Except as specifically exempted in this chapter, all disturbed areas shall be returned to their approximate original contour. All spoil shall be transported, backfilled, compacted (where advisable to ensure stability or to prevent leaching) and graded to eliminate all highwalls, spoil piles, and depressions. Backfilled material shall be placed to minimize erosion and water pollution both on and off the site, to minimize adverse effects on ground water, and to support the approved postmining land use. The postmining graded slopes need not be of uniform slope. Cut-and-fill terraces may be used only in those situations expressly identified in Regulation .03 of this chapter.