30 CFR § 816.105 - Backfilling and grading: Thick overburden.
(a) Definition. Thick overburden means more than sufficient spoil and other waste materials available from the entire permit area to restore the disturbed area to its approximate original contour. More than sufficient spoil and other waste materials occur where the overburden thickness times the swell factor exceeds the combined thickness of the overburden and coal bed prior to removing the coal, so that after backfilling and grading the surface configuration of the reclaimed area would not:
(1) Closely resemble the surface configuration of the land prior to mining; or
(2) Blend into and complement the drainage pattern of the surrounding terrain.
(b) Performance standards. Where thick overburden occurs within the permit area, the permittee at a minimum shall:
(1) Restore the approximate original contour and then use the remaining spoil and other waste materials to attain the lowest practicable grade, but not more than the angle of repose;
(2) Meet the requirements of §§ 816.102 (a)(2) through (j) of this part; and
(3) Dispose of any excess spoil in accordance with §§ 816.71 through 816.74 of this part.