30 CFR § 817.107 - Backfilling and grading: Steep slopes.
(a) Underground mining activities on steep slopes shall be conducted so as to meet the requirements of §§ 817.102–817.106 and the requirements of this section.
(b) The following materials shall not be placed on the downslope:
(1) Spoil.
(2) Waste materials of any type.
(3) Debris, including that from clearing and grubbing.
(4) Abandoned or disabled equipment.
(c) Land above the highwall shall not be disturbed unless the regulatory authority finds that this disturbance will facilitate compliance with the environmental protection standards of this subchapter and the disturbance is limited to that necessary to facilitate compliance.
(d) Woody materials shall not be buried in the backfilled area unless the regulatory authority determines that the proposed method for placing woody material within the backfill will not deteriorate the stable condition of the backfilled area.