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.
Locating and Marking Buried Utilities
The first step in locating buried utilities is to call the local one-call agency, a task simplified by the national, toll-free 811 number, which rings the one-call center nearest to where the call was placed. One-call then provides member organizations that locate and mark utilities they own at the location specified in the one-call ticket. It sounds simple, but there are many variables that underground construction contractors need to be aware of, including:
- Utility locates and markings are often made in utility easements only, not on private property. This means if an excavation is going to take place outside easements—for an irrigation system, for example—then cable and pipe from the easements to the home will not be marked.
- Some 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.
- Power and communications cable and water/sewer lines serving buildings of educational institutions, government complexes, and office parks are on private property and are not covered by one-call.
- One-call locates do not provide depth, but rather a window of horizontal space where utilities are estimated to be buried.
Locating Technologies and Tools
With so many variables, it is imperative that contractors know the precise location of existing utilities before digging. Fortunately, there are easy-to-use tools available that simplify utility location, including electronic locating equipment and vacuum excavators.
Ground Penetrating Radar
Ground penetrating radar (GPR) 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. The Ditch Witch 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.
The best way to be absolutely sure about the location of underground utilities is to uncover them—a process called potholing. 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 by making precisely controlled potholes quickly and efficiently. Depending on soil conditions, a 12-inch-square, five-foot-deep pothole can be completed in less than 30 minutes. Spoil can be vacuumed to a holding tank for reuse or disposal. Ditch Witch vacuum excavators 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.
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.
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