1. Notices of every public hearing held pursuant to the provisions of this article shall specify the time, date, place and purpose of the hearing.

2. Service of all processes of the commissioner pursuant to the provisions of this article, except subpoenas, shall be made in the same manner as a summons in a civil action or by registered mail upon any person to whom it is addressed, upon the mayor or counsel of a municipality or upon an officer of a district, authority, commission, private corporation or company, as the case may be.

3. Subpoenas issued pursuant to the provisions of this article shall be served upon a prospective witness personally and at the same time he shall be paid such fees therefor as may be provided by law.