‘Great Stress Fracture’ threatens main sewer line in Whitehorse
City of Whitehorse officials say one of the city’s main sewers is at risk from a likely landslide, maybe even this year — and it’s a $10 million solution to avoid a potential “uncontrolled release” of raw sewage.
City engineers say last spring a “major stress crack” was discovered along the Takhini plumbing line, which carries nearly half of the city’s raw sewage to the Marwell lift station. The crack is just east of the Pepsi Softball Center on Range Road, on a relatively steep section of the escarpment.
It is similar to other cracks seen elsewhere along the escarpment prior to a series of landslides last spring.
“Based on the hazard and risk assessment conducted by the city’s geotechnical consultants, there is a high probability of an imminent slope failure that will damage or destroy this portion of the mainline within the next year,” according to an analysis presented at a city committee meeting was presented on Mondays.
At a news conference on Tuesday, Gareth Earl, the city’s associate manager of engineering services, said a slide was “very likely.”
“So we’re preparing for that with our due diligence.”
The vulnerable steel pipe sewer line was installed in 1975 and carries raw sewage from an area encompassing the residential communities of Takhini, McIntyre, Arkell, Ingram, Copper Ridge and Granger, and Yukon University to the Marwell lift station. the Canada Games Center and the Whitehorse Correctional Centre. Earl says it moves about 40 to 50 percent of the city’s wastewater at a rate of about 150 to 200 liters per second, “which is equivalent to about 1,000 kitchen faucets that are still open.”
There are plans to build a new sewer line around the potential landslide area later this year. The City Council is being asked to approve the $10 million budget for a bidding next month and for work to begin this spring.
The design includes approximately 1.2 kilometers of sewer line that would run along the Range Road and then down a gentler slope to Marwell.
Meanwhile, city engineers have designed a temporary bypass that will be used once the spring meltdown begins, likely in April. The bypass is an above-ground line that will be used until the new main line is commissioned.
The city also dug a sump at the base of the slope over the past year to collect all sewage in the event of a spill.
Multiple landslides in 2022
The Whitehorse Embankment came under scrutiny last spring after multiple landslides during the spring meltdown. A large landslide blocked one of the main thoroughfares into the city center for several weeks.
The stress crack threatening the Takhini Sewer was discovered last June. It wasn’t there when it was inspected a year earlier, city officials say.
The city council approved $350,000 last summer to begin work on a sewer solution immediately. Now the council is being asked to raise an additional $9.75 million to complete the work.
The project would be put out to tender next month, and work is expected to start in May and be completed before the end of 2023.
In the meantime, Earl says engineers will continue to monitor the stress crack and effluent flow for changes.