Chicago celebrates its deep tunnel, with 20 times as many overflows

Unlike Milwaukee, Chicago loves its deep tunnel system for sewage, if the glowing Chicago Tribune editorial below is any indication.

Funny, considering that Chicago's system has already had 21 combined sewage overflows this year, including one on May 11, the day this editorial ran. Milwaukee, where the deep tunnel is widely condemned, has had one overflow in 2006.

Chicago's underground wonder

Chicago was founded because of its proximity to water... But disposing of sewage, draining floodplains and keeping drinking water safe always have been challenges.

Chicago's first great engineering feat to deal with these challenges was construction of a drinking-water tunnel extending two miles into the lake in 1867. Ending the city's reliance on polluted shoreline water helped end the cholera epidemics that had afflicted Chicago for the previous two decades, killing thousands.

A second feat, still considered one of the engineering wonders of the world, was the reversal of the Chicago River's course in 1900, so that the city's sewage would flow south rather than being corralled in the lake.

The third of these spectacular feats concludes Friday when the Metropolitan Water Reclamation District of Greater Chicago dedicates its Deep Tunnel project. Drilling 109.4 miles of tunnels 15 to 30 feet in diameter through limestone took 30 years. Friday is only a formal debut for a completed system that already has been operating at gradually increasing levels. Wastewater reservoirs to complement the tunnel system won't be finished until 2023. But Friday's debut shouldn't come and go without an acknowledgment of a remarkable construction achievement that has made a huge difference to many homeowners.

The $3 billion project has been under way for so long that many Chicago-area residents no longer know why it's being done--or have forgotten about it altogether. But those tunnels, coupled with regional reservoirs, promise to alleviate flooding and sewage backups that sometimes still plague low-lying neighborhoods.

As long ago as the 1930s, flooding and contamination were chronic problems. A $3 million sewer channel to protect Oak Park and other western suburbs was finished in 1937. The Tribune predicted then that for west suburban homeowners, flooded basements "after nearly every storm will be a thing of the past."

Well, not quite. Drainage problems continued. Deep Tunnel--its formal name is Tunnel and Reservoir Plan, or TARP--was envisioned in the 1960s after storms forced the city to pump sewage into the lake in 1954, 1957 and 1961.

The basic problem was Chicago's sewerage. It consisted of combined sewers, common to many older cities. They carried both raw sewage and storm water in the same pipe. As the region grew, more roadways were paved and more building foundations sunk. All that growth reduced the amount of natural ground surface available to soak up storm water. Storm runoff often exceeded sewage-treatment capacity.

How so? A torrential downpour can drop 20 billion gallons of water on the Chicago area. The early 1970s sewer system and treatment plants could handle only 1.5 billion gallons a day. That left 18.5 billion gallons of storm water and sewage with no place to go. That ugly brew bypassed treatment plants and spilled directly into rivers, streams or Lake Michigan. Before the Deep Tunnel project, nearly half of the pollution in Chicago's 70-plus miles of inland waterways came from those combined sewers.

Some of that contaminated water bubbled out of basement drains all over the area. Chicago would be forced to open the river locks, and contaminated water would flow into the lake--the primary source of the area's drinking water. Dozens of times in a typical year, enough rain fell that sewage backed into homes, businesses and schools, and raw sewage was discharged into waterways and the lake. The property damage and chronic health risks were enormous.

TARP's mission was to collect and store that overflow in the tunnels and reservoirs so it could be treated gradually and then safely released into the waterways--once the storms had passed...

Friday marks the third milestone of epic proportion in Chicago's long struggle to manage its proximity to water.

Copyright © 2006, Chicago Tribune