No one can dispute the importance of preventing damage to underground utilities.

Owners and managers of organizations providing utility services, the contractors who construct and maintain utilities, and general and specialist contractors know that accidental utility strikes disrupt essential services, require costly and time-consuming repairs, and can cause serious injuries and death.

For crew members working on the job, utility hits are more personal—they are the ones at risk if a power cable is severed or natural gas line cut.

"Preventing damage to buried utilities is something everyone—even the general public—can understand," says Mike Dvorak, account manager for electronics. "'Call-Before-You-Dig' messages are aimed at homeowners and professionals alike. Yet, every work day there are hundreds of accidental utility hits."

Citing the most recent Common Ground Alliance (CGA) Damage Information Reporting Tool (DIRT), there were an estimated 200,000 accidental utility strikes in 2008.

"And that is a significant improvement over the previous year," Dvorak points out. "The total for 2007 was 256,000."

However, utility owners compile the DIRT data from voluntary submissions and while the number of organizations providing information increases each year, it is believed that a significant number of accidental strikes are not reported.

Perhaps more important than numbers, is information about the root causes of accidents reported. In 2008, 37 percent occurred on sites where no request had been made to locate and mark utilities. Twenty-two percent faulted insufficient locating practices.

"These figures tell us that 59 percent of incidents documented in the report were caused by the failure to request locates or improperly locating and marking utilities," says Dvorak. "Clearly the place to begin reducing damage to utilities is making accurate and timely locates."

Locating and Marking Buried Utilities

The first step toward locating buried utilities is to call the local one-call agency.

That task has been greatly simplified by the national, toll-free 811 number which rings the one-call center nearest to where the call was placed. The number has been widely promoted with the theme "Know What's Below." One-call then provides member organizations to locate and mark utilities they own at the location specified in the one-call ticket. If everything works as it is supposed to, buried utility locations are flagged and marked by the appropriate color of paint when construction crews arrive to begin work.

However, one-call may be unable to mark all utilities on a project.

"One-call can only notify member companies to make locates," says Dvorak. "The key word is 'members.' For example, water and sewer service providers in many areas are not one-call members, so those pipes won't be marked."

Also, many times utility locates and markings are only made in utility easements, not on private property. That means if an excavation is going to take place outside easements—for an irrigation system for example—cable and pipe from the easements to the home will not be marked.

In some areas, utility owners take the position that a service line belongs to the property owner. For example, the water utility is responsible for pipe to the meter located in an easement, and pipe from the meter of the house or other structure is the responsibility of the property owner.

In addition, power and communications cable as well as water and sewer lines serving buildings of educational institutions, government complexes, and office parks, are on private property and are not covered by one-call.

"Two important points to remember about one-call," says Dvorak, "are situations where one-call has no authority to make arrangements for locates, and that locates scheduled by one-call will be made by the utility owner or a contract locating service hired by the utility owner."

Dvorak refers again to the DIRT report.

"DIRT data documents that 59 percent of incidents reported were related to no or improper locates," he says. "Of those, 22 percent were because locates and markings were not made or were not done correctly. Contractor crews should never assume lines actually are where they are marked. Proper procedures call for personnel to verify locates before excavating."

One-call locates do not provide depth, but rather a window of horizontal space where utilities are estimated to be buried.

"Many contractor crews are equipped with electronic locators to scan the jobsite," Dvorak continues. "Also a visual inspection of the location and applying common sense can alert on-site personnel of the possibility of unmarked utilities. Are there telephone pedestals or power transformer boxes present, but no markings of cable leading to or from them? Is there a gas meter by a structure, but no service line marked? Evidence of a trench dug in the past where fill has settled? All are warning signs to investigate."

In addition, when a new utility crosses one already in place, the buried pipe or cable should be physically exposed to verify its exact location, and potholing to accomplish what may be the contractor's responsibility.

Locating Technologies and Tools

Electronic locators.

Tools most used for basic locating are electronic locating systems consisting of a hand-held receiver and compact transmitter. A transmitter is connected to a non-emerged pipe or cable and transmits current read by the receiving unit. The receiver processes information and displays an estimate of depth and other data on an easy-to-read screen.

A simple basic locator is the Ditch Witch® 150R/T, an affordable, easy-to-use system. More sophisticated is the Ditch Witch 950R/T, which uses different frequencies and modes to find locations of different types of utilities by detecting magnetic fields created by electrical current passing through the lines.

In some situations, the receiving unit is all that is necessary to locate electrical and television cable signals. To find telephone cable and metallic pipe, the 950T transmitter is connected to cable or pipe and a current is sent through the line, creating a signal that is detected by the receiver.

Plastic pipe with tracer wire is located by energizing the tracer wire with the transmitter to provide a signal that can be read by the receiver.

GPR locators.

Ground penetrating radar utility locators can be used to detect and locate both metallic and non-metallic pipes and cables as well as other buried objects without requiring the presence of electrical current. To conduct a search, the handlebar-mounted unit is pushed or pulled across the surface. The Ditch Witch model 2150GR employs digitally controlled radar pulses to image the subsurface. Depending on soil conditions and antenna, the device can identify objects to depths of 19 feet. However, GPR effectiveness is limited by soil conditions and typically has difficulty penetrating dense soils.

Vacuum excavation.

Seeing is knowing—the best way to be absolutely sure where underground utilities are is to uncover them. Potholing is nothing new; for years, utilities were uncovered by workers using shovels, a slow and labor-intensive job. Backhoes speed the process, but pose the risk of hitting and damaging the utilities being uncovered.

Vacuum excavators have revolutionized the potholing process. Compact combination "soft" excavation equipment with vacuum systems, mounted on trailers or trucks makes precisely controlled potholes quickly and efficiently. Depending on soil conditions, a 12-inch-square, 5-foot-deep pothole can be completed in less than 30 minutes. Spoil can be vacuumed to a holding tank for reuse or disposal. The Ditch Witch organization offers two vacuum excavator models, the FX30 and FX60 that use high-pressure air or water, which is directed by a wand to displace soil. Soft excavation greatly reduces the risk of damaging in-place utilities during excavation. In addition, versatile vacuum excavators frequently are used to remove drilling fluids from horizontal directional drilling work sites, as well as cleaning out vaults, storm sewer, and virtually any other clean-up requirement.

Best Practices

Dvorak says with growing attention to the importance of protecting underground utilities and a good selection of tools to locate underground infrastructure, the industry must continue to educate its members and the public about how to prevent accidental damage to buried utilities.

The Common Ground Alliance (CGA) Best Practices are recognized as the most effective guidelines yet developed for preventing damage to underground facilities.

"We know what we need to do to protect buried facilities, we know how to train people, and we have the procedures in place and the tools to accurately locate and mark buried utilities," says Dvorak. "Finally it comes down to the crews on jobsites to implement best practice procedures, be attentive, and don't take risks in order to 'save time.' Statistics indicate the number of accidental utility hits is dropping. It's a trend we need to make sure continues."