Wash. Rev. Code § 35.43.260
Any municipal corporation, quasi municipal corporation, or political subdivision which has the authority to install sewers by establishing local improvement districts, which has charged and collected monthly service fees for sewers, that have been authorized and approved by the voters and have not been constructed for a period of ten or more years since the voter approval, is hereby authorized and directed to grant a credit against the future assessment to be assessed at the time of actual completion of construction of the sewers for each parcel of real property in an amount equal in dollars to the total amount of service fees charged and collected since voter approval for each such parcel, plus interest at six percent compounded annually: PROVIDED, That if such service fees and interest exceed the future assessment for construction of the sewers, such excess funds shall be used to defray future sewer service charge fees.
It is the intent of the legislature that the provisions of this section are procedural and remedial and shall have retroactive effect.
RCW 35.43.260