More than three million litres of diluted wastewater, a combination of rainfall runoff and sewage, flowed into the Assiniboine River Sunday night due to a power failure during a rainfall, according to the City of Winnipeg. 

It happened at the Aubrey Lift Station on Palmerston Avenue, with the overflow running from just after 11 p.m. until nearly 3 a.m. the next day. 

A city spokesperson said that location was offline for two hours, writing: 

“Typically, sewer system storage has capacity for two hours of flow storage during dry weather, to provide time for operational maintenance/response. However, the power failure occurred during a rain event, which used up the dry weather flow storage capacity.” 

The city also said a ratio for the wastewater discharge could not be provided as it would vary based on amount of rain, intensity, frequency and duration of rainfall, along with how high the river was and where the rain fell. 

City water & waste committee chair Brian Mayes said releases would continue to happen due to combined sewer systems dating back decades that exist within the city.

“It is a reality of the current state of the infrastructure, not just in Winnipeg but in other cities,” said Mayes. 

In November of 2017, the province mandated the city reduce its combined sewer overflow by 85 per cent by 2045, something Mayes said the city is working towards. 

Part of that includes $330 million already invested in combined sewer separation and its basement flood relief program.

Jonathan Challis is completing his PhD at the University of Winnipeg, with a focus on environmental contaminants in aquatic systems. He told CTV News it’s important to consider how much water flows through area waterways in providing context for a figure like 3 million litres. 

“The Assiniboine River and the Red River, they’re highly dynamic, high-flowing systems so that concentrated plume of waste water is being nixed and diluted very quickly,” said Challis. 

When asked about potential long-term effects, Challis stressed the connectivity of waterways and the threat of excess nutrients in Lake Winnipeg, with the Red River being the major contributor of nutrients to that body of water. 

“The Assiniboine River flows in the Red River and the Red River into Lake Winnipeg, and we all know the issues with Lake Winnipeg.”