- Fraser Valley Current
- The $7 million end of the line for Chilliwack sewage
The $7 million end of the line for Chilliwack sewage
City faces big bill to repair pipe that sends treated wastewater into Fraser
When you flush your toilet, you send water coursing through a long series of pipes en route to your local wastewater treatment plant. It’s easy to think that plant is the end of the line. It’s not.
And getting your waste to its final destination is no easy, or cheap, feat.
This year Chilliwack will spend $7 million—more than $250 per resident—to fix the massive pipe that carries its waste water from its treatment plant into the centre of the Fraser. *
The poop process
All wastewater treatment plants in the Fraser Valley are located along, or close to, the banks of the Fraser River.
There’s a reason for that. All the water and bits of other stuff that go into the drains of sinks, showers and toilets around the region end up at the wastewater plant. There it goes through a multi-step treatment process.
First grit, sand and inorganic material is filtered out. Then the water enters chambers that allow the heavier solids to sink to the bottom. Some bacteria-infested organic material, by this point, remains dissolved in the water so a complicated “activated sludge” process separates it out. And then, finally, chemicals like chlorine are added to the water to eliminate micro-organisms that could otherwise cause disease. Chlorine is then neutralized by the injection of sulphur dioxide gas.
At several stages, material leaves the water. The second anaerobic digestion stage pulls most of the actual poop from the water. It then is dried and becomes “biosolids” that can either be turned into fertilizer or burned for energy.
But the water itself has to go somewhere and though it is significantly less contaminated than when it arrived at the plant, it still needs to be diluted as it re-enters that natural system. So in the Fraser Valley, the water inevitably ends up in the single biggest waterbody in the region—and not from some riverside sewer grate but via massive pipes that return the water to the centre of the river. The pipes don’t pump the waste water into the Fraser in a giant stream, but use “diffusers” to spread it out over a longer area.
A broken pipe
In Chilliwack, that pipe is 1.2 metres in diameter and runs along the bottom of the Fraser for 180 metres. It is authorized to discharge a little more than an Olympic swimming pool’s worth of water into the river every hour. And, as of November, the pipe is busted.
Even before the break was discovered, the city’s staff had already figured the outfall pipe needed to be fixed.
“Some of the armoring had been washed away by the river,” engineering director Kara Jefford told council recently. But when the city began surveying the site, the news turned grim. An early November bathymetric survey using sonar beams detected a possible break. Later that month, the city sent divers to the site who confirmed that in person.
The city had planned to spend $4.5 million “rehabilitating,” enforcing, and improving the outfall to keep it in decent shape for the future.
But now the cost is going to be substantially higher—and the work needs to be done right away.
Having detected the break in November, the city immediately went looking for a contractor who could fix the pipe. Only one company—Jakes Construction—responded to a “request for pre-qualifications,” and now the city has hired it to do the work as soon as possible. The current repair costs are pegged at $7 million. (The city got estimates both from Jakes and its consulting engineering firm, Stantec.)
The work is challenging because the pipe is in “a very dynamic section” of the river. The final scale of the work is still dependent on the outfall’s condition. At this point the city plans to replace 160 metres of pipe, while reusing the current diffusers.
For $7 million, the City of Chilliwack would hope that the rebuilt pipe will last a while. Council was told that is likely to be the case.
“It will give us potentially another 40 years and maybe longer,” Jafford said.
In Langley, engineers will also be planning for a new outfall pipe in the coming years.
The Northwest Langley Treatment Plant currently serves about 30,000 people, but is being massively expanded to accept waste from nearly 10 times that population. When complete, the plant will treat waste from Langley Township, Maple Ridge, Pitt Meadows and North Surrey.
The expansion work is ongoing. As part of it, crews drilled a tunnel beneath the Fraser River, then pulled a 1.6km-long pipe through it to connect the Maple Ridge sewer system with the expanded Langley plant.
Once that work is done, construction is expected to start on a new outfall pipe that will transport the treated wastewater into the centre of the Fraser River, likely just north of the Golden Ears Bridge.
Abbotsford and Mission’s pipe
Abbotsford and Mission share a wastewater treatment plant located on Matsqui Prairie, just west of the Abbotsford-Mission Bridge.
Mission recently spent millions constructing a new raw-sewage pipe to the plant because of the perilous state of the old pipe.
Abbotsford and MIssion’s outfall pipe is the largest in the valley. Built 20 years ago, the pipe runs for more than one kilometre from the JAMES treatment plant to the Fraser’s north channel, near the eastern tip of Matsqui Island.
The pipe is authorized to discharge about 50% more effluent than Chilliwack’s outfall pipe and has 70 diffuser ports to spread it into the river. But it too has had its issues. Seven years ago, engineers discovered that some diffusers had become covered by sediment because of “low port exit velocities.” Essentially, the diffuser pressure was too low and not spraying waste water at high enough speeds to counteract the natural sediment accumulation on the river bottom. The engineers at the time were considering closing many diffusers to increase the velocity of wastewater coming from open ports.
Water quality is monitored directly upstream and downstream of the outfall location to test for any possible consequences on the environment.
*This story first said taxpayers will spend $7 million. That’s not totally correct. Municipal water and sewer systems are funded by users, not taxpayers. So only those hooked up to Chilliwack’s sewer system will pay for the new outfall (mostly through already-paid user contributions.)