It's just as depressing when something counts as "clean". My saddest example was a former sand pit, they spent 30 years digging out 15 meters of sand, then another 30 years filling it with anything from industrial to veterinary waste, "capped" it with rubble in the late 40s and called it clean enough.

Had a bigass job digging out the top 3 meters of random waste, including several thousand of barrels of whatever the fuck. And definitely no unexploded ordnance (spoiler, after finding several ww2 rifle stocks and helmets, the first mortarshells were dug up too). After makimg room, it was covered in sand, clay, bentonite and a protective grid.

So naturally, 3 months after that finished, some cockhead decided to throw an anchor and hit go all ahead flank on his assholes boat and tore the whole thing up. No need to fix anything though, just shovel some more sand it, that'll stop the anthrax!

This was all in open connection with a major river, of course. One people swim in.