Certificates shall be issued without examination under the following conditions:

(1) Certificates, in appropriate classifications, shall be issued without application fee to operators who, on July 1, 1973, hold certificates of competency attained by examination under the voluntary certification program sponsored jointly by the state department of social and health services, health services division, and the Pacific Northwest pollution control association.

(2) Certificates, in appropriate classifications, shall be issued to persons certified by a governing body or owner to have been the operator in responsible charge of a waste treatment plant on July 1, 1973. A certificate so issued will be valid only for the existing plant.

(3) A nonrenewable certificate, temporary in nature, may be issued for a period not to exceed twelve months, to an operator who fills a vacated position required to be filled by a certified operator. Only one such certificate may be issued subsequent to each instance of vacation of any such position.