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Evaluation of Potential Well Impacts From <br />The Proposed Nix Property Sand and Gravel Operation <br />Consideration of potential impacts from wet mining must take into account the leveling of the <br />groundwater table that results from creation of ponds by sand and gravel extraction below the <br />groundwater surface. Lake leveling occurs when, upon excavation, the sloping groundwater <br />table seeks an equilibrium elevation across the exposed pit (see Figure 3). The resulting <br />groundwater surface on the upgradient side of the pit is lowered relative to the pre-mining <br />groundwater elevation and comparably raised on the downgradient side of the pit. The <br />groundwater level in the exposed pit will equilibrate at an elevation representing the point at <br />which the inflow at the upgradient end of the excavation is equivalent to the outflow at the <br />downgradient end. In general, this is the pre-mining groundwater level elevation at the midpoint <br />of the exposed pit. The steeper the slope of the groundwater table, the greater the difference <br />between the post-mining ("leveled") and the pre-mining groundwater level. This generally <br />benefits groundwater users downgradient of the excavated pit by increasing the saturated <br />thickness of the aquifer. Alternatively, the upgradient groundwater users may be impacted by a <br />reduction in groundwater level (saturated thickness) in close proximity to the mined pit. <br />As a result of lake Leveling, WWE recommended modification of the mine pit configurations for <br />Mine Areas 3 and 4 from a predominately north-south configuration to an east-west <br />configuration. The purpose for the change was to minimize the historic groundwater elevation <br />difference across the pits in closest proximity to the upgradient water supply wells. This new pit <br />configuration is represented in Sheet 4, which also shows the interpreted groundwater table <br />conditions as observed on September 14, 2001. <br />Evaporation losses occurring from the ponds were assumed to impart an immeasurable amount <br />of change in the lake surface elevation relative to lake leveling and, as such, were ignored. <br />Nonetheless, evaporative losses represent an annual loss to the groundwater system that must be <br />accounted for from a water rights standpoint. <br />011-074.000 Wright Water Engineers, Inc. Page 5 <br />November 2001 <br />