Digging blind is expensive. The Australian Standard AS5488 sets a common language for locating and classifying underground services so projects plan safely, price accurately and avoid damage. The standard defines “Subsurface Utility Information” (SUI) quality levels, the methods behind them, and the way results should be recorded and shared. The most recent edition confirms that SUI is about verifiable location, position and attributes—not guesswork.
If you’re comparing providers, shortlisting property surveyors Perth who reference AS5488 in proposals helps you sort marketing fluff from proven workflow.
The four SUI quality levels—what they actually mean
AS5488 assigns a quality level from D to A based on how the information was obtained and how reliable it is:
- QL-D: records and recollections only. Useful for early planning, but accuracy is limited. If a drawing doesn’t state a level, treat it as QL-D by default.
- QL-C: surveyed above-ground evidence (e.g., lids, valves) reconciled with records.
- QL-B: geophysical detection (EM, GPR) with surveyed positions. Improves confidence without digging.
- QL-A: visual confirmation by safe exposure (typically potholing/vac-exc) with surveyed 3D position and attributes. Highest reliability; the level you rely on for construction near clashes.
For projects in WA metro areas, ask a Perth surveyor to state the planned quality levels up-front on the SUI scope so everyone knows what risk is being retired at each stage.
Quick reference: when each level fits
| Project stage | Typical level | Why it fits |
| Early feasibility / route options | QL-D/QL-C | Fast desktop picture of congestion and corridors. |
| Concept & preliminary design | QL-B (+ targeted QL-A at pinch points) | Reduce major clashes before design freeze. |
| Pre-construction / high-risk digs | QL-A | Verified position, depth and attributes for work near services. |
AS5488 links each level to methods and deliverables, so you can step up confidence as risk and spend rise.
How to order SUI that stands up to audit
A clean SUI workflow moves from records to survey, then detection, then proof by exposure. Start with current asset owner plans to assemble QL-D. Survey lids, pits and markers to lift it to QL-C. Use EM and GPR with a documented methodology to produce QL-B positions. Finally, schedule potholing on likely clashes to confirm QL-A in three dimensions (x, y, depth) and capture size, material and any condition notes. Keep photos, chainages and survey shots in the deliverable.
If the SUI is tied to a broader topographic brief, lock the deliverables into your site survey Perth scope so linework, spot levels and utility codes share one coordinate system.
Accuracy isn’t a vibe—state tolerances
AS5488 sets the classification; it also expects you to state spatial tolerances and how you achieved them. QL-A requires verified 3D position and attributes at the exposure point, while QL-B accuracy depends on technique, soil conditions and survey control. Store methods and tolerances with the data so land surveyors near me, designers and constructors understand what is certain and what is indicative.
Common traps that trip schedules
- Unlabelled drawings: if a plan doesn’t state QL-A/B/C/D, treat it as QL-D and price the risk.
- Misplaced faith in records: asset plans vary in age and accuracy; they’re a starting point, not a dig permit.
- Skipping exposure: geophysics narrows the search; only potholing confirms.
- No change control: if services are relocated or installed mid-project, update the SUI package, don’t wait for as-constructed plans.
Who does what: roles for PMs, locators and surveyors
- Project managers define risk areas, pick target levels by stage and set hold points (e.g., “no excavation within 1.5 m of suspected HV until QL-A”).
- Utility locators perform records reviews, field detection and safe exposure under traffic and safety controls, with photos and measurements.
- Surveyors establish control, position marks and lids, survey detections and exposures, and deliver CAD/BIM/point-cloud outputs to your model standard.
Working with licensed surveyors Perth brings rigour to coordinate systems, datum control and final deliverables so SUI sits cleanly with design and set-out files.
Specify it properly in your contracts
Use short, clear clauses. State: target quality levels by area; required methods; coordinate system and datum; file formats; photo and chainage requirements; and the sign-off process. Require the contractor to label every utility segment with its achieved level and to provide metadata for methods, dates and crew. Include safe-dig permits and traffic guidance where exposure is needed. These points echo best-practice guidance from Before You Dig Australia.
When to step up to QL-A
If an excavation falls within the tolerance band of a detected line; if design pushes clearances; if the asset has high consequence of strike (gas, HV, trunk water); or if records are inconsistent, move to potholing. Exposure gives the verified depth and offsets that construction needs, and it settles disputes before they start.
Hand-over that people can build from
Deliver a single, dated SUI model with layers for quality levels, attributes and photos keyed to chainage. Note any residual uncertainty. Put revision control around updates as works progress. A tidy package reduces RFIs, improves set-out, and transfers cleanly to as-constructed records.
If the works spill across titles or trigger approvals, involve subdivision surveyors Perth early so your SUI aligns with design submissions, utility approvals and later title action.
Take-aways
Treat SUI as a staged risk-reduction process. Plan where you need QL-B to shape design and where only QL-A will do before open trenching. Label everything, declare tolerances and keep your audit trail. Follow that pattern and you’ll protect people, budgets and programs—and you’ll hand the dig team information they can trust.