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3. The slurry wall and associated features around the Hazeltine mine were then inserted into the model <br />and the wet and dry annual cycles were simulated for a timeframe sufficient to achieve new seasonal <br />quasi-equilibrium conditions and assess post-mine effects. <br />3.2 Pre-Mine Simulation Results <br />As described above, pre-mine simulations were run to calibrate the model under average annual <br />conditions and to also implement seasonal variations in the hydrologic inputs. Provided below is a <br />summary of the results of these simulations. <br />Quasi-Steady State Calibration <br />Transient model simulations were made for varying lengths of time to ensure that the water table <br />conditions had reached aquasi-equilibrium condition and comparisons were made between simulated <br />and "observed" water table conditions mapped over the entire domain and at specific well locations. <br />Calibration was performed by testing varying hydraulic conductivity values, river/ditch parameters, and <br />recharge to obtain a reasonable match with water levels measured in local area wells and with regional <br />water level mapping. Levels measured in local area wells in February 2004 were in general agreement <br />with the regional water table mapping. As would be expected, some exceptions occur in the vicinity of <br />lined water storage reservoirs installed in recent years. <br />Figure 4 illustrates the comparison of simulated water levels with the general regional water table <br />mapping performed by the USGS (Robson, 1996). Some of the minor differences between the <br />simulated and mapped water table can be attributed to seasonality and the effects of recently installed <br />lined reservoirs. Near the proposed Hazeltine Resource, the simulated water levels were in good <br />agreement with local area well measurements. The match between simulated and observed water levels <br />shown on Figure 4 was deemed adequate for the purpose of assessing relative differences due to the <br />Hazeltine mining operation. Overall, the simulated head levels are quite close to, and the groundwater <br />flow directions and gradients are consistent with, the "observed" levels. <br />This match was obtained using aquifer parameters and hydrologic inputs that were consistent with the <br />expected values based on literature and site observations. The effects of changing hydraulic <br />conductivities, recharge rates and river cell parameters were tested. The valley-fill alluvium and the <br />alluvial terrace deposits were reported and observed to be similar, and the model adequately represented <br />the observed groundwater conditions using a uniform value for the two deposits. The hydraulic <br />conductivity of the alluvial portions of the aquifer was set at 300 feeUday and the wind blown deposits <br />were assigned a value of 100 feet per day. For recharge, a total of one inch per year was used in the area <br />of wind deposited sediments and 1.5 inches per year were applied to the non-irrigated alluvium. The <br />strip of higher recharge along the northwest boundary (to represent infiltration of hillside mnoff and <br />potential bedrock inputs) was set at a factor of four times the irrigation recharge rate of seven inches per <br />year, or 28 inches per year. All other aquifer parameters and hydrologic inputs were as described in <br />Section 2. <br />Seasonal Simulations <br />After the quasi-steady state calibration was complete, the model was re-started and simulations of <br />cyclical wet and dry seasons were performed to establish baseline seasonal conditions prior to <br />simulation of the effects of the Hazeltine Mine. For the simulation of wet and dry season variations, <br />changes were made to various river and ditch cells as well as area recharge. As described in Section 2.4, <br />- 5 - July 2004 <br />I:U919 018\GW ModdQfcportVlazdlinc Rm ] 2].doc <br />