"It's not us", "we have no idea", "our tests show we're clean" works for a shockingly long time in modern Western societies - the government has to prove that it is indeed 3M or whoever else who causes the pollution, and government agencies usually tend to take time until an investigation is complete. And even then, offenders can file a lawsuit... and until that lawsuit is finished and unappealable, it can take many years if not decades. And during that time, everyone claiming that a specific company is an offender is under severe risk of a defamation lawsuit.
We definitely need reforms both in staffing of regulatory agencies as well as in defamation lawsuits in cases of environment or labor offenses.