The first instinct isn’t always to look under something. But in the depths of the city of Chicago, lies a massive and impressive tunnel and reservoir plan.
The Deep Tunnel Project began more than 20 years ago as a way of solving a nasty merge of wastewater and storm water in the Chicagoland area. Back in the 1950s, much of the untreated sewage, diluted with storm runoff, was bypassing treatment plants and polluting area lakes, rivers and streams. The idea was to install 109 miles of massive underground tunnels to intercept combined sewer overflow and convey it to large storage reservoirs. The overflow would then be treated and cleaned before hitting a waterway.
Crews began work in 1985. Tunnel sections up to 35 ft in diam. were bored into limestone rock 240 to 350 ft below ground to hold 1 billion gal of water. The last piece of the actual tunnel system was laid into place earlier this year, with full completion of the Deep Tunnel Project expected to come online in 2019.
When completed, the reservoirs will increase the capacity of the tunnel system by 15.6 billion gal, providing major flood relief benefits and additional pollution control improvements to Cook County’s 375-sq-mile combined sewered area, which serves more than 3 million people. No longer do the majority of Chicagoland residents need to worry about storm water and sewage finding its way into their basements during major rainstorms.
How does the Deep Tunnel Project work? Storm water runoff that normally would have flowed into an inland waterway system is now forced into the deep tunnel system. This underground river captures the storm water runoff, which is then stored and eventually processed through a normal treatment system and released into the Calumet and Des Plaines rivers.
Furthermore, the system takes a major burden away from each local municipality. None of them have to worry about designing, building and operating its own system to capture and treat combined sewer overflow to comply with state and federal regulations.
Based on the success of Chicago’s Deep Tunnel Project, it is imperative that, over time, cities that face similar storm water problems research the plans necessary to adopt a comparable storm water treatment system.