How Does Ground Penetrating Radar Work?

Perhaps you’ve seen ground penetrating radar (GPR) services performed on documentary TV programs, and wondered how this technology is being harnessed to locate utilities and other buried objects. From a promising start in the early 20th century, using radar pulses to locate buried objects was largely employed by the military until the late 1980s, when the first equipment for consumer use was developed. While still utilized by geologists to study bedrock, soils, groundwater, and even ice, GPR is primarily the preferred tool used by law enforcement  and in engineering applications, such as utilities mapping.

A now standard application for ground penetrating radar is in locating underground utilities. Standard induction utility locating tools require conductivity with the buried object. However, as most utility lines and sewer pipelines are vinyl-clad conduits, or are constructed from concrete or PVC, such tools prove ineffective. As GPR detects variations in soil properties below the surface, it is ideal for locating these non-conductive utilities.

GPR is Not an Intuitive Technology

How do ground penetrating radar services work? These systems, which resemble a lawn mower, work by sending a small energy pulse into the soil via an antenna. A computer, which is integrated into the system records the time and strength required for the return of a reflected signal. A signal will only return if it encounters and reflects off a stationary object below the surface. Reflections are produced by many different natural and man-made materials below the surface including rocks, debris such as broken glass, building materials, and pipes and wires. Such reflections or bounce backs, are shown on the computer screen in real time as the GPR equipment passes over it. GPR equipment is sensitive to the point where it can indicate if the object is metal or not.

Ground penetrating radar equipment is not an intuitive technology. In fact, it can take days or even weeks of specialized training to use and interpret reflected findings with accuracy. Many municipalities now require that before homeowners and construction teams break ground, that the site’s utilities are mapped to prevent damage and more serious issues. As these sites fall outside of local One-Call system jurisdictions, private utility locating companies, such as PULS, Inc., provide accurate and reliable solutions using GPR and other supportive technologies to ensure the safety of any underground utilities at any worksite. For more information regarding our ground penetrating radar services, please contact us at (800) 883-6855.

Gas Leak Detection and Prevention Tips

On the job and around your home, vigilance in performing routine maintenance is extremely important. This is especially true for those who work in the manufacturing, warehousing, and other industrial sectors. Any facility where there are gas and/or propane systems present, should perform two types of gas leak detection surveys every year- mobile and walking surveys. Not only will these ensure the safe handling of machinery and facility maintenance, but also the safety of everyone present. In addition, such surveys will comply with agency regulations, as well as Department of Transportation Pipeline Safety mandates.

Gas Leak Detection Tips

Inside their premises, residential property owners may engage a home inspector who will detect leaks using equipment designed for that purpose. If any leaks are found, these will be tagged, the premises vacated, and the local utility’s emergency unit called for immediate remediation. But what about underground leakage from damaged or degraded lines? For private industries, when the plant facility has been inspected, how to determine the state of underground lines and other potential lead hazards under the property’s parking lots, driveways and grounds?

Property owners seeking gas leak detection services, should contact a reliable, and trusted underground utilities locator, such as PULS, Inc. In addition to our walking and mobile surveys, which detect leaks from gas, electric, telephone, sewer and water system manholes, we will also also inspect mains, valves and meters. If leaks are detected PULS, Inc technicians may utilize one or more of the most advanced technologies available today, including ground penetrating radar, closed circuit TV, vacuum excavation, and electromagnets to locate the precise source of the leak. For more information, call us at (877) 661-2530 or fill out our form.

Best Management Practice: Use Your State’s One-Call / Before-You-Dig-System

About five years ago in Saint-Hyacinthe, Quebec, a surveyor nicked a plastic gas line with an iron pin. At the time, nothing happened. But the following winter, a snow plow hit the pin, and a nearby house blew up.

The surveyor had not called his state’s “one-call number” before setting the pin – and the consequences proved catastrophic.

Fortunately, occurrences of surveyors causing damage to underground infrastructure are rare. “I know it happens, but the damages (so far) have been of a nature that they have not made a big enough story for it to be widely told,” said Curt Sumner, president of the American Congress on Surveying and Mapping (ASCM).

John Scrivner worked as an accident and claims investigator for Avista Corporation, which owns electric and gas utilities in eastern Washington state and northern Idaho: “I investigated cases involving surveyors pounding their survey stakes into the ground without first calling for locates. They damaged both high-voltage electric distribution lines and high-pressure gas lines. These accidents could have been catastrophic.”

The National Utility Locating Contractors Association (NULCA) sent a survey in February 2003 to primary members asking if they had encountered problems with surveyors hitting public or private utility lines.

“Overall, we found there was not a problem (among surveyors),” said Mike Bell, immediate past-president of NULCA. “But that doesn’t mean surveyors shouldn’t use their state’s one-call system. These systems are mandated – they’re the law. It’s in everyone’s best interest to call before any kind of digging, even if it’s to set a pin or a monument.”

There exists the potential for lawsuits should a surveyor or an excavator not properly use the applicable one-call system. “Utility companies do pursue restitution from those who damage their facilities,” Bell added.


What exactly is a one-call system? Literally, it’s a telephone hotline – oftentimes an 800 number – designed to initiate the process of providing no-cost utility marking in the name of damage prevention. The service is for contractors, homeowners, and anyone else who disturbs the earth, including surveyors.

Definitions of what it means to “disturb the earth” vary from state to state. In Virginia, for example, to disturb the earth – to excavate – means any operation in which earth, rock, or other material in the ground is moved, removed, or otherwise displaced by means of any tools, equipment, or explosives. Excavation includes grading, trenching, digging, ditching, dredging, drilling, augering, tunneling, scraping, cable or pipe plowing and driving, wrecking, razing, rendering, moving, or removing any structure or mass of material. (Source: Miss Utility Excavator’s Manual.)

In other words, anyone disturbing the earth even a few inches – especially those using mechanized equipment to do so – should use their state’s one-call system to determine where utilities are located.

“Many people are under the assumption that utilities are buried at 36 inches or greater, but this is not always the case,” Bell said.

Construction activities, grading changes, settling of the earth, and poor installation practices often can leave a utility much shallower than 3 feet. A utility company in Virginia reported that its infrastructure is as shallow as just 1 foot under the ground.

“My own personal feeling is that even real estate agents using augers to dig holes for ‘For Sale’ signs should call,” Bell said.


Each state (or a collection of states) has a one-call system. Some are state-operated; in other cases, the state government or a group of utilities contracts with a private company to administer the one-call system. How these systems work and what kinds of information they require from callers vary from state to state.

A study sponsored by the Office of Pipeline Safety (OPS) of the U.S. Department of Transportation’s Research and Special Programs Administration was conducted to determine the best of existing one-call notification systems and underground facility damage-prevention practices. OPS then sponsored an initiative that led to creation of the Common Ground Alliance (CGA), a nonprofit organization dedicated to the promotion of damage-prevention best practices. CGA is supported by a variety of stakeholders, including utility owners, contractors, and private firms. Since its inception, CGA has produced a “dig safely” video and also has published eight best-practices brochures that address each part of the damage-prevention process, including:

  • One-Call Systems
  • Planning and design
  • Reporting and evaluation
  • Compliance
  • Public education
  • Mapping
  • Locating and marking
  • Excavation

CGA also offers a toll-free national referral number to other state’s one-call numbers (1-888-258-0808) as well as a Web site that lists phone numbers and Web links of each state’s one-call system (

Two examples of one-call systems and how they work:

•  Minnesota’s one-call system, known as “Gopher State One Call,” grew out of a response to a pipeline accident in 1986. Minnesota law now requires anyone who engages in any type of excavation with motorized equipment to provide advance notice of at least two working days to Gopher State One Call. The utility-locating service is free to callers, according to its Web site (

Gopher State One Call is unique in a number of ways: It is one of very few statewide one-call centers in the country that not only covers a large geographic area but also requires utility owners and anyone who has underground facilities in the road right-of-way to belong to the system. The Gopher State One Call has received overwhelming acceptance since formally launching operations in 1988. The center handled 780,000 communications in its first year and topped 1 million in its second. Today, Gopher State One Call handles more than 5 million communications annually.

When a contractor, surveyor, or homeowner calls Gopher, the answering attendant asks the caller a series of questions, including contact information, exact digging location, and how long the digging will take place. “Being prepared to make the call will save the caller time and it can increase the accuracy of the locate from the utility company,” said Gopher’s General Manager Tonya Bethke.

The attendant enters the information about the digging site into a computer, applying that information to an online mapping system. This mapping system indicates what facilities need to be notified of the excavation. Once the facilities are determined, the attendant releases all information to the affected facilities, and the lines then are marked by the applicable utility owners. The caller must wait two working days before beginning excavation to allow the applicable utility owners time to mark the site. Once the 48-hour wait period is over, digging must begin within 96 hours – waiting longer voids the original ticket to dig.

Gopher warns diggers that they must be aware that markings are estimates of the exact location of the underground facility. Locators have a 2-foot buffer zone where diggers must hand dig to expose that facility for positive location. If an underground facility gets hit or damaged, 911 must be called if the digger has hit a flammable, toxic or corrosive gas or liquid or endangers life, health, or property. Also, the utility owners must be notified of damage, no matter how minor.

The state continues to invest heavily in state-of-the-art one-call technology and is enhancing its computer mapping system to stay on the cutting edge of one-call advancements. Two full-time Gopher One-Call representatives travel the state educating about 3,000 contractors and excavators annually about the importance of using the one-call system, said Michelle Stange, public relations coordinator.

•  “Miss Utility” is the one-call system for Virginia. In 1995, two nonprofit associations of utility companies formed: Virginia Underground Utility Protection Service, Inc. and Northern Virginia Utility Protection Service, Inc. These associations recently formed a limited liability company, Virginia Utility Protection Service (VUPS) LLC, for the purpose of operating a nonprofit one-call center. VUPS began operations last July for most of Virginia and will begin serving northern Virginia on July 1 of this year, according to Dave Price, director of communications for VUPS ( The northern Virginia association currently uses a private vendor to operate its one-call system.

Like Gopher, Virginia’s one-call systems notify subscribing underground utility owners of a caller’s proposed excavation plans. The service is provided free to callers by member utility companies.

The Virginia Underground Utility Damage Prevention Act requires that Miss Utility be called 48 hours in advance of the planned work to allow time for marking, that the marks be respected and protected, and that excavation is completed carefully. The Virginia system provides a “positive response” to let callers know whether the utilities notified have completed the marking process.


Oftentimes, a surveyor must set a pin, a stake, or a monument on private property. Private utilities can be found on military bases and college campuses, in industrial areas and mobile-home parks, on the properties of single-family and multi-family homes, at shopping centers, and sometimes in the road right-of-way.

Privately owned utilities also generally include those utilities that are installed behind or after the meter. If overhead distribution lines serve the property and the power is then distributed on the property by underground service facilities, those service facilities may be considered private. If the homeowner’s electric meter is located on the property line, then that electric line from the meter to the house is considered privately owned and may not be able to be located by a public one-call system.

Other private facilities to be aware of include:

  • Private water systems
  • Data communication lines
  • Underground sprinkler systems
  • Other gas or propane lines (such as for gas grills and pool heaters)

Unless the property owner participates as a member of his or her state’s one-call system, private or customer-owned facilities generally are not marked or notified. Surveyors with questions about whether a facility in an excavation area is considered private or not are strongly encouraged to first contact the state’s one-call system and then, if necessary, the applicable local utility offices. Private locating firms or engineering firms with utility marking and mapping capabilities such as Woolpert should be contacted if private utilities are involved.


Because there is no assurance that buried facilities will be deeper than the pins being driven, calling in an excavation notice can prevent time and energy loss fighting damage claims even when a notice is not required, according to Walt Kelly, a damage prevention consultant.

Should an accident occur when digging, being “ignorant” or “unaware” of the law may not exempt surveyors and others who did not use their state’s one-call system.

In Virginia Beach, Va., a 2-inch gas main was damaged by a survey crew setting a property corner pin. The crew had not called Miss Utility’s one-call system in advance, and the surveying company was fined $500. In Mechanicsville, Va., a gas line was damaged in the same way, resulting in a civil penalty of $300 to the surveying firm, with $100 suspended upon completion of a safety-training course.

In Connecticut, civil penalties for failing to use the state’s “Call Before You Dig” system are based on the severity of the resulting incident, according to Bill Petersen, center manager. “We look at whether someone was hurt or killed, if there was a significant utility outage, and if there is a past-history of non-compliance,” Petersen said. “First-time ‘offenders’ who don’t use the one-call system and cause minor damage must attend a one-call safety course.”

Petersen said he realizes a lot of surveyors and excavators are sensitive to the issue of fines, liability, and lawsuits. “In some cases, even if they’ve used the one-call system, and an accident still occurs, it may not be (the surveyor’s) fault because the utility owner may have mis-marked its own lines. Five years ago, a phone company was fined $43,000 and an electric company $46,000 for mis-marking. The law is enforced fairly,” Petersen said.

Washington and Idaho, like many states, also have statutes that allow for recovery of damages if a surveyor or an excavator fails to call for locates in advance, according to Scrivner, who now independently consults for insurance carriers, law firms, and utilities. “I’ve aggressively pursued cases in order to help utilities recover costs as well as for the benefit of public safety,” Scrivner said.


It’s a simple rule to remember, and it’s the law. Calling before digging can save surveyors from finger-pointing, fines, bad publicity, and angry bosses. More important, calling before digging can save money, infrastructure, and lives.


Who Locates Private Utilities

Working with the facility owner, existing records, maintenance personnel, and others, the private utility locator uses several technologies to pinpoint the precise location and depth of mains and lines that have been buried underground.

In the March 2008 issue of Underground Focus, Mark Palma along with Jim Holzer wrote about the challenges faced in getting private utilities marked. Palma’s article focused mainly on private utilities at the homeowner level. I would like to expand on his thoughts and address the issues and solutions related to the commercial side of locating private utilities. For the purposes of this article, a private utility refers to a utility owned and maintained by the property owner.

Who Locates Private UtilitiesToday’s underground environment is loaded not only with primary service networks, but also with unexpected and unique systems. This applies to private utilities as well. Private systems on commercial, educational and governmental property include electrical, communication, water, gas, sewer, video and fiber optic networks. In addition, specialty systems such as fire and security controls, irrigation systems, steam and fuel lines, and fiber optics, coexist with the more traditional utility systems. The availability and accuracy of their locational records varies for these systems and at best are useful only as guides. To add to the difficulty factor of locating private utilities at the sites mentioned above, one must realize the inconsistencies that exist, and that these utility lines do not conform to a set pattern. Over time, utilities have been added onto, repaired, replaced, or abandoned. In addition, contractors installing the utilities are typically not subject to the same requirements as those installing lines in the public right-of-way. This means that different construction techniques were used at each site, and possibly at the same site. Think of a property as a puzzle, and the location of its utilities as missing pieces.

Currently, contractors and engineers handle the problem of private utility locating in a variety of ways. Many contractors hand dig assuming that they will not encounter any conflicts, while others dig regardless of the presence of unmarked private utilities. Designers and engineers typically make an effort to utilize any existing records and integrate the information into a topographic survey. The engineers will often incorporate a note on the drawings, stating that the contractor is responsible for getting lines marked. This means that if any conflicts arise in the field due to unexpected facilities being found or hit, these need to be addressed and resolved at that time. “The pressure to redesign and or relocate utilities in conflict in mid-project, more than justifies the expense of employing a private locating firm,” according to Ronald R. Rotunno, P.E Senior Project Manager for Naik Consulting Group, PC.


The increasing density of buried utility structures, the success of one-call systems in raising contractor awareness, and amplified concerns by contractors and property owners over liability issues, has increasingly led to use of private utility location services. These specialty firms are providing contractors and engineers with the marking and mapping necessary to avoid hits that can shut down a complex or send a maintenance staff scrambling to find a shut-off valve. The marking and identification of utilities provides excavators the comfort and confidence to complete their work. Engineers have come to rely upon private utility locating services to ensure that their designs accurately reflect all utilities present. This helps provide costly construction delays and engineering redesigns. The private locator is “next to the last line of defense” wrote Mark Palma in his recent article.


There is no toll-free one-call system for private utilities. At best, there is an ad-hoc system in place to provide a list of companies providing private utility locating to the owner’s of a private utility system. The companies that fill this role are a varied group of providers, ranging from one-call locators who mark lines on the side, SUI companies, and specialty private utility locating firms. In nearly all private utility cases, it falls on the contractors or engineers to arrange for the location of private utilities. “Before the use of such locates, we spent approx. $85K in repairs to these facilities in a year and a half. This is not a risk we are willing to take” according to Sean Davis, Construction Supervisor, S & N Communications.


There are no standards in place within the one-call system for ensuring the location of private utilities. Most state laws address the issue by indicating that it is the responsibility of private utility owners to mark and protect their facilities. This is seldom enforced. Some one-call systems indicate in the ticket response codes the presence of private utilities. The state of Maryland, under Miss Utilities, uses a “Code 9” on its one-call tickets to inform contractors that the facility owner has marked up to a transition point, beyond that, the facility is privately owned. (See table on previous page).


The processes and mentality required for private utility locating differs from other types of utility locating. To begin with, private locating firms assume that records are inaccurate or nonexistent. For many private facility owners, the first accurate record of their facilities comes from the work of the private utility locating company. These utility locators must “read the landscape” for indications such as access points, road cuts, or clues that will indicate the presence and exact location of the private utilities. Working with the facility owner, existing records, maintenance personnel, and others familiar with the property, the locator begins piecing together the precise location for all the utilities on the property. It is at this point, using the traditional means available for utility locating, that the private utility locator identifies and correctly marks the location of all private utilities, thereby completing the puzzle.

Joseph B Geraghty – Founder, President & CEO

For more information or to obtain a quote, please contact us at (800) 883-6855.