Utility Detection Is Not a Crapshoot

Sept. 20, 2013

Utility detection is serious business. Poor utility location and management during the design and construction of a project, and when doing maintenance and repairs, can result in job shutdowns, liability claims, injuries, and even death.The bad news is that when it comes to detecting underground utilities, there’s no silver bullet. There’s no technology that works in all conditions, every time. And to hear the professionals tell it, even if the full arsenal of what’s available is deployed, contractors still can’t be sure they’re 100% safe. Added to this is the fact that the locating industry is notoriously unregulated, meaning field technicians are neither licensed nor certified, which can make for wide discrepancies in training and experience. The good news is you can improve the odds by making sure you not only hire the best professionals you can find but take responsibility for doing a little sleuthing yourself.

“What we preach to people,” says Peter Masters, application specialist at Geophysical Survey Systems Inc. (GSSI), “is to use as many technologies as possible and take advantage of every opportunity. This includes maps, talking to people, whatever’s available. Utility locating is difficult. There are no two ways around it, and there’s no one technology that’s going to solve all the problems. What people don’t realize is that while technology gives you information, you have to be a sleuth to pull it all together.

“Another challenge is the different interests of the stakeholders to a project. In addition to the contractor, who’s under extreme financial pressure to get the job done, you’ve got the engineer and the utility and, often, government. It’s hard for everyone to get on the same page, and often it can be the excavator who’s left holding the bag. His job is predicated on the efficient use of time and equipment. If he breaks something, the least that can happen is his job just got shut down.”

“The excavator wants to have a sense of absolute security when he digs” says Christopher Koch, president of Hance Utility Services in Buffalo, MN. “And the truth is you can’t. There are millions and millions of holes dug every year, and there is still some small percentage of those that result in damage to the underground infrastructure and sometimes a fatality. And when you step back and you look at what happened, you find it’s not really anybody’s fault. There are still surprises that lurk down below, such as utilities that weren’t on the print or abandoned facilities that mistaken for live ones. The fact is there’s nothing excavators can do to guarantee they’re going to have a safe dig every time they disturb the earth.”

“We use three or four different technologies simultaneously to be sure that we’re finding all the underground utilities,” says Mark Mason, president of Bloodhound Underground Utility Locations in Brownsburg, IN. “Because no one technology is foolproof. Although we specialize in locating utilities that are not owned by utility companies, sometimes we’re hired by the utility directly, in cases where the technician for their one-call locator can’t find a gas or water main and they turn the job back to the utility.

“When we go on a job like this, we’ll start just like a one-call locator would. We’ll look at the utility’s print, go to the hookup points and use EM [electromagnetic locators] to locate the known utilities we can see visually. Sometimes we can find what we’re looking for using this same technology the contract locator used. The difference is our crews are both trained and experienced in troubleshooting techniques that go beyond the general use of the equipment. After EM, we come through with GPR and run the area and look for targets. Having already located the known targets, we use radar to look for any unknown utilities. Then as a third layer of protection, we use EM induction scans, where instead of hooking up a utility to transfer a signal down through it, we use a transmitter above the ground, inducing a signal into the earth, and walk that same area with a receiver to see if we pick up anything else. Sometimes we can find targets, but they’re intermittent. When that’s the case, we might come in with a vacuum excavator.

“We provide a map on every job, at the minimum a digital field sketch, which is not to scale, sometimes a digital field sketch that is to scale or a 3D map with GPS and GIS coordinates all rolled into one. It’s all based on what the client’s needs are.”

Call Before You Dig
When we asked locators what they think about the 811 one-ticket system for locating public utilities, their opinions varied. “Statistically,” says Koch, “it’s been shown through the Common Ground Alliance’s DIRT Report and from other sources that if the excavator calls in a one-call ticket-if they go through those steps of dialing 811, waiting the required time and making sure that somebody shows up to mark-no damage occurs. So an excavator who calls in a ticket and backs that up with a private locator to cover the facilities that aren’t covered by 811 should be good to go.” That being said, Koch notes that when a contractor uses the 811 system, he has no control over who comes out to mark and how good they might be. “It’s up to the utility to find a suitable contractor. Some people have a misconception about public-versus-private utilities and where the boundary line is. As a private utility locator, I often get called out to private property because the owners thinks the 811 system doesn’t apply to private property. Another problem is the demarcation point, which is usually after the meter, the point where the public facility no longer takes responsibility.”

Mason, who comes from a one-call background, isn’t as sanguine. “The problem with the public locating world is that it’s built on volume. When pubic locating began, locators were getting something like $25 a ticket. Today they’re getting maybe $12-$14. Undercutting drove the price down, and a lot of those companies run off a small margin. They don’t have enough staff, and their technicians don’t have enough training. So, what we see is a lot of damages and a lot of late tickets. We have excavators who don’t trust the one-call system, and when they have us come to check for anything private, they also want us to verify the accuracy of the one-call mark. If we find something that’s off, we tell the contractor they need to call back and document that the utility was mismarked so the liability remains with the one-call locator.”

Another industry observer thinks the system is lopsided in favor of the utilities. “The 811 system is a step in the right direction, but there should be laws that require if a utility uses the public space, it has to know exactly where its lines are.” Additionally, Mason thinks statistics about the efficiency of the one-call system often get massaged in favor of the utilities, which makes the system look more effective than it is. Abuses include prioritizing tickets, which can mean a disproportion wait for contractors on higher risk jobs.

Should You Do It Yourself?
Asked if contractors are well served to purchase their own equipment, either to proof one-call locators or locate private utilities on their job sites, opinions also varied.

Credit: Pipehorn
The transmitter for an electromagnetic detection unit.

David Dodd, sales and marketing director for Pipehorn Locating Technology, manufacturers of high-frequency electromagnetic locators, maintains that one of the product’s selling points is that the technology offers contractors a back-up for the one-ticket system. “Pipehorn is known throughout the industry as the best sweeper. When a contractor shows up at a job site and he’s ready to sink his backhoe in the ground, how does he know the 811 locator didn’t miss a high-pressure gas line or a high-voltage line in the area he’s about to dig into? He can check by doing a two-man sweep.”

Matt Wolf, president of MALA GeoScience USA Inc., maintains that contractors who invest in ground-penetrating radar (GPR) do so because “they’ve been burned so many times with the one-call system that they want an in-house tool to verify the contract locator’s results. You’ll spend $10,000 to $12,000 on a GPR system, but if you find a mismarked water or gas line just one time, the system has paid for itself. The magnetic tools range anywhere from $1,200 to $5,000, depending on their complexity, but you pretty much already know there’s a utility there. With radar, you can have no expression whatsoever of a utility in the area and still detect it.”

“I would not recommend that the excavator start double-checking the 811 locators,” says Koch. “Because in the event of damage, it’s going to become a he-said-she-said argument about who located what, particularly if the excavator paints any paint on the ground. If you want to do that, hire a professional. Locating companies locate 40 hours a week plus. That’s all we do. It’s difficult for a novice or lay person who doesn’t operate the equipment regularly to replicate a professional’s level of skill.”

“When I first started, in 1999, private location was in its infancy,” says Mason. “If a contractor got hit with a $50,000 claim on a project, I’d get a call from his insurance company about what he could have done. I’d tell then the contractor could have spent $1,000 and located all the utilities. And I’d tell them they should require in their policy that the contractor must have a third-party locating company come in and inspect the area. A lot of insurance companies have done that on some projects.

“Hiring a third party provides an insulator. If a contractor is trying to do it themselves, and they haven’t purchased all the technology they might need and they don’t have a properly trained technician, they’re not insulated. If they hire it out and verify they’ve done that, they’re protected because if there is a utility strike, the contractor can essentially go back on the professional locating company.

“Typically, when somebody hires a company like us, it’s because they have no idea what’s out there. We have two different levels of service, Tiers 3 and 4. The end product’s the same, but the liability is different. With Tier 3 service, if something is missed and it couldn’t have been found-we ran radar over it and didn’t see-then we don’t take liability for that. It’s in our contract. With Tier 4, if you strike a utility that wasn’t marked, we’ll pay the repairs up to $15,000; ninety-nine percent of the time that takes care of it.”

All this being said, there is also the caveat that the decision about whether or not contractors should be in the business of locating: Either second guessing the one-call system or identifying private utilities on the job site depends to some degree on the technology, including the ever important variable of how regularly it’s being employed.

The electromagnetic detector (EM) is the workhorse of the utility-locating industry when it comes to metal pipe or plastic installed with a metal (typically copper) tracer wire. It’s usually the only piece of equipment a one-call contractor locator will use. “There are three different ways you can apply a radio signal through a line when you’re trying to locate it,” says Koch. “The most popular and the most often used and the one that’s recommended by best practices is direct connection. That’s where you actually physically attach an alligator clip to a line and put the radio signal on it. With the inductive method, you drop the transmitter down on top of the suspected location to try to energize the utility. The inductive method is particularly effective in solving access issues. Maybe the surface access point is behind a locked gate, or the access points are too far apart. Maybe I’m locating a pipeline system where one access point is a quarter of mile in one direction and a quarter of a mile in the other direction, and I have to locate somewhere in the middle. Using this inductive locator, I can locate anywhere I want if I have a general idea where the utility is.” For this kind of locating, Koch uses the Pipehorn high-frequency locator, which operates at a frequency of 480 kHz, considerably higher than other mainstream multifrequency digital instruments. (Pipehorn also makes a dual-frequency locator-480 kHz and 9 kHz.)

“Higher frequencies are good at overcoming gaps and troubleshooting lines that are not in the best shape,” says Koch. An example is when I was called out to locate a gas line on

Credit: Pipehorn
Hand-held sensors can be indispensible when direct-connect detection is not an option.

a farm where the utility to a number of out buildings had been privately installed. The system had been buried with a tracer wire, and when I hooked up to it I located maybe 20 or 30 feet, and then my signal died. I’ve been at this long enough to know what happened-the tracer wire had been broken by a shovel or fence point or something. There was probably a total of 500 linear feet of the utility that had to be located, but it had been damaged repeatedly. Most locators would have thrown up their hands and advised the property owner to shut off the gas and dig. But by moving the Pipehorn transmitter around repeatedly, from each little piece of wire to another, I was able to sew together this whole system over the course of about an hour. This was a locate that literally would have been impossible with any other piece of equipment. The Pipehorn is fully manual and fully analogue, which allows you to adjust to it to infinite degrees of sensitivity, and this capability was also important for this job.”

The third EM method is the sweep that Dodd talks about. “Locators are taught to always hook up to your conductor and use the lowest frequency that will run on the conductor. Low frequency will give you better isolation in congested areas. But our ultrahigh frequency is best for sweeping and poor conductors, which is basically the vast majority of the application among contractors. A contractor can keep a locator on their truck and to make a quick double-check to make sure they don’t hit anything when they stick the backhoe in the ground. Pacific Gas and Electric just bought 450 Pipehorn pipe and cable locators so their construction crews can sweep before they dig. They call it a safety sweep. The Common Ground Alliance is recommending that in addition to making the call right before you dig, contractors do a quick sweep across the area. If you can walk a straight line and keep a transmitter pointed and a receiver, even somebody who’s never touched a locator before can be an expert sweeper in 10 minutes.”

Using GPR
Ground penetrating radar (GPR), the other tool in the locator’s toolbox, has come a long way in the past 10 years, with better user interfaces and better display for analyzing results. It offers two capabilities needed by locators: the ability to locate nonmetallic pipe, and to find utilities blind. “GPR is not fringe technology anymore in the locate world,” says Wolf. “MALA offers a targeted GPR product designed specifically for utilities location. We have customers who literally hang the Easy Locator off the back of a truck just like a vacuum excavator. They do a quick scan, mark the ground, pot hole it and they’re done.”

Wolf tells a typical GPR application story. A horizontal directional drilling contractor was hired to install a new electric feed with a directional bore in a condominium complex in Hutchinson, FL. The list of unknowns included water, sewer, the fire protection line for the hydrant system, and the original major electric feed. The nearest manholes were several feet away, and both sanitary and water lines were plastic. The public utilities didn’t provide locate services beyond the meter, and the contractor hired Ground Hound Detection Services Inc. of Boynton Beach, FL, which used GPR to locate a 4-inch PVC water line and 8-inch PVC gravity sewer line directly in the HDD trajectory. Doing a grid of the corridor and performing several GPR scans, the field crew picked up an additional utility not anticipated in the proposed HDD path, located it back to its source off the property, and discovered it was the existing main electric supply to the condominiums, 8 feet off from where the power company had graciously marked it. Access to the metallic fire protection line was so far from the HDD path that conventional EM tools could not transmit a carrier signal to provide an accurate locate. All targets were verified with vacuum excavation, including the erroneously marked underground power line.

Mason describes a project that illustrates what can happen when a contractor gets impatient or doesn’t want to spend the money to do the job right. “The project was a large mall expansion. The water mains were plastic with no tracer wire. If we hadn’t brought out the ground-penetrating radar, the water mains would have been hit and the contractor would have shut down the entire mall. It turns out that happened about a year-and-a-half later. A different contractor hired a locator who didn’t recommend GPR, because they didn’t have it. The contractor let that go and went ahead. He struck the same water main we had protected a year-and-a-half before and shut down the entire mall for the rest of day. The strike was about 9:00 or 10:00 in the morning, and they didn’t get it fixed until the middle of the night. Using GPR, we had developed a map and given it to the original contractor, who I believe passed it on to the property owner, but it turns out the property had been sold.

“That’s one thing we emphasize: mapping. One of our clients is a large auto manufacturing facility. They can’t afford to have a map of the entire property made at once. So every time we go out there to do a project for them, as we locate, we are constantly using the capabilities of Sensors and Software Inc.’s GPR to GPS in the utilities and in that way are gradually updating their GIS map. That’s another important capability of GPR.”

But along with the capabilities come liabilities. “The basic physics of GPR is that the signal is electromagnetic, which means it’s composed of an electrical side and a magnetic side,” says Masters. “In order for it to work, these components need to stay together. Where the soil is not conductive, GPR works really well. The signal stays in the form we need it to and continues to penetrate the way we want it to. Sand is great for GPR, but clay soil isn’t, nor are areas with a high water table. If you’re looking for plastic and the soil is bad, you may be left with vacuum excavation or test pits. Contractors need to keep that in mind when they’re considering GPR for locating.”

Koch reminds contractors that another challenge in using GPR is interpreting what’s shown on the screen. “If you’re using EM, the unit makes a noise and a little bar graph or meter on the screen tells you you’ve found what you’re looking for. With the GPR unit, the user looks at an image on a screen that’s not unlike an ultrasound. This means that using GPR requires decision making from the user to determine what they’re looking at. Most of the companies that sell the technology provide training, but it’s really experience on the job after that initial training that gets you the expertise you need to determine and understand what you’re looking at. ”

“The technology is not daunting to learn,” says Greg Johnson at Sensors & Software. “But it’s also true that, if somebody is going that route, they really need to use it regularly so that they’re comfortable. One of the worse situations I run into in training is companies who say they bought the equipment a year ago, nobody’s touched it since then, and now everybody’s scared of it. If you’re going to buy it, make sure there are one or two people in the company who use it regularly. If you’re never going to be in that situation, then hire a professional who does this for a living.”

Or, says Tony Fisher, president of Fisher Concrete and Excavation in Green Bay, WI., you can do use SubSurface Instruments’ All Materials Locator. “We do a lot of interior work such as machine bases. In one case we were doing a water-jet base inside a local fabrication shop. Everybody knew there was a 2-inch water main that ran across the inside of the building. But nobody knew where it was, and it was installed without trace wires because the code doesn’t specify that on interior lines.

“Three weeks before we had worked at SubSurface Instruments’ test facility. We took the floor out and then dug in different sample utilities, ranging from PVC pipe to half-inch conduit to direct buried telephone wire. So when we had the problem with the interior water line, I got the bright idea to call them up ask them if I could try it. They gave me a quick run through, but I was really skeptical. I walked around the machine base with it-basically you’re looking for a pattern-and within 10 minutes of walking around, I had what I thought was a good pattern. I told my guy to dig right there. The second shovel of dirt he found a 2-inch water main. No trace wire, just the plain old PVC pipe.”

According to Scott Rauen at SubSurface Instruments, the AML uses radio-frequency technology that looks for a change in density. “It puts out a 2.4-GHz frequency into the ground, and when it comes across a change in density, it redirects that signal back to the instrument. This tells the operator there’s a change, and it’s up to him to figure out if it’s a telephone line or an electric line. What we’ve found is that when contractors call in for a one-call ticket, they sometimes come in with their equipment after an area has been marked and destroy a lot of the marks. With AML all you do is go to a flag with a mark on it, and you start looking, and you can refresh the marks. This way they don’t have to call for relocates.”

After his first experiment, Fisher purchased an AML. “It costs about as much as a decent wire locator,” he says, “but the way I look at, if I had hit that water line in the middle of a machine shop, I would have had water spraying all over a multimillion dollar machine. The only other alternative was to come back in their off time, when I could have shut the water off. In that case it wasn’t feasible, because their water jets are up 24 and seven. Every tool has its purpose. Are any of them 100%? They never will be that, and there’s always the human error factor. But everywhere I use this, people are in awe. It’s a real quick easy way to go, and it’s a heck of a lot better than somebody’s guess about where PVC pipe goes. I looked into getting GPR, but it’s much less expensive. And AML doesn’t take a rocket scientist to operate.”

“What contractors and locators need to understand,” says Masters, “is no matter what the technology is, you still have to do all the grunt work of walking about back and forth and figuring out where everything is going. You have to look for the valves and trace things out and make marks in the ground and think out where your utility is going and find a logical end point. It’s just not avoidable.”