You must be really good at holding your breath. A week, huh?
I think I would have been tempted to use plastic-pellet "sand-blasting" on it. You control the force of impact by the air pressure.
It should have been quicker.
Actually, they had to pull the shaft pier side, and to do that they had to pull the screw off first. They sat it on the pier, and promptly covered it to avoid satellite pictures.
The problem with the screw is that it is an alloy of bronze (can’t say what exactly), and subject to easy marring by any mechanical process. We actually had to go over it inch by inch and document every single scratch of a certain size, as they could result in excessive noise.
Besides, sand blasting would have been more expensive than four squids scrubbing away 12 hours a day.
Ah...the memories....