July rains strain wastewater treatment plant
Say an average of five inches of rain fell upon Wadena during the early morning hours of July 11, That's more than 400 million gallons of water over 5.4 square miles - far more than the city's infrastructure could handle.
Wadena's stormwater drains via a network of sewers that dump directly into Union Creek. The city's wastewater flows through a different sewer network to the treatment plant, which discharges treated "effluent" into Union Creek after removing solid waste (that's given to farmers for fertilizer).
Stormwater is not supposed to enter the sanitary sewer system, but plenty of it did following the rain storm, creating problems at the treatment plant. A manhole cover blew off, releasing sewage into Union Creek, a state designated trout stream. As required by law, the city reported the spill to the Minnesota Pollution Control Agency (MPCA).
Despite several days of recommended restrictions on water usage throughout the city, the treatment plant, designed for up to 750,000 gallons a day, operated at close to 1 million gallons a day for more than a week after the storm. That's nearly twice the ordinary flow.
Operating above capacity increases expenses and undermines the mission of the plant, said Public Works Director Dan Kovar. "We don't get effective treatment."
By late last week, the flow had returned to nearly normal levels, but Kovar is looking for residents to help make sure, in the long run, less storm water finds its way into a system designed to treat sewage.
One reason that's important, he said, is because starting in 2016, the city will have to start chemically treating the wastewater to meet state requirements to reduce phosphorus levels, adding significant cost to the process. Right now, it's a purely biological system; bacteria and ultraviolet lights do all the work.
Most of the increased flow into the treatment plant was beyond residents' control. It was due to the city's 30 miles of leaky clay pipes - some of it more than 70 years old - that allowed stormwater to enter the sanitary sewer network.
Most of the north side of Wadena has been replaced with sealed watertight PVC piping. The southeast side sewers are slated to be upgraded during a comprehensive infrastructure project in 2015 and 2016. The southwest side sewers won't be replaced until the next round of improvements, projected for more than a decade from now.
The southeast project will lead to a significant reduction, but Kovar believes the increased flow was also due, in part, to a controllable variable: Residents who have their sump pumps hooked up to the sanitary sewer system.
"(Sump pumps) are designed to be pumped up on to the lawn, not connected to the sanitary sewer," Kovar said. "That is an illegal hookup."
City code states it illegal to "discharge or cause to be discharged, any stormwater, surface water, groundwater, roof runoff, sub-surface drainage, uncontaminated cooling water or unpolluted industrial process water to the sanitary sewer."
Kovar added: "Mother Nature, we can't control. The old clay pipe, we're doing what we can. Anything else we can gain is a benefit."
Due to the sewage discharge incident, he said, the city might be required by the MPCA to inspect sump pump connections.
Other residents have been discharging their sump pumps into the streets, which is a violation of the city nuisance ordinance.
"The water is to be kept on the owner's property and recycled by watering trees, lawns, garden, etc. but kept on the owner's property," Kovar wrote in a letter explaining the groundwater issue that will distributed in this month's utility bills.