Records provide context, not a complete answer
Existing plans, asset information, and previous survey records can identify likely services and owners. They also help the survey team understand the site's history. Record the source and date of each input. An old plan may omit later alterations, show an approximate route, or use a reference that does not match the current site drawing.
Surface observations add context through visible covers, cabinets, valves, and other relevant features. Those observations should be located in the project reference and linked to their descriptions. A visible feature may suggest a connection, but it does not prove the full route or condition of a buried service between access points.
Electromagnetic detection follows suitable signals
Electromagnetic location can help trace conductive services or associated conductors. Its usefulness depends on the service, available signal, access, and surrounding conditions. Non-conductive pipes do not become detectable simply because an electromagnetic locator is present; suitable tracer arrangements or other methods may be needed.
The interpretation should state which method supports each reported route. Closely spaced services and complex networks can make signals difficult to distinguish. The survey team should record uncertainty and conflicting indications rather than forcing every response into a definite service line. Equipment capability and professional interpretation both matter to the result.
Radar adds a different type of evidence
Ground penetrating radar records responses to contrasts in subsurface electromagnetic properties. It can contribute evidence about metallic and non-metallic objects under suitable conditions. FHWA guidance notes that conductive ground, including some clay soils, can restrict signal penetration. A radar response needs interpretation; it is not automatically an identified utility.
The expected usefulness of radar should therefore be discussed against the actual site and investigation purpose. Do not assume a universal detection depth or promise complete coverage of every service. Combining complementary methods can strengthen an interpretation, while disagreement between methods is a useful reason to keep a feature unresolved.
Match the evidence to the project decision
A broad planning exercise and a detailed design interface may require different levels of confidence. Define the area of interest, proposed interfaces, information required, and acceptable uncertainty with the survey team. Where a critical question cannot be resolved by non-intrusive methods, further investigation should be planned by the responsible competent parties under the relevant site arrangements.
Direct observation at an appropriately authorised investigation point can confirm local information, but it does not automatically verify a whole route. Keep the extent of each observation clear. Likewise, the absence of a detectable response should be reported as a detection outcome, not converted into a statement that no service exists.
Request a report that preserves uncertainty
The drawing should be accompanied by an explanation of methods, coverage, interpretation, and limitations. Include inaccessible areas and locations where site conditions reduced confidence. If depths are reported, make clear how they were obtained and the reference used. Keep inferred connections distinct from supported observations.
HSE guidance treats locating and identifying services as one part of a wider safe system for work near buried infrastructure. The responsible project team must also address planning and safe working arrangements under the applicable local requirements. A utility survey is valuable evidence within that process, not an excavation authorisation or a guarantee of an obstruction-free area.
- Link each feature to its evidence source and survey date.
- Identify unresolved routes, conflicting records, and inaccessible areas.
- Use clear confidence descriptions whose meaning is explained in the report.
Common questions
Can ground penetrating radar find every underground utility?
No. Ground conditions, object properties, access, and interpretation affect its usefulness. The survey should describe coverage and limitations rather than promise that every buried service has been found.
Does an empty area on the plan mean it is safe to excavate?
No. It may reflect missing records, limited access, or a service that was not detectable. Excavation decisions require the responsible team's separate assessment and safe working arrangements.
Further reading
This article was rewritten in October 2026 around the subject of the original Geobiro post. The original publication date is retained; the update date identifies the current text.