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J:'iRED DAINS <br /> NON'F?;WR 21,2016 <br /> groundwater mounding and shadowing. Our model also includes the unlined pit to the north,as it was <br /> included in the 2004 modeling work. <br /> Results <br /> To create the reference or"baseline" condition,we first ran the model with the Duckworth Pits not <br /> present(i.e., pre-mining conditions) but with the unlined pits to the south and north both being <br /> included. The timeframe for construction of pits to the south appears to overlap the Duckworth Pit <br /> timeframe, but our approach limits the computed effect to what is caused by the Duckworth Pit and <br /> more closely represents field conditions since those neighboring pits are indeed now present. The <br /> model was then run with the Duckworth Pit cells being set to"no flow"conditions. The simulated <br /> water table results for the first run were then subtracted from the water table from the second run to <br /> map the areas with changes in water levels. <br /> An illustration of the model-estimated changes in water levels is shown in Figure 1 with mounding and <br /> shadowing contoured in 0.5-ft increments. Positive values indicate mounding(increased water levels <br /> over"background" conditions)and negative values indicate shadowing. The approximate outlines of <br /> the neighboring pits to the north and south are also shown for reference. <br /> Mounding on the south side of the Duckworth Pit may be exaggerated in this model. In reality, <br /> mounding might be reduced by the presence of Indian Creek. This dampening effect would not be <br /> captured by the model since Indian Creek was simulated as a specified flux boundary and not a head- <br /> dependant boundary. <br /> Standard Technical Limitations and Additional Limitations <br /> Subsurface data about geology, hydraulic conductivity,water levels,etc., is always limited in its spatial <br /> coverage and limited in its precision and accuracy. Groundwater estimates and projections therefore <br /> have inherent and unavoidable uncertainties. No one can provide certainty. Using standard methods <br /> and approaches, as we have done,does produce useful guidance and expectations, but it should be <br /> noted that actual conditions and changes in conditions may vary from the modeled projections. We <br /> note also that one can have more confidence in the computed changes in conditions(mounding and <br /> shadowing)than in specific elevations(water levels or depth to water). Finally,we also note that we <br /> focused on using the prior modeling framework to the extent possible. We did perform a cursory <br /> comparison of maps provided in the 2004 modeling report against our updated version of the 2004 <br /> model and we believe the updated model reasonably approximates the most relevant field conditions, <br /> but performing a more thorough critical review of the 2004 model and its correspondence to past and <br /> current field conditions was not in the scope of this task. <br /> Miller Groundwater Engineering, LLC Page 12 <br />