Combined Sewer Overflow (CSO)

When it rains, the sewer system can't handle the large volume of sewage and storm water. This is called a combined sewer system because both sewage and storm water flow into one pipe. Instead of allowing water to back up into people's basements during a rainstorm, the combined sewer system allows the polluted water to be discharged directly into the Rouge River. This discharge into the river is known as a combined sewer overflow or CSO.

At the beginning of the Rouge Project in 1992, combined sewers serviced about 20 percent of the Rouge River Watershed, with 168 CSO discharge locations. This mixture of sewage and storm water contained pollutants that resulted in a public health threat to those that came into contact with the water. At present, only a fraction of the uncontrolled CSO discharges still exist. Each of those remaining discharges is under a program to be controlled by 2005.

Outfall Monitoring

Monitoring discharges from selected combined sewer outfalls has been conducted throughout the watershed by the RPO. Flow rates are monitored continuously with autosamplers used to collect a series of discrete samples throughout a given discharge event. Samples are analyzed for a suite of parameters (oxygen demand, solids, nutrients, metals). Results are used to define loading for the hydrologic models of the watershed and the impacts land use has on quality. The results are also compared to the national databases for CSO quality. Procedures have been established for maintaining the equipment, managing the data, and validating the accuracy of the data.

Performance Monitoring

Sampling is done during and after a CSO discharge into a river. Samples are taken of the water discharged into the river and flow measurements are done to determine how much storm water and sewage is discharged. Samples taken from the discharge measure oxygen demand (OD) and metals. There are four permanent CSO monitoring stations and there have been several roving (temporary) sites.

For additional information on CSOs click on the links below:

• Preliminary Hydrologic Comparison of Demonstration CSO Facilities
• Rouge Projects Combined Sewer Overflow Program
• Interactive CSO Information Map
• Maps Pertaining to CSOs
• DataView and RPO Data CD
• Technical Papers and Presentations

Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.