What is a combined sewer system
A combined sewer is a system that simultaneously collects surface runoff and sewage water in a shared collection of pipes and tunnels. Construction of combined sewers in Edmonton was an acceptable practice prior to 1960 as it was more economical than building two separate sewer systems. Construction of the combined sewer collection system was discontinued in 1960 due to environmental concerns. Edmonton's combined sewer system consists of 826 km of pipes, 19 combined sewer overflows, and the North Highland Interceptor Sewer.
How a combined sewer system functions
During severe wet weather, when stormwater and sanitary flows in the combined sewer exceeds the capacity of the system, Combined
Sewer Overflow (CSO) events occur. In dry weather, all flows collected by the combined system are delivered to the
Gold Bar Wastewater Treatment Plant for treatment.
Although the volume of wastewater that bypasses treatment through the CSOs is about 2% of the total volume of all Edmonton discharges, EPCOR considers the environmental impact caused by this to be unacceptable.
The combined sewer system can be a cause of odour problems due to large pipes and slow moving water in some neighbourhoods. The sewer odour escapes from catch basins (or storm drains) and manholes connected to the combined system. EPCOR has a
corrosion and odour reduction strategy in place to reduce the impacts of sewer corrosion and odours, and to improve the quality of life for Edmontonians.
Continued improvement of Edmonton's combined sewer system
For the past several years, EPCOR has focused on maximizing environmental protection. To date, 43 storage tanks with a capacity of 25 million litres have been built to reduce the amount of overflow entering the river. In addition, the corrosion and odour reduction strategy has been developed to further control and reduce CSOs.
Questions or concerns with the combined sewer overflow system?
If you have a concern about sewer odours in your neighbourhood you can contact our 24 hour emergency line at (780) 412-4500 to report the problem.