Finding What Lurks in the Subterranean Depths

March 1, 2007

The days of explosions, electrocutions, and excessive damage should have passed. Almost all of us are more careful about how we approach unseen, underground obstacles. The technique of discovering what is buried by ramming a loader bucket, dozer blade, or simple shovel has shown its shortcomings and long-term costs. Don’t do it! The way to find out what’s below the surface of your job site is to look. It’s like an x-ray. You usually can’t see where and how a bone is broken or a lung is in danger of collapse just by looking at an arm or chest, but the x-ray can tell you. Think of today’s locating instruments as x-ray machines. Rejoice that those instruments are much less expensive and much easier to work than your local hospital’s x-ray machine.

You can, of course, get a good start by calling your local One Call (or similarly named) program to find out what obstacles are known to be buried where you want to excavate. The unpleasant truth is that we seldom know accurately what is buried. In some communities you are advised to call whenever you are going to dig deeper than 6 inches! That’s less than the length of the average garden spade. When the neighbor of my office had a new CATV line installed, the existing utilities were, in fact, just about a spade deep! No wonder the lilacs were so feeble.

“Ground penetrating radar [GPR] sounds like something extremely scientific or a tool straight out of a space movie, doesn’t it?” asks Cheryl Duszak at Geophysical Survey Systems (GSSI). “Although its name rings of technicality and science fiction, it is one of the most versatile, easy-to-use locating methods on the market. GPR was pioneered by GSSI over 35 years ago and began as a tool for scientists. The time since then has been used to simplify and perfect the equipment so that anyone in the utility locating, concrete scanning, road inspection, or construction lines of work can use it with ease. GPR systems work by sending a tiny pulse of energy into the ground from an antenna. An integrated computer then records the strength and time required for the return of any reflected signals. Subsurface variations like pipes [metallic and non-metallic], wire, and voids will cause signals to bounce back. When this occurs, all detected items are revealed on the computer screen in real time as the GPR equipment moves along. The data collected is then analyzed and specific recommendations can be made in relation to drilling, digging, and other underground procedures.”

Dan Welch is the training manager at GSSI and he runs classes (with eight or fewer students per class to allow for adequate individual attention) and teaches three different methods of learning to ensure that each student goes away with a firm knowledge of what GPR is all about and how to use the equipment in real-life situations. “Students find that GPR is a much easier technology to learn than they may have believed,” comments Welch. “Our training exposes students to a variety of data samples and situations in order to prepare our users for real-life situations.” The first part of the course offers a classroom setting where students new to GPR learn how radar actually works, with plenty of theory and scientific explanation. The second part involves an instructional tour of the GPR systems in the field, for real-life situations. The third and final class has students using GPR on their own. The data are collected and transferred to laptop computers, and students learn how to display scans and use 3D imaging.

Photo: GSSI
Ask your supplier about training for underground locating. It’s worth the brief time it takes to achieve.
Photo: Subsurface Instruments
Two popular aspects of locating devices are their light weight and ease of operation.

More on GPR
“In many cases, GPS is the only practical, non-destructive method available to locate non-metallic and non-conductive utilities such as cast-iron, PVC, or other plastic pipes, concrete, and various composite pipelines,” notes Erica Davis for Mala GeoScience, another worldwide leader in the GPR field. “GPR systems like the Easy Locator and the X3M can accurately locate and determine depths to utilities of many types, including pipes, cables, conduit, and duct banks in soils favorable to the GPR method.” Mala says its Easy Locator is affordable and designed uniquely for the utility locate professional. Among options available are the IXM upgrade, which records data collected in jpeg format for later printing and download, and the EXM+ monitor for readability in direct sunlight.

That readability just mentioned is important. Much of your locating work could be in bright sunlight and you will require a screen on which you can see the results. The Mala RAMAC/X3M has a monitor that provides the resolution you would expect from only the best laptop monitor, with a display that is fully readable in sunlight. The display is what is known as transreflective. About the middle of last year Mala introduced a Rough Terrain Cart for use with the two models mentioned. The cart offers oversized wheels and a strong frame with quick-release wheels for easy dismantling and transporting. “This new cart is the SUV of GPR vehicular systems,” adds Davis.

Carts are popular for users of GPR systems, because they allow you to move steadily along the area you wish to investigate (such as sidewalks, lawns, and roads) and they carry the weight of the system with little effort to yourself. Sensors & Software offers the Noggin SmartCart. The large wheels on the little cart make it an easy device to push; it has been described as easier than pushing a mower with no grass to cut. The real-time display is visible on a digital video logger, which is mounted at the handle of the cart, clearly visible to the user. There are several models of Noggin available. “GPR is particularly useful for locating and differentiating between metallic and non-metallic pipes and conduits,” comments the company. “Noggin can operate in a wide range of environments, rain or shine, and be stored at outside temperatures.”

Colors, Colors Everywhere
Each detected utility below the surface is identified on top by a spray or flag of bright color, and each color tells the next person at the site what is there … if that person has been taught what each color stands for. Obvious? Not really. When a new worker sees a splash of color at the spot he is supposed to dig, he knows something is there. He should not think that the chosen color just happened to be the locator’s favorite. (For example, green doesn’t mean the utility locator was an Irishman and red doesn’t mean he’s a Kansas City Chiefs fan.) You should be aware of the meaning of the colors in your state and your employees should be aware, too. We were a little surprised that the color code isn’t national. Perhaps it is, but we did find a few minor differences in several states.

Red indicates electric lines below; orange denotes telephone, cable TV, fire and police communications; yellow is gas and oil; blue shows us where the water lines are; green is usually the sewer, but we have seen brown for sewer and green for storm drains; pink indicates surveying in progress; in Illinois you can find purple for non-potable water and slurry lines; white indicates that excavation is proposed here. Although there are minor differences, the key (= the most dangerous) ones tend to be the same everywhere; those are the red, orange, yellow, and blue. Learn them and make sure your equipment operators know them. Here’s a sensible piece of advice from the State of Michigan. If colorful flags are used rather than squirted spots, they are attractive to children. Remind children not to remove them and don’t imagine you can simply put them back where they came from. Most of us cannot remember exactly where the flags were located. In these matters, accuracy is the name of the game and the key to harmless excavation. Operators of vehicles and machines going on the surface in the locating area should be advised not to flatten, erase, damage, or rip out any identification symbols. Children are not the only culprits.

Photo: Ditch Witch
Locators are simple to use and easy to carry.
Photo: Sensors & Software
The readout is positioned on the cart’s handle for easy reading.

Worth the Investment
Caution or skepticism about new devices in construction has surprised (and annoyed) some manufacturers, but Ridge Tool Co. seems to understand that it is the true value of a new tool—its value onsite—that makes the difference. Ridge Tool Co. already has more than 300 types of tools in 130 countries (mostly with the famous name Ridgid) so its concept of design and marketing has good history. When they introduced the SeekTech line of locating tools, it was after investigation of the market and consulting with potential users. “The market has been very pro Ridgid locating,” observes Mark Fleming, senior product manager of diagnostics for the company. “It is always a concern with a new technology that consumers will be slow to start. With our locators, however, we have minimized this concern by making our technology similar in use to that of existing technology. We simply provide the end users with more of the information they need, when they need it, to make better judgments when locating.” Here’s the practical, on-the–job site aspect. “The other factor we have in our favor causing strong market adoption is the frustration people have with mismarked or unmarked utilities,” continues Fleming. “The Common Ground Alliance estimates that, in 2004, there were 675,000 utilities hit. There is no silver bullet that will solve all of the problems in utility locating, but we at Ridgid strive to develop technology that makes locating these utilities faster, easier, and more accurate.”

A point that was made by Scott Aiello, director of marketing, diagnostic equipment, at Ridge Tool Co., was that accuracy is the most important factor in a locating device, followed closely by speed and confidence on the part of the user. He also mentioned the important factor that the Ridgid SR-20 will tell the user if the information he is getting is distorted or not. Ask any user. That is critical to accuracy. With the confusion of buried utilities in many urban areas, it can be rather like trying to identify a one-eyed member of a flock of wild geese passing overhead. (It can probably be done, but with difficulty.) Any device that helps reduce the problems of confusion is a practical godsend. The SR-20 combines the audio signal with the visible information on the mapping display (offering left-right guidance arrows, line direction, proximity number, and signal strength) so that the user can confirm the locate through the distortion that might be present in congested areas.

The depth of the hidden obstacles is of paramount importance. You should certainly check with your supplier or manufacturer about the efficiency of their devices at specific depths below ground. For some applications, the ability to see what is present at 4 feet below the surface is fine. The ability to look even deeper than that may be essential at some sites. The responsibility for selecting the correct technique and instruments is yours. Virtually all the devices advertised and marketed are good performers at the levels they offer and it is the user’s task to choose which levels are those most suited to his or her daily requirements. Some of the devices we mention in this article may be too much for your needs and not, therefore, wise investments. Some frank questions and site information from you should get the right answers from suppliers.

Photo: Ridge Tool Company
Note the colored markers and flags this man is using.

At the Job Site
“Easy-to-operate” is an important feature of locating devices. Ditch Witch makes and markets the Subsite product line; it includes several interesting locating tools. The new 300 SR/ST is designed to locate buried telephone, power, CATV, gas, sewer, and water lines. It is “easy to operate.” The receiver runs on six C-cell alkaline batteries, with a battery life of about 40 hours, and it shuts off after five minutes if no key is pressed. It’s almost a foot long and weighs only 5 pounds. The transmitter, with the same length and weight, uses six D-cell alkaline batteries and that battery life is about 150 hours. This system has found good acceptance by contractors, utilities, and rental yards.

“Job site awareness is critical,” advises John Bieberdorf. “You should gain as much knowledge as possible about the facilities before pulling out your pipe and cable locator.” Bieberdorf is product manager for Ditch Witch underground construction equipment. “Make use of any available facility records that indicate approximate location, number of facilities, and access points for buried facilities within your job site area. The facility owner usually has those records.” As those facility records are not completely accurate sometimes, Bieberdorf recommends that the crew should look for poles, dips, enclosures, pedestals, valves, meters, risers, and manholes to ascertain if there may be additional facilities or other obstacles not recorded.

“Employers should also understand the process involved in locating,” notes the Ditch Witch expert. “Pipe and cable locator systems actually locate the electromagnetic field produced by the AC current flowing on the line, not the pipe or cable itself. Many non-metallic pipes and cables have tracer wires buried next to them that can conduct electricity.” After identifying the best access point to the target line, the operator can place a signal on the line either by direct connection, clamp induction, or broadcast induction. “The most accurate method is direct connection, when the signal travels from the transmitter through the target line and returns to the ground stake,” says Bieberdorf.

To set up a direct connection, remove common grounds and connections to other lines; that prevents the signal from being placed on untargeted lines. Insert the ground stake to the left or right of the target line’s suspected path. The transmitter’s black ground wire should not cross other lines. Connect the black transmitter wire to the stake. Remove any paint, dirt, or corrosion from the target line and connect the red transmitter wire. On the transmitter, select the appropriate settings to match the conditions of the particular locate. Use the minimum power level and the lowest frequency required to locate the target line. As a rule of thumb, the higher the frequency, the easier it is to couple to adjacent lines and the less distance the signal travels. Now set the receiver frequency to match the transmitter frequency. Conduct a 360-degree sweep around the access point where the transmitter is connected to the target line. This will help locate the direction of the target line.

You can identify the target line by finding the location with the strongest signal response. Sweep the receiver perpendicular to the target line as you walk along its path. Retrace the path and mark with the proper color paint or flags. Ditch Witch notes that the receiver-transmitter system is accurate when used properly, but the only way to verify the exact depth and location of a target line may be to expose it. “Select critical areas along the marked path of the target line, and then excavate to the target line,” Bieberdorf advises. There are innovative products available that can make the process of locating, repairing, and replacing buried utilities more simple today, such as GPR systems, pipe-bursting systems, and vacuum excavation.

This shows you the size and convenience of today’s locating devices.

Buy the Product or Pay for the Service?
The big question for most contractors is whether to purchase their own locating equipment or hire somebody else (a professional locating company or individual) to do it for them. Most contractors told us it would depend on how often the tool was needed (making the choice similar to that in the purchase or rental of any equipment). The professional locator may seem more expensive but he or she will probably do the job more quickly, and possibly more accurately, and the contractor won’t have equipment in his yard not needed for another three or six months. There is no correct answer. The only requirement is to get the locating done as accurately and productively as the job demands.

Here’s a real example of how somebody decided to get the right equipment for a specific job. All Flow Solutions signed a large contract with the Moreno Valley Unified School District in Moreno Valley, CA. The district decided to construct lunch shelters or outdoor covered cafeterias at 20 sites for several of its schools. It was also decided to locate utility lines in advance to save the school district significant costs for materials and design. “I decided to use the SR-20 locator because I found it easier to use compared to other locators,” explains Preston McCormick, co-owner with his cousin Rock Tremblay of All Flow. “Also, we have been pleased with the quality of other Ridgid equipment that we own.” It was the signing of the large contract that prompted the owners of All Flow to reassess its equipment and procedures. They decided that hiring private locating contractors for this project would be costly. “The tool we used gave us information that the ground penetrating radar does not always give,” adds McCormick. “The penetrating radar can only locate lines that are up to 4 feet down and the SR-20 goes deeper.” So pleased was the school district with the efficiency and economy of the work done by All Flow that it recommended All Flow to another construction company engaged in installing portable classrooms, where there were requirements to determine points of connection and utility locates for the excavation work.

Like most decisions in grading and excavating that concern equipment use and purchase, the key consideration is the frequency or regularity with which the equipment will be needed. If you have one or two paving jobs a year, you probably won’t purchase pavers and rollers. If you have irregular requirements for locating underground utilities, you’ll probably hire an outside expert to do that work. It would still be wise to ask that professional what products he uses, to be sure that they are adequate for your project needs. To be practical, productive, and profitable, you may not be able to justify purchasing equipment described in this article, but you should certainly be aware of devices and technologies available.