Yes, it should be the responsibility of the supplier. That's how every other balanced system works in economics. You only have issues when there is moral hazard

Yes, it should be the responsibility of the supplier. That's how every other balanced system works in economics. You only have issues when there is moral hazard when someone is allowed to shirk their responsibility. Trying to have someone downstream make up for it is a fool's errand. In this case, the supplier should be required to put up collateral or purchase some kind of cleanup insurance for cleanup. i.e. there needs to be a basic regulation from the government on land granted to mining.