rehabilitating the cavity.

There is a report in 'The Australian', that UCG companies in the U.S.of A., have successfully convinced their authorities that underground cavities caused by the UCG process, can be rehabilitated to the satisfaction of all. Why don't our government bodies accept the same proof that the U.S. authorities have accepted ? now that's a stupid question; this is Australia, that's why, and they live under a rock here.
What happens to the cavities left by underground mining ?