When more than two inches of rain falls in the Chicago area, the deluge flowing into storm sewers mixes with the wastewater from homes and businesses. Often there is more water than the metropolitan area’s treatment plants can handle, so the excess is discharged untreated into the Chicago River and its connected waterways.
Such Combined Sewer Overflows — CSOs – are common in Chicago and many other U.S. cities where storm water and municipal wastewater are funneled into the same aging combined sewer pipes. Milwaukee and other cities discharge CSOs into Lake Michigan.
The discharges include high levels of bacteria, parasites, viruses, toxic metals including copper and cadmium, nutrient pollutants including phosphorus, and suspended solids. An average CSO outflow contains fecal coliform colonies in a concentration of 215,000 per 100 mL, more than 100 times higher than the concentration in treated wastewater, according to the 2006 report “Rooftops to Rivers” by the Natural Resources Defense Council.
CSOs are a major cause of beach closings across the Great Lakes region. But since most municipalities only release beach water testing results on a 24-hour basis, swimmers are frequently exposed to the worst pollution — which can cause ailments from gastrointestinal distress to pinkeye — before a warning is even issued.
The NRDC report says about 850 billion gallons of CSOs are discharged nationally each year, made up on average of 15-20 percent sewage and 80-85 percent storm water. In 2009, a recent report by the National Wildlife Federation found, the cities of Milwaukee; Gary, Ind.; Cleveland; Detroit and Buffalo alone released 41 billion gallons of CSOs — the amount that flows over Niagara Falls in 15 hours.
“CSOs are one of the most significant ongoing problems in the Great Lakes,” said Dave Ullrich, executive director of the Great Lakes and St. Lawrence Cities Initiative
In many cities, separating municipal and storm water sewer pipes is virtually impossible because of the cost and the scale of the disruptive construction it would entail. Meanwhile the Environmental Protection Agency estimates the Great Lakes region faces a $23 billion backlog in needed sewer improvements, just to keep the existing combined sewer and storm water systems intact.
So a primary way to address CSOs is to reduce the amount of storm water that flows into sewer pipes. This can be done by installing permeable pavement in parking lots and alleys; letting people collect rain in barrels for future use; installing green roofs and simply persuading people to use water more efficiently. Ditches or “bio-swales” can also be constructed to channel water into existing lakes or holding ponds where it can evaporate or sink into the soil. Even large planters that collect rainwater on city medians and sidewalks help.
“There are a lot of ways you can keep rain out of sewers,” said Josh Ellis, a water expert with Chicago’s Metropolitan Planning Council, which is pushing for state law changes to allow people to collect and reuse rainwater. Changing how water is priced could encourage developers and residents to reduce the water that goes into sewers, both from rain and household use. Incentives could encourage rain gardens and permeable pavement, and water could be priced to encourage conservation.
Chicago sends sewage to the Mississippi
Thanks to the famous reversal of the Chicago River a century ago, most of Chicago’s CSOs head through manmade channels and connected rivers to the Mississippi River — the same path taken by the city’s treated wastewater. This “Chicago diversion,” sends about two billion gallons daily from Lake Michigan down to the Gulf of Mexico.
When heavy rains produce too much water for the Chicago River and canals, locks and sluice gates are opened to allow water — including untreated sewage — to flow into Lake Michigan. This typically happens about once a year — most recently in July 2010. During a record release on Sept. 13, 2008, the city released 99 billion gallons of CSO into Lake Michigan.
Hence Chicago combined sewer overflows are at the moment a matter of concern more for users of the Chicago River and waterways than for the Great Lakes. But since “environmental DNA” or “eDNA” from invasive Asian carp was found in the waterway system near Lake Michigan, and even in a Lake Michigan harbor, environmental and planning groups have been pressing to separate the Mississippi River watershed from the Great Lakes basin.
Blocking invasive species could mean more pollution for Lake Michigan
Such separation — depending exactly where on the system it was made — would mean that much wastewater could not be sent down to the Mississippi River but rather would be discharged into Lake Michigan. This would mean that during heavy rains, untreated wastewater from CSOs would be released into Lake Michigan.
This is one of the reasons that the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) opposes separation to block invasive species like the Asian carp.
“We would hope hydrological separation doesn’t happen, because we don’t want to put CSOs into Lake Michigan,” said MWRDGC executive director Richard Lanyon. “We have a lot of CSO outflows right downtown, they’d be the first to get into the lake. Who wants to do that?”
Supporters of hydrological separation acknowledge that it would increase the risk of flooding and of CSOs being discharged into Lake Michigan. But they say this is a reason to address the issue of flooding and CSOs head-on.
“We get a pass on meeting water quality standards because that water goes into a river rather than a lake,” said Alliance for the Great Lakes president Joel Brammeier. “That strikes me as a really unhealthy way to think about sewage treatment.”
Cities ease problem with run-off reduction measures
Chicago and Milwaukee are already considered leaders for their green building and run-off reduction programs. Chicago requires all new public buildings to be LEED-certified, and the city has 2 million square feet of green roofs which absorb rain rather than letting it run off. The city already has an innovative system on a portion of Lake Shore Drive wherein the first flush of rainwater goes into sewers, since it is laden with oil and dirt, but the majority of run-off is channeled into nearby Lake Michigan.
The National Wildlife Federation study says Chicago research shows green infrastructure could handle the run-off from nine out of 10 rainstorms. Environmental and planning groups say Chicago should step up its green efforts, to reduce CSOs and make it possible to re-reverse the Chicago River without further impacting Lake Michigan.
Reservoirs hold water for later treatment
Lanyon said the MWRDGC has no plans to address CSOs other than completing the area’s massive $3.4 billion subterranean tunnel and reservoir system, known as TARP (Tunnel and Reservoir Plan) or simply the Deep Tunnel.
When wastewater and storm water overwhelm sewer pipes it can be held in these reservoirs and later pumped back into the treatment system. One reservoir is in operation, able to hold 2.5 billion gallons, and two more are slated for completion in 2015 and 2017, according to Lanyon, though other estimates peg the completion much later.
For the 2010 fiscal year Congress has allocated $2 billion for sewage upgrades nationwide under the Clean Water State Revolving Fund. Great Lakes states are slated to receive about a third of the amount. The American Recovery and Reinvestment Act (ARRA) also provided $4 billion for the fund, with a fifth of it designated for green infrastructure projects.
Sprawl, climate change fuel CSO worries
Meanwhile, unless large scale storm water reduction methods are quickly implemented, CSOs in Chicago and other urban areas are likely to increase.
Urban sprawl means increasing amounts of impervious pavement and more wastewater from homes and businesses; and climate change means more heavy rainstorms.
“The real wild card in this is climate change, and the effects of climate change are showing up already,” said Ullrich.
Among the most damaging situations expected to increase with climate change are heavy rains in the early spring, when the rainfall combines with snow melt and flows swiftly over frozen ground without being absorbed. Ullrich said climate change is just one more reason that cities including Chicago must immediately make green infrastructure and storm water run-off reduction a priority.
“What the urban landscape will look like 25 years from now has a lot to do with how you manage storm water,” he said. “It’s about going from gray to green, from hard to soft. Somehow we need more public resources to go into green infrastructure and storm water management. If we don’t we’ll pay for it in the long run.”
Editors note: This is part of a series of stories about Great Lakes sewer system issues.