On a recent project involving excavating a trench, Apex personnel suspected that the utility mark-out done by the state had mismarked a few lines. Acting on their hunch, Apex's crew hand dug around where the mark out was, as well as where they thought the line should be. The utility line was in the spot that was unmarked and a utility interruption was successfully avoided.
When preparing for underground work, many of the critical steps in preventing a utility mark-out are conducted prior to starting digging. Make sure everyone involved (PM, APM, Crew leader and field staff and site contacts) are aware of the work scope and location—many times lack of communication has led to utility interruptions. Mark-out the proposed location accurately in the field so the utility mark-out company knows exactly where the digging is to be done (white box with dashed lines—don't use arrows to point to area). Establish the scope of work and make sure that if there is a deviation in plans it is coordinated with the PM.
When excavating around utility lines do not assume the mark-outs are correct. Requesting that a second mark-out is done and that hand or soft digging is performed will help to ensure worker safety and avoid costly utility interruptions. Dig safe markings should be used as a guide but don't forget to use common sense.
After arriving onsite, go through a checklist of known or utilities that are assumed to be present. Try to follow these utilities from the street or source through the area to be excavated. When digging use clues to predict the presence of utilities—marking identifiers (caution tape, foil tape), gravel, soil not similar to native material, etc. Also use typical utility depths as a guide—electrical is usually 12-24" below grade, water usually >4' below grade, etc. Use common sense and the previously mentioned clues to reduce your risk of a utility interruption. Always dig with a spotter—an extra set of eyes to watch the digging.
If unsure—stop work—call the job Project Manager.