Underground Utility Markings Explained


Have you ever noticed spray paint markings and graffiti on the ground and wondered what they meant? 

Geoscope Utility Marking Services
Geoscope Ground Markings sample

What are Ground Markings?

Ground markings, markings on the ground, or site markings, however, you may want to call them, these only mean temporary markings of subsurface facilities to prevent accidents or service interruption by contractors, excavators, and utility locators. 

These markings are used by utility locating professionals to indicate where to and where not to dig, to help contractors and excavators be aware of what’s below before beginning any work, and most importantly, to help people avoid or prevent damaging any underground infrastructures when working on-site.

Why do these markings exist

It is simple, site ground markings exist to help represent the information, depth and location of underground utility services that were detected using different locating methods like Electromagnetic (EM) Locating and Ground Penetrating Radar or GPR.

These also serve as signs of what to avoid and what not to avoid by utility professionals who are working on-site to also ultimately help reduce risks or damages on underground utilities. 

Now that you have an idea about what ground markings are and why they exist, it is time to dive deep into what ground markings mean for Underground Utility Locating.

What do Ground Markings mean for Underground Utility Locating

Geoscope Utility Ground MArkings in Sydney Australia
Geoscope Utility Marking Services on Street of NSW, Sydney Australia

In this section, I will be giving you an in-depth understanding of what ground markings really mean especially for utility locating.

First thing first,

The Line Colours and Primary Codes Markings for different Subsurface Utility types

The line colours and codes of the markings have specific meanings, it indicates the presence of underground utilities. The reason why these markings are present is that they help utility workers, either prevent any underground utility damage, avoid trenches that will not be used, or save lives when planning to work near underground utilities.

Utility markings can be quite confusing if you don’t know what to look for. The colours and symbols used vary from place to place, so it is important to be familiar with them before beginning any work. 

In Australia, we follow the national standard format for recording subsurface utility information which is the AS 5488 or the Australian Standard for the Classification of Subsurface Utility Information. This standard includes codes, line types, and colours. Using this industry standard will help reduce confusion and misinterpretation. 


Used for Communications (drafted on white background as black)

White | Communication - C

Primary Code is C (used in AS5488) or TEL / OU (used in present)


Used for Drainage (Storm Water or Raw Water)

Green | Drainage - D

Primary Code is D (used in AS5488) or SW (used in present)


Used for Electricity

Orange | Electricity - E

Primary Code is E (used in AS5488) or EU (used in present)


Used for Fire Service

Red | Fire service - F

Primary Code is F (used in AS5488) or FH (used in present)


Used for Gas (all pressures)

Yellow | Gas - G

Primary Code is G (used in AS5488) or GS / GM (used in present)


Used for Petroleum Products (including oil) flammable and combustible materials

Brown | Petroleum Products - P

Primary Code is P (used in AS5488)


Used for Recycled Water

Purple | Recycled Water - R

Primary Code is R (used in AS5488) or RW (used in present)


Used for Sewer (Sewer Rising Main Vacuum Sewer)

Cream | Sewer - S

Primary Code is D (used in AS5488) or SW (used in present)


Used for Unidentified Services (Storm Water or Raw Water)

Pink | Unidentified Services - U

Primary Code is U (used in AS5488)


Used for Water (Potable)

Blue | Water - W

Primary Code is W (used in AS5488) or WS / WM(used in present)

There you go, you now have an idea of the standard colours we use for different utility types.

As you can see, there are some instances that some Utility Locating service providers use different colours due to a common situation like a lack of paint on-site, they also may change colours for contrast on specific utility surfaces. 

Like in the case of communications utility, the utility locating service providers paint white paint on black surfaces for communication lines.

Geoscope Utility Locating Service
Geoscope Sample of Communications Utility Marking

Another thing, with regards to the symbols, the symbols are not really that hard to remember or discern when you are on-site since each symbol only represents the first and second letters of their respective utility type.

These standard line colours for ground markings are not really what we use in Geoscope when we mark since it depends on the availability of the paint colours, but if you are interested in what line colours we use for marking sites, please refer to How we mark

How Geoscope Marks?

We primarily mark with a high-quality spot marking aerosol made by signet. This paint has consistent colour and spray patterns leaving us with quality looking markings. In some cases ...
How Geoscope Marks

After knowing the Australian standard line colours and their respective codes for each utility type, there are also other types of markings that can be seen on the site ground,

Utility Locating Marking Services by Geoscope

Have you seen markings like these before?

These markings are called “Quality Levels” based on AS5488 (2019).

Quality Utility Levels

These Quality levels are used to describe the amount and accuracy of the information that is collected or held on a subsurface utility.

There are four quality levels and they range from ‘D’ to ‘A,’ with ‘A’ being the highest and most accurate. 

To make it simpler, the higher the quality level, the more information is known about the subsurface utility and the more accurate that information is. An AS5488 Quality Level should be defined and recorded for all subsurface measurements shown in design or construction.

The importance of knowing such markings is to simply minimise the risk of damaging assets, especially when conducting an excavation process on-site. 

To tell you further information about these quality levels, here is a simple table guide to interpreting each of the Quality Levels as defined in AS5488 – 2019:

Quality Level D (QL-D Ⓓ)

Indication: Least Accurate / High-Risk

QL-D Meaning

It is the lowest among the four quality levels. Records research information where only records were able to be used. The attribute information and metadata of a subsurface utility may be compiled from any, or a combination of – (a) Existing records; (b) Cursory site inspection; and (c) Anecdotal evidence

Quality Level C (QL-C Ⓒ)

Indication: Low Quality / Probability of Damage

QL-C Meaning

Described as a visual utility or surface features to indicate subsurface alignment. Also defined as surface feature correlation or an interpretation of an approximate location and attributes of a subsurface utility asset using a combination of existing records, a site survey of visible evidence, and/or methods to indicate the existence of an undefined entity. The minimum requirement for QL-C is relative spatial position.

Quality Level B (QL-B Ⓑ)

Indication: Significant Risk Reduction

QL-B Meaning

Provides relative subsurface feature location in three dimensions by tracing (see Clause 1.4.32) or physical measurement that does not satisfy the spatial tolerance of Quality Level A. The minimum requirement for Quality Level B is relative spatial position. It is where surface geophysical methods successfully identify and depict the approximate position of subsurface utilities. Technologies include: Pipe and cable locators, CCTV, Laser Scanning (LiDAR), Ground Penetrating Radar (GPR), Multichannel GPR (MCGPR), Magnetometers, Elastic wave devices.

Quality Level A (QL-A Ⓐ)

Indication: Highest Quality / Lowest Risk

QL-A Meaning

Is the highest quality level and consists of the positive identification of the attribute and location of a subsurface utility at a point to an absolute spatial position in three dimensions. It is the only quality level that defines a subsurface utility as “validated”. Where the whole line segment cannot be verified by a line of sight, Quality Level A shall not be attributed to the line segment between validated points. It is physically locating utilities using minimally intrusive excavating equipment to determine the accurate and precise horizontal and vertical position, type, size, condition, and other characteristics. The technology used is Vacuum excavation

Without a Quality Level specified, the default Quality Level for subsurface information is ‘D.’ Because many Dial Before You Dig Asset Owner Members fail to specify an AS5488 – 2019 Quality Level, the default value of QL-D should be used.

Oops, before I forgot, did you notice the letter A, B, C or D with a circle around them next to service line markings?

Like these QL-A Ⓐ, QL-B Ⓑ, QL-C Ⓒ, QL-D Ⓓ)

These markings mean and symbolise the certainty or accuracy of that service line mark, and without this mark, it doesn’t conform to the AS5488 standard.

Now that you have a brief understanding of what Quality Levels are, let us now proceed to other ground markings which we can see on-site

Geoscope providing quality utility mapping services
Geoscope Quality Utility Locating Marking Services

These markings are called utility depths.

Utility Depths

What are utility depths? These are the utility measurement of depths captured from different locating methods.

But how exactly do we classify utility depths?

Well, we classify utility depths either by quality levels or by the number of depths themselves.

Utility Depths classified by Quality Levels

Geoscope Utility Locating Services
Geoscope Utility Marking Services - Utility Depths based on Quality Levels

For Quality levels, utility depths are classified based on the locating methods performed.

Quality Level A, there is a tolerance of ± 50 mm. This means that the measurement should be accurate.

Examples of locating methods classified as Quality Level A are as follows:

  • Sighting the pipe/ conduit from the pit then the depth will be measured from there.
  • Exposed pipes/ conduits
  • Potholing
  • Trenching

In general, QL-A can be classified from exposed pipes/conduits from the pits, measurement of the invert/obvert/centre, etc., using tape or other devices.


Quality Level B, there is a tolerance of ± 300 mm but is not as accurate as A. You need to use an instrument/equipment to identify the depth of the utility.

This method can be determined with the help of exposed pipes/conduits by connecting to them and then scanning throughout the site using Electromagnetic locating.


Examples of locating methods classified as Quality Level B are as follows:

  • Direct connecting to water meters, water taps, and any metallic material pipes/conduits
  • Clamping onto copper wires (e.g. Telstra/Communication)


For QL-B, you need to “get help” from the exposed/QL-A utilities and use the EM to distinguish the depths.


Quality Level C, the tolerance is unconfirmed, is not really an accurate one as you do not have a direct connection/access to the utility. There are times that it would be just based on the maps/plans.


Examples of locating methods classified as Quality Level B are as follows:

  • GPR
  • Poor signal/weak signals from QL-B locating methods
  • String line (connecting 1 QL-A to another QL-A) from the QL-A (E.g. stormwater pit to another stormwater pit)


Quality Level D, there is no tolerance on this one since we only reference it to existing records and/or anecdotal evidence we get from DBYB. In simpler terms, utility locators usually do not declare the depths for QL-D since it is really just from the plans which were marked on-site. 


For other locating methods, such as rodding, and Flexi trace sonde, most locators usually classify it as QL-C.


If you got all that, let us now proceed to the utility depths as classified by the number of depths themselves.

Utility Depths classified by the Number of Depths themselves

As for the number of depths themselves, it is usually based on the values from the electromagnetic locating and GPR. For quality level A, we usually measure it from a tape measure or the distance laser tape measure.


Now, much information has been shared already, and if you are still scrolling through this article to this point, then you must be really interested in learning about what markings on the ground mean especially in utility locating. 

Here’s a little teaser for you to see if you can now finally understand better what these ground markings mean: 

Geoscope Sample Ground Marking

You probably aced that picture!

Here is the breakdown of that picture just in case you want to make sure you understood the ground marking you just saw…

Geoscope Utility Marking Service Signature since 2013
Geoscope Underground Utility Marking Signature since 2013

Now, since you already have an in-depth understanding of what utility markings mean on utility locating, let me now give you the other additional ground markings that are also present on-site. 

These are the additional comments from the utility locating professional in situations when they are unable to locate the utilities, when there is no signal, when they are using their locating tools, or when it is already the end of the trace, and a lot more.

Additional Comments from Utility Locators

In cases such as this, you might be wondering what the comments of utility locators look like for different scenarios. Are they in the form of symbols or codes as well? Or do they write it like the normal writings we use in daily life? 

Well, below are the answers to your questions:

This list consist of additional site-marking comments from utility locating professionals

These are the additional comments or markings that are written by the professional utility locators which we can possibly see on-site grounds.


Now that you really have an in-depth understanding of what the markings on the ground mean, we can both agree that these markings are not just some sort of childish scribble or graffiti that has no meaning.

As we have discussed, utility markings play an important role in any site work since they serve as indications and representations of what underground utilities could potentially be below.

But despite having understood what they meant, when you are still planning to work on or near any underground utilities, it is still very important to hire not only any utility locators but certified utility locating professionals to locate utilities underground for you. 

Why should you hire Certified Locators to locate and mark underground utilities?

Geoscope Certified Utility Locators

Because even being equipped with such knowledge about site markings, considering hiring certified locators are actually what is going to not only help you from taking massive risks but also save you from actually causing damages or issues when working near underground utilities or assets.

If you want to know further details as to what could possibly happen when you accidentally damage an underground utility, please refer to this article Accidental Damage to Underground Services.

When it comes to hiring utility locators prior to working on-site, I highly recommend Geoscope Utility Detection Pty. Ltd. because, at Geoscope, the utility locators are not only experts in ground markings, but are also DBYB certified professionals when it comes to overall utility locating. And you can guarantee that they only work with the highest standard (Australian Standard 5488) when it comes to fulfilling the duty of care and completing the work safely. 

If you want to know more about the quality services being provided by Geoscope, feel free to send them a message here Contact Us or Request a Quote from us if you want to go ahead and book a job with them. 

Contact Geoscope

Whether you have a question about our services, pricing or anything else, our Geoscope team is ready to answer all your questions

More to explorer

Utility Locating at 52 McLaren Street North Sydney NSW 2060 by Geoscope Locating

Utility Locating in North Sydney, NSW

Geoscope Locating provides expert utility locating services in North Sydney and surrounding areas. With our local knowledge and advanced technology, we ensure the safety and efficiency of your excavation projects.

Underground Service Locating at Mandarin and Malta Street Fairfield East NSW 2165 by Geoscope Locating

Underground Service Locating in Fairfield, NSW

Need reliable Underground Service Locating in Fairfield? Geoscope are the local experts. Our technicians use premier ground penetrating radar (GPR), electromagnetic locating and non-destructive vacuum excavation to pinpoint underground utilities with unmatched accuracy. Avoid costly utility strikes — identify pipes, cables and more before you dig with our specialty mapping and detection services. Get a free quote now.

Utility Locating at Armstrong Court Bankstown Aerodrome NSW 2200 by Geoscope Locating

Utility Locating in Sydney, Australia

Geoscope Locating provides expert utility locating services in Sydney and surrounding areas. With our local knowledge and advanced technology, we ensure the safety and efficiency of your excavation projects.

Leave a Reply

Your email address will not be published. Required fields are marked *