There doesn’t appear to be any environmental damage yet, though it’s possible this incident will produce some in the future. Also, they are being penalized: they’re being fined for violating their original permit and being required to rectify the situation, either by removing the offending materials or coming to some agreement with Oregon to leave it there in exchange for as-yet-undpecified compensation.
With environmental pollution there doesn't need to be any actual damage to sue.
They left a tiny amount of clay. It’s not some special toxic chemical clay either. It’s literally the same clay people use for face masks.