Despite massive investments in its sewer system, Duluth reports overflow in Lake Superior
DULUTH -- Just nine months after a federal judge lifted a consent decree, which had ordered the city of Duluth to stem the flow of untreated wastewater into Lake Superior or face stiff financial consequences, Mayor Emily Larson delivered some unw...
DULUTH -- Just nine months after a federal judge lifted a consent decree, which had ordered the city of Duluth to stem the flow of untreated wastewater into Lake Superior or face stiff financial consequences, Mayor Emily Larson delivered some unwelcome news.
Despite the investment of more than $160 million in infrastructure to prevent future sewage overflows, a two-day rain in mid-March proved too much for the city's sanitary sewer system to handle.
"This is not the kind of news we like to share, but it happened. And residents need to hear that from us," Larson said.
Rains March 15 through 16 resulted in Duluth discharging an estimated 5.7 million gallons of wastewater, including untreated sewage, into the lake from which it draws its own drinking water.
Steve Gohde of the National Weather Service reported that 2.7 inches of rain fell over the two-day period, making for the largest March rain on record in Duluth.
Jim Benning, Duluth's director of public works, said the city has weathered larger rains at other times of year without incident.
"The most similar rain event we had compared to this was in September of 2015, and we had zero overflows. We had zero gallons of water go into storage. And we did not exceed our level of service with WLSSD (the Western Lake Superior Sanitary District)," said Benning, explaining that the wastewater treatment facility places limits on how many gallons of water it will accept on a daily basis.
Although that September rain was of similar intensity and duration, Benning said it resulted in "a non-event."
But the more recent March rain fell on ground that was already saturated with water, resulting in greater runoff and infiltration of Duluth's sanitary sewer system.
Backup storage tanks that normally sit dry were filled to capacity, and then some. The 12.5 million gallons of storage capacity Duluth had built to prevent future overflows wasn't enough. Untreated water entered the lake from three city facilities: Lift Station No. 6 in Canal Park, Lift Station No. 50 at 21st Avenue East and Lift Station No. 3 at 45th Avenue East.
WLSSD reported a smaller overflow, as well -- about 15,000 gallons near 40th Avenue West. Luckily the untreated sewage was cleaned up quickly with no runoff, said Marianne Bohren, WLSSD executive director.
Bohren said that line has historically needed cleaning every two years to remove debris because it's unusually flat in that area.
"We are looking into what exactly happened, but it's going to be cleaned out over the next month," she said.
It was the first overflow in the WLSSD's portion of the city sewer system since the June, 2012 flood.
With the exception of the flood as well, the city had been free of sewage overflows since November of 2010.
Larson referred to the March 15-16 rain as the first really big test of the city's upgraded sewer system, after considerable investment and hard work Duluth had been poured into its improvement.
"While it's disappointing that in this case not everything went the way we wanted it to, the systems worked," she said.
Benning noted that but for the city's backup storage capacity, an additional 12.5 million gallons of untreated wastewater would likely have wound up in Lake Superior.
"The system structurally did what it was supposed to do. It was just overwhelmed by the volume," said David Montgomery, Duluth's chief administrative officer.
'We're on it'
Larson said the city must do better.
"We're on it. We don't want this to happen again either," she said.
Benning said the city has been exploring its sewer system carefully with cameras in an effort to determine where water is infiltrating pipes.
"This is something that we would be doing anyway. We didn't stop working on this after the consent decree was lifted. It's a continual process, but this event brought to light that there's more work to be done, and we can't let our guard down," Benning said.
When the city locates problems in the sanitary sewer system, Benning said: "We've got the resources -- money and personnel -- to correct them. But we need to find what the issues are first."
Benning predicted the overflow was largely the product of cumulative small deficiencies, with many of them involving private rather than public lines.
"A lot of the older homes have clay tile sewer laterals, and they're not air-tight," he said.
The city is working to identify these problem private lines and will require property owners to line or replace sewer laterals, as necessary. The city will offer to pick up 80 percent of the tab, up to a maximum of $4,000.
"We're continuing to chase this," Benning said.
Larson said no water rate increases are anticipated to address needed improvements to the city's sewer system.
"I do want residents to know that we do have the capacity if we find problems, we do have the dollars set aside to address them, and we do have the staff to handle the situation," she said.
As for building additional storage capacity to impound more wastewater, Benning said that would likely be a last resort. He recalled that the city had been reluctant to construct all the wastewater storage required to lift the prior consent decree against it.
"We didn't want to build the big storage tanks. We wanted to remove the (inflow and infiltration) at the source, but the EPA said, 'That's going to take too long. You need to build some tanks.' So that's what we did, but I don't think we'll be investing in any new additional tanks," Benning said. He noted that additional storage tanks would be a very expensive fix, and finding room for another massive structure could prove a challenge, too.
Montgomery said one wild card is the potential effect of climate change.
"If weather patterns are changing long term and fundamentally, due to changes in the overall climate. And if it becomes the case that a March event like this is no longer a 150-year event, like the records indicate, and it's more like every five to 10 years we're going to have one of these, then you probably are talking about approaching it differently and saying: Well maybe we do have to build another tank somewhere, because the expectation, within a reasonable period of time, every so many years, is that you're going to have one of these," he said.
As required, the city of Duluth reported its recent sewage to the Minnesota Pollution Control Agency, according to Craig Weingart, a wastewater and stormwater inspector for the agency.
He said the incident is still under investigation, and more information still needs to be collected before any enforcement action or penalties can be considered.
"We won't know the next steps until we have the information that we are looking to obtain. So I don't want to speculate as to what type of action we will take. There's no blanket approach that the MPCA takes when we have these kinds of prohibited discharges," Weingart said.
"Our actions are determined based on case-by-case specifics, including: What was the weather event? What is the history of the facility? And some different factors. ... But I can't tell you, with this kind of release, the end result is X, Y or Z," he said.
But Weingart said the MPCA takes the incident seriously.
"We look at these as prohibited releases into the environment, and yes, absolutely, the MPCA is concerned with all prohibited releases into the environment, whether it's to ground surface, to a wetland, to a lake, to a river or a creek," he said.
Benning remains optimistic the city won't be penalized or subjected to another consent decree for a one-time discharge in the face of such challenging conditions.
"We don't anticipate anything at this time, but we haven't heard. If we make a habit out of this though, I'm sure they would take an interest," he said.
John Myers contributed to this report.