The Calumet TARP Pumping Station is the lowest point of the TARP System and lowest point in Chicago. View Full Caption Metropolitan Water Reclamation District of Greater Chicago

CHICAGO — How low can you go within Chicago city limits?

About 365 feet below ground, according to Kevin Fitzpatrick, managing civil engineer for the Metropolitan Water Reclamation District of Greater Chicago.

That's where the floor of the Calumet TARP Pumping Station pump rooms rest far below Chicago's Riverdale neighborhood at 400 E. 130th St.

It's the lowest inhabitable point in Chicago.

The pumping station is part of the Calumet Water Reclamation Plant, which is a component of a massive system in Chicago and the suburbs designed to protect water quality in Lake Michigan and the Chicago Area Waterway System and to manage stormwater.

TARP stands for "Tunnel and Reservoir Plan," which according to MWRD was adopted in 1972 to "comply with federal and state water quality standards in the 375 square miles combined sewer area consisting of Chicago and 51 suburbs." It is more commonly known as the Deep Tunnel project.

The Tunnel and Reservoir Plan, intended primarily for pollution control, is made up of four distinct tunnel systems: Mainstream, Des Plaines, Calumet and Upper Des Plaines. [Metropolitan Water Reclamation District of Greater Chicago]

The tunnel and reservoir system, according to the water reclamation district, consists of four tunnel systems: Mainstream, Des Plaines, Calumet and Upper Des Plaines, which run underground throughout Chicago and the suburbs. After storms, pumping stations like the Calumet station pump water out of the tunnels to make room for more water from future possible storms. The water is sent to water reclamation plants to be treated before it's discharged back into waterways.

The system also includes giant reservoirs intended for flood control like the Thornton Composite Reservoir in suburban Thornton and the Majewski Reservoir near O’Hare.

The public can schedule a tour at the Calumet Water Reclamation Plant by calling 312-751-6633 or by clicking here. All visitors must complete a tour waiver and submit photo identification at least three weeks in advance of the tour, according to Allison Fore, a water reclamation district spokeswoman.

The lowest point most humans go in Chicago is the Clinton Blue Line subway station, 426 S. Clinton St., or the tunnel just east of it. Those are both about 66 feet below the city's surface, CTA spokeswoman Irene Ferradaz said.

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