face at a particular point on the perimeter. The steady state distribution of drawdown is given by s = s o e x p ( x ) where s = drawdown at a point located a distance x from the face so = drawdown at the face 1