Excavators should observe a "Tolerance Zone" when digging close to a service line. The width of the Tolerance Zone is specified by law. The width of the facility (service line or pipeline, etc.) as marked plus at least 18 inches, or 450mm, measured horizontally from each side of the facility. See illustration.
Any excavation within a Tolerance Zone should be performed with non-powered hand tools or a non-invasive method until the marked facility is exposed.