Part 1 of a report on how fracking poses risks to BC Hydro’s Peace River dams
The WAC Bennett dam impounds the world’s seventh-largest reservoir. In 2012 a BC Hydro employee speculated a fracking operation may have caused a sudden change in the reservoir’s water levels. Photo: Jayce Hawkins.
BC Hydro has known for well over a decade that its Peace Canyon dam is built on weak, unstable rock and that an earthquake triggered by a nearby natural gas industry fracking or disposal well operation could cause the dam to fail.
Yet for years, knowledge of the dam’s compromised foundation was not shared widely within the Crown corporation. It was even kept secret from members of a joint federal/provincial panel that reviewed the Site C dam, now under construction 70 kilometres downstream of Peace Canyon in the Montney Basin—one of the most active natural gas fracking zones in British Columbia.
The disturbing revelation is among many contained in hundreds of emails, letters, memos and meeting notes released by the publicly-owned hydro utility in response to a freedom-of-information (FOI) request by the Canadian Centre for Policy Alternatives, BC office.
The documents show that BC Hydro officials knew from the moment the Peace Canyon dam was built in the 1970s that it had “foundational problems,” and that if an earthquake damaged the structure’s vital drainage systems it could be a race to stabilize the dam before it failed.
The documents also show that BC Hydro’s concerns about threats to the dam were discussed “at the highest level” within the provincial government ten years ago, but that unidentified provincial Cabinet ministers at that time rejected taking any action.
The documents have been augmented with a raft of emails supplied by a former BC Hydro construction manager, who oversaw $350 million in retrofits at the Peace Canyon and WAC Bennett dams in 2007, and who is speaking out publicly for the first time about his concerns.
A compromised foundation
Built in the late 1970s, the Peace Canyon dam lies a short distance downriver from the massive, earth-filled WAC Bennett dam, which impounds Williston Lake—the seventh-largest hydro reservoir on earth by water volume. The FOI documents show that the dam was built on top of layers of sedimentary rock, including shale—a rock known to be difficult to work with when big engineering projects are involved.
“A number of weaker bedding planes were identified underneath the dam during construction. Some of these exist directly below the dam within the foundation, and shear tests on bedrock core samples indicated shear resistance that was significantly lower than originally anticipated during design,” reads one internal report on Peace Canyon prepared by BC Hydro in 2017. “The dam is marginally stable under full uplift considerations, which does not meet modern design practice.”
The discovery was a bombshell. Since the shale rock underlying the dam was more susceptible to shearing or breaking than previously thought, it was vital to prevent any industrial activities nearby that could possibly trigger earthquakes.
But that knowledge was not widely shared within BC Hydro itself, even when disturbing tremors started to be felt at the dam in 2007—more than 30 years after problems were first detected. MORE