We've ruled out the bulkhead - cost was prohibitive and I didn't want to deal with the eventual (even if 20-30yr from now) need to replace it down the road, especially if deadmen were beneath the poured slab.

Looked at a concrete wall and slab all-in-one, but the "great" contractor we spoke and met with went repeatedly MIA.

So now, based on recommendations here, we're just making a 20ft wide by 50ft long soil/clay peninsula and will save that money for the important stuff - what's going on top!

Thanks to everyone for the suggestions.

Kris