Monday’s massive rainfall overwhelmed London’s pollution control plants, forcing the city to dump millions of litres of raw and partly treated sewage — enough to fill more than 25 Olympic-size swimming pools — into the Thames River.

But city engineer John Braam said while about three per cent of the released water was raw sewage at the Greenway Pollution Control Plant, improvements to the wastewater collection system will reduce the amount in future.

“We’re treating a lot of rainwater that ought not to be treated,” Braam said.

In the past, homes could have their weeping tiles connected to the city’s sewage systems where essentially clean rainwater would join water from washrooms and kitchens to be unnecessarily treated.

A pilot project begun last year has been disconnecting these weepers and connecting them to a storm system.

“(This) frees up capacity in that existing sanitary pipe,” said Braam, who added the pilot does this at 20 per cent of the cost of conventional methods. “We were very pleased with that pilot so we’re extending (it).”

Combined sewers, where wastewater and rain water are carried off in the same pipe to treatment plants, cause a similar problem. But the city is working to eliminate those, too, Braam said.

“We’ve had a fairly aggressive program,” he said. “We don’t have a whole lot of combined sewers left in London anymore.”

Most significant in combating dumping of raw sewage into the Thames will be expansion of the Greenway plant, which will take about 2 1/2 years to complete.

“The big problem with a storm like that is it’s all at once and it comes in as a wave,” said Geordie Gauld, division manager in wastewater treatment.

Once completed, the Greenway plant will be able to handle most massive rainfalls, with exception of those like Monday’s, he said.

The storm poured almost a month’s worth of rain in one night, flooding basements and swamping restoration companies and the city with desperate calls from homeowners.

The city’s flooding hotline received more than 120 calls by midday Wednesday.

And with the city’s inside workers’ strike hitting five weeks, there are concerns efforts to handle the aftermath may hit roadblocks.

“The actual checking of the sewers, first of all, which is done by sewer operations, is not affected because the supervisor takes care of that,” said Rick Pedlow, sewer operations manager. It’s later on in the process that it gets a little further impacted.”

Among the strikers are workers who take the data gathered and look at it to see what measures can be implemented to mitigate trouble in the future.

azzura.lalani@sunmedia.ca

THE NUMBERS



153,000:cubic metres of sewage that can be processed each day at the Greenway plant.

500,000:cubic metres of sewage that can be processed each day once Greenway expansion is complete.

47.7:millimitres of rain, or nearly two inches, recorded at the London airport during Monday’s storm.