After the markings have been made, excavators should maintain a minimum clearance within the Tolerance Zone which is: 24 inches on either side of the outside edge of the mark indicating a facility; a distance of one-half of the marked diameter plus 24 inches on either side of the designated center where a diameter of the facility has been marked; and 24 inches in each direction of the outside edge of a physically present above ground facility.
If excavation is required within the Tolerance Zone horizontally of any marking or above ground facility, the excavation should be performed with extreme care utilizing hand tools or other methods designed to avoid damaging underground facilities, including vacuum excavation tool and air knife.