Utility Locating vs. Subsurface Utility Engineering

We are often asked “what is the difference is between Public Utility Locating, Private Utility Locating and Subsurface Utility Engineering. It’s confusing to many because the basic purpose, which is to locate utilities subsurface, is the same but to varying degrees. The purpose of this post is to try to clear up the confusion.

Public Utility Locating

utility EM locatorThis is commonly known as a basic “Utility Locate” and is required by law in most regions prior to any excavation. It is used to mark specific utility lines owned by a public utility company prior to excavating.  These locates are generally conducted by your local utility companies at no cost to you. To help you coordinate the various utility locates you may only need to call a “One Call” or “Call Before You Dig” service in most areas.

A utility locator will mark the approximate horizontal location of that company’s buried utility. In most cases they will only mark utilities leading to a private property. Also, they do not mark all lines. They will only mark the utilities that belong to the companies they represent. Basic electromagnetic (EM) locators are used to trace the approximate location of the line. This is marked on the surface with paint or flags as per the standard utility color code.


Private Utility Locating

locate utilities using ground penetrating radarPrivate locators take utility locating to the next level. In addition to EM technology they use Ground Penetrating Radar (GPR) to locate utilities. The primary advantage of hiring a private utility locating service is their ability to locate all buried lines. This includes lines on private property that may have been installed by a contractor in addition to the ones installed by the utility companies.

By using GPR they are able to not only accurately locate the horizontal position of the line but also the exact depth. GPR technology is also able to locate plastic, fiber optic, cable TV lines, water and concrete sewer lines. The depth of penetration of GPR equipment is determined by the soil type.

The GPR equipment saves the subsurface imaging data which can be used to accurately map the location and depth of all the lines on a site plan for future reference. Since paint on grass can be mowed and flags can be removed this can be beneficial if the excavation is not conducted immediately after the utility locate has been completed.

Subsurface Utility Engineering

utility locating site mapThis is a mainly non-destructive engineering process that includes civil engineering, subsurface geophysical surveying and mapping, vacuum excavation and utility asset management technologies to identify and classify quality levels of existing data and maps the locations of underground utilities. They use original as-builts site plans and private utility locating data for design purposes. They may also use vacuum excavation or bore holes to confirm the location and depth of the utilities.

This information is most useful during the design phase of construction. If data reveals the existence of a utility conflict the engineers can develop a more viable design or alternatives to relocate the utilities. These changes can result in cost savings by moving the excavation away from the utilities during the design phase.


These 3 different alternatives to locating subsurface utilities offer different levels of information at different levels of cost. You will have to make the decision which service is most appropriate for your application and level of risk you are willing to take when excavating.

If you require more information you can contact us or visit our Utility Locating web page.

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