Wash. Rev. Code § 8.12.260
At any time after June 11, 1907, any such city may petition the superior court of the county in which said city is situated, that a board of eminent domain commissioners be appointed to make assessments in all condemnation proceedings instituted by such city. Said superior court shall thereupon, by order duly entered in its records, appoint three competent persons as commissioners who shall be known as and who shall constitute the "board of eminent domain commissioners of the city of . . . .," and who shall thereafter make assessments in all condemnation proceedings instituted by such city. The order of the court shall provide that one of the members of such board shall serve for one year, one for two years, and one for three years, from the date of their appointment and until their successors are appointed and qualified. Annually thereafter, said superior court shall appoint one such person as such commissioner, whose term shall begin on the same day of the month on which the first order of appointment was made and continue for three years thereafter and until his or her successor is appointed and qualified. If any commissioner shall be disqualified in any proceeding by reason of interest, or for any other reason, said superior court shall appoint some other competent person to act in his or her place in such proceeding.
RCW 8.12.260