Chicago Deep Tunnel and Reservoir Project

So what happens to all the excess water during big rainstorms in the city of Chicago? Like many cities Chicago has a combined overflow wastewater system. For those of you that don’t know what a combined overflow system is, it’s basically a system that combines wastewater from the toilets with the extra rainwater.

Chicago already has storm drains that channel the storm water from the streets into Lake Michigan, but it’s so old and has such a small capacity that heavy rains can flood the system and cause it to flow over into our wastewater system. This doesn’t really seem like a big deal. However, when this happens, it causes the raw sewage from our sewers to drain unfiltered into Lake Michigan. This is why often after rain storms the beaches are closed. It’s because of the rainwater-wastewater mix that comes out of the city. This is obviously not safe for humans, but also can be devastating to the lake ecosystem.

As previously mentioned, many cities have water systems that work exactly the same way as Chicago. So what are we going to do about it? Well, Chicago started the Tunnel and Reservoir Plan (TARP) in 1972. This plan means building an over 100 mile long tunnel under the city to a multi-billion gallon reservoir in a quarry built way outside the city. In total, the system will have a 17.5 billion gallon storage capacity. The system is going to cost the city many billion dollars over the course of the project.

Little did you know, right under your feet a 33 foot diameter tunnel is being built right under your feet. Much of the tunnel goes directly under the Chicago River in the middle of the city.

Some of the push to build the system was due to Chicago’s own desire to improve its infrastructure. However, the EPA mandated the Combined Sewer Overflow Control Policy in 1994 that is forcing cities to update their rainwater systems. The reservoir system is projected to be done in 2029.



City of Chicago (n.d.). City of Chicago :: Combined Sewers. Retrieved March 7, 2014, from

Environmental Protection Agency (2012, February 16). EPA Combined Sewer Overflows – Office of Wastewater Management. Retrieved March 7, 2014, from

North Town News Magazine (2006, December 21). Deep Tunnel Construction Project [Youtube]. Retrieved from

Wikipedia (2013, December 22). Tunnel and Reservoir Plan – Wikipedia, the free encyclopedia. Retrieved March 7, 2014, from




2 thoughts on “Chicago Deep Tunnel and Reservoir Project

  1. I didn’t know anything about this tunnel project before, so reading about it is extremely interesting. I definitely agree that the unsafe water system needs to be rectified, but it also concerns me that we’ll be adding a few more billion dollars to our already massive debt.


  2. This post definitely opened my eyes to the tunnel project in that I had never heard anything about it before reading this. I agree that the unsafe water system needs to be accounted for, however, it must be done so in a way that also respects the debt our country is already trying to get out of. But at the same time, I think its more important for Chicago to improve its infrastructure than to worry about our debt.


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