A safety review of the HB mine tailings dam south of Salmo concludes the potential consequences of a failure should be reclassified as “very high” based on Canadian dam safety guidelines.
The worst-case scenario report by Kelowna consultant Tetra Tech EBA released last week suggests that if the earthen dam breached, three people could die and clean-up costs could be in the tens of millions of dollars. The affected area would be less than one square kilometer but includes one home and Highway 3.
While there is no solid information on the total tailings volume of the dam, the consultant estimated it at 1.8 million cubic meters, and guessed about 40 per cent, or 714,000 cubic meters, would be released in the event of a failure. Flood levels could reach several meters with a potential loss of lives and the highway would be covered with mud and debris and likely closed three to four weeks.
The cost of cleaning up the tailings, restoring contaminated land, and rebuilding the dam is estimated at anywhere from $45.7 million to $89.4 million. The consultant said the wide range was due to costs being “highly sensitive to haulage distances, levels of restoration and material availability.”
In the last safety review of the HB tailings dam in 2002, the consequences of a failure were rated “low” based on 1999 guidelines established by the Canadian Dam Association. That equated to “significant” under new guidelines adopted in 2007, suggesting that if the dam failed, there would be no fatalities and only limited economic and environmental damage. The five categories on the scale are low, significant, high, very high, and extreme.
Uli Wolf, the regional district’s environmental services manager, attributed the more dire conclusions reached by the latest report to different methodology around vegetation, soil, and water permeation, plus the use of more localized precipitation data.
Wolf said it’s up to the Ministry of Energy and Mines to approve the dam’s higher consequence rating, although he expects it to be a formality. The result will be more frequent inspections and reviews as well as higher capital costs for remediation.
The consultant’s report is subject to a third-party review, required by a ministry order in the wake of the Mount Polley tailings pond disaster, although Wolf said it is mainly intended to check for underestimated risk.
“Dams certainly have received a higher level of attention from the general public since the Mount Polley incident,” he said. “Maybe rightfully so. For us that comes with added cost and work to our department. We will have address that in future budgets.”
The latest report doesn’t specifically address the likelihood of a complete dam failure but makes several recommendations including conducting an emergency exercise of RDCK staff involved in the dam’s maintenance and an engineering study to assess ways of reducing the risk of internal erosion. Wolf said some action has already been taken on reconfiguring the spillway and further construction is expected.
Cominco (now Teck) built the dam in 1955 to store lead and zinc mine tailings and operated it from 1955-66 and 1974-78. The company sold the property in 1981 and the Regional District of Central Kootenay acquired it for landfill purposes in 1998, paying $650,000 more for the site than the previous owner, a Panamanian company that bought it only a year earlier.
In the early summer of 2012, a sinkhole formed on the dam following heavy rain. The regional district spent more than $800,000 stabilizing and reconstructing the dam, which it billed to the province. Recently, the regional district filed a notice of claim against Teck, seeking reimbursement for ongoing remediation work.
The cost of failure
If the HB tailings pond failed, a consultant estimates that it would deposit 714,000 cubic meters of material over less than one square kilometer. This is the predicted cost of cleaning up the mess:
Removal of mud/tailings debris to secure landfill: $28.6 to $57.1 million
Restoration of impacted area: $13.1 to $26.2 million
Replacement of dam: $4 to $6 million
Total direct economic losses: $45.7 to $89.4 million*
* Actually given as $83.4 million in the report, due to an adding error
Source: Dam Safety Review of HB Mine Tailings Storage Facility, Salmo, Tetra Tech EBA Inc., May 2014