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storage coefficient, hydraulic gradient, and transmissivity were determined from aquifer <br /> tests and are presented in Table 17-3. <br /> Estimates of the overburden and Dakota coal ground water inflow are presented in Tables <br /> 17-1 and 17-2. These estimates were prepared assuming that the total inflow would be <br /> derived from two principal sources: 1) the interception of premining flow rates under a <br /> natural hydraulic gradient; and 2) the drainage of ground water from storage in the <br /> aquifers. The following is a list of assumptions made in using the McWhorter pit inflow <br /> analysis technique. <br /> 1 . Mining intercepts the saturated portion of the pit at the start of each year. <br /> 2. The length of pit opened on a daily basis is equivalent to the total pit length <br /> divided by the number of days required to open the pit. <br /> 3. Each daily pit increment is instantaneously opened. <br /> 4. Total pit inflow per year is equal to the sum of incremented daily inflows for that <br /> year. <br /> 5. Pit inflows for each year are independent of residual effects from preceding years. <br /> The method therefore tends to overestimate the amount of water coming into the pit. <br /> 6. Hydraulic conductivity, storage coefficient, and depth of saturation are constant for <br /> each mine pit for each year. <br /> 7. Pit inflow is from two sides for the first year and from one side for all remaining <br /> years (i.e., there is no additional flow from the reclaimed spoils). <br /> 8. Natural - gradient flow is over the entire saturated length of the pit, no <br /> corrections are made for the orientation of the pit in relation to the gradient <br /> direction; hence, the saturated pit length is assumed to be perpendicular to the <br /> gradient direction. <br /> 9. Natural - gradient flux is unaffected by reclaimed spoils from the preceding year. <br /> 17-4 Revised 04/11/88 <br />