Oregon Revised Statutes Mineral Resources § 523.260

(1) Use any just and reasonable method of determining the extent of any improvement district consistent with the benefits derived.

(2) Use any method of apportioning the sum to be assessed as is just and reasonable between the properties determined to be specially benefited.

(3) Authorize payment by the district of all, or any part, of the cost of any such improvement, when in the opinion of the board the topographical or physical conditions, or unusual or excessive public travel, or other character of the work involved warrants only a partial payment or no payment by the benefited property of the costs of the improvement.