Accurately locating and marking buried utilities is the first step in preventing accidental damage to underground infrastructure, and the basic tool for making locates is the electromagnetic locator, a dual-component system of compact electrical transmitter and handheld receiver.
However, electromagnetic equipment cannot locate plastic or composite pipes unless they have tracer wires to carry current generated by the locator’s transmitter, and there are thousands of miles of pipe in the U.S. that cannot be located with conventional electromagnetic locators.
A solution in many situations is a locator employing ground penetrating radar (GPR) technology. GPR locators transmit high-frequency radio waves into the ground. When a wave hits a buried object or a boundary with different dielectric constants, the instrument records variations in the reflected return signal which are processed and displayed to the operator on a screen, identifying the location of the pipe as well as other buried objects such as concrete, storage tanks, and conditions such as voids. GPR performance varies with soil conditions.
The Chesterfield County (Virginia) Utility Department uses its own personnel to make an average of 1,000 utility locates per week, said Keith Shelton, utility supervisor.
Most are in response to One-Call requests, but some are to assist department crews.
“We depend on electromagnetic locators most of the time,” said Shelton. “But there often are situations when they aren’t effective, and we regularly use GPR to make locates. Mapping of our systems is excellent, but our infrastructure contains composite plastic pipes with no tracing wires, and we use GPR technology to locate them.”
The GPR equipment operated by the county is a Ditch Witch 2450GR model mounted on a four-wheel cart pushed across the surface by the operator, similar to a lawn mower. Its earth-engaged antenna makes direct contact with the terrain, maximizing signal strength. The dual-frequency antenna simultaneously sweeps in two frequencies, allowing the operator to see both deep and shallow objects. Cart design allows the operator to quickly scan uneven terrain as well as level surfaces. The display provides clear, easy-to-read images.
“The 2450GR has been a ‘godsend,’” Shelton said. “It has more than paid for itself in time savings by its ability to quickly make locates in conditions where other equipment isn’t effective. We could tell story after story about how it has found lines other equipment couldn’t.”
Most important, Shelton emphasized, is how easy the 2450GR is to use.
“Just take it out of the box, turn it on, and you’re ready to go,” he said. “It calibrates itself and operation is very intuitive. Being so easy to use makes it easy to instruct others in its operation. I told our dealer, if you ever need someone to demonstrate one, I’m your man. I swear by this product.”
Chesterfield County is served by Ditch Witch of Virginia. Ditch Witch of Virginia has locations in Glen Allen, VA and Chesapeake, VA. They serve Central Virginia, Northern Virginia, Hampton Roads and the Eastern Shore of Virginia and Maryland. For more information on their dealership, visit www.ditchwitchva.com.
“If we need anything, all we need to do is pick up the phone,” he said. “They’re always available for whenever we have a need and do a good job staying in touch.”