Underground utility survey (PAS 128)
A utility survey shows where buried services run before you design or dig. We combine electromagnetic location with ground penetrating radar, so plastic pipes and unrecorded services are found as well as live cables.
What the survey finds
When you need a utility survey
- Before design. Engineers and architects need to know where services run before they lay out drainage, foundations, kerb lines or new connections.
- Before excavation. A utility clearance survey marks services on the ground so trenches, trial pits and foundations avoid them.
- Before directional drilling. HDD and moling routes need the services along and across the route located first.
- When records are missing or out of date, which is common on old industrial sites, campuses and estates.
How a utility survey runs
- Records. We obtain the statutory records (STATS) from the asset owners, or work from records you hold.
- Reconnaissance. We walk the site, lift accessible covers and note chambers, valves, meters and street furniture.
- Tracing. Each recorded service is traced with electromagnetic location (EML), using the signal already on live cables or one we apply to pipes and cables at chambers and valves.
- Searching. The area is swept on a grid with EML and GPR to find services that are not on the records. A passive sweep picks up live cables that aren't shown, and GPR finds plastic pipes that EML cannot.
- Marking and drawing. Services can be marked on the ground in paint. Every service is drawn in CAD with its PAS 128 quality level and indicative depth.
PAS 128 quality levels
PAS 128 is the UK specification for underground utility detection, verification and location. It gives every service on the drawing a quality level, so designers know how much to rely on it.
| Level | What it involves | What you learn |
|---|---|---|
| QL-D | Desktop search of utility records (STATS) | What the asset owners say is there |
| QL-C | Site reconnaissance: chambers, covers and street furniture | Records checked against what is visible |
| QL-B | Detection with electromagnetic location and GPR | Horizontal position, and depth where the method allows |
| QL-A | Verification by exposing the service, e.g. trial holes or vacuum excavation | Confirmed position, depth and type |
Most of our surveys are carried out to QL-B, supported by records and reconnaissance. We can obtain the STATS records for you, or work from records you already hold.
Why we use both EML and GPR
Electromagnetic location (EML) traces metal services and live cables, and it can follow a specific service from a chamber or valve. It can detect small-diameter cables, but it cannot find plastic pipes or clay drains unless a sonde or tracer wire can be used.
GPR detects metallic and non-metallic services alike, along with voids and old foundations. It doesn't need access to a manhole or valve, but it cannot tell you what a service is. Used together, the two methods find more services and identify more of them than either does alone.
Utility and topographical survey together
Many clients need both. One team surveys the surface features and the buried services in the same visit, so you receive a single CAD drawing in the same coordinates. Covers, valves and kerbs sit in the right place relative to the services traced between them, and there are no two drawings from two contractors to fit together. See our topographical survey page.
Planning for a utility survey
- Send the red-line boundary and any existing records.
- Tell us about traffic management, permits or restricted access.
- Allow time to lift covers: we need safe access to chambers.
- If you will dig near critical services, plan trial holes to verify them (QL-A).
Questions we're asked
Do I need a PAS 128 survey?
If the results will be used for design, or if excavation is planned near services, a PAS 128 survey gives you a clear statement of what was found and how reliable it is. Many clients and principal contractors now require it.
What do you need from me for a quote?
A clear boundary plan (a marked-up Google map, PDF or topographical survey), the PAS 128 quality level you need, and any statutory records you already hold. Tell us about access restrictions or preferred working hours too.
What is a utility clearance survey?
A survey that locates and marks buried services on the ground just before digging, so excavation can avoid them. It is usually a smaller area than a full mapping survey, and the marks are often backed up with a sketch or drawing.
Do you get the STATS records?
Yes. We can obtain the statutory records from the asset owners at extra cost, or you can provide them. A utility survey needs them before work starts.
Can you guarantee every service is found?
No survey can. Very deep services, small cables, poor ground conditions and congested areas can all hide services. Our report states the limitations on your site, and we recommend safe digging practice (HSG47) and trial holes before excavating.
How long does a utility survey take?
A typical development plot or road section takes one to three days on site, depending on size, access and how congested the services are. Drawings follow, normally within 15 working days.