Underground utility mapping provides you with accurate information about the location of subsurface utilities. Being able to properly identify and label the underground features of the construction site not only mitigates the risk of the operation, but also produces cost-saving opportunities for your endeavor. To achieve these results, there is an intricate process that must be used to ensure the discovery of all locatable utilities. In this article, we will explain the benefits of underground utility mapping and describe our processes and techniques to conduct these services.

Benefits of Underground Utility Mapping


There are both monetary and safety benefits to mapping underground utilities. Before you dig or build on a construction site, it is helpful to know the location of private utilities because you can mitigate the risk of striking a utility line. By providing accurate utility maps, you can avoid possible damages to the utilities, which could have resulted in expensive repair costs, lawsuits, and work stoppages. Additionally, you will have made it a much safer work environment for those on-site and in neighboring areas. Having accurate information reduces the risk of striking a utility line which can cause personal injury, or in the worst case scenario, fatality.

Another advantage of having a CAD map is that you will have an accurate model of the subsurface utilities that can be permanently stored on your computer for future use. Most of the time, utility lines are marked with paint, which can be washed away by rain or cut away if painted on the grass. Instead of allowing the natural elements to decide the permanence of the utility markings, having a CAD map will allow you to easily reference the job site again the future.

Underground Mapping Techniques


Upon being called to a job site, service technicians are asked to locate the utilities within a specified scope of work. Using electromagnetic (EM), ground penetrating radar (GPR), or a split box. Service technicians can identify and mark the utilities with a corresponding paint and flag color. The following combinations represent the color used to identify the type of utility line:

  • Red for Electric or Unknown
  • Blue for Water
  • Light Green for Sewer or Sanitation
  • Dark Green for Storm
  • Orange for Communications
  • Yellow for Gas
  • Pink for Different Surveying Markings or Unknown
  • White for Outside Scope of Work

Master Locators’ Process to Underground Utility Mapping


We use multiple location methods to ensure the discovery of all the locatable underground utilities. In doing so, we follow our proprietary and comprehensive guide called 7 Steps of Locating when we are on-site:

  1. Trace all surface features within the work area.
  2. Verify routes of surface features outside the work area.
  3. Verify routes of utility feeds to the adjacent buildings.
  4. Perform passive scans by sweeping circumference or grid scanning using all frequencies.
  5. Perform an inductive scan with a split box by sweeping circumference and using grid pattern search.
  6. Perform an inductive scan by dropping the transmitter in strategic areas.
  7. Perform two-man sweeps.

Upon completion of utility mapping, we create electronic sketches and findings reports as part of our standard deliverables. Advanced reports for all services and commentary on images are also available upon request.

We use a global positioning system (GPS) surveying equipment to collect coordinate points of where the utilities were previously marked. This helps us to determine the depths we put on the underground utility line map, in which a Philadelphia Rod is used to measure the invert elevation of utilities within a surface feature. These coordinates are sent to an engineer in our main office, who will import into our computer-aided design (CAD) software and delineate over a 2D map of the scope of work.

The overlaid map includes an approximate outline of the scope of work within the surrounding areas along with surface features such as manholes, fire hydrants, and utility valves. The safety features and corresponding utility markings can be found in the utility legend. There is also a distance scale provided on the map as well as notes provided with any additional pertinent information regarding the scope of work.

This final completed 2D CAD map with overlaying utility lines and approximate depths is then sent to you in a variety of file types as a means to provide you with all of the information needed to proceed with the project.