ORS § 450.825
As soon as practicable after the election of the first members of the board, the board shall make a study and survey of the existing sewage disposal facilities and systems in the authority and of its sewage disposal needs, both present and future, and prepare an overall coordinated plan for the authority which incorporates, so far as practicable, existing sewage disposal and drainage systems, future sewage treatment plants, including connecting trunk and lateral sewers, and future drainage systems. Such plan shall be revised from time to time as circumstances may require. In preparing the plan or revisions thereto, the board shall take into consideration expected fluctuations in population and in business and industrial activity.
ORS 450.825