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What are CSOs?

Located in the oldest parts of Peoria, combined sewers collect and convey sanitary wastewater (aka sewage) and stormwater (aka runoff). Under normal conditions, they carry both to the wastewater plant for treatment. But sometimhistoryes after a heavy rain or snow melt stormwater overwhelms the system and untreated sewage is released into the Illinois River. This happens between 20 and 30 times a year. That’s called a Combined Sewer Overflow, or CSO.

A Little History

Peoria built its first sewers in the late 1800s to carry runoff away from homes, businesses and streets. When indoor plumbing arrived, property owners hooked in their sewage lines. By 1931, these combined sewers were connected to the Greater Peoria Sanitary District treatment plant, but were still able to overflow when sewage levels got too high. (Without this escape valve, raw sewage would back up into basements and streets. New neighborhoods avoid this problem by separating sewers for stormwater and sewage.)

Overflow Locations

The dots on the map show where sewers may overflow during wet weather. Due to improvements completed in the 1990s, some of these overflow pipes are inactive. During a typical rainfall, CSOs occur at an average of five locations.

The Federal Mandate

The Clean Water Act makes it unlawful to discharge pollutants from sewer systems into U.S. waters without a permit from the National Pollutant Dischargeour_permit Elimination System (NPDES). Peoria has long maintained this permit. Now, the EPA has ordered us to develop a long-term plan to get our CSOs as close to zero as possible. We’re committed to meeting our federal responsibilities. We’d rather keep our dollars here to improve the river and our city’s infrastructure than send fines to Springfield and Washington, D.C.

Consent Decree Fact Sheet:
CSO-Fact-Sheet-12-9-2020_1607623358.pdf 2020 CSO Fact Sheet

Preliminary Environmental Impacts Determination:
PEID Document


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