I wouldn't worry to much about the dumping - one of my favorite deep water places to troll in CC Bay is where the canal dredging is dumped.
I think its mostly an issue in areas that have been polluted in the past and then the dredging stirs that stuff up again (like the PCB's in the Hudson River).
Pete,
If you have any questions about the dumping let me know. I'll see what I can answer. We (I) did a bulk of the work on site selection and general mapping of the area...