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1. What is a Combined Sewer System?

A Combined Sewer System is designed to transport both storm water and sanitary sewage within the same pipe.

2. What is a Combined Sewer Overflow (CSO)?

During large rainfalls when stormwater overwhelms the capacity of the pipes, combined sewer systems are designed to discharge the overflow into rivers and lakes. The overflow points are regulated and permitted through the United States Environmental Protection Agency in cooperation with the Illinois Environmental Protection Agency.

3. How many cities have Combined Sewer Overflows (CSO)?

Combined Sewer Overflows (CSO) are common among industrial cities that developed along the East Coast and Great Lakes regions in the mid 1800s. Nationwide, there are approximately 775 CSO communities. According to the U.S. Environmental Protection Agency (EPA) there are 108 combined sewer systems within Illinois. In addition to Aurora, the following Illinois cities have combined sewers:
- Chicago
- Elgin
- Evanston
- Hinsdale
- Joliet
- Morris
- Ottawa
- Peoria
- Rock Island

4. Does Aurora have Combined Sewer Overflows (CSOs)?

Yes. The City of Aurora has 16 permitted CSOs. Fifteen discharge into the Fox River; 1 discharges into Indian Creek.

5. What challenges do Combined Sewer Overflow (CSO) communities face?

During large rainfalls, combined sewer systems may become overwhelmed causing sewage to back up flooding streets and basements, as well as needing to be discharged into rivers and lakes.

6. What has Aurora done to improve the Combined Sewer System (CSO) and prevent sewer backups and overflows?

The City has made nearly $50 million in improvements since 2005. In conjunction with Fox Metro Water Reclamation District, the two agencies have made more than $200 million in improvements to the area’s combined sewer system in the last 3 decades, which has greatly reduced the number of CSO discharges.
- In 1983, the City experienced 1,100 CSO discharges.
- In 2010, the City experienced 198 CSO discharges.

7. Does anyone regulate Combined Sewer Overflows?

Yes. Combined Sewer Overflows are regulated and permitted through the United States Environmental Protection Agency in cooperation with the Illinois Environmental Protection Agency.
- Since its creation via the 1972 Clean Water Act, the U.S. Environmental Protection Agency (U.S. EPA) has progressively increased the regulation of pollutants discharged into the nation’s water ways.
- In 1994, the U.S. EPA published the CSO Control Policy.
- In 1997, an amendment to the U.S. EPA CSO Control Policy was adopted that required all combined sewer communities within the nation to develop and implement a Long Term Control Plan (LTCP).