Any administrative or nonjudicial hearings required by this chapter shall be held before the Secretary of the Department of Natural Resources and Environmental Control or before members of the Department designated by the Secretary. The Secretary, or persons designated by the Secretary to hear the case, shall have the power to subpoena witnesses and compel their attendance, administer oaths and require the production for examination of any books or papers relating to any matter under investigation in any such hearing. The respondent to a complaint made by it, or to it, pursuant to this chapter, shall subpoena and compel the attendance of such witnesses as the respondent may designate and require the production for examination of any books or papers relating to any matter under investigation in any such hearing.