Constructing covers over mining wastes at sites in cold climates involves consideration of these factors that are unique to cold climates:
- Short construction periods, unless you are prepared to work in frozen conditions in winter
- A shortage of construction materials, for the glaciers moved clays, silts, and sand south
- Remote and difficult access, unless you can fly in or traverse a frozen road
- Freezing conditions that make you consider freeze/thaw, ice lenses, boils, and wind-blown snow.
These and many other factors were discussed in detail the past three days at the seminar on Cold Cover just finished in Whistler.
Many case histories of successful cover construction at Northern Canadian sites were presented. I had not hitherto learnt of these case histories. The seminar was worth every effort if only because of the “publication” of the case histories. In due course all the presentations will be available in the InfoMine library. I will let you know when and where.
Most case histories involved placement of a sufficient thickness of inert rock or gravel over toxic tailings so that freezing and thawing occurs in the cover and the tailings remained frozen. The issue is: what is the depth of seasonal freeze and thaw? Easy to predict now. Easy to measure now. But not easy to do if you have to predict what will happen as climate change takes hold. For the participants at this seminar accept climate change as a given; as something to be dealt with as but another engineering parameter. There is no climate change denial in this part of the mining industry.
A major dispute arose in discussions on the issue of design life. As Andy Robertson said:
There is the design life, there is the stable period, and there is the performance assessment period. Andy believes that we can design closure works to be “stable” for 100 to 200 years; we can predict how closure works will perform in the next 1,000 years; but beyond that all is pure speculation.
None of the folk who compiled the document that gave rise to the seminar had thought about the role of surveillance and maintenance. Certainly not as regards its part in the design periods definition. They say in the document that you have to design for 100 years. This is easy to do if you can rely on active surveillance and maintenance. It is hard to do if the design has to be stable for 100 years in the absence of active maintenance. A major gap in the guidance document.
Then we “discussed” the establishment of a central Federal entity that would take over all closed mine sites. Apparently there is such a body in Saskatchewan. I proposed that Mike Nahir and his group, who are responsible for over 50 abandoned mine sites, are already doing this, although not in formal practice. As Andy said: “The easy way to walk away is to declare bankrupt, and pass the mine site over to Mike and INAC.” Why don’t we just formalize this system and face the inevitable fact that one day all closed mine sites in Canada will have to fall under the control of a central Federal department?
It is for the Canadian taxpayer to decide how much money the mining company will have to fund when passing their closed mine site over to the tender care of the Ottawa department that will take over perpetual close mine care. Make it too much and mining companies will go to other places. Make it too little and my grandkids will be taxed to pay for my excess life style.
Of course this issue arises at mines in places other than cold places. But most Canadian mines are in cold places, so the issues were debated—not settled—at the seminar these past few days. Maybe we can debate these terribly difficult issues at a future cold mine closure seminar.