Protecting the nation’s buried utility infrastructure is a continuing challenge for utility providers and the contractors that maintain and install the new pipes and cables needed to keep pace with growing demands of business and residential users.
Installing new utilities to replace old and failing infrastructure and to expand risks accidentally damaging utilities already in place in crowded easements often creates challenges. Of course, any type of construction that requires excavation or disturbs soil on a job site can accidentally strike buried utility lines.
Utility companies and contractors are bolstering efforts to prevent damage to underground infrastructure, yet each year thousands of hits occur resulting in millions of dollars in damage, lost services, injury and death.
A critical step in preventing incidents is accurately locating and marking existing buried infrastructure before construction begins. That process is initiated by contacting One-Call and initiating a ticket for locating and marking buried lines on a work site, a task done either by the member utility owner’s personnel or a contractor locating company.
The basic tools for locating underground utilities are:
• Electromagnetic Locators – the “standard” and most widely used tool for locating underground utilities;
• Ground Penetrating Radar – a transmitting component mounted on a wheeled platform that generates radio waves to penetrate the soil to identify locations of buried utilities and other objects;
• Passive Electronic Markers – a handheld locator generates a radio signal which is reflected to the transmitter identifying the marker’s location; and
• Potholing – physically exposes utilities to visually confirm their precise locations.
Each locating method has strong points and limitations. To effectively locate buried infrastructure, locating personnel must be trained in locating techniques and should be equipped with the latest locating equipment.
The electromagnetic locator is a two-component system: compact transmitter and handheld receiving unit. They are accepted throughout the industry and are accurate when correctly used in appropriate conditions.
To make a locate, the operator walks above where utilities are expected to be, and the receiver locates underground pipe and cable by detecting magnetic fields created by electrical current passing through the lines. Information is displayed on a window at the top of the receiver. For communications cable and metallic pipe, the transmitter is connected to cable or pipe and generates current through the line creating a signal which is detected by the receiver which processes information and displays it on a screen. For PVC and HDPE pipes with tracer wire, the wire is energized by the transmitter to provide a signal to the receiver. Different frequencies and modes help identify different types of utilities.
Electromagnetic equipment is the primary locating tool used by S&N Underground Utility Services, Midlothian, VA, said Steve Roark, director of utility locating. The company has 300 locating crews working in Virginia, Maryland, North Carolina and Ohio. Daily workloads fluctuate, but an average of 220,000 locates are made per month for telecom, power and gas lines, as well of locates on private sites and for subsurface utility engineering.
“Electromagnetic locators have been around for many years with early models operating on only one frequency,” said Roark. “Today’s models are much more sophisticated and have multiple frequencies to choose from. To reduce bleed-off or distortion from other signals, we train our personnel to start at the lowest and work up. The learning curve still has gone up from the day when single-frequency models ruled the market. However, with more companies offering multi-frequency equipment today, one of the biggest changes and benefits has been making equipment much more user friendly.
Competition drives improvements
The significant limitation, Roark said, is the electromagnetic equipment’s inability to complete a locate without the presence of electrical current. A live power line carries current and the equipment’s transmitter can introduce current to copper communications cable and metal pipes that conduct electricity, or plastic pipes with tracer wire.
“Plastic pipes and fiber cables without tracer simply can’t be located with electromagnetic equipment,” said Roark.
Ground penetrating radar (GPR) theoretically is the answer to locate utilities and other buried objects that can’t be detected by electromagnetic equipment and, indeed, there is GPS equipment specifically for locating utilities and other buried objects without the presence of electrical current.
A radio wave generating component is mounted on a platform with four wheels – from a distance the device resembles a lawn mower. Ground-engaging antennas send radio waves downward where they bounce off buried objects and reflect back to a receiving antenna. A graphic representation of information is displayed on the unit’s screen.
However, GPR locators have a significant limitation: they are not effective in dense soils.
Roark said from S&N’s perspective, GPR is another tool in the locating tool box. “It has its purposes, but it’s not a complete solution to underground locating by any stretch,” he said.
However, for areas that allow radio waves to pass through, many organizations do use GPR on a regular basis.
“Every week, we find something we couldn’t locate by any other method,” said the locating supervisor for a water utility. “If you avoid just one costly accidental hit, the unit has more than paid for itself.”
Passive Electronic Markers are another method to make plastic pipes locatable without the use of tracer wires. Passive RFID (radio frequency identification) marking “balls” have been used for years to mark the location of pipelines. Installed at intervals along the path of the pipe – either at the time the pipe is installed or added later – markers can be quickly located later with a handheld radio frequency locator. Maintenance-free markers have no electrical components and are corrosion resistant. Typically, electricity from nearby utilities does not interfere with the RF signal.
“We’re seeing increased use of ball markers, mostly by gas companies,” said Roark. “It seems there is a trend toward this technology, especially with gas companies. It’s a welcome development because it’s a smart way to locate. If there’s a ball every 20 feet, we can quickly locate the path of a pipeline.”
A recent development is the introduction of passive markers packed with a carrier similar to caution tape or on a rope that can quickly be installed on a pipe.
How better to know the exact location of an underground pipe or cable than to expose it and actually see it? Potholing is not new – for years crews have potholed with shovels, backhoes and compact excavators. Too often, however, mechanical digging methods damage the utilities they are seeking to find and protect.
Today the recommended method of potholing is by “soft” excavation with a vacuum excavator. Compact, trailer-mounted models are easily moved to and around job sites.
Vacuum excavators can dig a precisely-controlled hole 12 by 12-inches to depths of five feet in about 20 minutes. Excavation is accomplished either with high-pressure water or air, depending on brand and model. As the excavation is made, displaced soil can be sucked up by the machines vacuum system.
Roark said S&N routinely uses potholing when required by job specifications and in circumstances where conventional equipment cannot confirm the location of a utility. Soft excavation with vacuum excavators provides a low impact solution to potholing utilities. It is much safer and faster than traditional potholing techniques and provides less risk for damages that could have an impact to customers.”
Potholing also may be used in situations where a locate is difficult or impossible to make with electromagnetic equipment, when a line cannot be detected at all or if a signal is lost during a locate.
“When a technician has difficulty with locating a utility line, it is escalated to a senior member of our staff,” Roark said.
“That person,” he explained, “then evaluates the locate and takes all measures to locate the utility with electromagnetic equipment. If not successful, GPR may be used depending on location and practicality. If that is not an option or doesn’t result in a successful mark out, it would then escalate to the appropriate company or utility representative for resolution. Most often that leads to soft digging techniques to complete the locate.”
It has been said the most important component of a utility locator is the man or woman who operates it. To that point, a report released last year by the Common Ground Alliance cited statistics from 2011 that 22 percent of the utility hits reported in 2011 were the result of “insufficient” locating practices.
Roark said proper training is the key to developing a successful locate technician. S&N has an extensive training program that has been developed over the years.
“We utilize a mix of classroom and field instruction with certain benchmarks which must be achieved to move forward,” he explained. “Our program allows us to provide each trainee with the time and attention necessary to ensure each individual has all the skills necessary to become qualified locators.”
Training is only part of the equation for developing a locate technician, Roark continued.
“Proper supervision and auditing is essential for growth,” he emphasized. “We employ qualified supervisors and auditors to assure that our techs are supported with the best tools and the attention they need in order to get the job done properly. Locators are an essential part of each locality and state, and play a vital role across this nation. We have a responsibility to plant the seeds for success and proper training is the essential first step.”
In addition to directing S&N’s location services, Roark is a member of the Virginia State Corporation Commission Advisory Committee representing utility locators.
S&N Underground Utility Services is subsidiary of S&N Communications, based in Kernersville, NC. S&N Communications is a full service utility contracting company providing underground and aerial construction and engineering services throughout the United States. S&N recently expanded its locating capabilities with the acquisition of Utah-based Stake Center Locating.
FOR MORE INFO:
S&N Underground Utility Services, (336) 992-5420, http://sncomm.com