BEST PRACTICES CHAPTER 5 - EXCAVATION
Practice Statement 5-19: Excavation Tolerance Zone: The excavator observes a tolerance zone that is comprised of the width of the facility plus 18 in. on either side of the outside edge of the underground facility on a horizontal plane. This practice is not intended to preempt any existing state/provincial requirements that currently specify a tolerance zone of more than 18 in.
The following examples are of tolerance zones for a 1 in. and 12 in. line: 1