06-24-2019 Council Packet - Laserfiche WebLink

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STAFF REPORT TO: Mayor Keis and Members of City Council FROM: Bill Dircks, Public Works Director DATE: June 21, 2019 RE: Twin Lake Update The pumping progress on Twin Lake has been remarkably good. It took just over a week to pump the lake down from a starting point of 876.22 to 873.84 on the morning of June 20. The pump intake actually hit the ground on June 20 and started pumping muck along with the water. The service technician for Northern Dewatering shut the pump off for the morning and started it back up in the afternoon. Due to the likelihood of the same thing happening again, the pump was shut off on the afternoon of June 20. It was turned on again for the day on June 21. The permit with the DNR allows us to pump the lake down to a level of 873.5, which is the 100-year flood level of Twin Lake. Because the level was at 873.82 the decision was made to shift to maintaining the level of the lake. The pump will now be operated during the day by City forces. The level of the lake should be easily maintained by pumping during the day. Less fuel will be required, which will save money on the pumping operation. We have already committed to one month of the 16-inch pump so we will continue to use it and then make a decision as to how big of a pump will be needed going forward. The Watershed District is looking into pumping the water from the West Vadnais pipe into the MnDOT pond to circumvent Twin Lake and eliminate that as a factor in the lake level. If they succeed in setting up a pump for the West Vadnais water, a much smaller pump will be sufficient to maintain the level around 873.5. Barr Engineering is studying the effect a 100-year rain event would have on the lake level if it is at 873.5 to make sure the low home on the lake will remain dry. That information will be provided at the meeting if it is known by then. All of the City manholes on the west side of the lake are back out of the water. The Met Council manhole that sits higher than the City manhole near the overflow pipe is back out of the water as well. The City manhole near the overflow pipe on the south end remains under water. It is still quite wet/muddy around the manholes so maintenance will remain difficult until the ground dries up more. Flows looked good when the manholes were inspected on June 18.