Jack Caldwell, P.E. has a B.Sc. in Civil Engineering, an M.Sc. (Eng.) in Geotechnical Engineering and a post-graduate law degree. He has over 35 years engineering experience on mining, civil, geotechnical and site remediation projects. He has worked on numerous projects throughout southern Africa, Europe, Canada and the United States.
In one of the many article I read on the Mt Polley tailings failure was an estimate of what it will cost to get the mine going again. A figure of $50 million was quoted as the cost to pick up all the tailings and return them to the tailings facility. I imagine that figure is based on five million cubic meters of tailings at about $10 a cubic meter to pick up. Here is why I suspect the figure is grossly low.
In conventional civil or mining earthworks $10 a cubic meter would be generous. But the material to be picked up is still a near-fluid. It will slosh around in the truck and spill out through the opening in the truck bed. Also the bottom of the creek now covered with tailings is by no means uniform. It is probably rough and rugged and teaspoons will be required to pry the tailings out of every nook and cranny. So let us double the cost of picking up the tailings and taking them back to the facility.
While it will not be easy to pick up the tailings strewn along the creek, it may be impossible to get back the tailings in the lake. Do you dredge the lake? Of course you can dredge, but then you will pick up a lot of clean bottom sediment along with the tailing. Inevitably they will have to consider placing a subaqueous cover on top of the tailings in the lake. This was done off the coast of Los Angeles to cover PCB sediment on the ocean floor, so it could be done in BC. But at what cost? Say another $100 million.
Next the tailings facility breach has to be repaired so that the returned tailings will stay there. That means plugging the breach. I am not sure I would let a workman go near those steep slopes that subtend the failure zone. Continue Reading →