'Large tension crack' threatens major sewer line in Whitehorse

Whitehorse city officials say one of the city's main sewer lines is at risk from a probable landslide, maybe even this year — and it's a $10-million fix to avoid a potential "uncontrolled release" of raw sewage. 

City engineers say a "large tension crack" was discovered last spring along the Takhini sanitary trunk 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 Centre on Range Road, on a relatively steep section of the escarpment.

It's similar to other cracks that were seen elsewhere along the escarpment before a series of landslides last spring. 

"Based on the hazard and risk assessment completed by the City's geotechnical engineering consultants, there is a high probability of imminent slope failure that will damage or destroy this portion of the main within the next year," reads an analysis presented at a city committee meeting on Monday.

Speaking at a news conference on Tuesday, Gareth Earl, the city's associate manager of engineering services, said a slide is "highly probable." 

"So we're doing our due diligence to prepare for that."

The steel-pipe sewer line at risk was installed in 1975 and it carries raw sewage to the Marwell lift station from an area including the residential neighbourhoods of Takhini, McIntyre, Arkell, Ingram, Copper Ridge, and Granger, as well as Yukon University, the Canada Games Centre and the Whitehorse Correctional Centre. Earl says it carries about 40 to 50 per cent of the city's sewage, at a rate of about 150 to 200 litres per second, "roughly equivalent to like, 1,000 kitchen taps left on."

The plan is to construct a new sewer main around the potential landslide area later this year. City council is being asked to approve the $10-million budget so a tender can go out next month, and work can begin this spring. 

The design includes approximately 1.2 kilometres of sewer line that would go along Range Road and then down a more gentle slope to Marwell.

In the meantime, city engineers have designed a temporary bypass that will be used once the spring melt begins, likely in April. The bypass involves an above-ground pipe and will be used until the new main is operational.       

The city also dug a sump at the bottom of the slope last year to collect any sewage in case of a spill.

Several landslides in 2022 

Whitehorse's escarpment was under the microscope last spring after several landslides during the spring melt. One large landslide blocked off one of the main thoroughfares into downtown for several weeks.

The tension crack that threatens the Takhini sewer main was discovered last June. It was not there during an inspection a year earlier, city officials say.

City council last summer approved $350,000 to immediately begin work on a solution for the sewer main. Now council is being asked to find another $9.75 million to complete the work.

The project would go out for tender next month, and work is expected to begin by May and be done before the end of 2023.

In the meantime, Earl said engineers will continue to monitor the tension crack and the sewage flow for any change.