The illustration demonstrates the areas where it is safe to dig mechanically and where it is required to hand dig. The tolerance zone is 24 inches on either side of the utility mark plus ½ the diameter of the facility. Always hand dig to expose facilities in the tolerance zone.
Mechanized equipment is not to be used within the tolerance zone until the excavator has visually identified the precise location of the facility, or has visually confirmed that no facility is present up to the depth of excavation. The excavator is also responsible to ensure reasonable precautions are taken to avoid any substantial weakening of the facility’s structural or lateral support, or both, or penetration or destruction of the facilities or their protective coatings.