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ARDEN HILLS SPECIAL CITY COUNCIL WORK SESSION — JUNE 23, 2025 12 upstream structure. There is no significant risk with leaving them the way they are. However, we could choose to be forward thinking and add it to the project to get it completed. Fisher said the potential sediment removal at Karth Lake Deltas could improve constructability options, access and management level associated with it. The pricing outlined in this report is separated out into a design alternate. He has reached out to some contractors to try to scope this out because there is some difficulty with access. Other than the park access, the other four locations are going right between houses within existing easements. Four of the five locations are relatively steep. Nearly all of them have some level of tree impacts where some trees within those easements would need to be removed. Some of them have private landscaping that will be impacted. We would have to work with homeowners to potentially salvage or reinstall. We have done this type of improvement on the last project. We would get access to get down to the lake. A storm water pond can typically be fully drained. You drain the water, dig it out with an excavator and load the sediment into a truck. Most of the access locations for this project are so steep that we won't be able to get a dump truck back there. We can't entirely drain lake, like you can a storm water pond. You can create a cofferdam at each of the outlet locations. You take steel sheet piling and pound them in, in a half moon shape to isolate the outlet locations so you can de -water them. This would eliminate the water in the working area. There would still be the issue of getting dump trucks back there. It would require a smaller piece of equipment that would bring that material from the lake, to the truck in the road for removal. The higher costs outlined are due to the compounding issues. It is difficult to specifically identify pricing. Fisher outlined that the report identifies some options that could be explored further. These options include hydraulic dredging. That is the most common technique for clearing boat routes on lakes or hauling routes on rivers. Mayor Pro Tem Monson said realistically the best option is going to be using the coffer dam and then use smaller equipment to bring material to the dump truck. Fisher confirmed. That would accomplish the end goal. The dredging would need boat access. The last feasible option is using a vac truck. Then you would suck the materials underwater. There would be no way to quantify the totality of the benefit. We would just know by the amount of material that you suck up. That would be a cheaper option but less definable. Fisher discussed the sanitary sewer improvements. There will be spot rehabilitations. They will replace the castings on the manholes and install new chimney seals to improve I&I. The manholes that have significant rings at the top that deteriorate over time will be reconstructed. Fisher said they are looking to realign the existing watermain along Highway 96 and put it under the trail, closer to the retaining wall. Spot hydrant and valve replacements will happen based on what Staff had identified. There will also be some curb stop adjustments. Their survey team and City Staff will identify each curb stop in the project area that are either too high or too low and adjust those back to final grade. Fisher said for trail improvements, they would strip the trails and re -overlay them. They would add aggregate base, as needed. There is an electrical box at the pump system, with a four -tiered timber retaining wall that has been identified as failing and contributing to erosion into the lake. They would want to replace that with a single tiered wall.