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Evaluation of Potential Impacts <br />From The Proposed Nix Property Sand and Gravel Operation <br />On Shallow Groundwater Levels, Water Wells and Wetlands <br />• Mine Area 5 ± 4,790 <br />• Mine Area 6 ± 4,791 <br />Using this information, WWE computed the maximum elevation difference between the pre- <br />mising groundwater surface elevation and the average reclamation groundwater surface elevation <br />for the upgradient end of each pit. The estimated maximum elevation differences are also shown <br />on Sheet 4. <br />4.2 Effects on Water Wells <br />Evaluation of upgradient impacts to wells resulting from the elevation differences identified <br />above requires an understanding of the shape of the post-mining groundwater surface upgradient <br />of the pits. An initial assessment of potential impacts is to assume that the maximum change in <br />groundwater level upgradient of the pit is equivalent to the maximum elevation difference at the <br />upgradient end of the pit. However, the lake leveling effect does not remove groundwater from <br />the alluvial system (i.e., the lake inflow and outflow is in equilibrium) and, as such, does not <br />lower the regional groundwater surface. Lake leveling only imparts a localized change in the <br />groundwater table contours. <br />The resulting upgradient groundwater surface varies between the post-mining groundwater <br />surface at the pit and the pre-mining groundwater surface some distance away from the pit (see <br />Figure 4). This groundwater surface is r,oncave upwazd, with its steepest gradient neazest the pit <br />and shallowest gradient at its point of tangency with the pre-mining groundwater surface. Its <br />exact configuration is a function of the pre-mining slope of the groundwater surface and the <br />hydraulic properties of the aquifer. <br />WWE considered numerous methods for assessing the configuration of this curvilineaz post- <br />mining groundwater surface and the distance to where there would be no effects on the <br />groundwater table. Many of these methods, including those for determining agricultural drain <br />spacing, ignore aquifer properties such as transmissivity and specific yield. As a result, WWE <br />Ot 1-074.000 Wright Water Engineers, Inc. Page 9 <br />April 2002 <br />