The North Saskatchewan River flows southwest to northeast through a 22 kilometre valley in the City of Edmonton; the largest stretch of urban parkland in North America. It supplies drinking water for Edmonton and dozens of downstream communities. The City of Edmonton, like most pre-1940 municipalities, is serviced in part by combined sewers.
These sewers occasionally overflow into the North Saskatchewan River in heavy rains. The Rat Creek outfall was responsible for 60%~80% of the City of Edmonton’s combined sewer overflow volume, 3.2-billion litres per year, affecting water quality in the North Saskatchewan River and raising safety concerns in Edmonton and beyond.
The $44-million West Edmonton Sanitary Sewer Tunnel W12 across the North Saskatchewan River connects the Rat Creek combined trunk to the South Highlands Interceptor and then to the Gold Bar Wastewater Treatment Plant. This was expected to reduce the CSO discharges into the North Saskatchewan River by up to 80%, significantly improving water quality.