Completed in 1985 (and extended in early 2018) to prevent raw sewage polluting Lake Michigan when it rained Chicago’s ‘super sewer’ is being overwhelmed. The TARP (Tunnel and Reservoir Plan) reservoir stores up to 3.5 billion gallons of rainwater and sewage (almost 16 million m3) until the wastewater treatment plants have the capacity to clean it.

But, at the same time as metropolitan development in the U.S. has sealed up natural land, rainstorms are getting stronger. In the Midwest, the amount of rain falling in the heaviest storm events increased 37% between 1958 and 2012, and large two-day storms are now 53% more frequent.

In February 2018, one rain event completely filled the new 3.5 billion-gallon reservoir and sent another 3.8 billion gallons of sewage into local waterways. At the same time this is a centralised solution that cannot solve localised flooding incidents. As always large numbers of front of pipe solutions, like raingardens and another forms of SuDS need to be found.  Read more here

Chicago’s Super Sewer – USA – ech2o newsletter snippet