I think the parent comment is suggesting that residential units should not be allowed to be built around it, rather than that once someone builds a house around it the plant has to shut down.
"Surely they've had to get new permits over time as their operations changed"
I think your reading is very generous — this clearly implies that the factory should have had their operations at best frozen once the surrounding area was built out.
"As their operations changed" implying that perhaps the tanks weren't there when the houses were built.
Alternatively the tanks predate the houses in which case allowing housing so close to them seems highly questionable.
However given the long history of acrylic it's entirely possible that both the tanks and the housing predate modern safety practices in which case there's really not much to complain about. That possibility hadn't occurred to me when I first posted because I hadn't been aware of the history of the area.
Edit: And in the time it took me to write that someone else posted historic evidence that the houses were there before the plant. However it was the 1960s so safe bet that safety standards weren't what they are now.
However: In this instance, the residential units were present before the plant was. I covered the apparent timeline some here: https://news.ycombinator.com/item?id=48254291