There are pollutants, hazardous materials, and hazardous waste. To be a hazardous waste it must meet a list of requirements - fly ash doesn't. To be a hazardous material, there is a different set of rules - asbestos is the best known in this category, but not fly ash. Fly ash if released to open water is a pollutant and is highly regulated as such. The problem is that with fly ash, like pig manure, when there is a release, it is usually a big one, many thousands of gallons. That is the problem, the storage before the release. If pig manure, which is just like human for the most part, was treated like human, it would not be a problem. Same with fly ash. They allow it to be stored. But now, lots of fly ash is used in other products now like concrete and similar items.