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<br />vertteal hydraulic conducti vtty and thickness of intervening beds. 1n these simulations, <br />the drewdown caused by pit dawatering increases Lhe recharge to the aqui ter. <br />Tha overburden and coal layers were si mul sled Sn eaparate models. The model design was <br />the same in both models but the transmi sai vity end storage values were different. For the <br />overburden, a transmi sstvi ty of 26 (t2/day and storage value of 0.0001 ware used. The <br />coal layer alma) ationa assumed a transmi sai vl ty equal [e 2.6 ft2/day and a storage value <br />of 0.00007 (Table 17-3). <br />Model Calibration. Tha modal was calibrated by adJusti ng the recharge rate over the <br />made) area, until there was good agreement between water-table elevatf one between the San <br />Mf goal River and mtne area (Ff gore 77-3). Tha Ceneral Head Boundary package wag not used <br />for the steady-state calTbrati on. Tha final recharge rate for the overburden is 0.000027 <br />ft/day and for the coal is 0.0000027 ft/day. <br />These raeha rge rates are quite low, but are not unreasonable given the general low <br />permeability of shales and the fact that much of the shall on recharge di echarges into <br />Tuttle and Calamf ty Draws. It should again be noted that this model is repreaentati ve of <br />• the system where it Ss relatively unaffected by the axlatence of the streams. <br />Recalls. For the transient ai mulation, the General Head Boundary package was <br />introduced. This package requires input data for the leakanee parameter (vertteal <br />conductivity divided by thickness of the intervening low-pernwabilf ty layer). Tha <br />thickness was estimated by examining litho) ogle logs for core holes in the Nucla East <br />area, which indicated that shale was present in thSck nesaes of 10 ft or note. To avoid <br />underestimating the predicted rate of pit inflow, a thi cknesa of 10 ft was used. The <br />vertS Cal eontluctl of ty was estimated to bs 70 7 em/s based on a reasonable permeability far <br />a shale and produces resul to eonsf scent pith the observed dl echarges from Pond 001 Sn the <br />Nuela M1~ area. DS atharge free the pond, which lncludaa surface Tlow, ranges from <br />approximately zero to l.5 efs. Pit pumpage is a part of this discharge. Simulated pSt <br />inflow at Nuela Eaat is within this range. <br />T ransS ent ei mul ati one were performed for a Five-year period, using the maximum drewdown <br />estimstsa for the overburden and coal. For the overburden, the pit drewdown was 5.0 ft <br />for years 7 and 2, B.O ft during year 3, 15.0 ft during year 4, and 30.0 ft during year 5. <br />The renal tf ng averburtlen drawdowna after each year arc shown in Flqures 77-4 through 17-8. <br />17-13 Revisetl 04/11/t1B <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(3}2-20 <br />