Coal operations have slurry ponds where they store the sludge from washing the coal. And coal power plants have fly ash ponds which are bad for the environment. We’re shutting down the coal plants but these ponds will be around forever.

Here is a map of ash ponds from power plants

https://earthjustice.org/features/map-coal-ash-contaminated-...

Here’s a link to the slurry spill I lived through with no water for days

https://en.m.wikipedia.org/wiki/Martin_County_coal_slurry_sp...

And here’s some pictures of the “impoundments” https://earthobservatory.nasa.gov/images/8693/coal-sludge-im...

Edit to add this quote:

“ Although coal impoundments have a relatively low rate of failure, their extreme size—some hold more than a billion gallons of sludge—makes any breach potentially devastating.”