Revise the greenfield definition to read:
"greenfield area- that has not been graded, compacted, cleared, or disturbed and that supports (or could support) open space, habitat, or natural hydrology."

Add the term "previously disturbed":
"previously disturbed areas that have been graded, compacted, cleared, previously developed, or disturbed in any way. These are areas that do not qualify as 'greenfield.'"