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<br />1 <br /> <br />1 <br />1 <br /> <br />1 <br />1 <br /> <br /> <br /> <br />t <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />CHAPTER 4 - CHANGES IN GROUND WATER LEVELS AND POSSIBLE IMPACTS TO <br />NEARBY WELLS <br />In order to estimate possible impacts to water supply wells near the proposed mine, a hydrogeologic <br />investigation was performed, including the development of a finite difference ground water model. <br />The model was constructed using MODFLOW and GMS, a ground water modeling lire and post <br />processor. The model was used to provide a conceptualized simulation of water levels ir, the alluvial <br />aquifer at and neaz the mine, before, during and after mining. Model inputs included mapping of the <br />alluvial aquifer by the USGS and WMI, mapping of ground water elevations providf:d by Rocky <br />Mountain Consultants (RMC}, and water levels and geologic logs presented in well records. Model <br />inputs were also based on information collected as part of the hydrogeologic investigation, including <br />aquifer characteristics determined from pumping tests (one of which vas performed on a newly <br />constructed well), field measurements, and observations of ground and surface water features. <br />4.1 Review of Well Records and Yields <br />Existing registered wells within an approximate 1,000-foot radius ofthe mine were ide:~tified based <br />on the State Engineer's master well list and mapping by WMI. The locations of wells ~~ompleted in <br />the alluvial aquifer in the vicinity of the mine aze presented in Figure 2; Table I presents a summary <br />of the well completion and yield information for each well. The well data, including locations, aze <br />based on information available in the State Engineer's Office. It is possible that actual well locations <br />and records could deviate slightly from those presented in the State's records. The location <br />presented for permit number 26206 is slightly different than that presented in the well records; this <br />adjustment was made based on field observations. This well is located within the amended mine <br />permit azea and will be very close to, if not within, the actual mined azea. This well may be relocated <br />and replaced by WMI. Also, the Atkins well was identified based on field observations; records <br />could not be located for this well. Figure 2 and Table 1 do not include monitoring and observation <br />wells, well permits for gravel pits, and deep wells completed in bedrock (non-alluvia:) aquifers. A <br />total of 21 wells were identified within the approximate 1,000 foot radius. Most of these wells are <br />-g- <br /> <br />