What type of excavation is only permitted within a tolerance zone?

Hand digging is the correct type of excavation permitted within a tolerance zone due to its precision and minimal impact on the surrounding area. The tolerance zone is a designated area around underground utilities where excavation must be conducted with care to prevent accidental damage. Hand digging allows workers to carefully navigate around these utilities, ensuring that they do not disturb or rupture critical lines underground, such as gas, electric, or water pipelines.

In contrast, other methods of excavation, like power digging or mechanical digging, involve machinery that could easily cause damage to underground utilities because they are less precise and involve greater force. These methods are not suitable for use in the tolerance zone where the risk of contact with existing utilities is heightened.