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Prepared by: Bolton & Menk, Inc. PROPOSED IMPROVEMENTS 2026 PMP Street & Utility Improvements ǀ 25X.137753 Page 10 travel but has a number of other applications, including targeted sediment removal. This operation is less exact as verification of where the material is removed from and the exact volume is not accurately defined and the boat will not be able to get into shallow waters. The benefit to this operation is that only a singular access point to the lake is required and it is less impactful. However, to the best of our knowledge, there is no existing access location that can accommodate a boat launch which means one would need to be temporarily constructed. It is anticipated that this access would come from the Cummings Park area and would require significant tree removal and re- grading to accommodate. • Vacuum trailer – This operation involves sucking out accumulated sediment utilizing suction. Similar to a vacuum truck, a vacuum trailer is a smaller piece of equipment that is hitch mounted to a pickup truck which allows for it to be more accessible. This operation is the least exact as verification of the material removed and quantity is not accurately defined. However, it will certainly provide benefit in removing accumulated sediment to the extent practical. Pickup truck and trailer access to the water is required and may require temporary improvements within easements to accommodate. Each easement will require tree removal and most will require removal of private landscaping features to accommodate access. At the conclusion of sediment removal operations, impacted areas are restored. Consideration was made to performing sediment removal operations in the winter, when the lake is frozen to allow for easier access to the various outlet locations. However, a lack of safe means to access the sediment beneath the ice for removal limited the considerations for this option. Based on the options evaluated relative to the City’s stated goal for sediment removal, costs were evaluated for the cofferdams and dewatering option and included as a design alternate to keep costs separated for consideration on whether or not to incorporate with the project. If the accumulated sediment is not removed as part of the project, there are limited risks in the short term as the storage capacity is so large on a lake of this size, however, its removal provides benefit to the lake’s water quality. With other improvements proposed as part of the project, sediment making its way to the lake via the storm sewer system should be further minimized. The remaining major contributors to sediment accumulation in the lake after the project includes erosion from the banks of the lake and organic matter falling from trees around the lake (assuming the sediment capture devices incorporated into the storm sewer system are regularly maintained). See Figure 1 in Appendix A for the proposed project layout identifying the limits of each proposed sediment removal location in Karth Lake. The sediment sampling data and associated report completed by Braun Intertec is included in Appendix F. 2. Stormwater Pond BMP – Phase 2 Steep slopes from the industrial/commercial properties to the south towards Karth Lake to the north have caused major erosion and sediment pollution into the southern end of Karth Lake. A study was performed by Ulteig Engineers, Inc. in 2020 to explore a solution. The “Phase 1” project solutions included realigning the existing eroded swale to a zig-zag pattern to reduce slope and establishing a vegetated bottom and sides to minimize soil disturbance and erosion. As part of that study, a “Phase 2” improvement to treat the runoff was identified. DRAFT