Iowa Code § 314.12: Borrow pits — topsoil preserved.

In the award of contracts for the construction, reconstruction, improvement, repair or maintenance of any highway, the agency having charge of awarding such contracts shall require that when fill dirt, soil or other materials are to be removed from borrow pits acquired by title or easement, whether by agreement or condemnation, for use in the project, adequate provision shall be made for the restoration of the borrow pit area, either by removal and replacement of a minimum of eight inches of topsoil, or by fertilizing, mulching, reseeding or other appropriate measures to provide vegetative cover or prevent erosion, except where a lake or subwater table conditions are designed, or where the area is zoned for commercial, industrial, or residential use, or where the borrow is in locations of white oak, sand, loess or undrainable clays. When the borrow pit is acquired by easement, the restoration method shall be determined by agreement with the landowner.