DULUTH — The recent major snowmelt in the Duluth area led to sewage overflow for the Western Lake Superior Sanitary District (WLSSD), stressed by a broken piece of equipment crucial to cleansing water before its release into the St. Louis River.
WLSSD violated a national permit that allows it to discharge a certain amount of wastewater into the river, its Executive Director Marianne Bohren said.
Typically, the plant deals with about 38 million gallons of sewage per day, water flowing in for treatment ranged from 90 million to 125 million gallons daily for several days mid-April.
"In some ways, this was more difficult to deal with than the  flood," Bohren said of their last major flooding violation, when Duluth received more than 10 inches of rain in 24 hours.
Wastewater continued to flow at high levels for several days, as the plant operated with only three of its four clarifiers. Those tanks separate solids from water before water moves on to the next phase of treatment.
The amount of sewage released into the river that didn't meet standards was slightly over the allowed amount. With all four clarifiers working, the system could have handled the rapid snowmelt, Bohren said.
The 2 million-gallon clarifying tanks have massive steel pipes in their centers, and one collapsed last fall, rendering the entire structure useless. WLSSD is asking the state for $17.5 million in bonding money to help pay for full-scale repairs of that tank and the others, found to have similar issues that led to the collapse.
Because the water overwhelming the system was mostly clear storm water, the public health threat is slim, said Mackenzie Wilkinson-Hanson of the Minnesota Pollution Control Agency.
It's never good for untreated wastewater to enter the environment, she said, but it's unlikely people were swimming in the river or Lake Superior during last week's flooding.
The city had "unprecedented snow levels" with its record-breaking snowfall this season, Wilkinson-Hanson said.
"The pipes were just full of water, and there was nowhere else for it to go," she said.
WLSSD handles sewage from 16 communities and several major companies. In Duluth, extra water was diverted successfully into storage basins throughout the city, but nearby Proctor wasn't so lucky.
Residents there were put on severe water restrictions for several days amid a manhole overflow and an overwhelmed sewage collection system. Proctor City Administrator Jessica Rich said the city has requested a $3 million federal earmark to replace an outdated clay sewer line that allows groundwater seepage.
The temporary shutdown of the Cloquet Sappi paper mill, which evacuated because of potential St. Louis River flooding, is also affecting WLSSD, Bohren said. Its large amounts of wastewater are typically warm, which helps the plant in its treatment work.
WLSSD asks residents to ensure sump pump and drain discharges are directed away from foundations to reduce sewer overflows.