The Rapid City Council accepted a quote Monday from Quinn Construction to build a standpipe at Canyon Lake dam as part of the short-term fix to repair sinkholes undercutting the spillway.

A study earlier this year recommended the city should take immediate steps to plug upstream sinkholes that have tunneled under the spillway. The report also recommended a major renovation or replacement of the dam within the two years.

The council last month declared an emergency and started designing a short-term fix for the dam. The city has also started making preparations for a long-term solution that could involve complete reconstruction or replacement of the spillway.

Mayor Alan Hanks said the standpipe is only the first phase of the short-term repairs; it will allow the lake level to be reduced without injecting silt into Rapid Creek. Hanks said there is an existing gate in the dam that can be opened to allow water to escape, but the problem is it is basically buried in silt.

"If you open that gate, all you're going to do is suck that silt through to contaminate the creek, and we'd get fined by the EPA," Hanks said.

The standpipe will take water off the top of the lake, he said, instead of the lake bottom. The city plans to reduce the lake level by a couple of feet before starting the next phase of the short-term fix, which will involve plugging and sealing the sinkholes with bentonite, a material that expands when exposed to water.

The standpipe project will cost the city $14,750. The city has authorized up to $250,000 for the entire short-term fix, but Hanks said city staff does not believe it will cost that much in the end.

Alderman Tom Johnson was the lone vote against the expenditure at Monday's city council meeting.

"I continue to think the best way to fix the problem at Canyon Lake is to do it right the first time," Johnson said. "I don't see the imminent danger. I think there are alternatives to do a small draw down and not spend a quarter-million dollars."

Johnson has stated in the past that he prefers to lower the lake level to ease pressure on the spillway and then focus the city's effort on reconstruction or replacement of the spillway.

The council also agreed Monday to begin advertising for proposals from consultants interested in designing the larger spillway project.

Contact Scott Aust at 394-8415 or scott.aust@rapidcityjournal.com