Wash. Rev. Code § 35.73.040
If no protest is filed, or if protests are filed but the city council after full hearing determines that it is necessary to fill any portion of the private property it shall proceed to enact an ordinance for such improvement. By the provisions of the ordinance, a local improvement district shall be established to be called "local improvement district No. . . . .," which shall include all the property found by the said council to require the fill as a sanitary measure. The ordinance shall provide that such improvement shall be made and shall fix and establish the grades to which the said property and the different portions thereof shall be brought by such improvement, and that the cost and expense thereof shall be taxed and assessed upon all the property in such local improvement district, which cost shall be assessed in proportion to the number of cubic yards of earth and bulkheading required for the different portions of said property included in said improvement district and in proportion to the benefits derived by such improvement: PROVIDED, That the city council may expend from the general fund for such purposes such sums as in its judgment may seem fair and equitable in consideration of the benefits accruing to the general public by reason of such improvement.
RCW 35.73.040