Here’s What’s Being Done About the Raw Sewage Being Released into our Rivers During Heavy Rainfall

MMSD has a long, complicated way to go to meet its goal of eliminating sewage discharges into rivers by 2035.

Last Aug. 11, swim coach Conner Andrews and 67 other swimmers jumped off the Erie Street Pier into the Milwaukee River for the 1.5-mile Cream City Classic race.

“Being able to swim through historic Milwaukee, under those bridges, was great, and the water wasn’t even gross,” says Andrews, 30.

When Andrews was growing up as a young swimmer in Milwaukee, such a plunge would have been unthinkable. At the time, raw sewage was released into the city’s rivers 50 to 60 times a year when the combined sewers that hold rainwater and sewage overflowed.

As with other cities throughout the Northeast and Great Lakes region, Milwaukee’s original sewers were constructed to carry rainwater and sewage, and still do. When the volume becomes too much for the system to treat or hold, the mix is released through 153 different outfalls into the Milwaukee, Menomonee and Kinnickinnic rivers.

The Cream City Classic, which Andrews and other organizers hope will be an annual swim, was a sign of how much river quality generally and combined sewer overflows (CSOs) specifically have improved in recent decades. But two weeks after the August swim, heavy rains overwhelmed the system, and about 400 million gallons of sewage mixed with rainwater were released into the rivers – the first CSO of the summer.

By October, five more CSOs had taken place, tying the 1999 total of six CSOs, the highest number since the Deep Tunnel meant to hold excess sewage was completed in 1993. Under state permits implementing federal law, the district isn’t allowed to have more than six CSOs per year.

Heavy rains are only expected to get more common with climate change, and aging pipes and other infrastructural challenges mean curbing CSOs will be a continual challenge. The sewerage district has set a goal of eliminating CSOs by 2035.

“With the changing climate we’re facing, it’s like running uphill, and the hill keeps getting steeper and steeper,” says Milwaukee Metropolitan Sewerage District (MMSD) executive director Kevin Shafer. “And we’re facing limited finances and aging infrastructure all together.”

Cheryl Nenn of Milwaukee Riverkeeper says the group intentionally scheduled the swim in August because that is usually a drier month.

“It was a bit of a wake-up call,” she says of the CSOs that followed the race. “I’m afraid that despite years of progress we could be going into a time when we have more overflows as extreme weather increases. I think we can be proud of a lot of the progress that’s happened, but we need to be vigilant.”

MMSD serves a 411-square-mile area, with 23.5 square miles of Milwaukee and Shorewood having combined sewers. The rest of the area has separate sanitary sewers, where one set of pipes carries sewage to the district’s two treatment plants and another set carries stormwater to the region’s rivers.

In 1993, the district completed the billion-dollar Deep Tunnel – 19.4 miles long and about 300 feet deep – offering a place where fluid could be stored from both the city’s combined sewers and separate sanitary sewers until it’s treated and released.

Frequency of CSOs plummeted after the tunnel’s completion, with total CSO volume dropping from 8 billion gallons in 1993 to 176 million gallons in 1994.

But the tunnel didn’t entirely eliminate sewage releases as hoped. As a settlement stemming from legal action begun in 2002, MMSD expanded the tunnel system, adding the Northwest and 27th Street tunnels by 2010. Now, the tunnel holds 521 million gallons and stretches close to 30 miles.

How the Deep Tunnel system works

And sewerage managers knew they couldn’t end CSOs with “gray infrastructure” alone. So they turned to green infrastructure – porous pavement, green roofs, bioswales and other patches of native plants and soil that soak up rainwater rather than channeling it into sewers.

And sewerage managers knew they couldn’t end CSOs with “gray infrastructure” alone. So they turned to green infrastructure – porous pavement, green roofs, bioswales and other patches of native plants and soil that soak up rainwater rather than channeling it into sewers.

Thanks to green infrastructure programs run by the MMSD and the city, Milwaukee can now capture about 39 million gallons of storm runoff. By 2035, the plan is to have enough green infrastructure to capture 740 million gallons at a time, diverting the equivalent of the first half-inch of a rainfall from sewers.

In September, the City Council passed an ordinance mandating that all new development or redevelopment involving at least an acre include enough green infrastructure to divert the first half-inch of rainfall. The city also began drafting a comprehensive new green infrastructure policy, slated to be released in March. Environmental sustainability director Erick Shambarger says that among other things, the city will expand its partnership with Milwaukee Public Schools, helping them turn pavement into porous and green surfaces.

“It’s an equity thing for me,” says Shambarger. “A lot of suburban schools have plenty of green space and places for kids to get out there in nature. A lot of urban schools don’t look that way. They have pavement and fences. We can do a better job with trees and green space that manage stormwater, and make a better learning environment for kids.”

MMSD offers affordable rain barrels and encourages people to connect rooftop downspouts to the barrels instead of to sewers. A nonprofit known as Sweet Water offers small grants for individual projects that divert rainwater. MMSD works with the School of Freshwater Sciences at UW-Milwaukee and with Marquette University to study and educate people about the issue.

Shambarger notes that MPS’ 2019 budget for green infrastructure is $2.8 million, up from $866,000 in 2017, thanks to increased investments from the sewerage district. And he says the push for green infrastructure – and gray infrastructure upgrades – creates jobs. For example, nonprofit Walnut Way Conservation Corp. won a federal grant to train people from vulnerable backgrounds in landscaping for green infrastructure.

CSOs in the Great Lakes

A CSO near the Milwaukee harbor

There are 184 combined sewer systems in the Great Lakes basin, according to a 2016 report by the EPA, most on lakes Erie and Michigan. Indiana has 18 areas discharging CSOs into the Lake Michigan basin, and Michigan has 11, while Milwaukee is only one of two Wisconsin “CSO communities” in the Great Lakes basin. The other, in Superior, sends its flows into Lake Superior.

In 2014, the EPA told Congress, there were 1,482 CSO events in the Great Lakes. Ohio had 824, New York 376, while Wisconsin and Illinois had only one each.

Chicago’s CSOs dwarf those of Milwaukee, coming from a 375-square-mile area of combined sewers. In 2017 the Chicago area had 37 CSOs totaling 44.5 billion gallons. Milwaukee had basically no CSOs in 2017, and almost 1.3 billion gallons’ worth in 2018.

But Chicago’s CSOs are almost always into the Chicago River, which flows away from the lake thanks to the famous reversal of the river a century ago. When the system’s especially overwhelmed, usually once or twice a year, the river is temporarily “re-reversed” and CSOs flow into the Lake Michigan.

CLICK HERE to get a real look Under MKE — courtesy of photographer Robert Burns
Photo by Robert Burns

While CSOs get much attention – evoking images of unsavory “floatables” and other debris associated with toilets – officials say the systems with separate sewage and stormwater pipes may actually pose the biggest threat to Milwaukee’s river quality.

In Milwaukee suburbs with separate sewers, sanitary sewers bring sewage from homes and businesses to treatment plants, sometimes using the Deep Tunnel as a way station. Before the expansion of the system a decade ago, the Deep Tunnel would sometimes fill up and sanitary sewers – carrying pure sewage, not the rainwater-sewage mix of CSOs – would overflow into rivers. In a massive rain in May 2004, 4.6 billion gallons of overflow was released, half a billion of that being pure sewage from separate sanitary sewers.

Sanitary sewers are theoretically unaffected by rainfall. But stormwater is indeed getting into separate sanitary sewers, leaching in through faulty pipes and funneled in when basement drains are illegally connected to sanitary sewers. A city audit found that 13 percent of the rain that fell in separate sewer areas during a bad CSO spell in May 2004 – 7.6 billion gallons – made its way into separated sewers.

The sewerage district is faced with a delicate balancing act during storms. The combined sewers fill up with stormwater first, but the separate sanitary sewers being infiltrated with rainwater will typically become overloaded a few hours later. So, Shafer notes, he has to make sure he leaves enough room in the Deep Tunnel during the combined sewer influx for sanitary sewer overflow to come in later. If he predicts a big sanitary load, he may decide to release CSOs into the river before the Deep Tunnel has filled up.

Meanwhile, separate stormwater sewers send water directly into rivers as a matter of practice, not only during overflows. While the stormwater doesn’t come from the toilet, as it runs over pavement and through fields it picks up plenty of bacteria, oil, grease, fertilizer and other compounds that harm water quality.

“Everybody gets their underwear in a knot about raw sewage – they have this diaper fixation,” says Patrick Marchese, who led MMSD from 1984 to 1988 and worked underground building sewers before that. “But from a scientific point of view and pollution analysis point of view, by the time a CSO event happens, especially if it has a duration of seven to eight hours, that flow coming out is so diluted it has less pollutants than water coming from the surface area.”

Swimmer Conner Andrews is aware of efforts to improve the system and thinks that people will increasingly be able to swim and kayak in the river without fearing bacterial infections or encounters with floatables.

“With the push for green infrastructure and the community stewardship of the waterways, I think there’s hope,” he says. “You can never truly appreciate a river until it’s clean.”

“A Steep Hill to Climb” appears in the April 2019 issue of Milwaukee Magazine.

Find it on newsstands beginning April 1, or buy a copy at

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