They're enforced pretty rigorously in Calif. Under Prop 65, if you (knowlingly or unknowlingly, doesn't matter) expose someone to a cancer risk of greater than 1 in 100,000 (by air or water) without warning them, then the fine is $25,000 per day, per person. And if you're a 'bounty hunter' and discover these exposures you can get half of the fine for yourself. (So if you're talking about a few thousand people, for a few years... you do the math).
But, Joe, if you email me the name of the town and/or the actual numbers of the pollutant levels, I'll tell you how bad it really is.
It's Amino world without Chemists