How to Locate Underground Utility Lines

Utilities lines such as water, electric, gas, and communications underly the foundations of our modern world. These utilities allow us to live in comfort and security while supporting our homes, businesses, and quality of life. All utility lines are designed to deliver a necessary service to customers even though they are frequently located out of site and are therefore often out of mind.

Why are Utility Lines Located Underground

Utility lines are often located underground for a several of purposes. The first is that utilities buried beneath the ground surface are protected from damage caused by extreme weather events, accidents, or the general degrading effects of time and exposure to the environment. Another reason is the sheer number of utilities that are present in our modern cities, towns, and neighborhoods. If every gas, electric, water, sewer, and communication line was above ground, they would quickly overwhelm our streets, sidewalks, and airways. For these reasons, buried utilities are here to stay.

Types of Underground Utility Lines

There are many types of underground utility lines, each delivering a valuable service to businesses and communities. Without each of these services, modern life would be very different.

Water Lines

Underground lines deliver clean water from treatment facilities via water mains which branch into individual customer lines. Depending on the size of the system, these pipelines may range from several inches to several feet in diameter and may be constructed from plastic, metal, ceramic, or concrete.

Sewer Lines

Sewer lines act as a water supply system in reverse and carry away water that has been contaminated. Individual customer sewer lines feed into sewer mains which transport wastewater to treatment facilities. Like underground water lines, sewer lines may range from several inches to several feet in diameter and may be constructed from plastic, metal, ceramic, or concrete.

Electric Lines

Electric lines deliver power to cities and neighborhoods. Underground electric cables are classified by five features: the number of conductors in the cable, the voltage rating of the cable, the construction of the cable, the type and thickness of the insulation, and the installation method used. The voltage rating on underground electric wires can range from less than 1 kV to over 132 kV.

Gas Lines

Underground gas lines deliver heating, cooking, and laundry fuels directly to homes and businesses. These systems are safe, efficient, cost effective, and clean. Underground gas distribution systems are important in maintaining the quality of life that we have come to expect in modern society.

Communication Lines

Communication lines have long been installed underground and the buried telephone and television cables of the past are quickly being replaced by fiber optic cables. Fiber optic cables are classified by fiber type and by the number of fibers bundled in a cable. Fiber types are either single mode or multimode. Singlemode fiber is more useful over long distances as less refraction and reflection can occur to distort the signal. Multimode fiber is more useful for shorter distances where large amounts of data need to be transferred concurrently.

Why Locate Underground Utility Lines

Occasionally, a buried utility line may be damaged during construction or excavation. This is known as a “line strike”. A line strike can be very dangerous if it involves an underground electric cable or gas line.

A line strike of any type can also be very expensive to repair or replace. To avoid line strikes, responsible contractors and others who dig should locate utilities before breaking ground. Alternatively, they may have 811 or a Utility Location Company locate the lines for them. In addition to avoiding line strikes, workers may wish to locate underground utilities to work on repairs or to make replacements of existing lines.

Difficulties in Locating Underground Utilities

When underground utility lines are installed today, the installation is usually mapped into computer software systems using GIS satellite systems. Unfortunately, this technology was not available for the installation of older systems and if mapping occurred at all, it was generally done with a pen and paper.

For many utility providers, these older maps can be notoriously unreliable, and many smaller organizations have traditionally relied on the knowledge of senior employees to find underground utility locations. The downside to this is that, as the older generation of workers retire, the knowledge they have of system locations can be lost. This leaves new utility employees in the dark when lines must be repaired or replaced.

Equipment for Locating Underground Utility Lines

Fortunately, a variety of location tools are available to utility engineers and professionals. These locators can remove time consuming and expensive guesswork on repair and replacement projects. The type of utility locator used is dependent on several factors including the material of line being that is being located, the presence or absence of trace wires, and the environment in which a utility line is buried.

Traced vs Non-Traced Underground Utility Lines

For the purposes of locating underground utilities, line materials can be divided into two broad categories: conductive and non-conductive. Conductors allow the transfer of electrical signals along the length of an underground utility line. Materials for these lines can include metals such as ductile iron, cast iron, copper, lead, aluminum, and brass. Non-conductive materials used for underground utility lines can include plastic/PVC, ceramic, concrete, and asbestos and are resistant to the transfer of electromagnetic signals.

Non-conductive utility lines can be more difficult to locate, and utility engineers often install copper trace wires along sections of these lines to help in future locating efforts. The presence or absence of trace wires or conductive materials will determine which line locating device is most appropriate for the job at hand.

AML / All Material Locators

All Material Locators or “AMLs” are produced with proprietary technology by Subsurface Instruments. An AML works by projecting an ultra-high radio frequency into the ground. When a signal is reflected back to the receiver, it is interpreted by an onboard computer and the operator is alerted to any density change. This technology allows the user to search for any item with a density different than the surrounding environment. This can include both conductive and non-conductive utility lines. These locators are an excellent all-around tool for identifying all types of buried utilities in areas that are relatively free of other buried materials such as rocks, concrete, and tree roots.

Utility Locators

Utility locators have long been the industry workhorse for finding conductive and trace wire equipped underground utility lines. Utility locators work by projecting an electromagnetic signal along the length of a pipeline or cable with a transmitter device. A receiver wand is then used to scan the ground along the length of the line and to interpret the signal sent by the transmitter.

Utility locator transmitters can create a signal along a line using either conduction or induction.

Conduction: Involves a direct connection between the transmitter and the pipeline, cable, or trace wire. This is usually done with connector cables. A ground stake is also used to complete the circuit. Direct transmitter conduction is usually more powerful than induction and allows the pipeline to be traced at a further distance from the transmitter box.

Induction: Involves indirect signal transmission. The transmitter box is placed over the utility line to be traced and emits an electromagnetic signal into the ground near the line. This signal induces an electromagnetic signal in the underground pipeline, cable, or trace wire.

Alternatively, a transmitter clamp can be used to trace a line that may be encased in PVC or other non-conductive material. Induced signals usually do not travel as far along the pipeline since a large amount of the transmitter wattage is spent in projecting the signal through soil or air.

Utility locators are very accurate and can even provide an estimate of the line depth. However, they are of limited use if the line is non-conductive (plastic/ceramic/concrete) or if the trace wire has been broken.

If it is believed that a pipeline has a broken trace wire, a ground fault locator such as the A-Frame by Subsurface Instruments can help to locate the trace wire break for repairs.

Sewer Cameras

Sewer cameras, sewer snakes, and trace rods can be used in conjunction with utility locators. If the snake or trace rod is made of a conductive material, the transmitter box of a utility locator can be connected to create a traceable signal inside non-conductive pipelines. An alternative method is to use the sonde or transmitting head on a sewer camera. These sondes typically transmit at industry standard frequencies and can easily be read by most utility locator receivers.

Magnetic Locators

Magnetic locators can be used to find underground utilities if they are made of ferrous materials such as iron and steel. Magnetic locators can also be used if a non-conductive pipeline is equipped with ferrous joints, valves, or hydrants. The magnetic locator is limited in scope since it can only read ferrous components.

Subsurface Instruments produces a combination utility locator / magnetic locator known as the PL-TT. This powerful locator incorporates the advantages of both a magnetic locator and traditional utility locator systems.

Selecting the Right Equipment for Locating Underground Utilities

When considering purchasing an underground utility locating device, the most important considerations are what type of material the utility will you be locating is made of and what environment you expect it to be buried in. For most conductive utility lines made of a metal such as iron, copper, steel, or aluminum, a utility locator is likely going to be the best choice.

For the location of plastic pipelines and fiber optic cables, the locating device will be determined by whether the line is equipped with a trace wire. If there is a trace wire, a traditional utility locator will still be the best option. If there is no trace wire, or if you suspect that the trace wire is broken, there are two options.

If the utility line has a broken trace wire, a ground fault locator such as the A-Frame by Subsurface Instruments can help to locate the trace wire break for repairs.

If there is no trace wire, an All Materials Locator or AML should be considered, especially if the fiber optic cable is not buried in rocky soil or near tree roots.

For an all-around locator kit that can cover any underground wire locating situation, consider a combination of the Subsurface Instruments PL-TT Utility / Magnetic Locator, and the AML Plus All Material Locator. This will allow utility workers to find lines made of any material and will provide location versatility in nearly every environment.

Should You Locate Underground Utilities Yourself

Due to the potential for high voltage electrical shocks and gas explosions, line strikes can be very dangerous. Even non-hazardous line strikes such as water lines or fiber optic cables can be very expensive to repair. Considering this, it is always advisable that electric, gas, and other utility lines are located prior to breaking ground on a project.

Utility location services are generally provided free of charge through your state’s 811 telephone line. Calling 811 automatically routes you directly to your local 811 center and each state has its own specific locating guidelines. If your state accepts online contacts from homeowners and contractors, you may be able to file an “online request”.

If you are a contractor, or a utility service provider, utility location tools can also be useful devices for double checking locations provided by the 811 service. A second reading is never out of place and ensures that all underground utilities have been located properly. Having a utility locator on hand can also be useful in time sensitive projects where an 811 technician may not be able to arrive immediately.

Contact Us with Questions about Underground Utility Locators

If you are deciding on whether to purchase a utility locator, please feel free to reach out to us at Precision Outdoor Tech. We will discuss your needs and project specifications and will point you in the right direction to products that can help you to locate your utility lines. Give us a call with your questions, and we will be happy to help you out. If it is after hours, please use the contact form listed in the municipal contact section below and we will respond shortly.

If you have already decided on the type of locator that you would like to use for your project, you can find our product collections via the following links.

All Material Locators (AMLs)

For all underground utility types, including non-conductive materials. All Material Locators work best in non-rocky soils away from tree roots.

Utility Locators

Utility locators can be used for finding metal pipelines, cables, or other conductive utilities. These devices can also be used on trace-wire equipped non-conductive lines.

Sewer Cameras

Sewer cameras work great for tracing non-conductive pipelines with the help of a utility locator receiver. They can also record videos of pipeline interiors to inspect for damage.

Magnetic Locators

Magnetic locators are appropriate for steel, iron, or cast-iron pipelines, valves, septic tanks, and pipeline joints. The size of the target determines the depth at which it can be read.