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What are the common underground utility location methods?

by | on | in Damage Prevention of Utilities | 8 Comments

What are the common underground utility location methods? Since April is Safe Digging Month, we have been reminding everyone to call 811 to have your utilities located before you dig. Routinely we are asked about the different methods available to locate utilities. Within this article we will focus on electromagnetic utility locating, ground penetrating radar, acoustic utility locator, hydro excavation and even dowsing.

Electromagnetic Utility Locating

The most common method to locate private utilities is known as electromagnetic utility locating. In this technique the locating equipment generates an electromagnetic radio frequency and when applied to the ground, the subsurface utilities containing conductive material can be detected on a receiver. This method is very accurate and commonly used to detect gas, electric, telephone, cable, propane, water, sewer, storm and irrigation lines. The biggest limitation of this technology is that it cannot locate unmarked plastic, asbestos, concrete, tera-cotta or non-ductile pipes.

Gas lines are generally constructed of medium or high density polyethylene pipe, or plastic, which is why tracer wire is commonly run alongside or on top of the pipeline to make the line “locatable.” In these situations by having access to the system (e.g. a tracer wire box), a current can be induced on the tracer wire and the tracer wire can be located.

This technology also doesn’t perform well beyond the depth of 10-15 feet. Natural gas distribution lines are usually installed 3-4 feet deep while transmission lines run deeper, though it would be unusual to be buried more than 10 feet.

More information pertaining to this underground locating equipment can be found on 3M locating equipment

acoustic-pipe-locator-cThe SENSIT APL locates in soil, grass, concrete, gravel and asphalt, is easy to use and interpret, requires no system access and locates within minutes.

Acoustic Pipe Locator

Until only recently, acoustic location methods had been applied to locate mostly waterlines. With the recent introduction of the SENSIT ULTRA-TRAC APL (Acoustic Pipe Locator), now even unmarked plastic pipe (or where tracer wire has broken), water and sewer laterals can easily be located. This instrument sends a series of pings down into the earth, then monitors the acoustic wave pattern which ultimately produces a locate profile. The SENSIT APL locates in soil, grass, concrete, gravel and asphalt, is easy to use and interpret, requires no system access and locates within minutes. The APL is a long-awaited welcome addition, to utility locate options.  More information on this product offering can be found at Acoustic Pipe Locator.

Ground Penetrating Radar

Ground penetrating radar or GPR is a technology used for subsurface utility locating which also uses high frequency pulses. The radio waves are emitted into the ground and facilities deflect the radio wave back up to the operator where the objects will be displayed on the equipment. This type of locating equipment is generally used for buried pipes, tanks, manholes, cables and other buried objects that cannot be located with other more common methods, such as electromagnetic locating. Operating this type of equipment and understanding the results require experience and extensive training.

There are some limitations of GPR:

  • Some soils like saline, shale or clay have high conductivity which limits the GPR from penetrating the soil.
  • High frequency GPR antennas (300-1000+ MHz) can only penetrate a short distance down.
  • A common rule applied when using ground penetrating radar is that for every foot in depth, the buried facility must be an inch in diameter. For example, a six-foot deep pipe would need to be at least 6” in diameter to locate it via GPR.  
  • Soil density, environment accessibility and crowding of surrounding utilities can also influence the GPR’s effectiveness.

Hydro or Vacuum Excavation (potholing)

Vacuum excavation is a fast and non-destructive way to safely locate and expose underground utilities.  Here, high pressure air is used to break up the soil, which is then vacuumed into a tank. Hydro excavation is used in difficult soil conditions where pressurized water breaks up the soil which is then vacuumed into a tank. This is more commonly known as potholing, hydro-digging, hydro-trenching or soft digging.

Dowsing

While dowsing may not be recognized by many of the larger utility location services, many experienced locators will admit that they have and still use dowsing as a reliable way to locate underground utilities and water. Here dowsing rods, which can be made from coat hangers, can indicate whether you are standing on top of an active pipeline. It will not indicate the depth of the pipeline, but according to many experienced locators it is a dependable way to locate pipelines.  Skeptics claim that there is no science behind this method and some claim intuition is the driving force in dowsing. No matter who you believe, dowsing has been used to detect underground water since the Middle Ages.

As you can see there is a wide range of methods used to locate utilities, from state-of-the art equipment to coat hangers and intuition.

 

Linc Energy Systems specializes in damage prevention and offers a line of underground utility locating equipment

 

 

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About The Author

Susan Bender started selling to the natural gas industry in 1980. In 1990 she founded Linc Energy Systems, where she remains as President and CEO. She attributes her success to her philosophy, “The customer is king (or queen),” which remains part of her company’s mission.

Comments

  • Guest
    Ram Pal Sharma Monday, 29 September 2014

    What is methodology of utility identifiation

  • Guest
    Jason Richards Wednesday, 19 August 2015

    ProMark Utility Supply manufactures different types of underground locating posts such as CP Test Stations.

  • Guest
    Evgeny Dron Monday, 07 March 2016

    Hi Susan Bender !
    I need to look for the pipe at depth of 20 ... 27 m.
    Length of the pipe 300 ... 600 m
    It is located under the ground.
    Pipe diameter of 7 feet.
    Material - steel + concrete.
    Which device is suitable?
    Compass is suitable or not?
    If appropriate, what?
    Thank you
    Evgeny Dron

  • Guest
    Brian Cox Monday, 07 March 2016

    A member of our customer service team will be emailing within 24 hours.

  • Guest
    Hazel Owens Monday, 21 March 2016

    It's amazing what technology can do nowadays. Electromagnetic radio waves can be used to find metal lines underground, and sound waves can find what electromagnetic waves can't. It's important to know where utilities are underground when digging to prevent pipe breakages, and these technologies allow us to do so with ease. Thanks for all the information about different methods to find underground utilities!

  • Guest
    Kal Koychev Wednesday, 05 October 2016

    Hello there, Susan or anybody.
    PLEASE HELP
    I'm facing a similar challenge as Evgeny Dron. I need to find a tunnel with old utilities and it is about 80 feet underground. I need to get a clear picture because all the tools we've been using so far gave us wrong readings. They confuse water with cavities or air pockets with rocks or concrete etc. Could you please email me some information on what equipment we need to get, so we can get the job done.
    Thanks.

  • Guest
    Susan Bender Thursday, 06 October 2016

    Kal, a member of Linc Energy Systems will be in contact with you by email. Thank you for your inquiry.

  • Guest
    Dan B. Thursday, 06 October 2016

    Hi, I work for IDS a Ground Penetrating Radar manufacturer, we have many models and use our GPR technology to locate many things underground.

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