As an alternative, I know of a number of mine vent shafts that need fillin'.
Probably take some time to go all the way to the bottom (provided the gas, water or stuff sticking out in the way don't interfere) which should serve for time to repent or at least scream a bit.
Some cases I'd not only stay to listen but maybe sell tickets.
All I was looking for was an environmentally sound method in the spirit of the New Green Deal.
Maybe one of the tunnels they used for trafficking women/children is still open. They could be put in there and seal up both ends or just blow it up like they have been :)