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Mr. Alex Schatz <br />December 12, 2008 <br />Page 3 of 11 <br />conducted by the U.S. Department of Energy, hydraulic conductivity estimates for the <br />alluvium ranged from 20 to 200 feet/day (ft /day) which is within a reasonable range for <br />the alluvium found in the DAV and consistent with literature values. <br />Permitted Wells in the DAV <br />There are 19 permitted wells in the DAV identified in the State Engineer's Office <br />(SEO) Division of Water Resources Well Master List Database. Figure 3 presents a map <br />of the wells in the DAV located according to the SEO database. In Figure 3, the wells are <br />labeled by their depths (in feet). It is important to note, however, that the coordinates <br />provided in the SEO database reflect the well location based on the section lines in the <br />Public Land Survey System (PLSS). The actual location of the permitted wells may vary <br />considerably from those indicated on the figure. Figure 4 presents a close -up map of the <br />10 wells in the SEO database located within 1 mile of the Debeque Mine. Two of these <br />wells are listed as monitoring holes. <br />MODFLOW Model <br />A numerical ground water flow model of the DAV was constructed to estimate <br />the potential impact of mine dewatering on the local water table and to estimate the <br />potential impact of the site- dewatering on the permitted wells in the site vicinity. The <br />USGS "MODFLOW -2000 (MF2K)" code was used for numerical simulation. The <br />proprietary pre- and post - processing software, Groundwater Modeling System (GMS) <br />was used to design the model grid and develop the model files. MODFLOW and GMS <br />are both widely used and accepted ground water modeling software packages that have <br />become standards in the industry. <br />Spatial and Temporal Discretization <br />A one -layer model of the alluvial sediments in the DAV was constructed. The <br />ground water flow model simulated an area of 4,214 acres represented by 200 foot by 200 <br />foot cells. There were 4,589 active cells in the model domain. Figure 5 presents the <br />extent of the active cells in the ground water flow model area. <br />The alluvial sediments were modeled as homogenous and isotropic. A uniform <br />thickness of 50 feet was used as the layer thickness; this uniform layer thickness was <br />mandated based on the lack of any reliable depth to bedrock or spatially extensive <br />alluvial thickness /saturated thickness data for the DAV area. This thickness corresponds <br />to the approximate depth of many of the wells in the SEO database within the DAV. <br />Based on information provided by Banks and Gesso, the depth to bedrock at the mining <br />site ranges from 26 to 40 feet. However, a thickness of 50 feet provides a more realistic <br />