What is PAS 128?
PAS 128 is the British Standards Institution (BSI) and Institution of Civil Engineers (ICE) specification for how underground utility surveys should be planned, carried out and reported in the UK. It provides contractors, engineers and surveyors with a consistent way to describe the level of confidence in underground utility data, recognising that different survey methods provide different levels of information and verification.
The Four PAS 128 Survey Types
PAS 128 defines four categories of survey, each building on the one before it and offering a different balance of cost, speed and confidence.
Type D — Desktop Study
A records-based search carried out without a site visit. It collates existing utility company plans and data into a single report, providing a fast and cost-effective starting point for understanding what utility information is recorded for a site.
Type C — Site Reconnaissance
A visual inspection that verifies desktop records against what is actually visible on the surface. This can include valve covers, manhole covers, inspection chambers and other surface features that indicate a utility runs beneath.
Type B — Detection Survey
An on-site geophysical survey using equipment such as ground penetrating radar (GPR) and electromagnetic location (EML) to physically trace buried services. Type B surveys are further split into confidence sub-levels, from QL-B4 (limited detection, one method) up to QL-B1 (multiple detection methods used together, giving the highest achievable confidence without physical excavation).
Survey grid spacing, which determines how densely the ground is scanned, also affects confidence. This ranges from wider 5m spacing up to a detailed 0.5m grid on complex sites.
Type A — Verification Survey
Physical exposure of a utility, typically through trial pits or vacuum excavation, to directly confirm its exact position, depth and material. This provides the highest possible confidence level under PAS 128. Because it is invasive and site-specific, it is normally used only at a small number of critical points, for example, where a planned excavation is expected to cross a utility rather than across an entire site.
Which Survey Type Do You Need?
Cornerstone Projects provides PAS 128 Type D desktop searches: compiling utility company records into a single, fast and cost-effective report, typically delivered within 24 hours.
A Type D desktop search is an efficient starting point for almost every project, including planning applications, early-stage design and excavation work where you need to understand what is likely to be underground before deciding whether more detailed on-site surveys are required.
By bringing available utility company records together into one clear report, a Type D search gives you an accessible starting point for understanding the recorded utility information associated with your site.