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Site C construction reaches major breakthrough at river diversion tunnel

WATCH: BC Hydro says it has achieved a construction milestone on the Site C dam after breaking through one of its river diversion tunnels. Sarah MacDonald has more.

A major piece of the puzzle surrounding the construction of the Site C dam in northern B.C. has finally taken shape.

BC Hydro has released video showing crews breaking through the rock at the end of a 700-long diversion tunnel, one of two being built to reroute a section of the Peace River.

The diversion of the river will allow crews access to the heart of the project, which is being built across the main channel of the river.

WATCH: How the diversion tunnels at Site C will work

How the diversion tunnels at Site C will work
How the diversion tunnels at Site C will work

To build the tunnel, roadheaders were used to grind through the rocky slope and load the earth onto conveyors so it could be hauled away by truck and relocated elsewhere on the site.

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Lining for the tunnel started last week. The process involves pumping concrete through a slip form that cures it into a perfect circle within the tunnel, reinforcing the walls.

READ MORE: ‘Running 24-7’ -- Behind the scenes of Site C Dam construction

The lining is the last step before the tunnels are fully completed in early 2020. The diversion of the river is expected to begin next September.

Once completed, BC Hydro says the tunnels will be able to hold up to 3,000 cubic metres of water per second, but will only have to handle up to half of that.

Excavation began on the first tunnel in July 2018. The work was delayed a year after huge tension cracks appeared in the geotechnically unstable north bank of the river in 2017.

WATCH: (Aired Nov. 4, 2018) Behind-the-scenes tour of Site C dam construction

Behind-the-scenes tour of Site C dam construction
Behind-the-scenes tour of Site C dam construction

Since the cracks were found, workers have removed 11 million cubic metres of earth from the slope, laying it back to what BC Hydro says is a more gentle angle.

The instability of the earth at the site, which sits less than 10 kilometres southwest of Fort St. John, is one of many reasons why the project has been controversial since the BC Liberals gave it the green light in 2014.

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READ MORE: How stable is the land under the Site C Dam project?

Three years later, Premier John Horgan allowed construction to resume despite opposition from the BC Greens, Indigenous groups and environmental activists.

Several legal challenges have been mounted by local First Nations along with landowners and farmers in the Peace River Valley.

BC Hydro has declared victory 15 times so far, including in some court fights that made their way to the Federal Court of Appeal.

WATCH: (Aired Nov. 15, 2018) Concerns over land stability under Site C Dam

Concerns over land stability under Site C Dam
Concerns over land stability under Site C Dam

A judge has ruled a trial must take place by 2023 to decide whether the dam infringes on Indigenous treaty rights.

In January, a United Nations committee warned Canada’s ambassador that the dam may violate international agreements on the right to free and informed consent with Indigenous peoples.

The letter said it could also be in violation of a 50-year treaty on fighting discrimination, which Canada has signed with 88 other countries.

READ MORE: UN panel warns Canada that Site C dam project may violate international agreements

The dam, which won’t be operational until late 2024, was originally supposed to cost $8.3 billion. The budget was raised to $10.7 billion after an NDP-ordered review of the project. Horgan’s approval came after the completion of that review.

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When finished, Site C will produce enough energy to power 450,000 homes, which BC Hydro says makes it crucial to the province’s future energy needs.

—With files from Jordan Armstrong and the Canadian Press