10 billion seems like a crazy number to remove a dam. They probably want to jack hammer the thing apart and truck every piece of it 1000 miles away.
It's not just a crazy number: its a fantasy number: some critic just made it up. Its a rule, like the one that governs previous lives: no one was ever a peasant in Lithuania: everyone was a spirit nymph in the Black Forest. Nothing is ever projected to cost any number that does not end in a string of zeros numbering at least two thirds of the total digits. What are the odds that an actual, calculated cost of anything equals 10 billion dollars?