"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.