(a) The topsoil shall be removed from the land in a separate layer, replaced on the backfill area, or if not used immediately, segregated in a separate pile from other spoil. When the topsoil is not replaced on a backfill area within a time short enough to avoid deterioration of the topsoil, a successful cover shall be maintained by quick-growing plant or other means thereafter so that the topsoil is preserved from wind and water erosion, remains free of any contamination by other acid or toxic material, and is in usable condition for sustaining vegetation when restored during reclamation.
     (b) If topsoil is of insufficient quantity or of poor quality for sustaining vegetation, or if other strata or combinations of strata can be shown to be more suitable for vegetation requirements, then the operator shall remove, segregate, and preserve in a like manner such other strata which are best able to support vegetation.
     (c) The topsoil, or the best available subsoil or combination of soil which is best able to support vegetation, shall be restored.
     (d) The term “topsoil” shall be defined by the Department by rule. Such definition shall consider regional differences in conditions in this State.