Understanding Utility Locating and Reporting
A practical guide to AS 5488 and Quality Levels, for project managers, engineers, and site teams.
Why This Guide Exists
The problem with a line on a plan
Underground services are among the most common causes of unexpected cost, delay, and safety incident on a construction site. Yet the information a project relies on — the plans, the records, and the marks sprayed on the ground — varies enormously in how far it can be trusted.
A line on a drawing can mean a service was physically dug up and measured, or it can mean someone drew it from a record that was never surveyed. Both look the same on paper. The difference decides whether it is safe to put a machine in the ground.
This guide explains how that reliability is classified under AS 5488, what each level of confidence means for your decisions, and how to read and commission a utility locating deliverable so the risk is understood before anyone breaks ground.
What AS 5488 actually is
AS 5488, Classification of Subsurface Utility Information, is the Australian Standard that classifies how reliable underground utility information is. It does not locate anything, and it cannot make a service more accurate. What it provides is a common language — a set of Quality Levels — so that everyone from the designer to the excavator understands how much confidence sits behind a given line.
First published as AS 5488-2013 and revised in 2019, the standard now sits in two parts. Part 1 covers subsurface utility information — the Quality Levels this guide focuses on. Part 2 covers subsurface utility engineering, the framework for managing that information through design and delivery.
What the standard does not do:
- It does not prescribe how a utility must be located; the method is left to the locator.
- It does not guarantee that a service exists exactly where it is shown.
- It does not remove the need for physical verification before high-risk excavation.
The idea in one line. AS 5488 measures confidence, not correctness. A service shown at the highest Quality Level has been physically verified. A service shown at the lowest has been drawn from a record that may be incomplete, superseded, or simply wrong. Both can appear on the same plan, which is exactly why the level matters.
The Four Quality Levels
AS 5488 defines four Quality Levels of confidence, ranked from QL-D, the lowest, to QL-A, the highest. Each level reflects how the information was obtained, and therefore how far you can rely on it when planning or excavating.
Each step up the ladder adds a layer of evidence. Records tell you a service may exist. Surface features tell you roughly where. Geophysical detection gives a measured position on the surface. Physical exposure confirms exactly where it is, how deep, how big, and what it is made of.
Read every plan as mixed. A real utility plan is rarely a single Quality Level. One drawing routinely carries a potholed water main at QL-A, a traced cable at QL-B, an inferred drain at QL-C, and a gas main known only from records at QL-D. A good deliverable labels each, so you can see where confidence is high and where it is not.
The Lower Levels: QL-D and QL-C
The two lower levels are built from information rather than field measurement. They are valuable for planning and desktop work, but neither is a basis for putting a machine in the ground.
Existing records only
Information taken entirely from existing records: utility plans, as-built drawings, and Before You Dig Australia (BYDA) responses. It is the starting point for almost every project.
- Achieved by
- Desktop review of asset-owner records and BYDA plans. No field work is involved.
- You can rely on
- A general indication that a service may be present in an area, enough for early planning and design.
- Treat with care
- Records are frequently incomplete, superseded, or drawn without survey accuracy. QL-D alone is not a basis for any excavation decision.
Records correlated with surface features
Records reconciled with visible surface features, such as pits, valves, marker posts, and service boxes, to infer the likely alignment of a service between known points.
- Achieved by
- A site walkover that ties record information to what can be seen and measured above ground.
- You can rely on
- A more credible alignment than records alone, anchored to real surface evidence at each end.
- Treat with care
- The path between features is still inferred, depth remains unknown, and any service with no surface expression will be missed.
The Higher Levels: QL-B and QL-A
The two higher levels involve field measurement. QL-B fixes a service on the surface; QL-A confirms it in the ground. The step between them is the difference between a strong estimate and a certainty.
Detected and marked by geophysics
The horizontal position of a service detected and marked on the surface using geophysical methods, principally electromagnetic locating and ground penetrating radar.
- Achieved by
- Field detection with equipment such as the Radiodetection RD8100 and IDS C-Thrue, by direct connection to an accessible point or by tracing an induced signal.
- You can rely on
- A measured horizontal position for detectable services, marked on the ground and captured on plan. Confidence is substantially higher than QL-C.
- Treat with care
- Depth is an estimate, not a measurement. Non-conductive pipes and deep or congested services may be weak or undetectable, and a stated tolerance applies.
Physically exposed and measured
The highest level of confidence, achieved by physically exposing the service so its exact position, depth, size, and material can be measured directly.
- Achieved by
- Careful excavation, typically non-destructive potholing or vacuum (hydro) excavation at the point of interest.
- You can rely on
- Verified horizontal position, depth, diameter, and material at the exposed point. This is the only level suited to high-consequence excavation.
- Treat with care
- QL-A applies only at the point exposed. The service reverts to a lower level between potholes.
One Site, Four Levels
A single plan usually carries several Quality Levels at once. The cross-section below shows four services on one verge, each held at a different level of confidence.
On this verge, the water main was potholed at the proposed bore crossing, so it is held at QL-A: position, depth, diameter, and material are all confirmed at that point. The power cable was traced and marked from an accessible pit, giving a reliable surface line at QL-B, with depth noted only as an estimate. The stormwater pipe was drawn between two visible pits at QL-C — a sensible inference but not a measured path. The gas main appears only because a BYDA record places it there; with no field confirmation it stays at QL-D, and its true position is genuinely unknown.
The lesson is simple: do not treat a plan as uniform. Check the level attached to each service, and, where it matters, to each segment. Confidence is something you read off the drawing, not something you assume from the fact that a line has been drawn at all.
The Methods That Set the Level
A Quality Level is not chosen; it is earned by the method used. The stronger the evidence a technique produces, the higher the level it can support. Most site work combines several methods.
Traces conductive services — power, metallic water, copper comms — by applying or inducing a signal and following it on the surface. The workhorse of QL-B, but it needs a conductor or an accessible connection point.
Detects buried features from reflected radar, including non-conductive pipes that EM cannot see. Complements EM well, but attenuates in wet, clay-rich, or heavily reinforced ground.
Pushes a small transmitter or traceable rod through a non-conductive pipe or drain so it can be tracked from the surface. Requires internal access to the line.
Physically exposes the service to confirm it directly. The only route to QL-A, and the only way to measure depth, size, and material with certainty. Point-specific, slower, and higher cost.
| Method | Typical level | Principal limitation |
|---|---|---|
| Records & BYDA review | QL-D | Only as reliable as the source records |
| Surface feature correlation | QL-C | The path between features is inferred |
| Electromagnetic locating | QL-B | Needs a conductor or tracer; depth estimated |
| Ground penetrating radar | QL-B | Attenuates in wet, clay, or congested ground |
| Sonde / traceable rodding | QL-B | Requires internal access to the pipe |
| Potholing / vacuum excavation | QL-A | Point-specific, slower, higher cost |
Colours, Codes, and Line Types
A utility plan communicates through a consistent visual language. Three conventions do most of the work: the colour of a service, the code that names it, and the line type that shows how it was found.
Service colours
AS 5488 sets out a suggested colour convention used both for marks sprayed on the ground and for lines on the plan. The Australian convention differs from the American one in an important way: electricity is orange, and red is reserved for fire services.
Shades may vary between providers, and contrast sometimes forces a substitution, such as white paint for comms on a dark surface. What matters is that the plan carries a legend and that colour use stays consistent across every mark, sketch, and drawing for the site.
Asset codes
The standard also defines a set of short alphanumeric codes — around 150 of them — that label each service type on a drawing. Codes keep a plan readable in black and white and remove ambiguity where colours are hard to tell apart. They sit alongside the colour, not instead of it.
Line types
Line style carries meaning too. A solid line generally shows a service that was detected and marked in the field. A dashed line shows an alignment that was inferred or taken from a record. Reading line type alongside the Quality Level tells you how the line came to be on the page.
Notation and Annotation
Beyond colours and codes, a plan carries short annotations that record what was measured and, just as importantly, where a measurement stops. The common terms are worth knowing.
100mmØDiameter of a pipe or conduit; the Ø symbol denotes diameter.I.L 700mmInvert level, the depth to the inside base of a pipe.DepthDepth to the top of a service; at QL-B this is an estimate.EOTEnd of trace, the point beyond which a signal could not be followed.QL-A…DThe Quality Level attached to a run or segment.— / – –Solid for located, dashed for inferred or record.Note on EOT. An EOT mark does not mean the service ends. It means the trace ended. The line may well continue underground; it simply could not be confirmed past that point. Treat everything beyond an EOT as unlocated.
How we annotate. Our plan annotations state the finding, then use a semicolon to introduce any caveat, naming the methods that could not confirm it. For example: 100mmØ PVC stormwater, I.L 700mm; alignment beyond pit inferred, not traced. The reader sees both what was found and the limit of that finding in a single line.
A Worked Annotation
The plan below brings the conventions together on a small site. Colour identifies the service, a code and note record what was measured, an EOT marks where a trace stopped, and every run carries its Quality Level.
Reading the plan, the water main is a solid blue line: detected and marked at QL-B, with an EOT where the trace could no longer be followed past the valve. At Pothole A1 the main was exposed and confirmed, so that one point is QL-A. The stormwater line is dashed and green, drawn between two visible pits at QL-C: invert levels were read at the pits, but the run between them is inferred. The power cable is solid orange at QL-B, its depth noted only as an estimate, and it too carries an EOT. Every run states what was found and, in the note after each semicolon, the limit of that finding. Nothing on the plan asks the reader to guess how far to trust it.
Limitations and Realistic Expectations
Utility locating is a risk-reduction process, not a guarantee. Understanding where it is weakest is what lets a project use it safely. A few recurring limits are worth keeping in mind on every job.
Locating reduces risk. It does not remove it.
The best outcomes come from combining methods, from good records, and from verifying anything whose strike would be serious. No responsible locate can promise that every service on a site has been found.
Detection is not identification
A signal or a radar response shows that something is present. Confirming what it is, and how big, needs supporting evidence or exposure.
Depth is approximate
Positions from surface geophysics estimate depth from signal, which shifts with soil and congestion. Only QL-A confirms depth.
Not everything responds
Non-conductive poly water and gas, fibre without a tracer, and deep or congested services can be weak or wholly undetectable.
"Not located" is not "not there"
An absence of signal means nothing was detected, not that the ground is clear. Unrecorded and abandoned services exist on many sites.
Marks carry a tolerance
A surface mark is the centre of a tolerance zone, not a hairline. Hand-dig or use non-destructive methods within that zone.
Some areas cannot be reached
Access, surfaces, and structures create zones where no data can be collected. These are gaps, not confirmation of a clear path.
Specifying a Locate, and Digging Safely
A locate delivers most value when it is scoped around risk. The question is not simply "locate the services", but "to what level of confidence, and where does that confidence need to be highest".
Before the work: match confidence to consequence
Decide where a record or a surface trace is enough, and where the cost of a strike justifies physical verification. A comms conduit in soft ground and a charged high-voltage cable beneath a proposed bore are not the same decision, and should not be given the same level of confidence.
What to give your locator
- Share drawings, BYDA plans, and known site constraints up front.
- State the objective clearly: a clash check reads differently to a dig approval.
- Nominate the Quality Level you need, and where — QL-A at the crossings that matter, a lower level elsewhere.
The five P's of safe digging
Whatever the Quality Level, excavation near services follows a simple, ordered discipline.
Plan
Lodge a BYDA enquiry and review every available record.
Prepare
Have services located and marked to a level suited to the work.
Pothole
Expose critical services to confirm position and depth (QL-A).
Protect
Support, barricade, and clearly mark exposed services.
Proceed
Dig carefully, hand-dig within tolerance zones, and stop if the unexpected appears.
The single most useful habit. Ask, for every excavation, "what is the consequence if this is wrong". Where the answer is serious, lift the service to QL-A before you dig. Where it is minor, a documented lower level is a reasonable, deliberate risk. The point is that the choice is made on purpose, not by accident.
Common Questions
What is the difference between a BYDA enquiry and a utility locate?+
Can you find plastic (poly or PE) water and gas pipes?+
Why is the depth on my plan only an estimate?+
What does EOT mean?+
Do I need potholing on every job?+
Does a located mark mean it is safe to dig on the line?+
Can you guarantee every service has been found?+
Using the Results Well
Good utility information only pays off in the decisions it informs. Three habits carry most of the benefit through design, delivery, and the moment before excavation.
In design
Read each service at its Quality Level. Design clearances against confirmed information, and flag where low-confidence services sit inside the works for later verification.
During works
Keep the plan live. As services are exposed or added, record the new evidence and update the level. A locate is a snapshot, and sites change.
Before excavation
For any high-consequence dig, verify by potholing to QL-A. Treat records and traces as a guide to where to expose, not as approval to excavate.
Read a plan as a map of confidence
AS 5488 exists so that confidence can be stated plainly rather than assumed. Act freely where confidence is high, verify where it is low, and never let a line on a drawing stand in for a hole in the ground when the cost of being wrong is serious. Used this way, utility information becomes a genuine tool for managing risk, cost, and safety across the whole life of a project.
Let's talk about your site
Utility location, ground penetrating radar, concrete scanning, and structural diagnostics across South East Queensland — reported to AS 5488.
