Section 69N. The parties in interest to the proceedings on a petition for a certificate shall include the following: (1) the applicant; (2) each public officer entitled to receive notice of the filing under the provisions of section 69L or section 69L1/2, whichever is applicable, provided that such officer files with the board within thirty days of the date of filing specified in the notice of filing under 69L or section 69L1/2, whichever is applicable, a statement of intention to become a party in interest; (3) such other persons or organizations as may be permitted to intervene pursuant to the provisions of chapter thirty A, provided that they have filed with the board, within thirty days of the filing date specified in the publication of the notice of the petition, a petition to be admitted as a party in interest; and (4) any other person whom the board by a majority vote of its members, admits as an intervening party.