(a) After July 1, 1971, when any coal mine is worked out or indefinitely closed, such mine openings shall be properly sealed within ninety days after the mine is abandoned.
(b) Mines temporarily inactive for less than ninety days shall be adequately fenced with conspicuous signs prohibiting the possible entrance of unauthorized persons.
(c) Shaft openings shall be effectively capped or filled. Filling shall be for the entire depth of the shaft. Caps shall consist of a six inch thick concrete cap or other equivalent means approved by the director.
(d) Caps shall be equipped with a vent pipe at least two inches in diameter extending for a distance of at least fifteen feet above the surface shaft.