What Is PAS 128? SUE and Utility Mapping Quality Levels Explained

Subsurface utility engineering (SUE) is the practice of finding, verifying and recording buried services before design and excavation, and in the UK it is specified through PAS 128. It reduces strike risk, redesign and delay, and gives designers a reliable picture of what is underground.

Why It Matters

Government figures put the UK’s buried network at around 4 million kilometres of pipes and cables. It estimates that approximately 1 in every 65 holes dug results in an accidental asset strike (c. 60,000 a year), causing around £2.4 billion worth of economic cost. Strikes on gas mains or high-voltage cables put workers’ lives at risk.

PAS 128 Quality Levels

• QL-D, desktop records search: collating statutory undertaker records.
• QL-C, site reconnaissance: walkover to match surface features such as covers and valve boxes to records.
• QL-B, detection: geophysical survey, typically electromagnetic location (EML) and ground penetrating radar (GPR); see utility mapping and 3D mapping.
• QL-A, verification: exposing the service, typically by vacuum excavation, to confirm position, depth and type.

Specifying the quality level needed for each zone of a site, rather than one level everywhere, keeps cost proportionate to risk.

NUAR and Digital Records

The National Underground Asset Register is a digital map of pipes and cables in England, Wales and Northern Ireland. Government says the Data (Use and Access) Act achieved Royal Assent in June 2025, putting NUAR on a statutory footing. NUAR improves access to records, but records are not a survey: responsibility for safe digging stays with those excavating, and PAS 128 survey data remains the basis for design.

Safety: HSG47

HSE guidance HSG47, Avoiding danger from underground services, sets out the safe system: plan, locate with records and detection, and use safe digging practice. HSE advises that you excavate alongside the service rather than directly above it when exposing it.

Procurement Checklist

• Which PAS 128 quality level is required for each area?
• Which detection methods and GPR grid density will be used?
• Will the deliverable be in CAD or BIM-ready format? See CAD draughting and BIM modelling.
• Will drainage be surveyed by CCTV to confirm connections? See CCTV drain surveys.
• Is there a clear report of confidence and limitations?

Frequently Asked Questions

Is PAS 128 Mandatory?

It is a specification, not law, but clients and principal contractors commonly require it as evidence of a robust approach to locating services.

Does NUAR Replace a Utility Survey?

No. It provides access to owners’ records. Detection and verification on site are still needed.

Talk to Us

Civil Connect Subsurface Solutions delivers PAS 128 utility surveys, GPR, vacuum excavation verification and drainage CCTV. See pre-construction asset verification, contact us or call 0208 387 5591.

To commission a survey, see our PAS 128 utility mapping service, or 3D utility mapping for a 3D model.