Older American cities have a dirty problem — outdated sewer systems that use a single pipe to carry both sewage and stormwater to treatment facilities. As population growth and climate change have increased both sewage and stormwater, those pipes can get filled to capacity, and the untreated water sometimes ends up in waterways, where it wreaks havoc on the ecosystem. Chicago’s strategy for stopping the overflows has been to build massive reservoirs and a 109-mile-long system of tunnels hundreds of feet below ground. It’s a gargantuan holding tank for filthy water. Unfortunately, it may not be big enough.

Guests:

• Andrew Sargis, chief of operations, Chicago Water Taxi

• Margaret Frisbie, executive director, Friends of the Chicago River

• Richard Lanyon, former executive director of the Metropolitan Water Reclamation District, author of the books Building the Canal to Save Chicago, Draining Chicago: The Early City and the North Area, and West by Southwest to Stickney: Draining the Central Area and Exorcising Clout.

• Brian Wawczak, senior civil engineer, Metropolitan Water Reclamation District of Greater Chicago

• Michael Tiboris, Clear Water Farms Director, River Alliance of Wisconsin

Photo: Courtesy of Metropolitan Water Reclamation District of Greater Chicago