Locating underground utilities is becoming more of a challenge as the vast array of lines in the ground continues to increase. As the ground under our feet becomes more congested with utility lines, it’s vital to identify the location of utilities — gas, fiber, water, telecommunications and sewer — to ensure the safety of your crew and protect your bottom line.
The first step before digging is to contact your state’s one-call office and provide it with the location of the proposed area to be excavated. A one-call contractor will visit the site and mark the location of the existing utilities. One-call contractors do a good job of marking the location of existing underground lines and pipes. However, due to interference, the marks may not be as accurate as needed. In some cases, privately owned lines, not known by the one-call contractor, may not even be marked.
Many contractors show up and begin excavating. That’s fine if the one-call markings are accurate. However, a mark could be 6 in. off and you may not find that line. Now you need to make a decision: Do you keep going or contact the one-call contractor and request he or she come back out?
Either way it’s costing you time and money. However, if you have a utility locating equipment, then you can confirm the marks that are on the ground and identify underground facilities that could have been missed.
Understand Locating Methods
There are basically two locating methods — active and passive.
Active locating involves searching for a specific line using either the direct connection or inductive method. Each line gives off a signal, so the locator is either attached directly to the line or if you cannot make a direct connection to the line, a frequency is selected and induced into the ground, which attaches itself to the utility.
Passive locating is a method used by contractors to check the area for unknown lines. This method detects any frequencies created by energized powers and radio signals being radiated by utilities. However, this method does not allow the operator to distinguish between the types of lines.
The industry offers two types of locators — single- and multiple-frequency units — to accomplish active and passive locating. Each unit has its advantages and limitations.
Single-frequency locators have been around for decades. These systems consist of a transmitter that is placed on the ground and induces a single high-frequency signal. The signal is picked up by the underground line and then radiated back to the receiver. Single-frequency systems work well on lines and pipes in non-congested easements, but putting a high frequency into the ground has the tendency to light up everything underground and may produce a distorted signal. In other words, you cannot distinguish whether it’s a power, gas or communications line. The other limitation is that most single-frequency locators cannot determine the depth of the line.
Since lines and pipes are constructed of different materials (copper, aluminum, iron, steel, etc.), a higher or lower frequency may do the best job of locating them. Multi-frequency systems (some offer up to five frequencies) allow you to tune the frequency you are putting into the ground to the type of line or pipe you are trying to locate. Using a lower frequency reduces the chance that the frequency will jump from the cable you are trying to locate to another nearby line, thus making it easier to distinguish a gas from a water line.
Some locators offer a current measurement index (CMI) that measures the current you are putting onto the cable. This helps distinguish the cable, especially if it crosses over another line and helps ensure you are staying on the original line to be located and are not jumping to other lines in the area. Most modern receivers today can also 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, interference 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.
If a contractor is conducting the active method of locating, there are different ways to put the locator signal on the line or pipe. Direct connection is the most common connection method in the industry. This allows workers to connect cable leads, similar to jumper cables, to the line or pipe to be located and generate an alternating current down the cable or pipe. The only issue with this method is gaining access to facilities. If you are not a contract locator for the telephone company, you cannot legally open up a telephone pedestal and clip onto the line.
To overcome this challenge, contractors can use a locator with good inductive capabilities. Inductive locators induce the signal into the product. The inductive method requires the user to set the transmitter on the ground; a signal radiates down through the ground onto the cable and eliminates the need to connect clamps or coils to the line or pipe.
Changes on the Horizon
While locator technology has not changed much in the past five years, several manufacturers are adding enhancements to help provide a clearer signal and tie the locates to GPS coordinates.
Virtually all manufacturers are putting more power into their utility locators. While this extra power does not enhance the accuracy of the unit, it does provide a clearer and higher-quality signal. Many manufacturers have also made advancements in their receiver software to help filter out the extra noise in the ground and air, helping to provide a more accurate filtering of the signal. The other trend occurring in the industry is linking the locator with GPS devices and mapping the utility line with latitude and longitude coordinates, thus providing an accurate location of the line for future reference.
Before You Buy
While it’s important to select a utility locator that features the technology you need, don’t forget that the unit should also be simple to operate and durable.
You want to make sure that the unit is simple to use and doesn’t require you to send your operator to a day-long class to learn how to run. In a number of cases your operator may not use the unit from week to week and it should be simple enough for them to pick it up and recall how to use the unit without much instruction.
Durability is also important. Contractors take equipment in and out of a truck on a daily basis and unfortunately the locator may not be handled with absolute care. Make sure the unit is durable enough to handle your jobsite conditions.
Weather can affect your locator, so before you purchase ask if the unit has limitations when being used in various weather conditions, such as rain. Lastly, make sure the instrument features a multi-year warranty.
Locators can range in cost from $1,000 to $4,500 and while this may seem like a lot of money, you can lose more in one day on one simple bad mistake.
Matt Manning is the locating equipment product manager for McLaughlin, based in Greenville, S.C.