Mt. Polley: Expert panel review
We are heartened by today’s announcements re. the Mt Polley tailings facility failure. In particular we applaud the choice of experts retained to do the engineering review.
CBC New reports as follows on this issue:
Minister of Energy and Mines Bill Bennett says the B.C. government is setting up two separate reviews following the Mount Polley tailings pond failure earlier this month.
Bennett said Monday that:
- The first review by three independent experts will investigate the failure of the tailings dam at the Mount Polley mine.
- The second review will require all mines in British Columbia that have tailings dams to have independent experts conduct a review of their facilities and submit them to the government.
The first review will be completed and submitted to the government and the Soda Creek and Williams Lake Indian bands by Jan. 31, 2015, and the recommendations will be implemented by the government “where needed,” Bennett promised.
The minister said the reviews were necessary to restore public confidence in the mining industry.
“We have a responsibility, as the jurisdiction where this failure took place, to find out exactly why it happened, ensure it never happens again and take a leadership role internationally in learning from this serious incident,” Bennett said.
When asked what might have caused the dam to fail on Aug. 4, Bennett said there is no “leading theory” yet.
The three experts appointed to review the dam failure are:
- Norbert Morgenstern, an adviser to consulting engineers.
- Steven Vick, a geotechnical engineer from Colorado.
- Dirk Van Zyl, a professor at the University of British Columbia’s Normal B. Keevil Institute of Mining Engineering.
Zyl called the the failure of the tailings facility at Mount Polley “a dark day for the mining industry not only here in British Columbia, but worldwide.”
“It’s extremely important for us to understand how this breach happened and why so that we can move forward with the best possible practices in ongoing and future mining operations,” he said.
I do not believe a better panel could be found. Morgenstern is the leading Canadian expert on tailings dams. I first came across his name at university in the 1960s when we studied his theories for foundation design. I have made presentations to him in his capacity as a peer reviewer to Suncor on their tailings facilities. I have read many of his reports and listened to many of his lectures. He is old but still wise and sharp. He is an expert of repute.
Steve Vick I met in the early 1980s when we were working on tailings facilities in Colorado. On an old posting on this blog I wrote this about Steve: Steven Vick’s great book is Degrees of Belief, Subjective Probability and Engineering Judgment. This is the book that started and still underpins any enquiry into the nature of tailings facilities and their management via an understanding of the role of probability, judgment, and ultimately decision making in the mining context. And of course there is his book Planning, Design, and Analysis of Tailings Dams. I have read it again and again over the years for it is full of wisdom. Read his paper at this link to see how thorough he is.
Writing in 2012 about Steven Vick, I said the following:
Risk is the product of probability and consequence. In the long term, as time proceeds to infinity, the probability of an adverse event tends to one. When seeking to control the risk of long-term tailings facility failure, there is little we can do about the probability of failure. In the goodness of time it will occur. All we can do today, is to seek to limit the consequences of failure, adverse performance, and unacceptable impact.
Steve Vick reminded us of this inescapable conclusion in a magnificent keynote address at the Tailings & Mine Waste 2012 conference just ended in Keystone, Colorado. The authority and reputation of Steve, who is surely the doyen of tailings, ensures that his insight will force a change in the way we think about and act as tailings engineers.
Steve reminded us that the consequences of failure of a tailings facility go well beyond the physical impact of tailings that may escape the failed facility and impact the receiving environment. The consequences may include significant and even total loss of shareholder value, the closure of the mine, the shutting down of the company, and huge financial expense to society. And of course, there is loss of life, loss of reputation, and loss of industry credibility.
What can we do to minimize the consequences of failure of tailings facilities? The best is to undertake filter-pressed, dry-stacking. In the long term, things may move, but not flow—the worst consequence of failure. Put the tailings in a place where the inevitable migration of material and constituents is to an accepting environment. Avoid downstream rivers, lakes, and oceans.
Steve noted that in all cases the tailings facility will eventually become the ward of the state (society). Only in the case of the UMTRA Program is there a supposedly perpetual government agency charged with looking after the closed tailings facilities: twenty-four old uranium mill tailings piles.
Steve noted that only European cathedrals have cultural value sufficient to induce society to care for them in the long term. Closed tailings facilities will never be such icons of cultural respect. Of course we can turn the closed impoundment into a riding stable as was done at the Cannon Mine. But not all closed tailings facilities lend themselves to such conversion into socially beneficial places.
The inevitable conclusion from hearing Steve is that some mines just should never open. Some tailings practices are going to have to go the way of the dodo. His best example is a water cover. And maybe hydraulic fill in places where the tailings will not be totally dry or frozen forever.
Maybe we should get Steve to head up an international evaluation of how to undertake tailings practices that result in long-term, tolerable consequences. I suspect that if he or others do not do this, we will see no change in the rate of tailings facility failure and long-term negative consequences for too many places. Why we may see the demise of mining and society as we know and enjoy it.
I will credit anything he concludes.
Dirk Van Zyl is a long-time colleague and friend. I took his job many years ago when he left SRK to come to the USA to do his doctoral thesis. We are still working together on organizing conferences for InfoMine. Dirk is quoted in one report as follows:
UBC Engineering Prof Dirk van Zyl says failures like this are about one in a million per year.
“…you always hope it never happens at home and this time it did and so it’s a great force that’s released when you have such a failure
van Zyl says large failures like this and investigations of them often find there could be a number of ways the breach could have happened.
Actually his statistics are off by a thousand or two. Franco Oboni of Riskope writes the following in a comment on a previous posting on this blog:
On a portfolio of approximately 3,500 tailings dams world-wide we evaluated that in the decade around 1979 (1974-1984) the rate of failure was 10-3 (one dam in one thousand per annum on average) and the decade around 1999 (1994-2004) the rate of failure was 2*10-4 (two dams in ten thousand per annum on average). Those numbers mean respectively 3.5 major dams breach in average per year (1974-1984), 0.7 major dams breach in average per year (1994-2004). With those averages one could easily evaluate the probability of having more failures in one year, but we will leave this aside, for the moment. Again, we do not know if 3,500 is still correct, but we assume it is for the sake of the discussion, and there is no clear definition of what a major breach is, so we assume these are the most widely reported failures, that reach even non expert public through media exposure. The validity of the 3.5-0.7 range can easily be “verified” by looking at the Chronology of major tailings dam failures as published, for example, by Wise-Uranium in their website. As such, the decrease from 3.5 to 0.7 can be seen as an indicator of the mining industry performing overall a better job today than it did in the past, but we will also leave this discussion to another time.
Many hazardous industries (chemical, electrical, for example) around the world consider the limit of credibility for an accident at a probability in the range of 10-5 to 10-6 (one in hundred thousand to one in a million). By the way, hydro dams have historic record of failure floating around the credibility threshold. Thus tailings dams are to be considered more hazardous than hydro dams, and they unfortunately cannot be breached at the end of service life: they have to stay there “forever”. Obviously, with the estimated values of the prior paragraph, major tailings dams breaches are to be considered way above credibility now, and more so, in the longer run, although long term consolidation may help a bit.
No matter. Mt Polley simply confirms that there are two to three tailings failures per year. We had Duke Energy earlier this year and probably have one more to go before Christmas, well before the panel presents its findings.
The only misgiving I have is that these three gentlemen are extremely busy without the added burden of this panel work. Where will they find time to do it all? I suppose the answer is the old adage: if you want good work done, ask only those too busy to do it.
So we wish them speed and success at finding out why Mt Polley’s tailings facility breached.