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Prepared by: Bolton & Menk, Inc. PROPOSED IMPROVEMENTS 2026 PMP Street & Utility Improvements ǀ 25X.137753 Page 9 accumulating near the outlets, but the majority of sediment is being pushed out further into the lake and forming sediment deltas. There was a noticeable ‘hard- bottom’ at each outlet location assumed to be a mix of gravel and rock erosion delivered by the storm outlets. However, the limits of the sediment deltas relative to the ‘hard-bottom’ of Karth Lake’s natural lakebed is difficult to delineate and therefore the total accumulated sediment at each delta is not accurately quantified. Braun Intertec completed sediment sampling from the five outlet locations within Karth Lake to characterize the in-place sediment (future dredge material). These sediment samples were tested and evaluated in accordance with the Minnesota Pollution Control Agency’s (MPCA) current best management practice for Managing Dredged Materials. Sediments observed during the completion of the borings consisted primarily of dark brown to black silty sand with organic materials noted at four of the locations. Based on analytical results from the sampling and testing, sediment from location O-1 falls within the management Level 1 characteristic, sediment from locations O-2, O-4, and O-5 falls within the management Level 2 characteristic, and sediment from location O-3 falls within the management Level 3 characteristic. Therefore, sediment removal operation will require segregation of material from each location, or it all will be required to be treated at the most restrictive sediment management level. Unlike stormwater ponds, it is not possible to completely drain Karth Lake to perform sediment removal operations. Therefore, specialty construction methods will be required to conduct the operations. It is assumed that the accumulated sediment is generally contained within an approximate 100-foot radius of the outlet location. Easements exist over each of the four storm sewer outlets that run between residential houses and the fifth outlet comes from within Cummings Park, which is property owned by the City. However, the grades down to the lake, trees, and private landscaping features may make access to each location difficult or infeasible within the confines of the existing easements, especially as it relates to trucking out the excavated sediment. Three options for sediment removal operations were considered as part of this report but additional data collection and evaluation would be required during final design to verify feasibility of the selected option at each location, if proposed for inclusion as part of the project. • Cofferdams and dewatering – This operation involves the installation of temporary steel sheet piling around the anticipated sediment delta to create a cofferdam at each outlet location. This would then allow for the outlet locations to be dewatered utilizing pumps to expose the lake bottom. The accumulated sediment would then be removed by means of an excavator and hauled off in dump trucks. Dump truck access to the water within the existing easements appears unlikely due to existing grades. Therefore, the excavator will likely need to stockpile the material on the bank of the lake and then have it transported up to dump trucks at the street via skid steers or similar small equipment that can better traverse the landscape. 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, the steel sheet piling is removed and impacted areas are restored. • Hydraulic dredging – This operation involves the removal of accumulated sediment using hydraulic forces from a boat/barge to suction up the materials. This is most commonly used to maintain channel depths for marine DRAFT