Wash. Rev. Code § 70A.15.1540
Whenever there occurs a merger of an inactive authority with an activated authority or authorities, or of two activated authorities to form a multicounty authority, the board of directors shall be reorganized as provided in RCW 70A.15.2000, 70A.15.2010, and 70A.15.2020.
In the case of the merger of two or more activated authorities the rules and regulations of each authority shall continue in effect and shall be enforced within the jurisdiction of each until such time as the board of directors adopts rules and regulations applicable to the newly formed multicounty authority.
In the case of the merger of an inactive authority with an activated authority or authorities, upon approval of such merger by the board or boards of county commissioners of the county or counties comprising the existing activated authority or authorities, the rules and regulations of the activated authority or authorities shall remain in effect until superseded by the rules and regulations of the multicounty authority as provided in RCW 70A.15.2540.
RCW 70A.15.1540