Hydro and air vacuum excavation to physically expose and prove underground utilities — achieving AS5488 QL-A certainty before your plant moves in. Melbourne and Victoria-wide.
Non-destructive digging — commonly called potholing, daylighting, or vacuum excavation — uses pressurised water or compressed air to break up and remove soil around a buried service, with a high-powered vacuum collecting the spoil into an on-truck debris tank. No mechanical force contacts the utility at any point.
The two principal methods are hydro excavation (water jets loosen the soil, effective in Melbourne's clay-rich ground) and air excavation (pneumatic or air-knife, preferred near water-sensitive electrical and telecommunications assets). Both achieve the same outcome: the service is physically exposed, undamaged, and visible for inspection, measurement, and survey.
NDD is the terminal step in the subsurface utility mapping process — it converts QL-B detected data into QL-A verified data, which is the only quality level that gives excavation crews positional certainty to ±50 mm. For assets that may not appear on BYDA records at all, see underground services not on plans.
The Safe Work Australia Model Code of Practice: Excavation Work (October 2022) requires that where the position of underground services is uncertain, potholing or equivalent physical proving must be completed before mechanical excavation begins. The code is adopted in Victoria under the OHS Act 2004.
The same code and the WorkSafe Victoria / Energy Safe Victoria Guide to Undertaking Work Near Underground Services (December 2022) establish the 1 metre exclusion rule: no mechanical excavation within 300 mm of any located underground service, with the approach corridor between 300 mm and 500 mm restricted to hand tools and spotters. Near high-voltage cables and major gas pipelines, the No-Go Zone extends to 3,000 mm — meaning NDD is often the only permissible method of advancing the excavation face.
Before You Dig Australia (BYDA) data defaults to QL-D — indicative plans with no depth information, no condition record, and explicit disclaimers that position is not guaranteed. BYDA records are a mandatory starting point, not a substitute for proving. The No-Go Zone rules for excavation safety page explains the regulatory distances in full.
Under AS5488.1:2022 (Standards Australia, approved 14 June 2022), QL-A is defined as physical exposure of the utility with a surveyed position accurate to ±50 mm in both the horizontal and vertical planes. It is the only quality level that records material type, nominal size, depth to invert, and asset condition in a single field operation.
QL-B — achieved by EMI and GPR during subsurface utility mapping — provides ±300 mm horizontal and ±500 mm vertical positional accuracy. That tolerance is acceptable for preliminary design but insufficient for congested corridors, clash detection in BIM, or confirming clearance before a horizontal directional drill. QL-A via NDD closes that gap.
The QL-A survey record produced by HR Utilities is delivered in the same CAD and GIS formats as our broader utility data deliverables — georeferenced to MGA Zone 55 and AHD, with every exposed utility attributed to the fields required by AS5488 Table 1.
A four-stage process from desktop review to QL-A surveyed deliverable — every NDD engagement follows the same sequence.
We apply subsurface utility mapping (EMI and GPR) and review BYDA records to identify service routes and select pothole positions — minimising the number of exposures needed.
A Site-Specific Safe Work Method Statement is prepared. BYDA referrals and any authority notifications (e.g., Melbourne Water, gas distributor) are completed before mobilisation.
Hydro or air excavation removes soil incrementally around the target service. The utility is exposed without mechanical contact, inspected, photographed, and the spoil is retained on-truck.
The exposed service is surveyed to MGA/AHD with position recorded to ±50 mm (QL-A). Material type, nominal size, depth, and condition are documented and delivered in CAD or GIS format.
NDD operators working on sites in Victoria are expected to hold or be working towards MSMSS00021 — Conduct Vacuum Excavation (MSM Chemical, Hydrocarbons and Refining Training Package), which covers safe operating procedures for both hydro and air excavation equipment. Operator competency is a standard pre-qualification requirement on civil infrastructure projects managed by state and local government clients.
High-pressure water-jetting equipment — used in hydro excavation — is governed by AS 4233.1 and AS 4233.2 (High Pressure Water Jetting), which set minimum pressure ratings, hose and nozzle specifications, and operator safety controls. HR Utilities' hydro excavation operations comply with this standard.
Where NDD exposes gas mains or pipelines, Energy Safe Victoria (ESV) notifiable-works obligations apply. Where the pothole is within 5 m of Melbourne Water assets or easements, Melbourne Water Asset Services notification is required prior to works. HR Utilities manages these authority notifications as part of project setup.
Most projects begin with a BYDA referral and a desktop review (QL-D), progress through EMI and GPR detection during subsurface utility mapping or a Melbourne field locate with our underground utility locators (QL-B), then escalate to NDD potholing (QL-A) at the specific locations where design clashes are critical or mechanical excavation is imminent.
Not every asset needs to be potholed. The escalation decision is driven by risk: how close is the excavation, what is the consequence of a strike, and is the QL-B position tolerance acceptable for the activity at hand? HR Utilities advises on this escalation during the survey phase, so that NDD is targeted where it adds the greatest safety and cost benefit.
For assets that are particularly difficult to detect geophysically — non-conductive water and sewer mains in PVC or asbestos-cement, PE gas mains without tracer wire — NDD may need to be used more broadly, as EMI and GPR alone cannot confirm position to QL-A tolerances for these materials.
Non-destructive digging (NDD) — also called vacuum excavation, potholing, or daylighting — is the controlled removal of soil using pressurised water or compressed air to expose underground services without applying mechanical force. Spoil is collected into a debris tank by a high-powered vacuum, leaving the exposed utility undamaged and visible for inspection and survey. NDD is the only excavation method that achieves AS5488 QL-A, the highest quality level for subsurface utility information.
Hydro (water) excavation uses pressurised water jets to break up and liquefy soil, which is then vacuumed away. It cuts quickly through most soil types and is effective in clay-heavy conditions common across Melbourne. Air excavation (pneumatic or air-knife) uses compressed air instead of water; it is preferred where water-sensitive assets such as electrical cables or telecommunications conduit are being exposed, or where site conditions limit spoil disposal. Both methods are non-destructive and both achieve QL-A when combined with a licensed survey.
The Safe Work Australia Model Code of Practice: Excavation Work (October 2022) requires potholing or equivalent physical proving before mechanical excavation where the position of underground services is uncertain. In practice this means any area where BYDA/AS5488 data is QL-D or QL-B and mechanical plant will approach within 300 mm of a located service. In addition, WorkSafe Victoria and Energy Safe Victoria specify that no mechanical excavation is permitted within 500 mm of a standard underground service and within 3,000 mm of a high-voltage or major pipeline without first confirming service position — NDD is the standard method for doing so.
Yes. Under AS5488.1:2022 (approved by Standards Australia 14 June 2022), QL-A is defined as physical exposure of the utility with a surveyed position accurate to ±50 mm horizontally and vertically, with material type, size, depth, and condition recorded. Vacuum excavation achieves this when the exposed asset is surveyed by a licensed surveyor using total station or GNSS equipment referenced to MGA and AHD. QL-B geophysical methods (EMI and GPR) achieve only ±300 mm horizontal and ±500 mm vertical — insufficient for clash detection in congested utility corridors.
Most utility potholing in Melbourne reaches 1–3 m depth, which covers the majority of water, sewer, gas, and electrical services. NDD equipment can excavate to 5 m or beyond in suitable soil conditions. Where deeper services are suspected — such as high-pressure transmission mains or older sewer trunk lines — HR Utilities assesses soil type, shoring requirements, and safe-entry obligations before mobilisation. All NDD works are conducted under a Safe Work Method Statement (SWMS) in compliance with WorkSafe Victoria requirements.
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