Within 30 days after a petition is filed with the department, or later if authorized by the department, but not to exceed 90 days, the department shall cause due notice to be given of a hearing upon the question of the desirability and necessity in the interests of public health and welfare of the creation of the district, upon the question of appropriate boundaries to be assigned to the district, upon the propriety of the petition and of the proceedings taken under this part, and upon all other questions relative to this matter. All interested parties have the right to attend the hearings and be heard. Due notice of the time and place of holding the hearing shall be given to all of the executive officials of the municipalities included within the involved territory. If it appears upon the hearing that it is desirable to include within the proposed district territory outside of the area within which due notice has been given, or if it is made to appear that more data or information is needed, the hearing shall be publicly adjourned and due notice of further hearing shall be given throughout the entire area considered for inclusion in the district and a further hearing held. The department shall cooperate to the fullest extent possible with the local units of government included within the territorial limits of the proposed district in the making of the necessary investigations and engineering and financial studies that may be required for the proper decisions to be made by the department upon the conclusion of the hearing. After the hearing, if the department determines upon the facts presented and upon other relevant facts and information as may be available to it that there is need in the interests of public health and welfare for a sewage disposal or water supply district, or both, to be created and to function in the territory considered at the hearing, it shall make and record this determination and shall define the boundaries of the districts by the territorial limits of municipalities included within the district or by metes and bounds. In making the determination and in defining the boundaries, the department may give due weight and consideration to the physical and topographical conditions of the area considered, availability or nonavailability of water resources, engineering and economic feasibility of the construction and management of the works required, and all other relevant and pertinent facts that may be brought to its attention or of which it may have knowledge. Such additional territory shall not be included without the approval by resolution of the legislative body of any municipality affected, including the original petitioners.