Wash. Rev. Code § 85.08.410
At such hearing, which may be adjourned from time to time and from place to place, until finally completed, the board of county commissioners shall carefully examine and consider said schedule and any objections filed or made thereto and shall correct, revise, raise, lower, change, or modify such schedule or any part thereof, or strike therefrom any property not benefited, or set aside such schedule and order that such apportionment be made de novo, as to such body shall appear equitable and just. The board shall cause the clerk of the board to enter on such schedule all such additions, cancellations, changes, modifications, and reapportionments, all credits for damages allowed or awarded to the owner of any piece of property benefited, but not paid, as provided in RCW 85.08.200; also a credit in favor of the county on any apportionment against the county, of all sums paid on account of said improvement, as provided in RCW 85.08.210; and all sums allowed the county on account of services rendered by the county engineer or prosecuting attorney, as provided in RCW 85.08.360; and all credits allowed to property owners constructing crossings as provided in RCW 85.08.340. When the board of county commissioners shall have finally determined that the apportionment as filed or as changed and modified by the board is a fair, just and equitable apportionment, and that the proper credits have been entered thereon, the members of the board approving the same shall sign the schedule and cause the clerk of the board to attest their signature under his or her seal, and shall enter an order on the journal approving the final apportionment and all proceedings leading thereto and in connection therewith, and shall levy the amounts so apportioned against the property benefited, and the determination by the board of county commissioners in fixing and approving such apportionment and making such levy shall be final and conclusive.
The board of county commissioners shall also at said hearing, levy, in the manner hereinafter provided for the levy of maintenance assessments, such assessment as they shall deem necessary to provide funds for the maintenance of the system of improvement until the first annual assessment for maintenance shall fall due.
RCW 85.08.410