There's a single mine (Giant Mine) in Canada that is contaminated with 200k+ tons of arsenic trioxide - which will literally remain poisonous forever since the poison is a stable element not an organic compound. The current plan is to try to keep it frozen because the dust is odorless, tasteless, water soluble, and located just outside of Yellowknife. That's the weight of more than half the amount of nuclear waste ever produced on the planet, in one relatively unremarkable industrial site.

Nuclear waste can be reprocessed to reduce its volume, and the more "spicy" it is, inherently the less long lived it is. We could probably store all the nuclear waste in the world in a geologic repository on the canadian shield somewhere for the cost of actually cleaning up that one old gold mine to make it non toxic.