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Background
As in most urban areas across the nation, Greater Cleveland's earliest sewers (primarily within the City and its inner ring suburbs) are Combined Sewers. Built around the turn of the 19th century, these sewers carry sewage, industrial waste and storm water in a single pipe.
What is a Combined Sewer Overflow (CSO)?
During a rain storm, run off can cause a dramatic increase of water flowing through the combined sewers. When this happens, control devices may allow some of the flow - a combination of storm water and sewage - to overflow into area waterways to prevent urban flooding. This event is called a Combined Sewer Overflow.
Locations, Frequencies, and Occurrences of Overflows
The Northeast Ohio Regional Sewer District has 126 permitted locations, known as outfalls, where overflows may discharge in the Greater Cleveland area.
In addition to predicted CSO frequencies, the District also monitors discharges on a daily basis at various CSO locations. The most recent date of overflow occurrence at these locations as a result of rainfall can be found by clicking here.
Click here to see a map of CSO outfall locations in the District's service area.
What has the Sewer District done to alleviate combined sewer overflows?
Since its inception, the District has invested nearly $900 million in projects that have reduced CSOs. In certain locations, computer controlled gates and inflatable dams store CSO flow in large pipes during rain events. The stored CSO flows are released to a District wastewater treatment plant following the rain event.
Adjacent to the District's Westerly Wastewater Treatment Plant, a Combined Sewer Overflow treatment facility stores and treats CSOs. Construction of the District's Heights Hilltop, Northwest and Southwest Interceptors has reduced CSO discharges in various locations. Floatables control netting facilities have been constructed at ten locations to reduce the amount of litter and debris being discharged from CSOs.
Recently, the District has overseen the construction of a number of CSO control "early action" projects in the Easterly and Westerly Treatment Plant areas, and more are planned in the Southerly Treatment Plant district. Ongoing construction of the Mill Creek CSO Tunnel has dramatically reduced CSOs to Mill Creek.
Yet there is still more work to do.
Click here to see pictures of a CSO from Mill Creek before and after it was eliminated.
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