Calls for an independent safety review of the Site C dam project are mounting following a large landslide near the project’s worksite that has blocked the only road to a small community and led to the evacuation of residents by boat.
Retired BC Hydro engineer Vern Ruskin said this week’s mushrooming slide is a reminder that the project is located in an area prone to landslides and that a major landslide close to the Site C dam structure could compromise it.
“If the landslide is a long way off and all they get is a wave then the dam can withstand it,” Ruskin told The Narwhal. “If the landslide is close enough it could damage the dam structure and it may fail.”
Ruskin, who directed the team that designed the five dams originally planned for the Peace River, including Site C, said he has repeatedly asked the B.C. government and BC Hydro to conduct an independent safety review of the project due to its location in a valley with a history of large landslides and because of a change to the design of the dam structure.
When former B.C. premier Gordon Campbell announced his government would proceed with the Site C project in 2010, the dam structure was depicted as a very slight arc. But in 2014 an L-shaped structure — which Ruskin says to the best of his knowledge has never been used anywhere in the world for an earthen dam — was revealed when former premier Christy Clark announced final approval of the project.
The new structure is described by one engineering firm that helped design it as “unique” and an “innovative solution” to stabilize the original river valley wall.
Ruskin said that is all the more reason for an independent safety review of the $10.7 billion dam, the largest publicly funded infrastructure project in B.C.’s history.
“Someone outside of BC Hydro has to do the review,” said Ruskin, who taught engineering economics at UBC for 14 years. “It seems to me that if you are going to do something completely different you should test it.”
Dam safety under fire around world
Announced in 2010 as a $6.6 billion project and given final government approval in 2014 as an $8.8 billion project, the Site C dam’s price tag climbed by an additional $2 billion late last year.
Dam safety practice around the world “has been shaken” by the recent collapse of tailings pond dams at B.C.’s Mount Polley mine and in Brazil, the Site C project’s technical advisory board noted in its February meeting minutes. The board, charged with providing technical reviews and engineering advice, also noted the 2017 failure of California’s Oroville dam spillways following heavy rains, which led to the evacuation of more than 180,000 people downstream.
“Considerable re-evaluation of site documentation to better inform future dam safety assessment is currently underway in the industry,” the board noted in its minutes. The board also said it was “of the view” that the Site C project should “engage in these evaluations to be able to assert that it is adopting Best Available Practices.”
The Narwhal had previously requested technical advisory board meeting minutes through a Freedom of Information request, but the response was so heavily redacted it was impossible to determine if the board had any dam safety concerns.
In a statement e-mailed to The Narwhal, the B.C. energy ministry said BC Hydro has conducted extensive engineering studies into the geology of the Site C project area — including the dam site — for decades.
“The issue of historical slides in the area is well documented and its being addressed by BC Hydro with the excavations and stabilization measures that have been taking place at site since construction started in 2015,” said the statement.
The Peace valley landslide, which began overnight on Saturday, has left engineers scrambling to survey the unstable slope close to one entrance to the dam worksite, which is not affected.
Landslide near dam site forces evacuation orders
The landslide, which continues to gather momentum, has displaced five million cubic metres of earth — almost half the amount BC Hydro has excavated from the river’s north bank over the past three years to prepare for building the Site C project’s river diversion tunnels and the dam structure.
On Tuesday the Peace River Regional District — which has issued evacuation orders for three properties — evacuated people by boat who opted to leave their homes in Old Fort, a community of about 50 residences that has been isolated by the slide.
BC Hydro spokesperson Mora Scott said in an e-mail to The Narwhal that “there is no evidence to suggest that the slide that took place over the weekend is related to Site C or any of the work taking place on the project.”
The slide occurred immediately below a former gravel pit operation, where piles of stockpiled construction materials were clearly visible.
According to Peace River Regional District documents, when the gravel pit operation closed down in 2015, the B.C. ministry of energy and mines advised the owner that any future mining activities at the site would require a mine plan developed by a qualified professional, due to “past geotechnical and slope stability issues.”
“We all know the slopes are very unstable in the valley,” said Ken Boon, president of the Peace Valley Landowner Association, representing 70 landowners who will be impacted by the Site C dam. “An independent review of the Site C safety issues would be prudent.”
Arthur Hadland, the former Peace River Regional District director for the area that includes Old Fort, has repeatedly asked successive provincial governments to establish an independent panel of academic and non-academic geological experts to investigate the safety of residents of Old Fort, Taylor and Alberta, downstream from the Site C dam.
Hadland said in an interview that his concerns were heightened following BC Hydro’s confirmation in August that the Site C dam will be anchored to shale bedrock instead of to firmer bedrock such as granite.
“Shale is old mud,” said Hadland. “It’s 80,000 year-old mud. When it’s exposed to air and a little bit of moisture it turns back to mud.”
In August, BC Hydro spokesperson Dave Conway told local media that the Crown corporation has not been searching for stronger bedrock at the dam site, where it has removed 11 million cubic metres of earth in an effort to resolve geotechnical issues that have added to the project’s escalating cost.
“We know what rock is here,” Conway said.
“The dam is going to rest on shales, and the powerhouse and spillway structures are going to be anchored into shale materials as well.”
Ruskin said it’s not uncommon to build dams on shale, even though it is weaker than other types of bedrock. But what concerns him is the combination of shale and the new L-shaped design structure that includes construction of a roller compacted concrete buttress that will serve as the foundation for the generating station and spillways.
“That has never been done before,” he said. “They are pioneering.”
“There’s nothing wrong with a new idea,” Ruskin said, as long as the new design passes a safety review by a committee independent of BC Hydro and its contractors. Such a committee should include representation from the U.S. Army Corps of Engineers, which operates and maintains 700 dams, because it has extensive experience building on shale, he said.
Slope instability identified as issue during environmental review
The Joint Review Panel that examined the Site C project for the federal and provincial governments noted that slope instability and landslides in the valley “would potentially adversely affect” the project and “could result in landslide-generated waves or overtopping of the dam that could result in direct damage to infrastructure.”
In its most recent quarterly Site C report, made public in late September, BC Hydro referred to a June rockslide near construction of one of two river diversion tunnels as a “minor geotechnical event,” noting that remediation work is underway to minimize schedule impacts.
BC Hydro also stated in the same report that “changes to geotechnical ground conditions remain a risk to the project schedule and cost.”
The energy ministry said BC Hydro has identified 16 other earthen dams around the world that rest on a similar shale foundation. There are 57,000 large dams in the world, according to the U.S. non-profit group International Rivers.
The valley where the Site C reservoir would sit has experienced huge landslides in the past.
In 1973, a landslide in the future Site C reservoir area hurled 14.7 million cubic metres of debris a distance of almost one kilometre, damming the Peace River for 12 hours and generating a wave so high it snapped trees more than 20 metres above the river.
Sixteen years later, a slide at the nearby Halfway River, which would be flooded by Site C, sent 3.6 million cubic metres of debris into the Peace, blocking it for six hours and sending the river north.
And in 2016, a series of landslides at Lynx Creek, a Peace River tributary that would also be inundated by Site C, sent a plume of toxic metals, including arsenic, barium, cadmium, lithium and lead, into the Peace River.
According to BC Hydro technical reports, engineers expect as many as 4,000 landslides will be triggered by the Site C reservoir, which will be up to 50 metres deep, several kilometres wide and stretch for a total 128 kilometres along the Peace River and its tributaries — about the same distance as driving from Vancouver to Whistler.
Many of the landslides will be small, but some will be so large they are expected to generate waves reaching so far above the reservoir they may damage a planned new bridge across the Halfway River, according to BC Hydro reports.
BC Hydro says the Site C project is designed “to the highest recommendations” of the Canadian Dam Association, to withstand major events such as earthquakes and floods, and that the project design is in keeping with international best practice.
* The article has been updated from an earlier version that stated the landslide began following intense rain. In fact, there was no rain the night of the landslide.