I can't remember the exact EPA wording on this but an empty lot can be declared a wetland. IIRC even the ones in Detroit could be under EPA terms.
No, this proposed highway cuts across several real flood-plains and swamps. But frankly, there's no way to cross the Pee Dee region to Myrtle Beach without doing so. The whole region is flat and criss-crossed with rivers and streams. It's a swamp!
I guess the EPA wants them to either follow the existing road-beds of Hwy 9 or 501 to reach the beach. That would preserve the wetlands but would cost the gov't a fortune buying all the developed property.