Wouldn’t it be great to have x-ray vision to see exactly what’s

2M Locating’s utility locators use electromagnetic location and ground penetrating radar (GPR) to identify and locate utility infrastructure underground, but sometimes these methods are not enough.
The only way to know the exact location, depth and size of some utilities is by potholing and excavating until the utilities are ‘daylighted.’
Potholing, hydro excavation and vacuum excavation are three techniques utility locators use to reveal the location and features of utilities underground.


Why are these techniques needed?

Each are two main reasons these techniques are needed:

Regulations and the increased use of horizontal directional drilling (HDD).


Working around utilities involves high risk. Even when excavators have information about where a line is buried, they must always exercise extreme caution because maps, information and drawings may be inaccurate, outdated or incomplete.

Most state and/or local regulations don’t allow mechanical excavating within 18-36 inches of a marked utility line in order to keep workers and others on the jobsite and in the surrounding area safe. Within that safe zone, soil and debris around a utility have to be removed by hand or using a non-destructive method (vacuum or hydro excavation). Removing the dirt manually can endanger workers if they are using metal tools, or if there is a risk of unstable ground material overhead collapsing.

Hydro excavation and vacuum excavation handle these risky situations safely, neatly and efficiently.

Horizontal Directional drylling (HDD)

HDD is being used increasingly to lay cables and pipes because it reduces the number of road closures for utility installation projects. HDD also reduces the environmental impact, especially to rivers, lakes and wetlands.

However, the use of HDD makes it harder for GPR to locate utilities because it results in less soil disturbance and no traceable ditch line – two features that GPR would normally detect.

For this reason, when HDD has been used in an area, utility locators need to use potholing and daylighting to locate the utilities.

What is Potholing?

Potholing involves making a series of test holes through soil, concrete or asphalt to locate underground lines accurately.
Potholing crews then use vacuum excavation or hydro excavation to remove the soil between the hole and the utility.

The method used depends on the soil’s composition.


Potholing is not just used for locating utilities. It is also used to dig holes for fence posts, utility poles and signage posts.

What is Daylighting?

Daylighting means exposing an underground utility to daylight so a worker can identify its features.

  • Horizontal position of the utility
  • Depth as well as the top and bottom of the utility
  • Type of line (water, gas, electrical, fiber optic or telecommunications), and
  • Possible damage to the line.

Three Kinds of Excavating



Hydro excavation uses pressurized water to move soil and rock debris out of the way. A long hose suctions away the displaced dirt, debris and water to a holding tank on a truck. These wet spoils are hauled away for disposal, adding to the time and expense

For locations that experience cold weather, hydro excavation can use hot water (up to 115 degrees F.) to excavate frozen soil.

When we think of excavating, the first image that comes to mind is usually the hydraulic excavator that we see on construction sites. Traditionally, a hydraulic excavator would be used up to 3 feet away from the utility, and then the remaining dirt and debris would be removed by hand. This kind of excavation leaves a large footprint.below].

Now it is common and much safer for utility locators to ‘daylight’ utility lines using “soft excavation” techniques: either hydro excavation or vacuum excavation.


Vacuum excavation uses pressurized air to break up compressed soil around the utility. The dry spoils are then vacuumed and reused as backfill. In light soils, the vacuum excavator may be able to use high-speed suction to remove soil straight down until the utility line is partially revealed.

Vacuum excavation is preferred but heavily compacted soils may require hydro excavation. The water helps keep the suction hose cleaner by preventing the soil and excavated debris from building up.

What kind of equipment is used for hydro and vacuum excavation?

These two kinds of excavator are often combined on one truck, called a vacuum excavator or hydrovac truck. It is equipped with a high-pressure water and air excavation system, a water supply tank and a large tank for the spoils vacuumed up from the site along with the drilling fluids. Some excavators are mounted on a trailer.

The hydrovac truck or trailer has a wand or hose that injects water under pressure into the soil. The pressurized water breaks up the soil but isn’t strong enough to damage utility lines. The water liquefies the soil, producing a slurry which the vacuum carries to a tank attached to the truck. The truck can remove the slurry from the worksite, keeping the site tidy.


Benefits of Potholing and Daylighting with Hydro or Vacuum Extraction

These techniques have multiple benefits:

  • They allow utility locators to ‘daylight’ utilities without risk of damaging them.
  • They are less disruptive, destructive and invasive than mechanical excavating.
  • There is less environmental impact and the site is easier to restore or repair afterwards.
  • Because they leave a smaller footprint than mechanical excavating, theyreduce the time needed to complete a job.
  • They can be used in locations that traditional excavation machinery cannot access.
  • They can be used in locations that traditional excavation machinery cannot access.
  • The compact truck or trailer can operate easily in urban areas.
  • They eliminate life-threatening accidents.
  • They keep projects going by decreasing delays.
  • Most importantly, they won’t accidentally cut a utility line or other underground feature.

The safest way to expose an underground utility is to pothole (make a series of test holes) and then use vacuum extraction until the utility can be ‘daylighted’. This process allows utility locators to identify the type of utility and take horizontal and vertical measurements. Where vacuum extraction is not possible, hydro extraction may be used.


How Much Will My Potholing Project Cost?