Okla. Stat. tit. 45, § 45-748: Conditions where backfilling, compacting, and grading are

necessary.

In surface coal mining:

1. Which is carried out at the same location over a substantial

period of time when the operation transects the coal deposit;

2. The thickness of the coal deposits relative to the volume of

the overburden is large; and

3. Where the operator demonstrates that the overburden and

other spoil and waste materials at a particular point in the permit

area or otherwise available from the entire permit area is

insufficient, giving due consideration to volumetric expansion, to

restore the approximate original contour;

the operator, at a minimum, shall backfill, grade and compact, where

advisable, using all available overburden and other spoil and waste

materials to attain the lowest practicable grade but not more than

the angle of repose. The operator shall provide adequate drainage

and cover all acid-forming and other toxic materials, in order to

achieve an ecologically sound land use compatible with the

surrounding region.