Laserfiche WebLink
Joe Lamanna <br /> December 21, 2022 <br /> Page 4 <br /> Ground Water Flow Effects <br /> The lining of Stage 7A and 7B not only has the potential to affect the elevation of the ground <br /> water table around the pits, but also the ground water flow patterns around the pits. We have <br /> investigated the potential impacts to ground water flow paths as they relate to regional ground <br /> water flow and the interaction between the alluvial ground water system and the South Platte <br /> River. Figure 3 presents an elevation map of the ground water table prior to the lining of Stage <br /> 7A and 7B and includes general indications of ground water flow paths in the vicinity of the <br /> gravel pits. Figure 4 presents an elevation map of the ground water table after the lining of Stage <br /> 7A and 7B which again includes general indications of ground water flow paths. As presented, <br /> while the lining of the gravel pits has a slight impact on ground water elevations in the vicinity of <br /> the pits, the lining of the pits does not disrupt the pre-existing ground water paths in a manner <br /> that restricts ground water flow from interacting with the South Platte River. Figure 3 indicates <br /> that ground water upstream from the pits flows in a northeastern and eastern direction to the <br /> South Platte River and that ground water to the west and downstream from the pits flows in a <br /> northern and then northeastern direction around to the pits to the South Platte River. Figure 4 <br /> indicates that ground water flow upstream from the pits is unaffected with similar northeastern <br /> and eastern flows to the South Platte River and that ground water flow to the west and <br /> downstream from the pits is also unaffected with similar flows to the north and then northeast <br /> towards the South Platte River. The modelling suggests that the lining of the pits does not <br /> interfere with ground water flows and their ultimate interaction with the South Platte River and <br /> that subsurface drains installed around the pits to maintain ground water flow paths are not <br /> necessary. <br /> Summary <br /> • A MODFLOW model was developed and utilized to estimate the potential impacts of the <br /> lining of the Stage 7A and 7B gravel pits at the Morton Lakes site on the local ground <br /> water system including potential changes to the ground water elevations and ground <br /> water flow paths in the vicinity of the pits. <br /> • Figures 2 presents the modeled changes in water level elevation associated with the <br /> gravel pit lining. <br /> • Figure 3 presents the pre-lining ground water elevations and flow paths and Figure 4 <br /> presents the post lining ground water elevations and flow paths. <br /> • Lining of the pits may result in mounding of as much as approximately 1.3 feet in areas <br /> around the pits and shadowing of as much as approximately 2.0 feet on the downstream <br /> side of the pits. Based on the depths to water indicated by the existing monitoring wells <br /> and the modelling, ground water will not be exposed as a result of pit lining. <br /> Accordingly, no additional infrastructure (including subsurface drains) is required to <br /> address ground water elevation changes resulting from mounding and shadowing around <br /> the pit liners. <br /> . . . ... . . ... <br />