About Utility Locating

Underneath today’s city streets exists a labyrinth of underground water, sewer, gas, electric and telecommunication lines.  As urban populations increase, 50% of a predicted 7-9 billion people are expected to be large town or city dwellers by the year 2021, so the quantity and complexity of underground utilities rises to meet the demand for potable water, telecommunications, energy and sewerage services.  The location of such underground utilities has, historically, been based on utility record information maintained by the utility companies.  Unfortunately, this information, if it exists, is often inaccurate, incomplete or out of date making it sometimes difficult for a utility locator to accurately mark out these utilities.  Furthermore, such information very often locates the utility line in only two dimensions, usually in the form of a line on a map.

The third dimension, depth, is critically important for the construction of accurate three-dimensional plans of all buried utilities – a prerequisite for the installation of utility networks by modern trenchless techniques.  Various non-destructive detection techniques exist for pipeline location.  However, compounding the location problem for the utility locator is the fact that the conduits for utilities range from metallic materials, such as steel and cast iron, through traditional materials such as clay and concrete, to synthetic materials such as polyethylene and polyvinyl chloride.

ATLANTIC LEAK DETECTION & PRIVATE UTILITY LOCATING in New Jersey provides private underground utility line locating services prior to excavation.  Our clientele-base consists of: Surveyors, Architects/Engineers, General Contractors, Solar Energy Providers, Government Departments, School Districts, Private-facility owners and Residential Property-owners who find it a vital concern in knowing the locations of their underground-infrastructures.  Damage prevention to the utilities, as well as, the safety to the community is the foremost concern prior to excavation. Prior knowledge of the underground utilities, marked out by a private utility locator is also an important and cost-effective way in assuring a safe and successful out-come of your project.

ATLANTIC LEAK DETECTION & PRIVATE UTILITY LOCATING in New Jersey uses the most advanced and state-of-the-art EM Locating Instruments and Techniques in a comprehensive search for underground utility lines.  Our Certified Private Utility Locators apply the “best effort” approach, utilizing their ability and knowledge to the up-most standards of “competence” in identifying each utility-line being mapped on the surface of the ground.

The Electromagnetic (EM) locating equipment we use to locate metallic pipes and or cables provides us with a range of frequencies necessary in a survey. Having the choice of frequencies at-hand, gives the Private Utility Locator the ability to adjust to the un-foreseen soil conditions as well as pipe/cable conditions which can be encountered unexpectedly on the job-site.  Measure of accuracy is 93% to 97% allowing a “hand-dig” tolerance of 24” on either-side of the utility-line.  Depth-readings are limited up to 13-feet. The depth-readings maybe provided upon request.

Electric cables must be energized (have power flowing through them) to be detected magnetically by the utility locator. Indirect mode allows for the detection of the magnetic fields generated by the electrical power cable. Direct mode allows for a similar effect to be induced into metallic pipes that would not normally create their own magnetic fields.  This is done by the utility locator attaching a clamp (connected to a low-voltage power source) to the pipe or cable (target line) and inducing an electrical current. This transmits a strong signal directly to the target line, allowing the utility locator to trace it at a greater depth and for a longer distance.

If the target line is not accessible for attaching a clamp, place the transmitter over the target line and activate it.  This is broadcast induction mode.  Then use the receiver in the same manner to trace the signal emitted from the target line, regardless of the transmitter mode used.

Most detectors for utility locating provide an audio signal to the operator that indicates the detector is over a buried utility.  As you walk along without encountering any iron or steel items, the receiver’s two magnetic-field sensors will balance out the Earth’s magnetic field and the frequency of the audible indication will remain at a low level (approximately 40 Hz).  However, as you approach a buried vertical piece of iron pipe, for example, the frequency of the audio indication will begin to increase as the strength of the magnetic field becomes stronger at one of the sensors. When the tip of the receiver is directly over the pipe, the strength of the magnetic field at the first sensor is maximized, which causes the frequency of the audio signal to peak. After you’ve outlined the target area, reduce the sensitivity level and slowly move the receiver back and forth in an X pattern over the area. Very quickly the well-defined peak of the audio signal will pinpoint the target.

Electromagnetic and Radiofrequency Line Locators Electromagnetic and Radiofrequency line locators operate either in “passive” mode by locating a background signal or in “active” mode by locating a signal introduced into the utility line using a transmitter. Three sources of background signals exist as follows:

  • Background signals due to the flow of electrons in a conductor acting like an antenna. These oscillate producing fields which can be detected by an electromagnetic receiver (Radiofrequency method).
  • Current carrying conductors producing a 60Hz signal can be detected by an electromagnetic receiver (Electromagnetic method).
  • Utilities in close proximity to power lines or used as grounds may also be picked up with a receiver.
Signals introduced into a utility line can be either indirectly or directly induced. Introducing a signal indirectly consists of generating and transmitting a magnetic field from a transmitter above ground.  For optimum results the transmitter should have the same general orientation as the utility line which can be obtained through trial and error.  Alternatively, a signal can be introduced directly using an induction clamp, a circular clamp, which induces a signal only in the particular conductor that it is clamped around.

The best possible tracing signals are those which are generated using the direct connect method.  By virtue of the closed current loop, there is very little chance of the resulting signals being distorted.  This is the preferred method of tracing a utility when and where possible by the private utility locator.

The main weakness of this method is its inability to trace non-metallic objects, although this can be overcome by using an “in-pipe transmitter” sonde or a trace wire.  When access can be gained by the utility locator to a pipeline, a flexible insulated trace wire can be fed into the conduit.  The transmitter is connected to the trace wire and the signal in the wire can be traced as before.  The need to insert a trace wire into the pipeline could be, at least partially, overcome if all new non-metallic pipes incorporated tracer wires.  Alternatively, an “in-pipe transmitter” sonde can be used in the same manner.  Sondes are small, self-contained radio transmitters, which create an electromagnetic field of their own.  In both cases the receiver is passed over the approximate location of the pipeline and the location with the highest signal strength is marked by the utility locator as the horizontal location of the pipeline.  By rotating the receiver until the highest signal strength is received the approximate orientation of the pipeline is determined.

Finally, the depth of the pipeline can be estimated, but this measurement is prone to error.  A particular area of error is the situation where a pipe, situated near the target pipe, possesses a strong magnetic field causing extraneous currents to be induced thus leading to misinterpretation.  This would indicate a single utility with greater depth than the actual depth due to the combined field. Conversely, the presence of a conductor above the pipeline being traced could lead to a shallower than the true depth being recorded.

Electromagnetic Locators Used to locate buried pipes, cables, and sewers, this type of device detects the alternating magnetic fields that surround a conducting metallic line.  As a result, it can’t locate nonmetallic lines, such as plastic pipe, unless it is installed with tracer wires.  This technology works in all soil conditions, even under water.

There are several major manufacturers of electromagnetic locators.  The company’s line of products features a self-contained transmitter that generates an AC signal that creates an electromagnetic field around a buried conductor.  These signals are picked up by a handheld receiver.

By determining the proper method, a private utility locator can use this equipment to detect both passive and active signals.  Passive signals include those emitted by power cables, telephone lines, power-system return currents, and radio-frequency currents from long-wave radio transmissions that penetrate the ground and flow along buried pipes and cables.  Locating a line using passive signals requires only a receiver.  Passive signals can’t identify a specific line, however, if multiple lines are present.  That’s where the ability to detect active signals produced by the transmitter pays off.  It allows utility locators to identify lines more precisely in terms of depth and signal strength.  By varying the transmitter frequencies, private utility locators can use this type of electromagnetic locator to positively identify and trace a single line in a congested area, such as below-street services in a city.