Laserfiche WebLink
Getty Task 2 Page 3 Msrch 1, 1983 <br />the iaitisl head array <br />following arrays: <br />The inflow portion of the program also requires the • <br />TON - time mining begins is grid (days) <br />TOFF - time reclamation begins in grid (days) <br />These arrays are used by the program to determine if a particular grid is <br />being actively mined daring nay time period. For grids that are not mined, <br />the value of TGN is set to a time greater than the total time of analysis. <br />I Grids that are not reclaimed, i.e. areas where room and pillar mining is <br />utilized, and in which water mast be removed are handled by setting TOFF to a <br />time greater than the total time of analysis. All arrays, with the ezception <br />of D% sad DY, contain NR : NC elements. <br />These data described above aze used by the computer program to simulate <br />lateral flow is the modeled aquifer. It should be noted that the model is not <br />capable of simulating three dimensional flow that would be encountered in a <br />series of vertically interconnected aquifers. The recharge/discharge values <br />• specified is the QC array are constants. If the recharge is due to leakage • <br />from a separate aquifer, a reduction of head in the modeled aquifer would <br />result is an increase in recharge from the supply aquifer. Since it is likely <br />r <br />_ that such a system exists in the atndy area, an analytical solution was <br />utilized to estimate a 'worst case' inflow due to vertical, upward leakage <br />from as underlying aquifer. This solution is presented is a subsequent <br />section. <br />Since the Twentymile Sandstone is saturated in much of the study area, <br />l the reduction of head in the overburden aquifer daring mining will cause the <br />gradient between the two aquifers to be increased and inflow from the roof may <br />be encountered as water from the Twentymile aquifer leaks through the <br />intervening marine shale. The model calculates this component of the mine <br />inflow by assuming that the flow occurs as one dimensional, vertical flow is <br />L <br />response to a unit gradient. In areas that have been mined, this assumption <br />is realistic because the vertical permeability of the marine shale is much <br />L <br />less than that of the Twentymile sandstone. Under these conditions, the flow <br />~ from the Twentymile aquifer into the mine is essentially equal to the <br />saturated vertical hydraulic conductivity of the marine shale. To prevent <br />inflow from those areas rhere the Twentymile aquifer is not saturated, the <br />elevation of heed in the overburden squifer is compared to the elevation of <br />