Darrel Matson and other city officials took media on a tour of the flooded Atlantic Avenue sewage treatment plant Wednesday. (Matt Prokopchuk/CBC)

The Atlantic Avenue sewage treatment plant in Thunder Bay was not staffed the night it was flooded, a city official said Wednesday.

Darrel Matson, the head of the Infrastructure and Operations department, led the media on a one-hour tour of the plant. He said that although the plant is staffed seven days a week it is not staffed 24 hours a day.

"The plant continues to run to run in automatic mode with all of the alarms that are connected through computer systems and are received at a central location, Matson said.

"We have an individual on call, it’s a standby, and when an alarm is called in, and then that standby person responds to that particular call."

That standby person is then responsible for calling in the appropriate staff.  Matson says that process was followed the night of the flooding, and that crews had the first temporary pumps installed in an attempt to de-water the plant within two hours of the staff arriving.

Matson would not say whether he thinks having staff overnight at the plant would have made a difference in regards to the flooding.  However he added that's difficult to know as officials are unaware of the exact cause of the breach.