4.2.b PCSR 05-23-2023 - Laserfiche WebLink

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PERMIT APPLICATION TO THE CITY OF ELK RIVER APRIL 2023 Introduction 1.2 management (eliminating the lift station) and reduce the amount of controlled fill placement required for perimeter berm construction. For the previous design, stormwater discharge from the site was under the exterior roadway, then under the City of Elk River trail, and ultimately to an upstream wetland on property owned by ERL. The modified design allows for discharge directly west of the proposed pond to an existing low area, on property also owned by the Landfill, east of the trail (eliminating the need for the City trail crossing). The proposed sedimentation pond includes settling basins at the east and west ends. A safety bench has been incorporated into the design and perimeter access for cleaning / maintenance activities has been considered. The proposed pond has been designed to provide flexibility depending on mining activities in the area. The bottom elevation of the pond will be at maximum an elevation of 964; the actual elevation may be 964 or lower depending on mining activities. The design presented herein represents the minimum storage capacity that would be provided and storm events that would be managed. Actual conditions following mining activities may provide for management of larger storm events by increasing the available storage capacity. 1.1.1 Landfill Development and Closure Construction Modifications to the stormwater management system features have allowed for a reduction in the width of the perimeter berm on the south termination of the MSW disposal area. Changes to the perimeter grading plan result in a reduction in fill materials required to complete construction / landfill development. Consistent with the previous design, stormwater generated from the southern portion of the Landfill will still be controlled and routed by drainage terraces, downslope structures, perimeter ditching, a nd related stormwater management infrastructure. Stormwater will be routed through these features to the proposed large stormwater basin. The modifications to the stormwater management system components on the Landfill will be incorporated during phased closure construction. The modifications to the Landfill discussed above will primarily be on the existing property permitted and approved for Landfill activities and will be addressed in a subsequent minor permit modification application to the MPCA. 1.1.2 Landfill End Use The current end use plan for the Landfill will not change and provides for open green space. Long term, the open space planned for the site would be compatible with any adjacent future use. The end use determined for the site will be consistent with the terms of previous agreements.