The Tolerance Zone

By law, each type of marking requires that the excavator observes a certain Tolerance Zone. 

If the diameter of the buried facility is known, the Tolerance Zone is the distance of one-half of the known diameter plus 2 feet, on either side of the designated center line. If the diameter of the buried facility is not known, the Tolerance Zone is 2 feet on either side of the designated center line.

Before the excavator can use mechanized digging equipment in a tolerance zone, the presence and location of the buried facility must be verified by hand-dug test holes or vacuum excavation.  If it is necessary to remove pavement or masonry, mechanized equipment can be used, but only to the depth of that pavement or masonry.

If the excavator is unable to find the facility after performing a reasonable search, the excavation cannot begin. The excavator will contact you directly and you should respond immediately. Once the facility is located, mechanized equipment can be used.

If the excavator will be exposing a facility during the excavation, they will be required to provide adequate support and protection for it. In addition, the excavator will be required to provide an adequate backfill upon completion.

Ensure that the excavator is aware of any special needs (e.g., cast iron, asbestos) of your facility.