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Catty Task 2 Page 11 March 1, 1983 <br /> <br />of the discharge and recharge areas for the aquifer. Principal recharge areas <br />I <br />l include the mounded area is the Tieken lease area, the outcrop along the <br />northwestern flank of the basin (Tow Creek Mound Area), sad, possibly, the <br />area where Fish Creek passes over the outcrop as it eaters Tweatymile Park. <br />The aquifer discharges to Fish Creek through the Middle Creek fault along the <br />j northeastern edge of the basin. Measurement of the aquifer recharge and/or <br />7 <br />discharge is difficult and generally these values are obtained indirectly <br />! <br />r based on more easily me asnred psrameters. CXCC personnel have conducted <br />I streamflow studies in the Tweatymile Park basin and have estimated that Fish <br />Creek gains approzimately 2000 acre-feet/year (1240 gpm) as it traverses the <br />basin. This total flow increase includes direct runoff, irrigation return <br />flows, and discharge from other aquifers as well as discharge from the <br />overburden aquifer. This value does provide nn upper limit as to the amount <br />of flow through the overburden aquifer, however. <br />( The most difficult recharge value to quantify is that causing the ground <br />water monad in the Tieken Lease area. As discussed is the Task 1 report, it <br />is believed that the source of this recharge is an underlying aquifer. Water <br />flows upward from the underlying aquifer (presumably the Trout Creek • <br />Sandstone) through joints and faults that ezist is the area. This water is <br />then discharged laterally through the Wadge overburden aquifer. The amount of <br />LLL <br />vertical upward leakage delivered to the aquifer is probably small at steady <br />state end the large gradients in the vicinity probably result from low <br />l permeability. It should be noted, however, that reduction of head in the <br />overburden aquifer will cause the gradient between the aquifers to increase <br />with a resultant potential for additional inflow to the mine. <br />~i. <br />Because it was assumed that Figure 1 represents the steady-state flow <br />conditions for the aquifer, the total amount of aquifer recharge must be equal <br />to the total amount of aquifer discharge and it was possible to estimate the <br />L steady-state flow through the overburden aquifer. During the calibration <br />process. known recharge and discharge grids were established as constant Lead <br />L grids and the permeability was adjusted to obtain a heed distribution similar <br />to that presented oa Figure 1 at near steady-state conditions. The flow <br />contributions from each such grid was then ealcnlated upon acLieviag I <br />calibration, l <br />TLe model also requires the vertical saturated permeability of the marine • <br />shale that separates the Twentymile aquifer from the Wadge overburden aquifer. <br />