> The only minimum standard that get enforced is that the waste should not leak into the ground water.

In the case of the Asse II mine it is not clear how strongly connected the water at the mine is to water at the surface. Given it is a salt mine I would not expect a strong connection.

> Everyone has consistently treated mining waste as an unavoidable side effect of mining

Yes, there are better and worse ways to dispose of it. Tailings are a huge problem and have caused many a dam disaster. Plainly Difficult Youtube channel dam disasters makes for sobering viewing. https://www.youtube.com/@PlainlyDifficult/playlists