1. If the commissioner determines that the petition is properly filed, he shall hold a public hearing.

2. The commissioner shall give at least ten days' notice of the time and place at which the hearing will be held, as follows:

a. By posting in at least five of the most public places within the affected area; and

b. By notice by mail to each of the petitioners and to each manufacturer, supplier and dealer furnishing the chemical substances complained of within the affected area, so far as is known to the commissioner, after diligent inquiry.

3. Proof of notice shall be evidenced by affidavit of the commissioner appended to the minutes of the hearing at which the petition is considered.