I mean, sure, you can seal the entrances of the mine.
But like ice, salt under pressure will slowly flow, and all the tunnels will eventually get squeezed shut. Which also sounds great to seal up the buried waste.
But this basically is a very slow collapse of the mine. And as everyone living in areas of heavy mining knows, when the mine collapses, the ground above will settle as well. And how watertight will the rock be then?
