It happened after I managed to get under nine layers of aquifer
That's a good point, what is the best way to get through multi-layer aquifers? You sound like you didn't punch through it immediately but what is the fastest/safest ways? All I have ever done is use a plug or find a spot where the aquifer isn't there but I feel like learning how to deal with them the proper way would be a good idea.
I used a variation on this technique:
Pump Stack Tutorial This is something I've been practicing a bit, and I'm getting a lot better at it. I love the feeling of successfully making it through the aquifer and out the other side. I used to only do the "drop something on it" technique. It's pretty fun to do, BOOM SPLASH etc, but with this many levels, it wouldn't have worked anyhow.
Problem is, after the fourth or so level to pump, the damn thing starts needing more power than only 100u, and seizes up. So I had to come up with a new way of doing it. I was in a rather bad situation, with no room to add another reactor, so I started deconstructing the pumps, intending to try again in a better location, then realised I could just put in some axles from my one-wheel reactor, linked by gears, and put in the pumps on only the lowest level, dig it out, dig and wall-out the aquifer, take the pumps out again, fill and add more axle and put them in one lower, etc. I did NOT expect to pierce nine levels of aquifer, I thought it would be one or two more, one or two more... again and again, for four dorfyears. So yeah, the difference is that I made that pierce using only one reactor. The tutorial doesn't say how to do that, so I improvised. It's a good tutorial otherwise.
...Think of it as really slow mechano.... With insane little brothers as your actual hands. They do what you ask for, even if it turns out not to be what you want. The four dorfyears of work was at least one third "whoops, that didn't work, try it this way this time".... Every time I do it it's faster. I used the tutorial to dig a two layer aquifer in five years the first time I tried it. Many repeated learning events, and rather a lot of dead engineers. Whups. But I got there in the end.