Underground utility survey.
PAS 128 detection and mapping of buried services, QL-D to QL-A.
A utility survey, or underground utility survey, locates and maps buried services — water, gas, electricity, telecoms, fibre and drainage — using GPR, EML and sonde tracing reconciled with statutory undertaker records. Every detected line is classified to a PAS 128 Quality Level: QL-D records, QL-C reconnaissance, QL-B geophysical detection, QL-A verified by excavation. Angell Surveys delivers RICS-standard CAD on OSGB36 with a PAS 128 report and full audit trail, UK-wide.
In-depth guide: PAS 128 Quality Levels Explained →
What is a utility survey?
A utility survey is the measured detection, classification and mapping of buried services across a site — water, gas, electric, telecoms, fibre, drainage, district heating — combined with the reconciliation of statutory undertaker records. The deliverable is an AutoCAD DWG with utilities on dedicated layers (one per service type and PAS 128 Quality Level), referenced to OSGB36 horizontally and ODN vertically.
It is the single most important risk-management deliverable in the early-design and CDM dutyholder workflow. Designers, civil engineers, principal contractors and asset owners use it to design around live infrastructure, evidence their Regulation 11 risk assessment, and avoid the legal and safety consequences of damaging buried apparatus. Every Angell Surveys utility deliverable is produced under the RICS Surveys of Land, Buildings and Utilities professional statement and the PAS 128 quality framework.
What do PAS 128 Quality Levels QL-D to QL-A mean, and which do you need?
The four Quality Levels describe how a buried service was located and therefore how far to trust its position. QL-D is records only, QL-C adds site reconnaissance, QL-B is geophysical detection with GPR and EML, and QL-A is physical exposure and survey in place. Specify QL-B as the minimum wherever excavation or piling is planned, and QL-A at the clash-critical points.
Every detected service is recorded on the drawing with its Quality Level explicit alongside it, so the designer knows the confidence interval on every line. The RICS band column gives the equivalent positional accuracy class from the RICS Measured surveys of land, buildings and utilities band table (RICS, 2014), which itself maps QL-A to Band E and QL-B1 to Band G.
| Quality Level | Method | Plan Accuracy | Depth Accuracy | RICS Band | Use Case |
|---|---|---|---|---|---|
| QL-D | Statutory records desktop study only | Variable / unverified | None | I / J | Initial feasibility, route option appraisal |
| QL-C | Site reconnaissance, records reconciliation, visible feature survey | ±500 mm | None / inferred | I | Outline design, early-stage cost planning |
| QL-B | Geophysical detection (GPR + EML + sonde) with cover-lift verification | ±150 mm | ±15–40 % | G (QL-B1) | Standard design base; Network Rail / Highways minimum specification |
| QL-A | Intrusive verification by trial pit or vacuum excavation | ±50 mm | ±25 mm | E | Critical setting-out, working adjacent to live apparatus |
Every detected utility on the deliverable DWG is annotated with its PAS 128 Quality Level. Quality Levels are mixed within a single survey — a site may have a QL-B trunk main reconciled with a QL-C records-only branch and a QL-A trial-pit-verified manhole connection. The drawing legend records the survey type per service type. PAS 128 accuracies are quoted from the specification; RICS band equivalents are those given in the RICS band table (RICS, 2014).
Is a utility survey the same as a PAS 128 survey?
Not necessarily. "Utility survey" is the generic term for locating buried services; a PAS 128 survey is one scoped, carried out and reported to the BSI specification, with every detected line labelled by the Quality Level and the method that found it. A survey not scoped to a Quality Level gives the designer no stated confidence in position or depth. Every Angell Surveys utility survey is delivered to PAS 128.
What does an underground utility survey report contain?
An underground utility survey report sets out how each buried service was located and how far it can be trusted. Ours contains the PAS 128 methodology statement, the equipment and detection techniques used, the statutory undertaker records obtained and how they were reconciled, an observation log, site photographs of cover-lifts and surface evidence, a drawing register, and the Quality Level assigned to every detected line. It is issued with the AutoCAD DWG (services layered by type and Quality Level) and a PDF plot at 1:200 or 1:500, so the report, the drawing and the PAS 128 specification for utility surveying can be read together by the designer, the principal contractor and the CDM principal designer.
How we detect.
Multi-sensor detection combined with records reconciliation and cover-lift verification — the only reliable way to classify a buried service.
Ground Penetrating Radar (GPR)
Multi-frequency GPR for non-conductive services (drainage, fibre, plastic gas) and depth measurement of all detected lines. 250–800 MHz antennas matched to ground conditions and target depth.
Electromagnetic Locator (EML)
Active and passive EML for conductive metallic services and live electricity. Power, RF and signal-clamp modes used to disambiguate parallel and crossing services.
Sonde & Signal Clamp
Inserted sonde tracing through chambers, rodding eyes and accessible pipework for non-conductive lines that GPR cannot resolve. Signal clamps for traceable conductive services.
Records Reconciliation
Statutory undertaker records (Cadent, NGN, SGN, water and sewerage operator, DNO, Openreach, district heating) requested up-front, reconciled with detection on the deliverable drawing.
Cover-lift Verification
Chambers, valves, hydrants and inspection covers opened where accessible to verify service type, material, diameter and invert level. Recorded with photographs in the report.
QL-A Intrusive Verification
Coordinated vacuum excavation or trial pits where critical setting-out requires QL-A accuracy. Issued with photographic record and section drawings of verified positions.
When you need a PAS 128 utility survey.
Civil & Highways Engineers
Pre-construction utility clearance for site setting-out, drainage design and earthworks. Reduces CDM risk and avoids the cost of striking live apparatus.
Principal Contractors
Site possession evidence for statutory undertakers and works coordinators. PAS 128 QL-B is the minimum specification for Network Rail and National Highways.
Design Consultants
Foundation, drainage and SUDS design coordinated against detected utility positions. 3D BIM utility model on request for clash detection.
Asset Owners
Operational record verification for water, energy and rail operators. Reconciliation of as-laid drawings with current ground truth.
How we work.
A documented, PAS 128-aligned workflow from records request through to QA-signed deliverable.
Records & Scoping
Statutory undertaker records requested up-front. Site boundary, target Quality Level and works window agreed. RAMS prepared for site safety and access.
Site Detection
Multi-sensor sweep with GPR + EML + sonde where applicable. Cover-lift verification at every accessible chamber. Survey control referenced to OSGB36 / ODN.
Reconciliation & Drawing
Detected services reconciled against statutory undertaker records. AutoCAD DWG produced with utilities on layers by service type and PAS 128 Quality Level.
QA & Issue
PAS 128 report issued with methodology, equipment, observation log, photographs and accuracy statement. Drawings revision-controlled and signed off before issue.
Where this method has limits.
PAS 128 defines how far a located service can be trusted; it does not make buried infrastructure fully knowable.
Detection limits
Electromagnetic and GPR detection depend on ground conditions, depth, congestion and the material of the service; non-conductive, deep or shielded services may not be detected at QL-B.
Completeness
A utility survey cannot guarantee that every service present has been found; QL-B results are a detection survey, not a warranty.
Positive identification
Only QL-A (physical exposure) confirms position and depth; where a design depends on it, trial holes are specified.
Records
QL-D utility records are frequently incomplete or wrong; they are a starting point, not evidence.
Angell Surveys delivers this service across the UK from a London base, under RICS regulation, with the same documented control, check-point verification and QA on every project. Accuracy is specified and reported against the band table in RICS Measured Surveys of Land, Buildings and Utilities, 3rd edition (RICS, 2014), using independent check points rather than a marketing figure.
Utility survey questions.
The questions clients ask us most often before instructing a utility survey.
What is a utility survey?
What is PAS 128 and which Quality Level do you survey to?
What survey methods do you use to detect buried services?
Is a utility survey required before planning or construction?
What deliverables will I receive?
Are you RICS regulated?
How long does a utility survey take?
Do you cover the whole of the UK?
Need a PAS 128 utility survey? Scoped and quoted within 24 hours.
Most scoping responses sent within one business day.
RICS-regulated work, led by Philip M. Angell MRICS.