technology exists?
name it.

No problem. I've answered each of your questions, and all you do is quickly
change the question.
Standard removal of layered PCB's involved dredging. Open water dredging and
dumping if actually used to relocat pollutants in some cases. It isn't possible
in this case of course. Vaccum type systems are costly, but greatly limit
sediment damage. Treatment of the materials is also possible. GE's claim that
it will creat a PCB "cloud" is actually true, but the duration of the cloud is
not serious enough to have any impact comperable to leaving the PCBs in place.
And sediment lifting is a minimal factor with new dredging technology.
Leaving it there forever is not the answer.

RB