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Member Research and Reports

Member Research and Reports

Combined Sewer Systems Lead To Risk of Illness after Heavy Rains, UIC Study Finds

Consumers whose drinking water can be contaminated by the release of untreated wastewater after heavy rains face increased risk for gastrointestinal illness, according to a UIC School of Public Health study reported in the journal Environmental Health Perspectives.

“Combined” sewer systems collect both sewage and stormwater runoff on the way to treatment facilities. When heavy rainfall fills these systems beyond their capacity, untreated wastewater can back up into homes. To reduce the risk of home flooding during heavy precipitation, municipalities often discharge some of the untreated flow into nearby bodies of water. The release of untreated waste is known as a combined sewer overflow.

Many older cities such as Chicago have combined sewer systems — along with 772 other communities, primarily in the Northeast, Great Lakes, and Pacific Northwest, serving a total of 40 million people. While some cities are building infrastructure to handle sewage and runoff separately, other regions with combined systems depend on reservoirs to provide extra capacity during extreme rainfalls. Chicago’s Deep Tunnel was designed to hold 2.3 billion gallons of untreated wastewater during storms to prevent combined sewer overflows and flooding of basements. During one massive 2013 storm, the tunnel reached capacity and its entire contents were rerouted and ultimately discharged into Lake Michigan.

“Existing infrastructure is already stretched beyond its ability to manage severe precipitation, and with climate change, extreme rainfall events are becoming more frequent, and so are combined sewer overflows,” says epidemiologist Jyotsna Jagai of the University of Illinois at Chicago School of Public Health and lead author of the study.

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