MANKATO — With spring floods looming, the Minnesota River’s bank receding, and Mankato in danger of losing one of its most productive water wells, the price tag for an emergency fix is falling fast.
City officials hope to begin laying hundreds of tons of erosion-resistant quartzite rock along the east bank of the Minnesota River in Land of Memories Park later this month. The riprap project aims to stem the rapid erosion of the bank, something that is otherwise expected to swamp Mankato’s Well No. 15 in coming months or years.
In December, when the city received bids for mining the quartzite and hauling it to the park, low bids by contractors left the Phase 1 costs nearly $438,000 less than estimated by city engineers. But City Manager Pat Hentges warned then that Phase 2 — reshaping the river bank and precisely placing the quartzite along the bank — was the most labor-intensive and expensive portion of the project.
On Monday night, though, the news was even better as bids came in more than $1 million below expectations.
The construction contract for Phase 2 was anticipated to cost just under $3 million, but Dirt Merchant, Inc. submitted a bid of $1.88 million. Two other bids — $2.04 million from Mathiowetz Construction and $2.17 million from Rachel Contracting — also came in well below the estimated price.
Dirt Merchant crews are expected to start work by the end of this month with the goal of armoring the riverbank along Well No. 15 before spring floods arrive.
“The river is still at a high mark,” Hentges said, adding that long-arm excavators should still be able to accomplish the work. “It’s a challenging project but not unusual.”
Dirt Merchant’s winning bid on the Phase 2 work came after it lost by a whisker in competing for the Phase 1 job in December. In that round of bidding, the company’s proposal was just $85 higher than the $520,167 bid by Mankato-based W. Lorentz Construction. W. Lorentz did not bid on the Phase 2 contract.
The strong competition for the river-erosion work means the entire project is currently expected to cost about 36% less than originally predicted.
If heavy flooding comes earlier than normal, those savings could start to erode, however.
“If they get delayed by weather, that’s going to add to the cost,” Hentges said.
But waiting — with hopes that a future winter will bring lower river levels — wouldn’t be wise, according to city officials and consultants hired by the city. Well No. 15 represents about 40% of the municipal drinking water production for the city, and its fate had been looking doubtful after consistently high flows in the Minnesota River rapidly carved away the riverbank near the well.
“Since 2009, the distance between the riverbank and the well-house fence has gone from 73 feet to 15 feet,” according to a memo to the council. “This is a loss of 58 feet of riverbank, with over 50% of that taking place in the last three years.”
If river levels allow the riprap placement to be completed late this winter along 1,150 feet of the riverbank, only one smaller phase of the project will remain. Phase 3, which is expected to cost $250,000, will involve landscaping and plantings appropriate for river-bottom terrain.
The total project — including engineering, contingency funds, interest costs and administration — is now projected to be just over $3.2 million, which is $1.78 million less than first estimated.
A request from the city to the Minnesota Legislature seeks state funding for the Well No. 15 project and a larger riverbank stabilization project farther downstream that aims to protect Riverfront Park and the city’s sewage treatment plant, along with making improvements to the park and the riverside bike trail.
The state is being asked to cover 80% of the total cost through its statewide capital investment legislation, which borrows money through bond sales to finance infrastructure projects across Minnesota. The money the city is currently spending for the emergency work near Well No. 15 is expected to count toward the 20% local match that would be required if the Legislature agrees to fund the broader river-stabilization project.