POLITICAL TENSION RISES ON SITE C TENSION CRACK
Construction halts in the vicinity of 400-metre-long opening on river bank
B.C. Hydro was still in the early stage Monday of assessing the 400-metre-long crack that opened up last week on the north bank of the Peace River, upstream from one of the anchor points for the Site C hydroelectric dam.
The tension crack, as Hydro characterizes it, appears to be stable, according to preliminary readings from monitoring instruments at the site.
However, the company mobilized a drill rig to install additional monitoring instruments to gain a more detailed understanding of the crack and expects to have more data in hand later this week.
Those researches will guide engineers in crafting a remediation plan for that critical part of the construction site, where a vast amount of soil was being removed to stabilize the river bank and prepare for eventual anchoring of the dam itself.
In the interim, construction has been halted in the vicinity of the crack and some 30 members of the estimated 1,500 workforce have been reassigned to other parts of the vast construction site.
Hydro is keeping the provincial environmental assessment office apprised of the situation and possible responses, as part of the conditions imposed when the project was granted a certificate of approval to proceed.
Energy Minister Bill Bennett, whose cabinet bailiwick includes responsibility for Hydro, is continuing to receive updates as well. He told me Monday that his first concern, once worker safety was assured, was to determine if the crack would affect the lengthy and complex construction schedule for the estimated $9-billion project.
The crack is a bit upstream from where the dam will be anchored on the north side of the river, on the riverbank that will flank the eventual reservoir. It’s an area where the steep riverbanks are being lowered and then “recontoured” to a more gradual slope, reducing the risk of landslides into the reservoir.
Bennett hopes Hydro can come up with a workaround for the crack, so that it does not delay work on the tunnels necessary for the eventual diversion of the river, which is scheduled to commence in September 2019. (The plan is to begin filling the reservoir in 2022 and begin generating power in 2024.).
Hydro CEO Jessica McDonald herself publicized the problem with the crack on social media Friday morning, via her increasingly active (531 postings since last June) @bchydroceo Twitter account.
“As part of the Site C project schedule, work has been underway for the past 19 months to remove unstable soils to create stable slopes for eventual dam construction,” the statement read in part.
“During the construction of a haul road to support this excavation work, a tension crack has appeared … this particular crack requires attention due to its significant 400-metre length.
“While there was some initial movement of soil, it has now stabilized,” the statement continued.
“This area of unstable soil was already slated to be removed as part of engineering new stable banks for dam construction.
“Our next step is to determine how to continue soil removal which will need to be undertaken carefully to maintain the stability of the slope.”
The statement was the first time Hydro issued a specific news release about geotechnical concerns on the dam since construction began, as Jonny Wakefield noted in a news story Friday in the Dawson Creek Mirror.
But the general concerns about the geotechnical risks of building along the river date back decades.
They were a factor in the 1957 failure of the Peace River Bridge at Taylor, downstream from Site C, as Hydro itself acknowledged in a filing last June to the B.C. Utilities Commission.
“Key geotechnical risks” spelled out in one unsettling passage in the report include “unexpected shears encountered during construction; deeper than expected relaxation joints; bedding planes worse than expected; larger than expected deterioration of shale bedrock once exposed during construction; and rock rebound/swell.”
Nor are those geotechnical concerns merely hypotheti- cal, as the report to the BCUC went on to disclose in reference to an earlier problem on the north bank.
“Events associated with this risk have occurred on the north bank gully crossing, where unexpected slope failure occurred. B.C. Hydro has been working with the contractor to provide an engineered solution, and expects to address this issue within available funds.
“Once the main civil works contract is beginning excavation B.C. Hydro will have additional information about this risk.”
Geotechnical concerns were also flagged last fall in a report on risk management at the Site C project, commissioned by Hydro from the consulting firms of Ernst Young and BTY Group.
“Extensive investigation of the site was undertaken during planning of the project, but it is impossible to understand every nuance of the subsurface conditions of such a large site,” reported the consultants. “As a result, unforeseen problems have arisen, and will continue to arise, requiring innovative engineering responses to contain cost increases.”
With excavation now well underway and the crack looming on the north bank, Hydro is presumably learning more about conditions at the site, albeit not in the orderly fashion envisioned in the aforementioned reports.
With information still coming in, I asked Bennett last Tuesday if he envisioned a worst-case scenario where, say, the slope collapses over the hauling road at the base and spills into the river?
“The Hydro CEO would not want me to speculate about hypotheticals,” the minister returned, determined not to add to the uncertainties surrounding the controversial project with an election approaching.
They were a factor in the 1957 failure of the Peace River Bridge at Taylor, downstream from Site C, as Hydro itself acknowledged in a filing last June.