Wash. Rev. Code § 43.52.450
The provisions of this chapter shall be cumulative and shall not impair or supersede the powers or rights of any person, firm or corporation or political subdivision of the state of Washington under any other law. The rights of all persons, firms, corporations and political subdivisions or operating units of any kind under existing contracts, renewals thereof or supplements thereto, with the United States, or any agency thereof, for power, are hereby preserved and such rights shall not be impaired or modified by any of the provisions of this chapter or any of the powers granted by this chapter.
The rates, services and practices of any operating agency in respect to the power generated, transmitted or sold by it shall not be governed by the regulations of the utilities and transportation commission.
RCW 43.52.450