[footfootfoot]

Their logic runs, The PCBs are all at the bottom and the river is now healthy, if you dredge the PCBs up to remove them, then the river will become irreparably polluted.

So, the river being healthy now is the result of the magical, one time only settling of PCBs?

You still can't eat the fish from the river, PCBs or not. More like if we set a precedent of culpability for polluting this river then we'll be on the hook for cleaning all the other rivers we polluted.