Before anyone breaks ground, you need to know what is already under it. An underground utility survey locates and maps the buried services on your site, water, gas, electricity, telecoms and drainage, and provides information to support design and excavation planning. 360 Surveys NI carries out PAS 128 utility surveys across Northern Ireland and the Republic from our base in Portadown.
Record drawings can be incomplete or out of date, particularly where private services or later alterations are involved. Site investigation helps compare the records with evidence on the ground. It cannot guarantee that every buried feature will be detected.
What an underground utility survey involves
We combine electromagnetic location and ground penetrating radar for utility detection. Each contributes different information, and neither can identify every service in every ground condition.
Electromagnetic location picks up the signal from metallic pipes and live cables. We can trace a service directly by connecting a signal generator to it, or detect the signal a live power cable already gives off. The appropriate tracing method depends on the service and the available access.
Ground penetrating radar sends a radar pulse into the ground and reads what comes back. It can help investigate non-metallic pipes, ducts, voids and other subsurface features that may not be traceable electromagnetically. We use a Leica DS4000. More on our GPR survey work.
Running both over the same area, and cross referencing against any record drawings you hold, gives a far more complete picture than either method alone.
PAS 128 quality levels
PAS 128:2022 is the British Standards specification for underground utility detection. It sets out quality levels describing how thoroughly a survey has been done and how much confidence you can place in the result. Our confirmed scope covers QL-D through QL-B. The required investigation and achievable quality depend on the brief and site conditions. QL-A verification requires trial excavation and is quoted separately.
| Survey type | Quality level | Information and limitations |
|---|---|---|
| D, desktop records search | QL-D | Available asset records; positions are not verified on site |
| C, site reconnaissance | QL-C | Records compared with visible site evidence |
| B, detection | QL-B4 | Assumed route where the utility has not been detected |
| B, detection | QL-B3 | Detected horizontal position; no reliable depth |
| B, detection | QL-B2 | Detected position and depth, with the achieved confidence recorded |
| B, detection | QL-B1 | Higher-confidence detection supported by the required evidence |
| A, verification | QL-A | Physical verification by trial excavation; separately quoted, not included as standard |
A P suffix identifies GPR post-processing. Agree the required processing and deliverables when the survey is scoped.
QL-A verification requires trial excavation, so it is quoted separately rather than included as standard.
Detection methods and search resolution
PAS 128 also sets out how densely the site is searched. The right method depends on how congested the ground is.
| Detection method | Search planning | What to agree |
|---|---|---|
| M1 | Lower-density investigation | Coverage, service records and site constraints |
| M2 | More detailed investigation | Search resolution and the utilities relevant to the brief |
| M3P | Detailed investigation with GPR post-processing | Coverage and processing for the agreed investigation area |
| M4P | Intensive investigation with GPR post-processing | Coverage and processing for complex or congested areas |
The method affects the fieldwork and processing required. Tell us the site and what you are planning and we will recommend the level that fits.
What you receive
- A measured drawing in CAD showing the services found, their routes and, where established, their depth
- Each service classified to its PAS 128 quality level, so you can see exactly how much confidence attaches to each line
- Services marked on the ground in paint or pegs if you need them for an immediate dig
- Drawings coordinated with a topographical survey where this is included in the agreed brief
- A statement of what was looked for, what was found, and where ground conditions limited the survey
Typical turnaround is 6 to 10 working days from the site visit, depending on the size of the site and the number of scans captured.
Who needs a utility survey
- Contractors about to excavate, who need to avoid striking a live service
- Civil and structural engineers designing drainage, foundations or services routes
- Architects and developers at feasibility and design stage, where a buried main can change a layout entirely
- Councils and public bodies managing works in the public realm
- Utility companies verifying their own apparatus
- Homeowners and self builders planning an extension or a new driveway
If you are applying for a consent of discharge or setting out a new drainage run, knowing what is already in the ground is usually the first step.
Why it matters
Striking a buried service is expensive and it is dangerous. A damaged power cable can injure or kill the person operating the machine. A struck water main floods the site and the neighbours. A severed fibre cable can take out service to a whole area, and the bill for that does not stop at the repair.
Beyond the safety case there is the programme. Work stops while the service is repaired and the incident is investigated. A survey helps inform the planning of excavation, alongside the appropriate safe working procedures.
What a utility survey costs
Cost depends on the size of the area, the quality level and detection method required, the ground conditions and how much is buried. The amount of work varies with the site. A town centre street with a full set of statutory services under it is a different job entirely.
Send the location, site boundary, purpose and required deliverables for a site-specific quotation. The quotation should identify the agreed scope and any separately priced verification work.
Ground conditions and what they affect
Radar performance varies with what is in the ground. Dry sand and gravel give good penetration. Heavy clay, common across much of Northern Ireland, absorbs the signal and reduces the depth we can reach. Reinforced concrete, made ground and heavily contaminated fill all scatter the return.
None of this makes a survey pointless, but it does mean an honest report says where confidence is lower. Depths taken from GPR data are to the crown of the reflection unless stated otherwise. We would rather tell you that up front than hand you a drawing implying certainty we do not have.
Where we work
We cover the whole of Northern Ireland from Portadown, including Belfast, Armagh, Craigavon, Newry, Lisburn, Banbridge, Dungannon, Ballymena, Coleraine, Enniskillen and Derry, and we work across the border into the Republic including Dublin, Dundalk and Drogheda.
Working alongside other surveys
A utility survey is often done at the same time as other work, which saves mobilising twice:
- Topographical surveys, so services and surface detail sit on one drawing
- Measured building surveys
- Drone surveys for larger sites
- As built manhole surveys, which tie the drainage network into the utility picture
Frequently asked questions
Do you work to PAS 128?
Yes, to PAS 128:2022. We cover quality levels QL-D through QL-B, with detection methods M1 to M4P depending on how congested the site is. QL-A verification involves trial excavation and is quoted separately. Tell us the level your client or designer has asked for and we will confirm what is achievable and what it costs.
How accurate is an underground utility survey?
Accuracy and confidence depend on the achieved quality level, the service and site conditions. The drawing should state the quality level and limitations for each service. Detection is not physical verification: QL-A requires trial excavation and is quoted separately. Agree any numerical tolerance requirements before commissioning the survey.
Will you find everything that is buried?
No survey can promise that. The survey is non intrusive, so it always remains possible that there are anomalies within the boundary we have not detected. Deep services, small plastic pipes in heavy clay and anything beneath reinforced concrete can all be missed. A good survey tells you what was found and where the method was limited, so you can judge the residual risk rather than assume there is none.
Do I still need to hand dig?
Yes. Any utility detected should be treated as live unless the asset owner confirms otherwise, and safe digging practice near located services still applies. In critical areas, trial excavation is the only way to confirm identification, position and depth.
How long does it take?
Site time depends on the agreed scope and site conditions. Typical turnaround for drawings is 6 to 10 working days from the site visit, depending on site size and the number of scans.
Can you mark the services on the ground?
Yes. If you are digging imminently we can paint the routes on the surface as well as supplying the drawing.
Get a quote for your utility survey
Send us the site location, a boundary if you have one, and what the survey is for. We will come back with a price and a date.
Request a quote or call 028 38339820.