Del. Code tit. 7, § 6024

The Secretary, or the Secretary’s duly authorized designee, in regulating water pollution, air pollution, solid waste disposal or any other matter over which he or she has jurisdiction pursuant to this chapter, may enter, at reasonable times, upon any private or public property for the purpose of determining whether a violation exists of a statute or regulation enforceable by him or her, upon given verbal notice, and after presenting official identification to the owner, occupant, custodian or agent of said property.