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County reports Airport Lake overflow leak, weighs drawdown vs. cofferdam repair options
Summary
Engineering staff told the board they believe a failed valve or connection in a drawdown structure is causing an overflow leak at Airport Lake; options include drawing the lake down to repair the valve or building a cofferdam and using sheet piling—both have cost and campground-timing trade-offs and DNR grant cycles likely delay funded repairs until the next grant cycle.
Chad reported the county has discovered a leak in the Airport Lake overflow structure and described two repair paths: draw the lake down and fix the underground valve structure, or build a cofferdam and perform repairs while the lake remains full.
"We believe that valve has failed or a connection into that 8-inch (drawdown line)," Chad said, describing the 8-inch connection into a larger vertical shaft. The county is temporarily using an inflatable bladder to hold water levels while staff and DNR representatives determine the next steps.
Chad said drawing the lake down is risky because it could take weeks to refill and could disrupt campground revenue and recreation; the alternative—cofferdam and sheet piling—carries high costs for removal and reinstallation. He also said a likely DNR fish-habitat grant could be appropriate, but that application cycles mean funds would not be available until after the November cycle and paid in the following calendar year.
Staff will continue investigations, coordinate with the DNR and the city of New Hampton (which may have property interests in part of the dam infrastructure), and return to the board with cost and schedule estimates.
