Wash. Rev. Code § 35.17.280
Within ten days from the filing of a petition submitting a proposed ordinance the city clerk shall ascertain and append to the petition his or her certificate stating whether or not it is signed by a sufficient number of registered voters, using the registration records and returns of the preceding municipal election for his or her sources of information, and the commission shall allow him or her extra help for that purpose, if necessary. If the signatures are found by the clerk to be insufficient the petition may be amended in that respect within ten days from the date of the certificate. Within ten days after submission of the amended petition the clerk shall make an examination thereof and append his or her certificate thereto in the same manner as before. If the second certificate shall also show the number of signatures to be insufficient, the petition shall be returned to the person filing it.
RCW 35.17.280