By Jack Caldwell - Mining Engineer - Robertson GeoConsultants

This morning a pleasant-voiced lady from the Canadian Broadcasting Corporation (CBC) called me and asked my opinion about the recent failure of a tailings impoundment in Hungary and its impact on towns, villages, and the Marcal River. She asked simple, direct questions and asked if I would be prepared to be interviewed for a piece CBC-TV was running that night on the topic.So I walked down to the CBC’s offices in downtown Vancouver and there they interviewed me.

Click here to see the clip on the CBC website. Only about 10 seconds of my interview appear near the end of the clip.

As for the rest of the questions, I cannot recall the precise ones I was asked, nor can I recall my precise answers. Nevertheless, here follows more or less what I can recall.

Q: Could the same failure occur in Canada?

A: I am not aware of any impoundmentsin Canada that are like the one in Hungary that failed. However, failure of a tailings impoundment is an ever presentpossibility. Impoundments have failed in Canada; there could be failures in the future.

Q: What do we do different in Canada as compared to Hungary to prevent tailings impoundment failures?

A: In Canada we have reasonable regulations at the Provincial level and at the Federal level for uraniummill tailings. The Mining Association of Canada has published many fine guidance documents on the topic of tailings—andthese constitutea good overarching approach. We have many fine consultants who have great experience and expertise in designing tailings dams. We haveresponsible mine operators. And many mines in Canada insist on regular independent peer review of their tailings facilities. Also we must recognize thatthis facility was uncomfortablyclose to houses and buildings.Most Canadian mines are more remote from humanhabitation–although not nature.

Q: Should we have more regulations to prevent a failure like this in Canada?

A: Good regulations are but a part of achieving tailings dam safety. Professional societies must act to disseminate the lessons we learn from such failures. We must constantly involve qualified professionals, experienced consultants, and independent peer review. In my opinion, ongoing engineering review is the most important part of a safe tailings dam. Keep in mind a tailingsdam is always alive: constantly growing, being used, and expanded. A tailings dam is constantly responding to the forces of nature–which constantly change. For example groundwater flow changes; soil strengths adjust to the forces imposed on them; it rains and water is impounded on the facility. Regulations cannot keep up. Only regular observation, inspection, and intelligent evaluation of data is able to move fast enough to keep abreast of the ever-changing conditions at a tailings impoundment.

Q: Are Canadian regulators and inspectors active in keeping an eye on tailings dams?

A: It varies from province to province. In Alberta, the regulators, particularly ERCB,are vigilant, active, even proactive in keeping watch on the oil sands tailings facilities. But inspectors can only go by general guidelines and are generally not the most highly trained or experiencedof people. Their involvement is no substitutefor the involvement of independent professionals.

Q: What aspects of a tailings dam do you talk about with your clients?

A: Start with the foundation soils and rocks; then move to groundwater conditions; next address the perimeter dikes, berms and/or embankments; then worry about the tailings themselves and their geotechnical properties; finally think and calculate hard regarding the snow, the ice, and the precipitation.

Q: Why do you think the facility in Hungary failed?

A: We will have to await the final, formal findings. But from examination of the pictures, I would guess that the perpendicular side dikes moved away from each other as the forces of the tailings pushed them apart. The berm side slopes look very steep, too steep for conventional safety. Then there was probably weaker soil, high groundwater pressures, and maybe a pool too close to the edge. All the standard things that make tailings dams fail. Plus the impounded tailings were not filter pressed or dry stack; they were subject to liquefaction and obviously flowed out once the perimeter dike was breached. But these are only guesses for now.

PS. There are hundreds of pictures and comments on the web. Dave’s Landslide Blog is excellent.