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Page 2 <br /> Mr. Peter Hays <br /> October 14,2022 <br /> - Mounding(upgradient;south):Mitigation measures addressing the modeled mounding <br /> have been thoroughly discussed and described and include gravity underdrains and <br /> dewatering wells that can be activated in response to elevated groundwater conditions. <br /> - Shadow(downgradient,north): The lower groundwater elevations modeled downgradient <br /> (north)of the slurry wall are do not pose a significant impact to the area alluvial wells <br /> because the saturated thickness of the alluvium is still eighteen(18) feet. However,a <br /> recharge area will be preserved on the Site to allow the upgradient dewatering discharge to <br /> be used to raise the groundwater level locally adjacent to the agricultural production wells. <br /> Refer Figure 7. <br /> The unnamed slough is modeled as a drain with a very large conductance which sets the upper <br /> elevation of the groundwater table and therefore it serves to limit the potential drawdown in the <br /> "shadow"area. The model results have been included with the email version of this letter(model <br /> output SW TOT SP). <br /> 5. Please provide the details(length, diameter and timing of installation)of the underdrain proposed to <br /> mitigate the mounding effects to the south of the site.Additionally, provide the modelling results that <br /> demonstrate the proposed underdrain will mitigate the mounding. The model outputs have been included <br /> in the email copy of this letter. <br /> 6. Please provide the details(diameter, depth and timing of installation)of the dewatering wells <br /> proposed to mitigate the mounding effects to the south of the site.Additionally, provide the <br /> modelling results that demonstrate the dewatering wells will mitigate the mounding. Dewatering wells or <br /> the eastern underdrain will be installed during construction of Cell 4. The finally designed system <br /> will remove a minimum of 3.25 cfs at full buildout and will require a 12"pressurized discharge line or <br /> 24"gravity underdrain. The model results demonstrating dewatering wells will mitigate mounding <br /> have been included with the email version of this letter. The west underdrain will be a 24"slotted <br /> pipe with the invert set at 4,735 in the east(west side of Western Ditch along CR 44)and 4,733 in the <br /> west. The elevations are subject to change as more data on seasonal water levels are collected. The <br /> west underdrain will be installed during construction or prior to construction of Cell 6. <br /> 7.What will determine what southern mitigation scenario will be used; underdrain, dewatering <br /> wells or a combination of both? The final design of the mitigation measures will be determined with <br /> input from the Town of Gilcrest and the local permitting process. <br /> 8. The Figures 7 and7A referenced in the report were not provided.Are they the same as Figures 6 <br /> and 6A that were provided? Please update the text as needed or provide the missing figures. Report has <br /> been updated. <br /> 9. Please provide the details of the drain recharge manhole and associated piping to be installed <br /> to mitigate the shadowing to the north of the site, also referred to as Optionl.Additionally, the <br /> paragraph before Table 7 states that water will routed to the river for Option 1. Please clarify if <br /> the water will be routed to the drain recharge or to the river. Report has been updated. <br /> 10. Option 2 of the three mitigation options states water will be routed via the surface to discharge <br /> to the river. Please show the route the piping will take to get to the river and where the <br /> discharge point will be located. The possible routes have been shown on the attached mitigation <br /> maps. <br />