Underground Utility and Pipe Locating Using GPR

Penhall Technologies provides utility locating service to help understand what subsurface hazards or obstructions in the ground. We can locate gas lines, sewer and drainage lines, underground storage tanks, PVC pipes and telecommunications lines on private residential, commercial, and industrial properties. Additionally, when utilities are detected, our trained analysts can estimate the depth of both metallic and nonmetallic objects. With resources across the US and Canada, Penhall can respond quickly to help deliver the results you need. Penhall Technologies’ analysts are extensively trained to properly mark your site, interpret the data, provide written reports and help you take the guesswork out of the equation. We also provide concrete scanning and x-ray imaging.

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

Locating Common Subsurface Utilities

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.

Utility Locating Service Equipment

Underground utility locating requires different equipment and technologies to complete a project properly, best practices and standards for a thorough and efficient survey, and experience. Utility locating 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 Locator

The RD 7000+ Pipe and Utility Locator is the backbone of our utility locating service.  With multiple frequencies, power modes, and both passive and active systems, the RD is almost always the proper way to start locating undergroundFeatured Image 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.

RD 7000 Series Pipe and Utility Locator

Utility Locating Device with GPR technoloy

GSSI Utility Locating Cart with 400MHZ Antenna

2. GSSI Utility Locating Cart with 400MHz antenna

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.

The Science of Utility Locating – Electromagnetic Induction

electromagnetic induction to locate utilitiesProducing 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 locating equipment.

Utility locating devices  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.

Utility Marking Standards

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 locating 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

Frequently Asked Questions

How does Ground Penetrating Radar help with Utility Locating?

Unlike traditional utility locating 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?

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

When should I use a private utility locator?

You are probably OK digging a few inches in your home garden. However, the more you dig or cut, the more likely you are to accidentally hit a utility. Underground hazards can be anywhere that only GPR analysts can detect. At Penhall, safety is our No.1 priority in excavating. Without the right skill sets and equipment, scanning for utilities can be a potentially disastrous gamble.

  • 811 will not locate utilities on privately owned property
  • Property owners are responsible for damaged utilities on private property.

Experienced utility locator identifying sewer lines

We Locate and Identify

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