Water Resources for Chicago— History and Future

Combined sewer systems in much of the Chicago area negate many of the benefits of the largest and most advanced system of water reclamation plants in the world. On an average of 100 times a year, combined sewer flows overload District interceptors and surge into the rivers at 645 different points. Occasionally, the gates from Lake Michigan have to be opened to allow the rivers to relieve themselves in the Lake. The Tunnel and Reservoir Plan (TARP) will include 131.1 miles (211 km) of tunnels 150-ft - 300-ft (46-m - 91-m) below the rivers and the streets of the City. Drop shafts will intercept the flow in the combined sewers before it can reach the overflow points. The tunnels will convey this flow to reservoirs where it will be stored prior to being pumped to sewage treatment plants. Phased implementation of TARP will reduce the need for Lake Michigan water for dilution, making a larger proportion of the 3,200-cfs (90.6-m³/s) court allocation available for domestic and industrial use in the expanding Chicago metropolitan area.