The damage done by the May 28 floods in Thunder Bay was not the result of equipment failure at the sewage treatment plant, city councillors heard at a meeting Monday night.

According to an independent meteorologist based in the city, forecasters didn't know how hard the storm would hit Thunder Bay.

Graham Saunders said it was about 15 minutes after the city set a rainfall record that Environment Canada issued a severe weather warning for the city on May 28.

Sewage plant breakdown

  • As a result of too much water, a screen eventually blocked up and forced the water through a series of tunnels that connect buildings at the sewage plant.
  • The tunnels filled within a few hours and water was eventually forced back to the original pumping station
  • Once the water hit the drywell pumping station, the motors flooded.
  • Under normal operating conditions, the motors usually sit six metres higher than the water.
  • The sewage plant’s first alarm went off at 1:09 a.m. on May 28.
  • An operator came to the plant at 1:33 a.m.
  • A report notes the city couldn't do much more than it did to prevent the flood as more than a billion litres of water, per day, was flowing into the plant — 30 per cent higher than its capacity of 766 million litres per day.
  • The sewage plant’s pumps couldn't take the water out of the sewers fast enough.

"That's embarassing for people who do warnings," he said.

The rainfall was like nothing ever seen before and "very exceptional records for 15 minutes, 30 minutes, one hour, [and] two hours were set in this storm," Saunders added.

That hard rain made it impossible for the sewage treatment plant to keep up.

‘More than its capacity’

An independent engineer hired by the city to look at what caused the plant to flood, said there was too much water trying to get through a screen. Troy Briggs said the water backed up and eventually flooded the plant.

"The pumping station actually did what it was supposed to do," he said.

"It pumped — more than its capacity throughout the event — and it wasn't until it actually failed, due to drywell flooding, that there was the issue."

Briggs said equipment failure was not to blame. It was simple a case of too much water — about 14 times more than the plant usually processes.

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Independent engineer Troy Briggs said Thunder Bay's sewage plant equipment was not to blame for flooding. (Jeff Walters/CBC)

Consultants recommended the city remove one of four screens at the sewage treatment plant to improve the flow of water and allow more water to flow into the plant.

For the long term, consultants noted the city should build a bypass system around the screens, which could cost about $1.4 million.

That recommendation will come to council in January, along with a more detailed look at the sewer system.

During the meeting, council also approved a residential drainage assistance program, which would help subsidize the cost of sump pumps and backflow prevention valves installed in people’s homes.