Two days of rain overwhelmed Chicago’s underground labyrinth of sewers Friday, forcing a noxious mix of sewage and stormwater into local waterways and Lake Michigan.
At 2:30 a.m., the Metropolitan Water Reclamation District opened a sluice gate separating the lake from the North Shore Channel in Wilmette, allowing millions of gallons of human and industrial waste to flow with runoff into the water supply for 7 million people in Chicago and the suburbs.
It marked the second time in seven months that a surge of murky, debris-strewn water prompted the district to rely on the region’s sewage outlet of last resort.
Up to 4.5 inches of rain fell across the Chicago area on Thursday and Friday, flushing a torrent of waste mixed with runoff from rooftops, streets and parking lots into sewers and stormwater tunnels stretching from Wilmette to Westchester.
Even a flood-control reservoir more than 20 times bigger than Solider Field couldn’t handle the deluge.
When construction began during the mid-1970s, officials billed the Deep Tunnel as an engineering marvel that would “bottle up rainstorms.”
But it remains incomplete, and the Tribune has previously reported that billions of gallons of bacteria-laden sewage and runoff still routinely pour into local waterways during and after storms.
As little as two-thirds of an inch of rain can lead to sewage overflows.
The problem begins with the city’s location. Chicago was built on a swamp, and storm runoff has become more difficult to manage as development paved over the city and suburbs.
To make matters worse, sewers in Chicago and older suburbs handle runoff as well as waste from homes and factories. When it rains, the combined sewers quickly fill up, forcing a noxious brew to flow back into basements and out of dozens of overflow pipes into local streams.
Waste poured out during the past two days at 64 locations on the Chicago River, North Shore Channel and Des Plaines River, district records show. The Chicago Department of Water Management fielded 350 calls about basement flooding as of Friday afternoon.
Locks and gates to Lake Michigan are opened only if waterways are saturated to capacity and the Deep Tunnel is full.
Climate change is challenging the system more than ever.
Despite the region’s giant tunnels and reservoirs, Lake Michigan has been hit harder during the past 12 years than it was in the previous two decades combined, mostly because of a handful of monsoonlike storms that were among the most intense downpours in Chicago history.
From 2007 through 2019, records show, the water reclamation district released more than 36 billion gallons of runoff and wastewater into the lake. By contrast, 12 billion gallons poured out from 1985 through 2006.
The McCook Reservoir eventually will be capable of holding 10 billion gallons, up from 3.5 billion today. But it won’t be fully operational until 2029.
The nonprofit Center for Neighborhood Technology is nudging government officials to change their focus with a program it calls RainReady, which combats flooding with building, plumbing and landscaping improvements that in some cases are coordinated with sewer upgrades.
Suburbs including Midlothian, Oak Park and Wilmette offer grants to help residents install rain gardens, regrade their lots and make other improvements to protect their homes from flooding.
In Chicago, an ambitious version of the program developed for the Chatham neighborhood has been repeatedly delayed by City Hall.