Butch, I don't recall how much was taken out. We had less than 2' at low tide in about half the marina and we were dredged to 6' below low mean tide. I keep hearing we were lucky to have a site to pump the spoils to, since trucking is expensive. However, I was impressed that the pumping went for about 1/4-1/2 mile in about a 10" pipe. So, maybe you can find a site to rent for 1.5yrs...then sell off the topsoil. Also, the machine that did the dredging was relatively small and easy to operate....almost looks like it can be a DIY project.
In regards to hazardous, are you sure about that? We had to hire a company to take soil samples from around the basin prior to dredging. Everything came back fine...as expected. I think there's alot of mis-information on dredging.
I also believe marinas are full of silt when they tell customers they want to dredge. Why? If my neighbor across the way just completed a project I found impossible, I would go talk to them. To the best of my knowledge, not ONE marina has come to us and said "hey, how'd you do that?"
Oh well, we're good to go with the silt. This year, we're finishing replacement of all the I-Beams on the seawall. Last year, we replaced half and the year before that, we replaced all the panels. Next year, I really want to remove the barges that are falling apart on the south end. The difference is, we're a not-for-profit organization so we have no problem spending to keep things in order.