Within fifteen days after receiving a petition for a declaratory order, the department shall notify all interested persons as required by chapter 34.05 RCW about the petition and any other person it considers necessary. If a petition for a declaratory order is set for specified proceedings under RCW 34.05.240 (5)(b), the department shall give at least seven days advance written notice of the proceedings to the petitioner and all interested persons required by law and any other person it considers necessary. The notice must contain the time, date, place, and nature of the proceedings and shall describe how interested persons may participate in the proceeding.