30 CFR 819.19 - Auger mining: Backfilling and grading.
(b) Remining. Where auger mining operations affect previously mined areas that were not reclaimed to the standards of this chapter and the volume of all reasonably available spoil is demonstrated in writing to the regulatory authority to be insufficient to completely backfill the highwall, the highwall shall be eliminated to the maximum extent technically practical in accordance with the following criteria:
(1) The person who conducts the auger mining operation shall demonstrate to the regulatory authority that the backfill, designed by a qualified registered professional engineer, has a minimum static safety factor for the stability of the backfill of at least 1.3.
(2) All spoil generated by the auger mining operation and any associated surface coal mining and reclamation operation, and any other reasonably available spoil shall be used to backfill the area. Reasonably available spoil shall include spoil generated by the mining operation and other spoil located in the permit area that is accessible and available for use and that when rehandled will not cause a hazard to the public safety or significant damage to the environment. For this purpose, the permit area shall include spoil in the immediate vicinity of the auger mining operation.
(3) The coal seam mined shall be covered with a minimum of 4 feet of nonacid-, nontoxic-forming material and the backfill graded to a slope which is compatible with the approved postmining land use and which provides adequate drainage and long-term stability.
(4) Any remnant of the highwall shall be stable and not pose a hazard to the public health and safety or to the environment.
(5) Spoil placed on the outslope during previous mining operations shall not be disturbed if such disturbances will cause instability of the remaining spoil or otherwise increase the hazard to the public health and safety or to the environment.