'Storms push Chicago area's flood prevention efforts to limits,' NBC 5 Chicago

Storm water has always been a challenge in Chicago, and the area's Tunnel and Reservoir Project (TARP) has been a decades-long effort to combat those issues.

Also known as the "Deep Tunnel," the project has unfolded over more than 50 years, costing an estimated $3-to-4 billion.

Simply put, the system is built to do two things: prevent residents' basements from flooding, and to keep all the excess stormwater and sewage from flowing down the Chicago River and into the source of the area's drinking water: Lake Michigan.

Needless to say, this year's heavy rainfall is pushing that system to its limits.

The massive McCook Resevoir in southwestern Cook County is completely full after this weekend's rain, with 3.6 billion gallons worth of water currently stored there. The southern Thornton quarry is also more than 90% full, according to officials.

Those reservoirs are operated by the Metropolitan Water Reclamation District of greater Chicago (MWRD), a taxpayer-funded government agency that manages the region's water supply - and MWRD officials say they are working round the clock to manage the 13 billion gallons of stormwater that has been captured in the last week

That water is first pumped into the three reservoirs the agency oversees, and then is eventually treated and put back into area rivers and streams, along with the lake.

"Right now we're actually pumping down the resevoirs - we're pushing over 600 million gallons every day out of those resevoirs - and back into the system to be treated at our treatment facilities," said Ed Staudacher, who is Director of Maintainance and Engineering for the MWRD.

Construction began on the Deep Tunnel and Reservoir Project more than 50 years ago. Excess stormwater is routed through the deep tunnels, some of which are located more than 300 feet underground, into one of the three regional resevoirs and stored until water levels go down.

But 2026 is proving to be a record setting year - and the system is being taxed like never before.

"McCook has filled six times this year alone and previously, between 2021 - 2025 we filled it five times," Staudacher said. "We're only halfway through the year.

MWRD Board President Kari Steele says the tunnels and resevoirs are holding for now but could overflow if the weather Gods send more rain to the Chicago area.

"There's always that threat because rainstorms are unpredictable," Steele said.

Steele says climate change has caused heavier and more frequent rain events - meaning TARP is no longer enough - so they are focusing on localized projects.

On Tuesday, MWRD officials and Chicago Mayor Brandon Johnson unveiled a "wing storage" unit - designed to store excess stormwater across several blocks near Central and North Ave. on Chicago's far west side. But Steele says each household plays a role too, and they are often called to do so via so-called "Overflow Action Alerts."

"What we're asking people to do is conserve water at home. We need to make sure we have space available in local sewer lines so we can get it to MWRD if we have capacity to store that water," Steele said.

There's a third reservoir located in Des Plaines that is currently empty, and MWRD officials say its that way because the rainfall was a lot lighter in the northwest portion of the county.

MWRD is currently building additional reservoir capacity in McCook that is designed to store six billion more gallons of water in coming years.

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McCook Reservoir timelapse