In January 1995, pile-driving crews knocked out all electrical power at Newark International Airport’s three passenger terminals and forced the airport to close for a day. All international and many domestic flights were canceled or diverted from Newark, which handles 1,200 flights a day. Electricity to the air traffic control tower and runways was not affected, but there was no power for baggage systems, computers, lights, restaurants, escalators, or jetways.
“That is what prompted our contract with the Port Authority,” says Jonathan Tan, president of Geotrack Inc, a subsurface engineering firm based in Lake Forest, IL. The firm is on call to do all necessary utility locates for facilities operated by the Port Authority of New York and New Jersey, which include all three New York area airports, the George Washington Bridge, and other bridges and tunnels. Geotrack works every day for the Port Authority.
“We probably do about 1,000 locate tickets per month for them,” says Tan. “And in 17 years with the port, we have never had a hit. We do things a little bit differently. We take our time, and we don’t want to be paid per ticket. We are paid either by a unit cost, such as linear feet of a utility, or by the hour or by a daily rate.”
Some contractors work for $8, $10, or $20 per ticket, which Tan calls ridiculously low. The low prices prompt locating contractors to emphasize the number of tickets they handle, and they compromise quality. “That is a big problem in our industry,” says Tan.
By all accounts, the industry still doesn’t do a very good job of locating underground utilities, but it does better than it used to. Years ago, utility “hits” or strikes, averaged in the area of half a million per year. Since the one-call system was developed, that has dropped to about 250,000, says Tan. Still, the one-call system locators average one hit per hundred locates.
An example of a Geotrack project comes from the Amtrak/Union Station in Chicago, which has been upgrading its track, buildings and facilities for high-speed rail. “There were multiple contractors at Union Station and we were responsible for marking out utilities during the summer of 2010,” says Tan. “It was a low six-figure contract for us.”
Workhorse of the Industry
Tan says an electromagnetic detector is the workhorse of the utility locating industry. Such a detector is used to locate pipes that are metal. Geotrack uses an electromagnetic system to trace utilities with either an inductive or deductive method. With the inductive method, you have access to one end of a pipe. You clamp onto that end and induce a signal through the pipe from a transmitter. The receiver, a separate device, can trace the utility out for hundreds of yards if the signal is strong, Tan says.
The deductive method is used if there is no access to the utility. A transmitter box emits a signal and is held by one person. A second person carries the receiver. “That is a method to detect undocumented utilities,” says Tan.
Another method used to locate utilities is ground-penetrating radar (GPR) for pipe that may not be locatable by an electromagnetic system. That could include concrete or plastic pipes. Again, a transmitter and a receiver are used. Tan says the Geotrack’s GPR system looks like a fancy lawn mower.
“With a GPR system, the equipment is right there on top of the ground, sending a signal down into the ground,” says Tan. “The signal reflects back from anything hard that can be visualized in the ground, such as rocks or pipes, and reads out on the screen. In order to determine if it is a pipe, you need to cover a site in cross sections. Once you see a pattern, for instance, that an anomaly occurs at the same depth in linear fashion, you know it is a pipe. If it is just a rock, it will show up in just one spot and not in linear fashion.”
Tan says GPR has limitations, as does all detection equipment. GPR systems do not work on clay soils to detect clay pipes, because the clay pipe is similar to the ground. “High water tables and clay put limitations on ground penetration radar,” says Tan. He says such systems are good to about 10 feet below the surface.
Peter Masters is an application specialist with Geophysical Survey Systems Inc. (GSSI), a manufacturer based in Salem, NH. The company manufactures GPR equipment for a number of different applications, including utility detection.
“People I talk to tell me they use the one-call system to come out and mark their assets, but they find they often still need more information,” says Masters. “Not everything was located.” He says construction contractors can do their own locating to double-check the one-call system. “They either are going to run into unforeseen problems or they can do their own locating and try to solve that problem themselves,” says Masters. In the current economic climate, he notes that idle equipment and crews wreak havoc on project budgets. Being more cautious about locating before the job starts saves time and money.
The PL2000 works with three frequencies to meet different circumstances.
GSSI has two primary products for the utility market: an entry-level product called the Utility Scan LT, and a full-featured utility scan system. He says the entry-level system is easy to use, quick to get started, and easy to read. It sells for approximately $14,500.
The full-featured system has a range of options. You can connect various antennas to it, and it offers optional ways to display data. “You can either display information in the 2D real-time format or you can produce 3D images with it,” says Masters.
GPR is affected by the conductivity of the soil that it’s moving through, so learning about soil types in your area is the first important step. “Like any technology, GPR has its limits, so learning more is key to succeeding practically and being able to set the right expectations for clients,” says Masters.
In a utility locating application, a GPR user will typically use a frequency of 400 megahertz to scan through dirt, asphalt and concrete, but there are other antennas near that range. “In general, we match the antenna to the job at hand,” says Masters.
“The lower you go in frequency, the deeper the antenna is going to go,” says Masters. “But the resolution on your scan goes down with that as well. Lower frequency means more depth, less resolution. Conversely, higher frequency means less depth but you get better resolution on your screen.”
GPR is complementary to any other locating instrument that a user may have, Masters says. “They all have their benefits. With the standard electromagnetic locator, if you can clamp onto a pipe, you can quickly and easily follow that pipe a good distance. It is very quick and efficient”
GPR systems work well alongside electro-magnetic (EM) systems because GPR is not subject to the same type of problems that EM locators are, Masters says. For example, if you have an area that is highly congested with utilities, that might be a problem for EM, but not necessarily for GPR. Also, GPR can help if you’re searching for a plastic pipe with no tracer wire on it.
“And so GPR can see pipes that cannot be located with the EM instrument,” says Masters. “My point is, if you use the EM, and you use the GPR, you have gone pretty far in terms of what is available to you in finding as many utilities as possible.”
Matt Manning is products manager-electronics for McLaughlin Group Inc., which manufactures utility locating equipment and vacuum excavation equipment. Construction contractors do well to use their own locating equipment to improve upon the locating precision of the one-call system, Manning says. Each state has a legal window of space in which the one-call system will mark a utility.
“If you are looking for a 1-inch cable within a 3-foot window at a depth of 3 or 4 feet, that is a pretty big area to be finding a cable in,” says Manning. “But if you get a multifrequency utility locator that gives you depth, then you’ll have an idea of how close the one-call mark is to the actual location of the utility and you’ll have some idea of how deep that line is. Will I have to dig around 3 or 4 feet or 6 feet?”
McLaughlin offers the Verifier G2 locator and the Vision FLX. Both are electromagnetic detectors but the FLX can also find damages in electric cable, telephone and TV cable. Most construction contractors would use the Verifier G2, Manning says, because he would not need the added sophistication of the FLX model.
In-Cab Utility Warnings
On July 1, 2010, Caterpillar announced that it had acquired all assets of Underground Imaging Technologies Inc. (UIT) through its majority-owned affiliate, Underground Imaging Technologies LLC. UIT is an advanced geophysical services company and technology developer based in Latham, NY. The acquisition gives Caterpillar the ability to provide geophysical services-utility locates. UIT specializes in providing 3D representations of underground utilities and other targets.
If an excavator, for example, is fitted with Caterpillar’s AccuGrade GPS, UIT’s digital dataset can be uploaded into the cab to show the operator avoidance zones in real time as work progresses. In other words, a machine operator can see underground utilities on his display screen and avoid them in real time. “According to the Pipeline and Hazardous Materials Safety Administration, $1.7 billion worth of property damage and 421 deaths would have been averted had (this technology) been available and utilized,” says Mark Wellborn, chief executive officer for Underground Imaging Technologies LLC.
All of UIT’s subsurface mapping activities are tied to an extremely accurate global positioning system (GPS) or a robotic total station that provides the required spatial information and can provide the actual elevation-not just the depth of cover-of all targets, says Caterpillar. Extensive post processing and interpretation of the developed datasets, acquired from favorable soils, result in a foot-by-foot map with accurate three-dimensional target locations formatted for computer-aided design (CAD) or other geographical information system (GIS) compatibility.
“UIT’s geophysical expertise and advanced technologies add dynamic new subsurface infrastructure capabilities to our Connected Worksite offerings,” says Hans Haefeli, a Caterpillar vice president. “But most importantly, this service provides detailed information that enables design engineers and contractors to proceed on underground projects with a clearer picture of the subsurface environment, which contributes to both project cost savings and increased safety on the worksite.”
Ridgid Tool Co. makes transmitters and receivers for utility detection, as well as inductive signal clamps and many of the accessories required for utility line traces, says Josh Sooy, senior marketing manager for the company. Ridgid Tool’s two main locators, or receivers, are the SR20 and the SR60. “The SR60 is our high-end receiver and has a few extra bells and whistles that our SR20 doesn’t have,” says Sooy. “And the SR60 supports a wider range of frequencies.”
One can dial up any frequency up to 35 kilohertz on the SR20. “So it has standard frequencies that are part of the default and you can select any brand of transmitter,” says Sooy. “The SR60 will go all the way up to 490 kilohertz.”
“We have three transmitters for utility line locates,” says Sooy. “They have different powers, and some are better at induction and some are better at direct connections. But those transmitters can be used with either of our receivers.”
The effective depth for Ridgid’s detection equipment ranges up to 20 or maybe 30 feet under ideal conditions. Effective depth of the equipment depends on many variables, including soil type and depth and height of the water table. “Some of our competitors claim their systems go 100 feet deep and that is an absolute 100% optimum situation with your transmitter turned up as high as possible,” says Sooy.
The frequency you use depends on what kind of utility you are trying to locate, says Sooy. Certain frequency ranges work better for gas lines and certain frequency ranges work better for cable or fiber optics. “Cast iron is completely different from water line,” says Sooy. “So you have a set of frequencies and when you go out there, you try different things to line up better. You want a good quality locate. Certain frequencies are more prone to bleed off on other lines around them. So having multiple frequencies in your equipment gives you more versatility in locating a wider range of utilities. You might even use a different frequency if it rains or if it is really dry in the middle of the summer.”
The utility locate business is very good for Ridgid Tool, Sooy reports. People are becoming more aware of the dangers and costs of utility strikes. “They see the benefit of locating everything before they dig,” says Sooy.
Subsurface Instruments Inc. offers two models of pipe and cable locators. One is the PL1500, which is offered in two frequencies. “We offer two frequencies because the water industry has a better tendency to stick with higher frequencies,” says Scott Rauen, sales manager. “So water and sewer companies would probably order the PL1500 because it would work better in that application.”
Lower frequencies are better for the cable TV, telephone and electrical cables because they are not buried as deeply as water and sewer pipes. “If you are working in depths of 10 to even 20 feet, many times that higher frequency will have a better opportunity to get to the surface for your receiver to pick it up,” says Rauen.
Gaskets at water pipe joints can pose a problem for some frequencies. “The higher frequency will jump that gasket and allow it to continue to locate past the 20 foot mark,” says Rauen. “The lower frequencies have a tendency to maybe get one or two pipe lengths and that is about it. It loses the signal after it tries to jump one of those gaskets.”
The second model of pipe and cable locator offered by Subsurface Instruments is the PL2000. It can work in three frequencies, which allows one person to locate all utilities, Rauen says. “If you have two or three or even more frequencies available to you, you have a better chance of locating your utilities in really difficult circumstances,” he says.
The PL2000 has frequencies ranging from 27 kilohertz, which is the highest it offers, to 8 kilohertz (similar to the PL1500’s low), and a very low frequency of 5/12 hertz.
From MALA comes the Easy Locator, which the company says is the world standard in Ground Penetrating Radar (GPR) Systems for locating buried objects such as non-metallic and non-conductive utilities. Based on MALA’s more than 60 years of experience in product research and development, the Easy Locator is designed solely to meet the needs of utility locate professionals. The Easy Locator is an invaluable tool to detect and locate utilities such as PVC water and gas lines, ductile iron, concrete, terra cotta, or other conflicts.
Adding to the already powerful features such as seamless GPS integration and jpeg screen capture (IXM+) is 3D grid capability. The latest functionality allows the user to collect data on prescribed grids and represent the data as a time slice or “virtual excavation.” In addition to this latest feature is a depth calibration tool that readily computes the depth to targets onscreen.
Ditch Witch recommends that contractors use locators to verify the mark on the ground before the work is done and then throughout the job. There may be times that utilities are on private property and the contractors would need a locator to mark utilities that they will be working around.
The Ditch Witch organization offers a full range of utility locators from single frequency units to multifrequency units, including GPR.
The single frequency range includes inexpensive units targeted for rental and private markets. Those include the 150R/T and 250R/T locators. Other products such as the 830R/T are designed for the water and gas industries and have specific performance requirements for the needs of the markets.
Ditch Witch also offers multifrequency products like the 900 series locators that are for advanced users and one-call companies. The GPR product, 2450GR, is one of the only dual frequency GPR’s on the market today allowing the user to scan an area in two different frequencies simultaneously which minimizes time on the job.
