Building house in former flood area-DEP issues?

I am considering bidding on a property that is listed as the last house in a flood area on the official map dated from the fifties.Since then the Army has made improvements and their has been zero flooding-even blocks away for 40 years.I understand that I will have to deal with the DEP if I want to build a new house and their primary concern is elevations. What I want to know is would I submit my site plan to the town first or the DEP.How long will the procedure take and will I need a lawyer? The existing house is un repairable and I am concerned about carrying this project for too long waiting on approvals, I also don't understand why the engineers don't update the maps when work is done and their are no issues for years. I am one house away from missing the listed flood area.