You Must Hand Dig Within 18” of Utility Marks

In Maryland and Washington DC, the tolerance zone around buried utilities is 18”, which means you must hand-dig within 18” of all markings to expose the facility.

What is the Tolerance Zone?

The tolerance zone is the horizontal space extending 18” from the outer edge of a line or pipe. Respecting the tolerance zone is a key step to protect underground utilities in any excavation.

How Do I Respect the Tolerance Zone?

Excavators must respect the tolerance zone of marked utilities by hand digging within 18” of the outer wall of the facility. Using mechanized equipment within the tolerance zone can damage utilities and result in serious injuries and fines.

Excavating Safely in the Tolerance Zone

  • Do not use power excavating equipment, sub-surface boring excavations or heavy equipment supports (e.g., outriggers) within the tolerance zone.
  • Determine the exact location of underground facilities by test pitting or pot holing (hand digging) all marked lines within the planned excavation area to confirm the exact line location and depth.
  • During perpendicular crossings, facility lines should be exposed to visually confirm no damage occurs. Any excavation within close proximity to underground facilities may require the person to provide bracing or shoring to protect the lines.
  • Only after confirming the exact location and depth of facilities can you begin to use mechanized equipment or sub-surface boring equipment.
  • Always assume all lines are active or energized.

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