Underground Utility and Pipe Locating Using GPR

Penhall Technologies, a division of Penhall Company, provides utility locating service to help understand what subsurface hazards are in the ground. We can locate underground lines and buried pipes on private residential, commercial, and industrial properties. We pride ourselves in our experience, expertise, and sophisticated equipment. Coming into any projects, our goal is to deliver quality-assured services that meet the customers’ expectation. As a result, keeping your utility locating project on budget and on time is our top priority.

Our analysts who perform locating service are extremely knowledgeable of the subjects. Indeed, they are required to go through extensive training before they can assist you with any underground locating needs. They are trained to properly mark your site, interpret the data, provide written reports, and help you take the guesswork out of the equation. The training includes both in-class meeting and field instruction that equips the analysts with vital information and hands-on experience. Before being sent out to you, the analysts are tested and interviewed to make sure that they are fully capable of providing you with the best services around.

When Penhall analysts arrive on site, you will find that you have gained a trusted partner who will assuredly add value to your project. Regardless of the project scale, our analysts always come prepared and ready. Our trucks are fully equipped with everything that is necessary to get the job done right. Upon the customers’ request, we can provide an initial job walk and even a written report afterward.

Difference between Public and Private Utility Locating

Penhall Technologies is a private utility locator. We do not compete with public locating companies (such as 811), who only locate underground lines on public property. As stated, if your water pipe or post-tension cable is on a private property, public locator will not assist you in marking the site. That is when our service comes into to play.

  • Dial #8-1-1 to reach your local public utility locator.
Learn more about the difference between public (811) and private utility locating

Locating underground storage tanks using GPR Locating all buried utilities prior to trenching

According to the Common Ground Alliance, there are more than 20 million miles of buried utilities in the United States. Utilities are often buried in the ground for aesthetic reasons in addition to necessity or convenience. The most common underground utilities are electrical, water, gas, communication, sewer and storm drain lines/utilities.  Although not an exhaustive list of underground hazards, these utilities make up the overwhelming majority of underground hazards one would likely encounter when preparing to do any type of sub-surface penetration such as trenching, digging, or boring.

Types of Utility Locating

1. Electromagnetic Detection

electromagnetic induction to locate utilities

Producing a force or voltage by moving a conductor across a magnetic field is known as electromagnetic induction. It can be found in many technological applications such as generators, transformers, and utility-service equipment.

Devices  used for private utility locating transmit a radio wave at a certain frequency and this radio wave is electromagnetic by nature. The magnetic field inherent in the radio wave moves across an object and generates a voltage that runs along it’s length. This current, which has been induced, generates its own electromagnetic field. Most of the voltage travels down the outside of the object, such as a pipe or wire, rather than penetrating the inside.Placing a receiver on the ground directly above the buried utilities will detect the electromagnetic field allowing an analyst to locate a metal pipe or cable that is buried in the ground. The distance a signal can travel down a pipe or wire is determined by the resistivity of the surrounding soil and pipe itself, as well as the frequency, transmission power, distance from the transmitter, and capacitance of the pipe or cable.

2. Ground Penetrating Radar (GPR)

Locating underground utility lines using ground penetrating radar

Photo Courtesy to Worksmartinc.net

GPR is a technology to locate underground utilities based on high frequency pulses. The machine emits radio waves into the ground. After detecting the objects, the radio waves would reflect back to the operator. The shape of the objects will also display on the equipment screen. Ground penetrating radar works best in situations where you need to locate: buried pipes, cables, tanks, manholes, etc. Throughout our locating experience, GPR is often better than electromagnetic detection in assisting our analysts perform the job successfully.


At Penhall, our No.1 priority is to deliver results that live up to the customers’ expectation. Therefore, we will utilize our available resources to help you complete the tasks. Regardless of the job size and location, we will use either utility locating technologies or both if needed to complete the work. 

Experienced utility locator identifying sewer lines

Utility Locating Colors

Color codes are used to mark existing underground utilities to protect them from damage during excavation. Markings can be made by spray painting lines, using flags, or both to highlight the location. Penhall Technologies adheres to the standard underground utility marking color chart used all over North America.  This color protocol conforms with both the Concrete Sawing & Drilling Association (CSDA) and the American Public Works Association (APWA) marking depiction of underground utilities. Below is the color scheme:

Redelectrical lines, conduit, and cables
Orangetelecommunication lines
Yellowgas, oil, steam, and petroleum
Greensewers and storm drain
Bluedrinking water
Purplereclaimed water and irrigation
Pinktemporary or unknown survey markings
Whiteproposed survey or excavation area

Professional Equipment for Private Locate

Private locators require different equipment and technologies to complete a project properly, best practices and standards for a thorough and efficient survey, and experience. Locating underground lines can be a complex undertaking. Each project is different and unique and there are many variables to take into consideration such as:

  • Which utilities need to be identified
  • Moisture content of the soil
  • Terrain
  • Natural and man-made obstacles

At Penhall Technologies, our analysts employ several different instruments when conducting a utility survey for optimum accuracy.  The following are some of the tools an analyst might use on any given survey.

1. RD 7000 Series Pipe and Utility Locating Equipment

RD 7000 Series Pipe for utility locating service The RD 7000+ Pipe and Utility Locator is the backbone of our private utility service.  With multiple frequencies, power modes, and both passive and active systems, the RD is almost always the proper way to start locating underground utilities. The RD system works by applying a current via the transmitter to the metal pipe, valve, or tracer wire and using the receiver to trace the electromagnetic field down the length of the pipe or wire.


2. GSSI Cart with 400MHz antenna

GSSI Cart with 400MHz antenna for utility locating service The GSSI manufactured utility cart with 400MHz antenna can locate both metallic and non-metallic utilities to a maximum depth of approximately 9ft under ideal soil conditions.

GPR penetration and resolution is entirely dependent on soil conditions.  GPR prefers dense, resistive mediums and will be limited in wet or conductive soils.  Despite those limitations, GPR is often the only way to detect abandoned lines, utilities with no surface valves, PVC, transite (asbestos-cement), or similar non-metallic utilities.

FAQ for Private Locating Service

How does ground penetrating radar help with Utility Locating?

Unlike traditional systems, GPR can detect plastic, concrete, and metal pipes. This makes GPR an ideal technology to locate underground utilities of all kinds. GPR technology works by sending a flash of energy into a surface material like concrete or ground soil via special antenna. Each GPR unit is embedded with a computer system that can register the time and strength required for the return of any reflected signals. Dynamic subsurface differences will create reflections that are logged by the system and archived. These reflections are produced by several variables such as conduit or pipes. As a result, GPR only requires access to one side which is an added benefit when needing to search for utilities.

What are the consequences of hitting an underground utility line?

Striking an underground utility can be absolutely disastrous both in terms of monetary cost and loss of life. The cost of hitting an underground utility can range in the thousands of dollars and more importantly can cause injury or even death.  The best way to reduce the chances of a safety accident on your next project is to contact Penhall Technologies to locate all underground utilities prior to trenching.

Natural Gas Pipeline Exploding

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We Locate and Identify

  • Sewer Pipes
  • Gas & Propane Lines
  • Sprinkler Lines & Pipes
  • Storm & Drainage Pipes
  • Electric Cables & Conduit
  • Telecommunication Lines