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Joe Lamanna <br /> December 21, 2022 <br /> Page 3 <br /> All model simulations were run in steady state conditions. The model was first run without the <br /> Stage 7A and 7B liners to determine pre-liner ground water conditions. A model scenario that <br /> included the Stage 7A and 7B liners was then performed. Final water levels from the model <br /> scenario including the liners were compared with pre-lining conditions to determine the impacts <br /> of the pit lining. <br /> Sufficient data was not available for the area to allow for a full calibration of the model. The <br /> model was refined by adjusting cell bottom elevations to match measured saturated thicknesses <br /> indicated by the limited well data. <br /> Pre-lining Ground Water Conditions <br /> Modeled ground water elevations range from a high of approximately 4,940 feet above sea level <br /> at the upstream (south) side of the model to a low of approximately 4,850 feet above sea level on <br /> the downstream (north) side of the model. At some locations along the edges of the model, "dry <br /> cells" were present indicating areas within the aquifer that are not saturated. These "dry cells" <br /> were consistent with expectations based on review of geologic and hydrogeologic information. <br /> At the Stage 7A and 7B locations, modeled depths to water level are approximately 1 to 3 feet <br /> below the ground surface with saturated thicknesses averaging approximately 35.7 feet. The <br /> modeled saturated thicknesses at the pit locations were generally consistent with the limited data <br /> for the area, but monitoring well data suggests depth to water is slightly deeper than modeled. <br /> Gravel Pit Lining Impacts <br /> Mounding and Shadowing Effects <br /> The lining of the Stage 7A and 7B gravel pits during mining will have an effect on the ground <br /> water elevations around the pits causing mounding (higher water levels) in some areas around <br /> the pits and shadowing (lower water levels) in other areas around pits. The modelling indicates <br /> that water levels may mound by as much as approximately 1.3 feet in areas around the pits with <br /> the greatest mounding between Stage 7A and a neighboring unlined gravel pit pond. The <br /> modelling indicates that water levels may be shadowed between and on the downstream side of <br /> the pits by as much as approximately 2.0 feet. Figure 2 presents a map of the potential mounding <br /> and shadowing effects associated with the lining of the gravel pits. As presented, modeled <br /> changes in water level elevation are greatest centered around the location of the pit liners, as <br /> expected, with impacts generally decreasing with distance from the liners. The ground water <br /> mounding on the upstream side of the pits along Big Dry Creek is limited to approximately 0.26 <br /> to 0.5 feet and is limited by the creek which allows for water to flow as surface water <br /> downstream away from the pits as mounding occurs. Water level mounding is greatest between <br /> Stage 7A and the neighboring unlined gravel pit as ground water flows through the alluvial <br /> material between the two features. Based on the modeled water depths, existing monitoring data <br /> and the modeled mounding, ground water will not be exposed at the ground surface as a result of <br /> the lining of the pits. Ground water shadowing will also not have a detrimental impact on the <br /> ground water resource in close proximity to the pits. <br /> . . <br />