Locators and vacuum excavators go hand in hand when locating underground lines.
Underground contractors must safely and efficiently identify existing infrastructure. This task has become complex and time-consuming. The vast and intricate array of underground lines means that the One Call contractor’s marks may not be as accurate as your underground project demands.
“The One Call contractors do a good job of marking the location of existing under-ground lines and pipes,” says Dave Gasmovic, president of McLaughlin. “But underground interference could cause the marks to be 3 to 4 inches off the actual line or pipe. If you use a shovel to visually locate the line, it may take some time to ﬁnd it.”
Gasmovic encourages contractors to purchase their own locator to double-check the accuracy of the original markings. Under-ground contractors can make a sweep of the area and might pick up something that the One Call contractor may have missed. It’s all a matter of preventing damage in today’s maze of underground lines.
“The old philosophy of ‘I’ll cut, ﬁx it and go on’ are over,” says Gasmovic. “Using a locator and a vacuum in combination will help you locate the cable and get on to your main excavation work in a timely manner.”
Selecting a Locator
There are various types of locators on the market. Single-frequency split-box locators have been around for decades. These systems consist of a transmitter that is placed on the ground and induce a signal. The signal is picked up by the cable or
pipe and then re-radiated back up to the receiver. Single-frequency systems work well on lines and pipes in non-congested easements but put such a high frequency into the ground that they light up everything underground and may produce a distorted signal.
Multi-frequency systems allow you to tune the frequency you are putting into the ground to the type of line or pipe you are trying to locate. The lower the frequency, the better it will stay on the cable you are trying to locate.
Most modern receivers today can estimate the depth of the line or pipe at the push of a button. The locator measures signal strength and uses an algorithm to convert this information into an estimated depth. However, inter-ference can distort the depth estimate. Despite the possible inaccuracy, the estimated depth gives the contractor an idea of the location of the line or pipe as they hand-dig or excavate the area with a vacuum.
No matter the features, Gasmovic encourages contractors to select a locator that is simple for the operator to pick up and use within a week.
While locators are becoming more accurate, it’s important to see exactly where the line or pipe is located. Contractors are not allowed to dig in the safe zone, which may be from 18 inches up to three feet from either side of the marked line. The required distance varies by state. Contractors are only allowed to dig by hand or use a non-destructive method like vacuum excavators in the safe zone.
Using a vacuum excavator instead of a shovel has advantages. A shovel against a water pipe is non-destructive, but on a ﬁber optic line, a shovel can be as destructive as a back-hoe, especially in hard ground conditions.
Since vacuum excavators use low-pressure air or water to remove spoil, they are perfect for potholing or identifying existing utilities during underground construction projects.
“Damaging existing utilities can be costly in terms of project downtime and potential contractor ﬁnes,” says Gasmovic. “The low-pres-sure water and air will not damage existing utilities like a backhoe, compact excavator or shovel. In fact, the air and water move around the existing utilities, giving the operator a clear view.”
Taking the extra steps to verify the One Call contractor’s markings and then potholing may seem like an added expense or more time, but Gasmovic stresses that safety is important.
“Hitting a gas line with a backhoe, trencher or HDD could be catastrophic. A water line hit could put a hospital out of business,” says Gasmovic. “The cost of shutting down a project for a day is sure to exceed the cost for a $3,000 locator and a little extra time.”
The Capabilities Guide appears in Underground Construction. For more information please visit ucononline.com