Page 6 - Tennessee 811 Magazine 2021 Issue 3

By Jason Kouba
Damage Prevention Liaison Tennessee811
Why Can’t They Just Mark it Right?
Icalled in a locate request to have underground utilities marked prior to starting my project. The utilities came out and marked but I found a buried line three
feet away from where the utilities marked it. Why can’t the locators mark their lines accurately? Unfortunately, this is not an uncommon statement coming from a contractor. Let’s talk about some of the things that cause utility markings to be inaccurate.
Let’s start with the basics of utility locating. Locating is a science, but not an exact one, so it’s also kind of an art. In a perfect scenario, a locator direct connects to a buried utility that is grounded at the far end. When the locator applies signal to the target utility, that signal travels down the line to ground at the far end where the signal enters the earth and returns to the ground rod placed
by the locator to complete
the circuit. If every utility
was placed by itself and
everything was perfectly
grounded, it would be hard
to mislocate underground
utilities. Unfortunately, with
time and age these facilities
deteriorate and become more difficult to locate. Let’s discuss a few scenarios that may cause mislocates in the field.
Gas utilities, and many water and sewer utilities too, use plastic pipe to carry product. Conventional locating methods are unable to locate plastic as it is not a conductor that will carry a locate signal. In these cases, a tracer wire or locate
tape is buried with the facility allowing a locator to use the wire to carry the locate signal down the utility. Years ago, 811 was not required when doing
wire became more common in recent years, and there are new products coming to the market all the time to help with the locating of plastic pipe.
Even with more reliable tracer wires and the new products available, you can still run into issues while locating. If a contractor
has previously dug in an area where you are doing excavation and cut the tracer wire without reporting it to the utility to be repaired, that section of pipe is now unlocatable. This reinforces the importance of treating the tracer wire as a part of the utility and reporting this damage just as you would if you damaged the utility. This ensures the integrity of the system is in place and the utility can be located in the future.
If a tracer wire is nicked and not completely severed, this can still cause issues with locating that facility. We talked earlier about a locator sending a signal down the tracer wire and that signal returning to the ground rod to complete the circuit. If
a tracer wire is nicked, the signal has the capability of then entering the earth and
taking the path of least resistance back to the ground rod, be it through the dirt or by jumping on an adjacent utility and traveling back to the ground rod.
This brings us to another obstacle that needs to be navigated: today there are way more buried utilities in the ground than there were years ago. A
4 • Tennessee811 2021, Issue 3
excavation work and so many of the older systems have no tracer wire with the pipe. In early stages of requiring locates before excavation, locate tape or other means were buried with the facility allowing it to be located. Over time, the locate tape deteriorates and is no longer able to carry signal causing the utility to be unlocatable. Tracer