Md. Code, Environment § 12–301

(a) Except as otherwise provided in this section, an individual shall be certified by the Board in an appropriate classification before a waterworks, wastewater works, or industrial wastewater works may employ the individual as:

(1) A superintendent; or

(2) An operator or industrial operator in a job function determined by the Secretary.

(b) This section does not prevent a governmental agency or a person from continuing to employ in a waterworks, wastewater works, or industrial wastewater works, until July 2, 1982, an operator or industrial operator who is not certified under this title.