Winnipeg faces at least $1.2B tab to stop sewage from flowing into rivers

Preventing sewage overflows into Winnipeg's rivers will cost more than $1 billion, regardless of what choice is made, a report from the city's water and waste department says.

The city currently averages 22 combined sewage overflows through each of its 79 outflows (locations where pipes overflow directly into the rivers), the report says.

That means sewage is released into the rivers more than 1,700 times every year. City staff estimate an average of approximately 900 million litres of sewage go into the rivers annually.

The major reason the city's antiquated combined sewer system — storm water and sewage use the same pipes in many older areas — can't handle heavy rainfalls without overflows into the river.

Prior to the 1940s, sewage and storm runoff flowed untreated into the rivers down the same sewer pipe. Gates called "weir dams" were later installed in each of the 79 outlet pipes in order to divert the mixed water toward municipal treatment plants.

During periods of heavy precipitation, the system can get overwhelmed, leading to what the city calls "combined sewer outflows."

• 5 million litres of raw sewage leak into Red River in Winnipeg
• 185M litres of raw sewage dumped into Winnipeg rivers since 2004

The overflows add to the nutrient load in Manitoba's lakes, although the number is relatively modest — overflows add 0.3 per cent of all the phosphorus and 0.1 per cent of all the nitrogen going into Lake Winnipeg, the report states.

The city has been reviewing options to reduce combined sewage overflows along with the provincial government and advice from other municipalities. Options include total infrastructure upgrades such as sewer separation, or enhancements such as in-line storage, offline storage or end-of-pipe treatment.

The city's water and waste department staff have a preferred option, based on in-line storage, that would capture 85 per cent of overflows in a year. The plan is loosely estimated to cost $1.2 billion.

A complete sewer separation would cost approximately $4.1 billion.

The proposal from water and waste would be the least disruptive in terms of planning and construction, the report says.

The Manitoba government has set a deadline of 2017 for the city to submit a final master plan.

But it could be decades before the number of combined sewer overflows is actually cut down. Water and waste's solution has a timeline to be completed by 2030.