So, I went to do a practice run on this and totally forgot to bring extra stone, all I embarked with was an anvil and 2 copper nuggets and a bunch of doggies. At first I thought all was lost, but I started thinking and it all became clear...
And here is what I did to punch through a double layer aquifer with nothing but 2 copper nuggets, and anvil, and a pack of dogs:
1: Deconstructed wagon, built carpenter shop and made 2 training axes, then chopped some wood.
2: Built wood furnace from 1 copper nugget and made some charcoal, deconstructed furnace.
3: Built smelter from copper nugget and smelted the 2nd nugget, deconstructed smelter.
4: Built forge from copper nugget and anvil, forged copper pick from copper bar.
Now I had a pick and some wood, but how do I rig something to safely drop these rings of dirt with no mechanisms? Wood... I have tons of wood, how can I use wood??
Here is what I came up with:
Here is Z+1, more on what is going on with the funny floors in the next caption
Here is Z 0. Floors on the Z level above are built between the walls on this level, the one on the left to support the outer ring, and the one on the right to support the center plug. I also have not channeled out the 2 tiles in the middle of the top edge, those I channeled right before dropping, channeling the lower one first then the upper one, so as to not trap any dwarves.
Here is Z-1, showing the ring and plug. Not much special here...
And here is Z-2, with the area channeled out ready to drop the outer ring. The channeled tile on the bottom is for drainage, and for somewhere to pump the water after dropping the ring.
So there was the setup. My plan was to deconstruct the southernmost walls supporting the ring and plug to drop them, keeping the dwarves far enough away from the hole to not get sucked in, which worked quite well in the end:
Heres Z0 after channeling the supports and deconstructing the leftmost wall.
And here is Z-2, with the pump constructed and all the water pumped out.
After this I built a staircase to get down and channel the area out for the plug to fall into:
So I deconstruced the right wall, dropping the center plug in, then pumped the water out again and dug my staircase down to the tasty stone!
Any questions?