ORS § 450.845
Whenever the board deems it expedient or necessary for the protection of the public health, safety and welfare to cause to be constructed treatment plants or trunk or lateral sewers or drains, or any combination thereof, the board shall determine the proposed boundaries of the area to be directly benefited thereby and have a registered professional engineer prepare plans and specifications for such plants, sewers or drains. Such plans and specifications must be approved by the Oregon Health Authority and the Environmental Quality Commission and shall be filed in the office of the sanitary authority. Parcels of land which may be served practicably by lateral sewers or drains connected with treatment plants or trunk sewers or drains and are not adequately served by existing plants, sewers or drains, as the case may be, are considered to be directly benefited by the plants, sewers or drains of the sanitary authority. If all or any portion of the cost of construction is to be specially assessed against individual property, the engineer shall include in the plans and specifications, a description of the location and assessed value of each lot, tract or parcel of land, or portion thereof, to be specially benefited by the improvement, with the names of the record owners thereof and an estimate of the unit cost of the improvement to the specially benefited property.
ORS 450.845