Iirc, it did not contain the leak, except in the narrow sense that the barrel did not leave the site.
In actuality, the barrel contents, a sloppy mix of nitric acid process waste and sawdust, hugely overheated and much of the material was vaporized.
Because of contractor negligence, the fire doors that should have automatically closed could not, so the contamination spread widely. The doors had been wired open because they had too many false alarms, which was inconvenient.
The venting system that should have contained the fumes did not work, so the plant environs were contaminated.
The estimated $2 billion clean up cost is an estimate, probably will be exceeded, as these cleanups rarely work as planned.
Afaik, apart from some bonus payment reductions, there has been no penalties to any entity from this disaster.
Accountability is entirely lacking by all appearances.