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Chicago flooding Q&A: Freak storm, aging sewers and Chicago's topography lead to flooding woes

Source: Chicago Tribune
Publication date: 2011-07-28 

July 28--Chicago's Deep Tunnel was billed as an engineering marvel that would "bottle rainstorms," but one of the nation's most expensive public works projects was no match for the biggest rainstorm in the city's recorded history.

Last weekend's deluge quickly saturated aging sewers in the city and suburbs and soon overwhelmed the Deep Tunnel, a cavernous $3 billion backup system built to prevent flooding and protect Lake Michigan, the Chicago River and suburban waterways from water pollution.

As a noxious mix of bacteria-laden sewage and stormwater backed up into basements, the Metropolitan Water Reclamation District was forced to take emergency action to relieve the pressure. About 2:20 a.m. Saturday, huge metal gates separating the North Shore Channel from Lake Michigan were opened at Wilmette, and dirty water started to flow into the Great Lake.

When that step failed to do the trick, locks near Navy Pier were opened an hour later. For the next 11 hours, the area's waste surged out into the lake, forcing Chicago to boost the amount of chlorine used to purify drinking water and leading to a precautionary ban on swimming at Lake Michigan beaches.

Even then, parts of the city and suburbs continued to flood, renewing a decades-old dispute about who is to blame when sewage backs up into basements. Officials caution that with parts of the tunnel system still about half full and more rain in the forecast, the area's water woes might not be over soon.

"When you've got storm after storm hitting us, saturated ground and waterways that are full, there's no other place for the water to go," said Ed Staudacher, the district's supervising civil engineer.

Q: Why did my basement flood?

A: There are a number of reasons, starting with the sheer amount of rain that fell Saturday. The 6.86 inches was the most in one day since Chicago began keeping records in 1870. Since much of the area was once a swamp, it is naturally prone to flooding. We also have built and paved over many areas that once absorbed stormwater, leaving little choice but to flush it into sewers.

Q: Why can't the sewers handle it?

A: Like many older cities, Chicago long ago built sewers that combine waste from homes and factories with storm runoff. When it rains, the pipes quickly fill up. Bigger sewers, called interceptors, help handle the flow. But it doesn't take much rain to fill those up too. While the problem varies from city to city, a 2009 study conducted for the Chicago Department of Water Management found that 40 percent of the city's combined sewers have trouble handling rainfall greater than two-thirds of an inch. Color-coded maps show that large swaths of the city are expected to remain at risk for basement flooding for years to come.

Q: How can officials improve the system?

A: Chicago and other cities have been working to upgrade aging sewers. Nonprofit groups like the Center for Neighborhood Technology promote smaller-scale "green infrastructure" projects designed to soak up rainwater and keep it from flushing into sewers. Homeowners are encouraged to disconnect downspouts from sewers and divert runoff into their yards. Chicago also has overhauled 140 alleys with porous pavers or pervious concrete that allows rainwater to seep into the ground. But funding more aggressive improvements remains a challenge in an era when Chicago and other cities are slashing expenses and Congress is mulling massive cuts in the federal budget. The occasional public outcry about flooding doesn't seem to translate into calls for higher taxes to pay for sewers or green infrastructure.

Q: What about the Deep Tunnel? I thought that was supposed to solve everything.

A: Officials at the Metropolitan Sanitary District (now the Water Reclamation District) broke ground in 1975 on the Deep Tunnel, a subterranean labyrinth of giant sewers connected to reservoirs designed to hold sewage and runoff until it could be safely treated. The first phase, 130 miles of geological ductwork, was completed in 2006 and was intended to protect Lake Michigan and "eliminate waterway pollution." But the Tribune reported in March that nearly 19 billion gallons of stormwater teeming with disease-causing waste was allowed into the lake from 2007 to 2010. Figures for the latest storm aren't available yet.

The ongoing sewage overflows are prompting an investigation by the U.S. Environmental Protection Agency. The EPA already has brokered legal settlements with other Midwest cities, including Cincinnati, Cleveland and Indianapolis, that require sewer upgrades to reduce sewer overflows to once or twice a year.

Officials in charge of the Deep Tunnel promise that flood-control reservoirs near O'Hare International Airport, southwest suburban McCook and south suburban Thornton will largely solve the problem. But in recent regulatory filings, the Water Reclamation District revealed that the McCook reservoir, 11 times larger than Soldier Field, won't be operational until the end of the next decade. They blame the delay on declining federal support and the recession, which dried up demand for limestone at a quarry that will be converted into the district's biggest retention pond.

Q: During last weekend's storm, why didn't they open the locks and gates earlier?

A: Allowing the Chicago River, North Shore Channel and Cal-Sag Channel to flow back into Lake Michigan, the area's source of drinking water, is considered the option of last resort. The Water Reclamation District doesn't open the locks and gates unless the waterways are poised to overflow their banks.

The district occasionally is sued by businesses and other governmental agencies that claim it didn't do enough to prevent flooding. Cicero, for instance, filed a lawsuit last year demanding $42 million for damage caused by flooding during June and July storms. Insurers for the Chicago Public Schools filed their own lawsuit this week seeking about $5 million for damage caused by the same storms.

Q: I live in the western suburbs. Does opening the locks and gates help prevent my neighborhood from flooding?

A: No. The farther you live away from Lake Michigan, the more likely your flooding problems have nothing to do with what happens with the Chicago River system. Most suburbs are on the western side of a divide that separates the Great Lakes drainage basin from areas that naturally drain toward the Mississippi River, meaning that your floodwater more likely goes into the Des Plaines River or other waterways.

Q: What can we expect in the future?

A: Climate change could make the area's flooding problems even worse. The Tribune reported in April that researchers hired by Chicago officials estimate that warming global temperatures will lead to more intense rainfall. Although the Deep Tunnel system will hold massive amounts of water when it's finally completed, questions remain about whether the tunnels can move large amounts of runoff fast enough to avoid flooding. The Water Reclamation District already has been forced to limit how fast water drains into the system. Shortly after the first tunnels were opened during the mid-1980s, rapid changes in water pressure shot geysers of sewage out of ventilation shafts along city streets, in one case flooding the car of a 61-year-old Bridgeport woman who had stopped above a manhole grate.

mhawthorne@tribune.com

Twitter: @scribeguy

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