Employees specifically authorized by the Department shall inspect, at frequent intervals, vehicles, equipment, and the recordkeeping office used by an official portable emissions testing company. Department employees under this Section shall have access to all records, relating to tests and work done or parts sold as a result of such tests, to ascertain whether tests are properly, fairly, and honestly made. Department employees under this Section may examine the owner of an official portable emissions company or any officer or employee thereof under oath. The Department shall conduct periodic nonscheduled inspections of the premises of vehicles owned and operated by a licensed official portable emissions testing company.