Steve,
They have plugged a lot of the mines around here with concrete. They have a plug in that one but the rock is so porus and fractured in that mountain that it is like a sponge. They even tried shooting grout in under pressure, but the whole mountain is just one huge pile of fractured rock. Maybe one of the earthquakes will sink it. Our main fault line up here isn't very far from it and that is where most of our quakes originate. And of course they just keep making more cracks in the rock.
Ron