"Impervious surface" means any surface modified by or as a result of human activity that cannot effectively absorb or infiltrate water. The term includes but is not limited to roofs, decks, and patios, and, unless specifically designed and maintained to effectively absorb or infiltrate water, paved, gravel, or crushed stone driveways, parking areas, and walkways.
N.H. Admin. Code § Env-Wt 602.24