Before learning how a utility locator works, we should understand that there is an entire world of utilities underground that can be as complex and dangerous as the world we know above ground. There are high-voltage electric lines, natural gas transmission lines, telephone and cable TV trunk cables, and fiber optic lines that connect to hospitals, police stations, army bases, businesses, and private residences. While excavation is often necessary to continue improving upon our existing infrastructure, the consequences of damaging underground utility lines can be both financial and personal, including fines, repair costs, and even injury or death.

Excavation around utility lines can only be done safely if we know where the lines are. That is where using a utility locator comes in.

utility locatorMost utility locating devices operate roughly the same way, though there are many different types with differing specific functions and settings. A standard radio detection (RD) locating device has two pieces, a transmitter and a receiver. The transmitter transmits an electric current to the utility you are trying to locate, either by direct connection or by non-metal-to-metal induction (using a magnetic field to transmit a current). The utility then transmits this current, which creates a magnetic field around the utility, which the receiver can sense. The current that the transmitter creates is low enough that it doesn’t affect the operation of the utility you are locating, so phone and cable TV lines will not be garbled, and power lines will not be disturbed.

Once the transmitter is transmitting its signal, the receiver is held over the area where the facility is present, and the receiver indicates the position and sometimes direction of the utility, usually with a sound or graphic display, or a combination of both.

So using a utility locator should be easy, right?

Unfortunately, it is not so easy. Since we are sending an electric current through the utility, we have to remember the rules of electromagnetism, the most important being that an electrical current always follows the path of least resistance to ground. This means that the current doesn’t necessarily follow the path of the utility you are trying to locate, even if you are connected directly to it. If there is a nearby non-target utility that is shallower (closer to the surface of the earth) or more conductive, or if your target utility has a break or wear on the protective sheathing, it can affect your ability to locate your target facility accurately. The signal can “bleed off” from your target facility onto a facility you were not intending to locate, and this can cause major problems when excavating.

Figure 2: Typical locating marks, with green paint for sewer, blue for water, and yellow for gas. The numbers next to the marks indicate the depth of the utility at that point. Accurate depths are not always possible, but can often be verified using GPR.

For instance, if you attempt to locate a gas line and an electrical line that are running near each other, and the gas line “bleeds off” onto the electrical line, it may be impossible to tell where the gas line is, and a careless excavation could lead to property damage or even death. This indicates that it is vitally important to understand that the device is only as accurate as the person operating it.

So what do professional utility locators know that your average person doesn’t?

A professional utility locator is always looking for signs that the signal is unaffected by other utilities or anomalies, by measuring depth and the “shape” of the signal, using locating techniques that are difficult to teach without hands-on experience. Most professional locators go through weeks of initial training, followed up by periodic retraining and auditing, to make sure that the locator continues to be effective at marking utilities safely.  Since the cost of marking a utility inaccurately can be anywhere from thousands to millions of dollars, and even result in injury or death, it is always a good idea to get a trained professional to perform your utility locates.

GPR

 

Some companies, including Encompass Inspections, also use Ground-Penetrating Radar for all utility locates. Ground-Penetrating Radar (GPR) sends a radar signal through the earth that will bounce off of underground targets to a receiver above ground, which gives a trained technician a picture of what is underground. On the job site, contractors often remark that it resembles a “fish finder,” and while the fish finder uses sonar and a GPR uses radar, they are somewhat similar.

If Something Seems Fishy, We’ll Find It

There are hazards to this method, most prominently that the GPR does not indicate what is underground, only that there is or is not something there. Like a fish finder, the GPR may be able to tell you roughly how large the object it is targeting is, but it could be a sunfish or a trout (or in our case, a hidden utility). However, used in concert with standard radio detection locating, it is a very useful tool for verifying radio detection locating marks and potentially finding utilities that were not detected during the standard RD locate, and for finding utilities that are not metallic and do not transmit current. In other words, radio detection is great for finding what you know is there, and GPR is great for finding what you don’t know is there.

811 and Blue Stake

It’s always a good idea to know before you dig where the utilities in the dig area are, but it’s also the law. Federal and state Blue Stake laws govern 811, which is a nationwide free service to protect public utilities from damage during excavation. Simply dial 811 to reach your local One Call center and utility companies will mark all the utilities they own and maintain within the scope of the work. However, 65% of underground utilities are privately owned, and utility companies are prevented from marking private lines. Private locating companies engage in private line locating and provide accurate utility mark outs for any private utilities, and can also be used to verify public utility locating marks.

Encompass Inspections has been a nationwide industry leader in private utility locating for years, working with the highest quality locating devices and personnel to ensure your entire job is marked thoroughly and efficiently. We offer competitive prices for jobs of all sizes, from residential jobs to major corporate and industrial projects, with services ranging from utility locating to concrete scanning with GPR, leak detection, GPS mapping, and video pipe inspections. To protect your home, business, employees, and family from financial or personal loss, let us give you the most accurate picture of your subsurface world.

Visit our website at www.encompassinspections.net for more information, or contact us.