The Director or Hearing Officer may compel by subpoena or subpoena duces tecum the attendance and testimony of witnesses and the production of books and papers and administer oaths to witnesses. The hearing shall be conducted at such place as designated by the Department. The Director shall give written notice of the time and place of hearing, by registered or certified mail, to the owner, operator, licensee, permit holder or applicant, as the case may be, at least 20 days before such hearing. The Director or Hearing Officer shall permit the owner, operator, licensee, permit holder or applicant to appear in person or to be represented by counsel at the hearing at which time such party shall be afforded an opportunity to present all relevant matter in support of his application for permit or license or in resisting the revocation or suspension thereof.