Okla. Stat. tit. 45, § 45-749: Restoring excess overburden, spoils and waste materials

In surface coal mining where the volume of overburden is large

relative to the thickness of the coal deposit and where the operator

demonstrates that due to volumetric expansion the amount of

overburden and other spoil and waste materials removed in the course

of the mining operation is more than sufficient to restore the

approximate original contour, the operator shall after restoring the

approximate contour, backfill, grade and compact, where advisable,

the excess overburden and other spoil and waste materials to attain

the lowest grade but not more than the angle of repose, and cover

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

ecologically sound land use compatible with the surrounding region.

Such overburden or spoil shall be shaped and graded in such a way as

to prevent slides, erosion and water pollution and shall be

revegetated in accordance with the requirements of this act.