Wash. Rev. Code § 34.05.562
(1) The court may receive evidence in addition to that contained in the agency record for judicial review, only if it relates to the validity of the agency action at the time it was taken and is needed to decide disputed issues regarding:
(2) The court may remand a matter to the agency, before final disposition of a petition for review, with directions that the agency conduct fact-finding and other proceedings the court considers necessary and that the agency take such further action on the basis thereof as the court directs, if:
[ 1988 c 288 s 514.]