I do have sand, but found out that I could use a source closer to the workshops and main staircase. Only problem is that it's an aquifer. I don't deal much with aquifers, if at all, in this fort I found aquifer long after hitting magma sea and adamantine. Here's the picture:
Blue is damp stone (actually soil) border, red is (more or less accurate) aquifer proper border, and yellow is a border of sand pillars/walls. There are two levels of aquifer.
I'm asking what would be the possible or best method to get to that sand, without flooding the fortress in the process. I was thinking:
1. Bringing it down a few levels to create a sand pillar. That would make 8 sand bearing tiles. I would use cave in for that, by digging from below. But won't the pillar retain it's aquifer status?
2. Dig some dump tiles next to a sand tile, and use grates to let water fall somewhere else. Grates don't prevent dwarves from using sand bearing tiles which have their sand from nearby pillars, but I'm not sure how fast the aquifer is. Alternatively leave the sand pillar free, hanging from a support (there is a floor z-level above), surrounded by grates or hatches. Maybe that would make water fall faster.
3. Dig some dump tiles next to a sand tile, but pump water out instead, hoping that temporal flooding won't cause much interruption.
The best would be smoothing the sand somehow, but that's probably not possible. What is possible?