The mine wastes, some call it tailings, but the regulators would term it a significant waste, was placed in a lined pond. Beneath the liner is a leak detection system. And above the liner is a drain “spine.” Rain has kept the materials wet and during the wet season, water ponds on top of the materials. The spine drain flows continuously. The outlet from the leak detection system also flows, but at a much lesser rate.
Today I read the closure plan submitted to the authorities. In essence, this consists of placing a cover on the materials and collection water seeping from the drains that will then be placed in another lined pond constructed over the closure cover where the water is calculated to evaporate. The idea is that with time, the waste will seep itself “dry,” or at least seep to the point where it meets the regulated moisture content of no longer draining under gravity.
To monitor achievement of this auspicious point of “no gravity drainage,” two piezometers are proposed just above the basal liner, and the criterion, again based on regulations, is that when the head on the basal liner drops below 12 inches, the materials will be deemed “drained & dry.”
I await with interest the outcome of the regulators’ comments on and, hopefully, their acceptance of this closure plan. In the meantime, I wonder about your comments on this plan, this approach, these criteria, and the idea of such a closure. The specifics, of course matter, but for reasons of confidentiality, it is better not to give them. But the general approach is applicable to so many a mine and to most tailings impoundments and heap leach pads, that it is, in my opinion, worth a short debate on the merits/demerits of this approach.