Existing hills, trees and ground cover fronting along public roads or adjacent property shall be preserved, maintained and supplemented by selective cutting, transplanting and addition of new trees, shrubs and other ground cover for the purpose of screening and noise reduction. If, however, the existing topography and natural vegetation do not allow an economically feasible supplement plan, the operation can, if properly landscaped with grass, trees and shrubs, grade back overburden around the perimeter of the excavation site to create a berm for the purpose of screening and noise reduction. No berm shall be constructed within 25 feet of any right-of-way line or other property boundaries.