Just like it’s nice to have more than one toilet in a home, both for handling peak demand and for having a toilet in reserve when one needs repairs, the City of Mankato prefers to have some redundancy at its Wastewater Treatment Plant. And right now, it doesn’t.
Changing that will mean about $7 million in new construction and repairs at the facility, a project the Mankato City Council will be asked to send out to bid tonight.
“It’s almost a prerequisite for obtaining our permit renewal,” said City Manager Pat Hentges of the permit that must be obtained again next year. “... You have to have that redundancy.”
Specifically, it’s the systems’ “secondary clarifiers” that have no reserve capacity. The clarifiers are large open vats with mechanisms for circulating the wastewater and settling out the solids.
The plant has two large ones that are working fine and allow the plant to operate at two-thirds of its peak capacity. Two smaller clarifiers, which technically account for the other third of capacity, have been offline for 10 years. And both the big ones are in need of some routine maintenance in the highly corrosive environment of a sewage treatment plant — work that’s been postponed for several years because the smaller ones can no longer be used as back-ups during repairs.
So, the $6.5 million to $7 million project — which includes a 10 percent contingency and nearly $1 million for engineering, legal and bond fees — will result in the construction of a third large clarifier pool, new mechanical equipment for the existing large clarifiers, and repairs to concrete, walkways, piping, valves and more. A study by consulting firm Bolton and Menk recommended that approach over repairing the older, smaller clarifiers.
“These improvements will provide the city greater reliability, flexibility and redundancy ...,” the Bolton and Menk report concluded. “These improvements will also address continual maintenance problems and provide the city of Mankato and surrounding communities with quality wastewater treatment.”