If you’re looking for your ultimate guide to utility potholing, we’ve got you covered. Learn more about what you should know here.
Are you just starting a new construction contract?
Not only is underground utility mapping often a legal requirement for new projects. But without an accurate map, there’s the potential of them becoming a costly and dangerous undertaking.
According to a government survey, accurate utility mapping resulted in an 89% reduction in personal injury accidents. Not to mention, a higher likelihood of projects being completed on time, and saving upwards of $700,000!
If you’re having visions of messy and precarious exploratory digs and potholing, you’ve come to the right place!
Let’s take a closer look…
What’s Utility Potholing?
Utility potholing, also known as hydro-excavation or air-excavation, requires the creation of a test hole to reveal subsurface utilities.
While hydro-excavation relies on high-water pressure to break through the earth, whereas air excavation utilizes air pressure.
Air excavation is a less traumatic approach, and as such, excavated material can often be reused. But, on the downside, air excavation takes longer and is ineffective for denser or harder soils.
Other types of potholing methods include traditional hand digging and backhoeing. That’s as well as less destructive processes such as vacuum excavation.
Whatever approach you take, utility potholing ensures gas, water, and electrical pipes remain undisturbed and undamaged.
As a civil engineer, contractor, or project manager, determining the exact location of both vertical and horizontal facilities is time-consuming. However, it’s an essential procedure for any excavation project.
Luckily technological advances have further developed the technique called underground utility scanning. This process eliminates the need for labor-intensive and destructive methods for mapping out utilities before excavation.
Which Utilities to Locate
When potholing, the principal utilities that contractors are looking for are color-coded. In the US and Canada, the American Public Works Association’s (APWA) color-coding system is used:
- Red: For electric power, cables, conduit, and lighting lines
- Orange: For telecommunication, alarm and signals, and conduit lines
- Yellow: For natural gas, oil, steam, and petroleum. As well as other gaseous or flammable material pipes
- Green: For sewer and drain pipes
- Blue: For drinking water pipes
- Purple: For reclaimed water, irrigation, and slurry pipes
How Does Underground Utility Scanning Work?
In 2003, the ASCE (American Society of Civil Engineers) developed the US standard for Subsurface Utility Engineering. The info at each level determines the risk employed to design and construct a project.
These quality levels allow project managers to draft disclaimers about the
accuracy of the info they find. Not to mention, they’re much better positioned to manage potential risk.
This can consist of data sourced from:
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A pull box
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Electrical reports
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Potholing reports
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Underground mapping
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3D modeling
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Surface markings
According to the ASCE, there are four levels of info for utility locating. Quality levels of information range from A being the highest level to D, which is the lowest.
Quality Level A
This level offers the most accurate information on subsurface utilities. Plus, you can collect data through non-destructive means.
Not only can it identify subsurfaces utilities, but it can also specify the following:
- Type
- Material
- Condition
- Size
…and other relevant characteristics of subsurface features, along with horizontal and vertical positioning. This data can help contractors map utilities in congested and/or built-up urban areas.
Quality Level B
This is often used to offer preliminary info at the beginning of construction projects.
It implements Subsurface Utility Engineering (SUE) to identify the presence of any utilities and their horizontal position.
This level is usually compared with data sourced at quality levels C and D.
This helps to correct any inaccurate, missing, or unrecorded utility records.
On top of that, this info also goes a long way to help manage utility locations and design adjustments by locating preexisting:
- Drainage systems
- Foundations
- Footers
…That may cause issues. Thereby reducing the cost of pricey utility relocation in the future.
Quality Level C
This level utilizes surveys of visible facilities. For instance, manholes, fire hydrants, meters, and valve boxes.
It also uses information found at quality level D to identify utilities that have been mistakenly plotted or omitted.
This is often useful for rural projects where relocation and repair are inexpensive, or many utilities are present.
Quality Level D
This is the most basic level of information as it relies on existing utility records or verbal recollections, which can often be unreliable.
You can also source info from geographic databases, construction plans, and distribution maps. But, it is typically not an accurate or comprehensive overview of utility locations.
Even so, it comes in handy for the initial route selection and project planning. With this data, you should get a general idea of where utilities may be present.
For this reason, levels D and C are often employed first to develop planning strategies that minimize risk and avoid relocation. These levels apply over the entire project area.
How It All Pulls Together
As the specificity of information increases, the exact project area can be investigated at levels B and A.
The critical method for utility locating at these levels is electromagnetic locating. The technique works by detecting the electromagnetic field around utilities.
This can occur either passively, whereby the utility omits naturally occurring detectable radio frequencies. Or actively, where a technician induces the frequency.
It is a cost-effective means of investigating the exact location of utilities before and during excavation. Though it is often used in coordination with several other tools. The most common methods for electromagnetic locating include the following:
Method 1
This direct connect method requires physical access to the service, usually on the surface of the feature connected to the utility.
The technician will send down a tracer wire with a receiver down to read the frequency from above. This is ideal for electrical, communication, and gas lines.
Method 2
Electromagnetic Induction is a method for locating buried services that cannot be directly connected to for whatever reason. For example, you can identify and trace utilities through an alternating electrical current sent to the utility.
When this happens, the utility transmits the signal back through the transmitter, which is received above. This then estimates the position and depth, just as with the direct connect method.
Method 3
Sonde locating can identify buried water lines, gas pipes, and any other non-magnetic utilities. Sondes are self-contained transmitters inserted into a utility or conduit. Receivers can pick these up above the surface.
You can establish the utility’s entire path, rather than just the end, by using tools such as crawler cameras, push cameras, and ramrods. For example, you can find blockages by pushing until the Sonde stops and then locating that position.
Method 4
The last method is a passive way to pick up the naturally produced frequencies of buried utilities. To use this method, it will need to be an active electrical power or communications line emitting a signal, or this location method will not work.
Once the utilities have been located, the technician will then use the appropriate industry color-coding to directly mark the surface of the utilities.
Generally, water-based paint is used, but when this is not possible, chalk, wax, or other marking material can be used instead. Then the area above will be designated with flags or whispers to highlight the project area.
Are You Ready to Start Utility Potholing?
Now you have the basics of utility potholing, you might be questioning where to go to receive the most accurate and comprehensive utility information for your project.
However, you needn’t look further than C Below. We utilize the most advanced equipment in the industry to gather the information you need for successful project management. Not only is our approach tailored to the specifications of your project, but our technicians are experts at underground utility locating and mapping. So, what are you waiting for – why not get a free estimate today?