Utility quality levels grade information about existing underground utilities by how it was obtained: from records only, from site reconnaissance, from detection with geophysical equipment, or by exposing and measuring the utility. The UK's PAS 128 and the US standard ASCE 38 both use levels D, C, B and A, from least to most reliable.
At a glance
| Purpose | Say how reliable each utility position is |
| UK reference | PAS 128 (specification for underground utility detection, verification and location) |
| US reference | ASCE 38 (standard guideline for investigating and documenting existing utilities) |
| Levels | D (records), C (reconnaissance), B (detection), A (verification) |
| Used for | Design clearances, trial holes, risk management, model properties |
The levels
| Level | How obtained | Typical reliability |
|---|---|---|
| D | Desktop search of records | Approximate; lines may be missing |
| C | Records plus site reconnaissance of visible features | Better near covers, valves, markers |
| B | Detected on site (electromagnetic location, ground-penetrating radar) | Good in plan, depth less certain |
| A | Exposed and measured (trial holes, vacuum excavation) | Position and depth verified |
Both standards subdivide some levels (for example by detection accuracy or by method), and define deliverables and reporting. The exact definitions depend on the edition the contract cites.
How they are used on projects
A utility survey is specified to a required quality level along the route, often higher near crossings and foundations. The results go into the design model and the GIS with the level attached to each line. Design rules then follow the level: larger clearance zones and mandatory trial holes for D and C lines; detailed design at crossings only on A positions. Quality levels also support risk registers and the contractor's safe digging procedures.
Variations
- PAS 128 (UK) and ASCE 38 (US) differ in detail and sub-levels; other countries have similar national guidance.
- Some clients set their own minimum levels by project type.
- Levels apply per line or per segment, not per survey: one survey can produce several levels.
Common mistakes
- Treating a record line as a surveyed position.
- Losing the quality level when utilities are imported into the model.
- Reading a blank area on a record plan as proof that nothing is there.
- Assuming detected depth is as reliable as detected plan position.
Where to read more
PAS 128 (BSI), ASCE 38 (American Society of Civil Engineers) in the edition named by the contract; national safe digging guidance (for example HSG47 in the UK); and the utility owners' own requirements.