CHICAGO (MCT) — After several days of rain, an overnight deluge overwhelmed Chicago’s underground labyrinth of aging sewers and giant tunnels on Thursday, forcing a noxious mix of sewage and stormwater into local waterways and Lake Michigan.
The surge of murky, debris-strewn water so overloaded the system that sewage began to back up in basements and geysers of wastewater shot out of several sewer manholes — stomach-churning sights captured by smartphones and posted online.
To relieve the pressure, engineers at the Metropolitan Water Reclamation District were forced to rely on the region’s sewage outlet of last resort. For the first time since July 2011, they opened locks and sluice gates separating the Chicago River system from the lake, allowing millions of gallons of raw and partially treated waste to flow with runoff into the water supply for 7 million people in Chicago and the suburbs.
It is unclear when the locks will be closed again, said Allison Fore, a district spokeswoman. Estimates of how much sewage-laden river water flowed into the lake won’t be available until several days after the storms subside.
Tom LaPorte, a spokesman for the Chicago Department of Water Management, said the city so far has not noticed any unusual contamination in water drawn from intake cribs farther out in the lake.
Department officials are constantly monitoring the situation, LaPorte said, and as a precaution started adding more bacteria-killing chlorine to lake water before pumping it to households and businesses.
Chicago turned its namesake river into a sewage canal at the turn of the last century, building locks and gates and digging concrete-lined channels to direct the burgeoning city’s waste away from the lake and toward the Mississippi River.
Like many older cities, Chicago also long ago built sewers that combine waste from homes and factories with storm runoff. When it rains, sewers quickly fill up and spill into local streams through overflow pipes. If waterways are saturated to capacity, the locks and gates to Lake Michigan are opened to reduce flooding.
Construction of the Deep Tunnel, a $3 billion system of giant sewers and reservoirs designed to capture and store stormwater, was billed as an engineering marvel to alleviate the region’s sewage and flooding woes.
But the Chicago Tribune reported in 2011 that billions of gallons of bacteria-laden sewage and runoff still routinely pour into the Chicago River and suburban waterways during and after storms. Even rainfall as small as two-thirds of an inch can lead to sewage overflows.
Steady rainstorms like the ones that hit the Chicago region this week make the problem even worse. Lake Michigan has been hit harder during the past six years than it was in the previous two decades combined, mostly because of a handful of monsoon-like storms that were among the most intense downpours in Chicago history.
Between 2007 and 2012, records show, the district released more than 21 billion gallons of runoff and wastewater into the Great Lake. By contrast, 12 billion gallons poured out between 1985 and 2006.
Researchers hired by former Mayor Richard M. Daley estimated that global climate change will lead to more of these intense storms in the not-so-distant future, challenging the region’s aging sewers and the Deep Tunnel more than ever.
Rains of greater than 2.5 inches a day, the amount that can force runoff into Lake Michigan, are expected to increase by 50 percent by 2039, according to a study by scientists from the University of Illinois at Urbana-Champaign and Texas Tech University. By the end of the century, the number of big storms could jump by a whopping 160 percent.
As more research points to a changing climate, local officials are grappling with the likelihood that Chicago will need more solutions beyond the Deep Tunnel, which now isn’t scheduled to be completed until a giant flood control reservoir is fully operational in 2029.
Under a legal settlement with federal environmental regulators, the Water Reclamation District will be required to invest in more small-scale “green infrastructure” projects that allow storm runoff to seep into the ground rather than drain into sewers.
Local officials once scoffed at such initiatives, but they now promote them as critical solutions for a city built on a swamp.
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