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Modeling Procedures and Assumptions <br />To model the groundwater flow in the New Horizon North area, WHI Software's Visual <br />MODFLOW program was used. Visual MODFLOW is a graphical interface which uses <br />the USGS modeling engine MODFLOW to create ground water models. <br />In modeling the New Horizon North area, two models were run. The first was an <br />overburden ground water model based on current conditions at the site and the second a <br />prediction of overburden groundwater flow with an active mine pit across the area. <br />These models can be seen (see Appendix 2.05.6(3) -2) as Figures 2.05.6(3) -2d and <br />2.05.6(3) -2e, respectively. <br />Both models were built using the same grid and base map. The grid cell size was <br />155x142'. The models made the following assumptions: <br />- Steady state with Second Park Lateral Ditch off <br />- Transmissivity: 58 ft /day <br />- Conductivity: 2.1 ft/day <br />- Average saturated thickness: 20 ft <br />- Drain (highwall) conductance: 2313 ft /day (calculated model parameter) <br />-Actual porosity: 12% (estimate from geophysical log) <br />- Effective porosity: 3% (estimated) <br />Prior to mining, the Second Park Lateral Ditch will be replaced with an HDPE pipeline. <br />During mining, the Second Park Lateral Ditch will not be recharging the area. All <br />models assume that the ditch will be off and all head data input into the models was from <br />observations when the ditch was not running. Several initial models were run to simulate <br />the ditch turned on, yielding significant affects to the recharge versus models with the <br />ditch off. <br />The first model, simulating current conditions at the site, added a higher conductivity <br />value (40 ft/day from GW-N27) to cells south of the old Peabody Nucla Mine highwall to <br />take into consideration the higher conductivity of the spoil. Initial models used drain <br />cells along the highwall to simulate the increased flow in this region. Water in this area <br />flows from the old highwall, through the spoil, issuing at Spoil Spring #1. The reclaimed <br />highwall is acting as a drain, however, it appears to be acting as somewhat of a barrier as <br />the water level at GW -N8 has recovered to about 80% of previous levels since the <br />highwall was reclaimed in 1992 (See Figure 2.05.6(3) -2a, this appendix). <br />Based on groundwater head observations from monitoring holes in the area, constant <br />head values were assigned to various cells. Higher head values in the northeast area <br />provide recharge to the area and a flow moving generally to the southwest. After running <br />MODFLOW, the model produced an equipotential surface, drawdown, and velocity <br />vectors. Figure 2.05.6(3) =2d depicts an equipotential surface striking to the northwest <br />and dipping to the southwest with a fairly consistent head gradient. The velocity vectors <br />