How Underground Utility Locating Works

Explaining Subsurface Locating

How Underground Utility Locating Works

Explaining Subsurface Locating

Whether planting a tree or laying new utility lines, breaking ground puts you at risk of damaging an existing subsurface utility or other obstruction.

Subsurface damage is dangerous and costly – but it’s also preventable if you hire a professional utility locator to perform subsurface scanning before you break ground.

Utility locating involves utilizing technology such as ground penetrating radar (GPR) and electromagnetic (EM) locating to detect and map power, gas, water, and various other types of buried utility lines in an area where groundbreaking activities are planned.

Public vs. Private Utility Locating

An illustration of a facility with its underground utilities highlighted.
Private utilities represent 60% of the utilities that lay beneath the surface.

There are two types of utility lines: public and private. Private utilities represent 60% of the utilities that lay beneath the surface.

As GPRS Senior Vice President of Internal Operations, Chris Moore, recently explained in an appearance on the Industrial Safety & Hygiene Podcast, there is a big difference between the two types of utilities.

“The difference resides in the location of, we would say, the meter, the water meter, gas meter, or the meter where power enters the facility or property,” Moore said. “In most situations, we consider the public utility as that which feeds the meter. At my house, for example, I have a water meter that sits out at the road, at the right of way. The utility that feeds water to that meter owns, and operates, and maintains everything, from a pipe standpoint, underground up to that meter. That is considered a public utility because it’s a public place where they’re overseeing those utilities. Then it becomes private once it goes on the backside of that meter and runs to my house. At that point, now any damage or issues are now my responsibility, should something happen to that line. It’s the same water, same electrical current, same gas flowing through, but either side of that meter is the line of demarcation for public versus private.”

In the United States, every state administers its own 811 One Call service to locate public utilities at any site before excavation. It’s required by law that you call 811 to locate these public lines prior to breaking ground, regardless of the scope of the work planned.

However, 811 Call Before You Dig services locate only public utilities, not private ones, and One Call does not provide depths on its locates, only identification.

The problem is that because more than 60% of all utility lines are private, and 811 will not locate private utilities, you could knock out power to an entire neighborhood, cause a water emergency for a municipality, or cause serious injury or death with a gas line explosion if you attempt to dig or drill without knowing the depth of your electric and telecom lines, or your water, sewer, and gas pipes.

This is what makes it vital to utilize private underground utility locating services as well as contact 811.

Tools of the Utility Locating Trade

Ground penetrating radar and electromagnetic locators are the primary tools used by utility locators such as GPRS to locate and map underground utilities.

Workers evaluate asphalt with electromagnetic (EM) locators
Professional utility locating technicians use a variety of tools, including electromagnetic (EM) locators, to locate and map underground utilities.

GPR involves sending a radio wave from a receiver into the ground. The radio wave bounces off material it encounters, and those bounces are displayed in a reading as hyperbolas, which are smooth curves lying in a plane. Different types of subsurface objects will produce different looking hyperbolas. Professional utility locating technicians can interpret this data to tell you the type, and exact position of each located object.

The display screen on a utility locating ground penetrating radar scanner is shown.
Professional utility locating technicians can interpret the data provided by ground penetrating radar to tell you the type, and exact position of each located object.

The effective range of GPR depends on soil consistency. Radar is limited when it scans through water, air, or an object. Therefore, if there is sandy soil, the signals will travel faster and further because there is less moisture in the soil as opposed to clay soils where the signals do not travel as far. Typical depth in clay is 2’-3’ and in sandy soil 5’-7’.

Above all, the technology relies on the knowledge and experience of its operator. 

The best utility locating professionals complete an intensive, months-long training regimen. They receive 320 hours of field training, and log 80 hours of classroom training where they tackle real-world scenarios in a safe and structured environment. All this training ensures that these professionals can accurately interpret the readings provided by a GPR unit.

When you receive a GPRS private utility locate, you can rest assured that your workers will be safe from the dangers of subsurface damage. We have achieved an unprecedented 99.8%+ accuracy rate in utility locating and concrete scanning thanks to embracing Subsurface Investigation Methodology, or SIM, and requiring all our Project Managers to become SIM certified.

SIM protocols require 80 hours of classroom education on the methods and technologies used in non-destructive testing (NDT) for utility locating and concrete scanning, and 320 hours of mentored field experience. That is more than ten times the industry training and education recommendations.

In cases where GPR is unable to penetrate soil for whatever reason, GPRS Project Managers will use complimentary technologies such as EM locating to visualize what’s hidden. EM locating involves either sending an electromagnetic signal through an underground utility line by a transmitter or using a receiver to search for existing electromagnetic signals in active lines.

The data collected from GPR and EM locating is compiled to create an accurate map of a property’s underground infrastructure. This map can include the location of any buried utilities, underground storage tanks (USTs), and more. 

What Can Be Found During a Utility Locate – and Why it Matters

Performing a utility locate reveals all forms of buried utility lines, underground storage tanks (USTs), and other subsurface objects.

Utility locates should occur before any excavation or other destructive activities begin, because hitting even a single utility line could result in costly and dangerous subsurface damage. 

The 2021 Finch Report, prepared for GPRS by a leading research firm who polled facility managers nationwide, determined that the average total cost of a single utility strike is $56,000. This includes project downtime, repairs, medical costs, and in the worst cases, evacuating surrounding neighborhoods. But the biggest risk of not having a utility locate performed before breaking ground is not to the pocketbook; it’s to the workers performing the task.

A ruptured gas line could lead to serious injury or even death to those on site. A severed power line could cause electrocution, which also could lead to death.

No matter the extent of the repercussions, subsurface damage hurts a company’s reputation. You don’t want to be the contractor known for hitting buried utilities. 

How Long Does It Take to Locate?

The time required for a utility locating project depends on various factors including the amount of space being scanned, the client’s needs, the number of subsurface objects located, and more.

If you have an open field, the time to scan is drastically less than if you are in a congested intersection on a main roadway. We look at every job and ask our clients what their scope of work is, why do they need us, and when they plan on executing their work. Once we have this information, we can begin to compartmentalize how we would go about scanning their specific site.

GPRS Project Managers immediately interpret the information collected from GPR and/or EM locators, and we even provide free PDF and .KMZ files on all outdoor utility locates.  

The GPRS Difference

Anyone can rent or buy a GPR unit and/or an EM locating system. But having the equipment readily available to you does not mean you will be able to easily locate and map your subsurface utility infrastructure.

The type of GPR required to locate underground utilities has a purchase cost of somewhere between $14,000 and $100,000. As the number of available frequencies, the user interface, and GPS mapping applications expand, so does the cost. Then there’s the additional cost and time investment required for proper training on how to operate that equipment.

Through our use of GPR, EM locating and other technologies, and our dedication to industry-leading training and standards, GPRS is able to provide services such as utility locating to Intelligently Visualize The Built World™ for our clients and customers.

It is vital to visualize what you cannot see before you break ground. GPRS’ utility locating services are here to provide you with 99.8%+ accuracy on every utility locate we do, and our Project Managers can work with you to help create a ground disturbance policy that allows you to spend your infrastructure dollars as efficiently and responsibly as possible.