In this subchapter:
(1) "Develop" or "development" means an activity on or related to real property that is intended to lead to the construction or alteration of an enclosed structure for the use or occupation of people for a commercial or public purpose or to the construction of residences for three or more families.
(2) "Municipal solid waste landfill unit" means a discrete area of land or an excavation that receives municipal solid waste or other solid wastes approved under this chapter and that is not a land application unit, surface impoundment, injection well, or waste pile as those terms are defined by 40 C.F.R. Section 257.2.