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Combined Sewer Overflows

Lincolnwood and other Chicago suburbs, typical of older metropolitan areas, have a combined sewer system, in which both sanitary waste and storm water are conveyed in the same pipe.  Suburbs built since 1950 have separate sanitary and storm sewer systems.

A combined sewer overflow (CSO) is a discharge from a combined sewer system directly into a waterway.  A combined sewer system is designed to collect a mixture of rainfall runoff, domestic and industrial wastewater in the same pipe for conveyance to a wastewater treatment plant.  A CSO may occur during heavy rainfalls when the inflow of combined wastewater exceeds the capacity of the combined sewer system and the wastewater treatment plant.  The CSO outfalls to the waterway act as relief points for the excess flow in the sewers, thereby reducing the frequency and severity of sewer backups and flooding.

Although CSOs may contain highly diluted sewage that could include bacteria which may cause illness, they may also cause temporary water quality degradation in the waterways.  Regardless of CSO activity, the Chicago Area Waterways may contain disease-containing bacteria at any time.  Therefore, swimming, canoeing, or other activities where immersion in water is possible should be avoided and is not recommended, particularly during and immediately following rainfall.

For more information and to be informed of combined sewer overflows in the region, click here to visit the Metropolitan Water Reclamation District's webpage and sign up to automatically be notified via email of a CSO.