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n U Nadel Deai gn. Two modals were developed. Tha model of the overburden was deci gnetl ~ to exarot na long-term, }ar-field of Facts due to mining, and does not cones der the shallow overburden materials (except as a recharge source), or Tuttle and Ca]ami ty Draws. The modal }or the coal represents only the coal aquifer. The hytlrogeol aglc system wee represented in eaefi model as a confi nod, one-layer, homoga~woua unit. Tha ganerali zetl ground water flow direction was along the secondary mo0e1 axis from northeast to southwest. She San Miguel River was defS ned ss a eonsta nt-head boundary along the downgradient adpa (Figure 17-1 ). The three other model boundaries represented no-flow condi clone. the mine pit was represented as a raetanguiar set of grid Cella 2400 ft x 150 ft (3b0,000 ft2) 1n the center of the modal grid. Thaae di mensi one ware based on the approximate pit width, and the greatest length of pft expected during the Five-year perf od of mulcted. Figure 17-2, a model grid overlay, is provided to orient the reader to the actual scale locations of the Nucla East mS ni ng area a:xf the San Miguel RS ver. The drain optt on in MODFLOM was used to almul ate face seepage and Oenatering of the mina p1 t. The ten model cells def t of ng the pit were designated as drain tells. The DRAIN • package was used to simulate the pit for two reasons. First, it allowed the pit to be modeled as a constant-head boundary for discharge of water, but did net allow the pit to baeosa a constant-head recharge boundary. Second, it allowed for separate accounting o/ the water discharged Into the pit. The drains maintained pretlatermi ned water elevations for the Oura tion of a gi van stress period (length, 1 year). Tha elevations of Me drat na, and hence the drawdown 1n the pit, was changed on a yearly beats, Dosed on projections of the Oepth of the pit beneath the existing water table. Water was added to the modal using two methods: the RECHARGE Dackaga and the General Head Boundary package. The recharge value used represents the long-term recharge to The unit Deirg modat ed, and is not indicative of The recharge to the shallow grwnd water system during the irrigation season. This shallow recharge appears to drain rapidly Into Tuttle and Calani ty Draws. Tha model thus represents the deeper overburden, and may untlerestlmate the amount of dt aeharge into the Dii du rS ng the trrt gait on season. Tha General Head Boundary peckaga was used to aiwlate the increase in recharge caused by drawdonn during the drewdo,m ealeul ationa. This package calculates leakage on iha basic of the difference In head in the aqui ter and Sn the beds providing recharge, and the 77-70 Revised 04/11/88 • REVISED MARCH 2006 Attachment 2.05.6(3)-2-17