Within two years following August 30, 1987, all wastewater treatment facilities shall be under the supervision of an operator certified by the director at least to the level of classification of the wastewater treatment facility to be supervised by such operator, except that individual septic tank systems and individual wastewater treatment lagoons for domestic wastewater treatment shall be exempt from the Wastewater Treatment Operator Certification Act. No operator shall be required to be certified in a classification other than that corresponding to the classification of the wastewater treatment facility to be supervised by the operator.