At any time the department may hold a hearing on its own motion, and shall hold a hearing upon petition of at least fifty or one-fourth, whichever is the lesser number, of the holders of valid rights to withdraw public groundwaters from any designated groundwater area, sub-area, or zone, to determine whether the water supply in such area, sub-area, or zone is adequate for the current needs of all such holders. Notice of any such hearing, and the findings and order resulting therefrom shall be published in the manner prescribed in RCW
90.44.130 with respect to the designation or modification of a groundwater area, or sub-area, or zone.
If such hearing finds that the total available supply is inadequate for the current needs of all holders of valid rights to withdraw public groundwaters from the particular groundwater area, sub-area, or zone, the department shall order the aggregate withdrawal from such area, sub-area, or zone decreased so that it shall not exceed such available supply. Such decrease shall conform to the priority of the pertinent valid rights and shall prevail for the term of shortage in the available supply. Except that by mutual agreement among the respective holders and with the department, the ordered decrease in aggregate withdrawal may be accomplished by the waiving of all or some specified part of a senior right or rights in favor of a junior right or rights: PROVIDED, That such waiving of a right or rights by agreement shall not modify the relative priorities of such right or rights as recorded in the department.