Md. Code, Environment § 9–721

(a) The powers granted to political subdivisions by Part III of this subtitle are supplementary to any other powers of the political subdivisions.

(b) This section does not:

(1) Invalidate any procedures initiated or completed by any political subdivision before June 1, 1972; or

(2) Limit or modify any provision of any general or local law effective before June 1, 1972.