The largest wastewater treatment plant in Calgary is being repaired to meet provincial water quality standards, after the facility was overrun by floodwaters in June and forced to release raw sewage into the Bow River.
“Our objective is to get the plant back into compliance and we need to do this as quickly as possible,” said Kevin Colbran, manager of wastewater treatment for the city.
“During the flood, we were out of compliance. The goal behind all we are doing is to get back into compliance, but the plant is still damaged and working in a manual mode.”
The Bonnybrook Wastewater Treatment plant, serves about 600,000 people in Calgary,
It was inundated with floodwater from the Bow and Elbow rivers on June 20 and 21.
As the water level rose, parts of the plant were shut down to prevent a catastrophic failure.
Staff was forced to dump raw sewage into the Bow River and alert downstream communities about the situation.
There was no impact to Calgary’s water safety because the city’s supply is taken upstream of the plant.
“The difference between this flood and the one in 2005 is we got it from both sides of the plant,” said Colbran.
“The river backed up into the plant from the outfall and when the downtown core flooded, the sanitary system was inundated. So, we got it at the head works facility through the sanitary collection system and from the outflow from the river.”
The flow into the plant was so high that it flooded the tunnel system, which houses the majority of the processing equipment.
Pumps, electric motors, electrical cables, control and communication systems, instrumentation and lights were all damaged.
The process air piping in the tunnel was not anchored to the support, so it was lifted up to the ceiling and damaged.
The ultra violet systems including bulbs, lamps and transformers were destroyed.
Colbran said his staff rented every pump they could find and pumped out the tunnels, which took several days.
“The plant was completely shut down electrically and we had to wait for the water to recede before we could get in to pump out the tunnel system and assess the damage,” he said.
“We had to put water back into the tunnel to prevent further structural damage because the water table was too high.”
Initially, Bonnybrook staff started to clean up the facility and work with Alberta Environment to meet provincial water quality standards.
After the plant was inundated with floodwater, Colbran said, it was only possible to screen out solid material larger than six millimeters.
When wastewater reaches a treatment plant, it passes through screens that remove larger materials such as plastic bags, toilet paper, toys, sticks and tennis balls.
The wastewater then travels into grit tanks, where the heavier material settles to the bottom and is taken to the dump.
The remaining water is treated before it’s released as clean water into the Bow River.
Since the control system of the plant was damaged, staff are operating the treatment process in manual mode.
Next, staff and Graham Construction began the process of repairing the facility.
“Essentially every electric motor we had that was submerged had to be removed and sent for assessment or replacement,” Colbran said.
“We had an assembly line of pumps going out and new pumps coming in or repaired. We are systematically removing all pumps and field devices for the distributed control system, which were damaged beyond control.”
The repair process was made easier by the level of redundancy that is built in to the plant.
For example, there are two pumps installed next to each other, so one can be taken out for repair while the other operates.
According to Colbran, most of the mechanical work is complete, except for the continual pump rebuild.
The repair of the communication system in the tunnel and field devices is currently taking place.
Once this is done, equipment will be replaced and Bonnybrook staff will start developing programs to prevent another event of this nature.
“Eventually, we will put some sort of system in place that will prevent the tunnels from being flooded,” said Colbran.
“We have some work underway and are looking at a plant expansion to be delivered in 2020. The engineering work has started and as part of that work resiliency will be considered.”
For the City of Calgary, the term flood resilience refers to the ability of various departments to cope with, and recover from, flooding at property, neighbourhood and city levels.