2026-04-21 · 7 min read
Every buried utility record carries an unspoken question: how much can I actually trust this? Two international standards answer that question with a four-level grading system. ASCE 38-22 (the American Society of Civil Engineers) and PAS 128:2022 (UK Publicly Available Specification). They are different documents but converge on the same Quality Level framework.
The Quality Levels in plain English
Both standards use four tiers, with subtle naming differences:
| Level | What it means |
|---|---|
| QL-A | Utility has been physically exposed and precisely measured. Highest trust. Used by designers and excavators. |
| QL-B | Utility has been detected by surface geophysics (GPR / EM locator). Position is inferred but not exposed. Used for design. |
| QL-C | Surface evidence (manhole, hydrant, valve box) plus correlation with existing records. Lower confidence. |
| QL-D | Information from existing records only. No site verification. Lowest tier. |
Why this matters
The Quality Level on a utility record carries legal and engineering weight. A QL-A record is admissible as evidence in a strike-claim dispute. A QL-D record is not. A designer who issues a drawing for excavation based on QL-D records carries professional liability for any subsequent strike. The Quality Level is therefore not bureaucracy — it is risk grading.
ASCE 38 vs PAS 128 — the differences
- Geography. ASCE 38 dominates US and parts of Asia-Pacific. PAS 128 is the UK / EU / Commonwealth standard. Singapore agencies and consultancies routinely cite both.
- Detection methods. PAS 128 is more prescriptive about geophysics (specific GPR / EM coverage requirements at each level). ASCE 38 is closer to a framework — methods are at the surveyor's discretion.
- Output requirements. Both require attribute schemas (size, material, depth, accuracy) but PAS 128 specifies report content more tightly.
- QL-A definition. Functionally identical: utility was physically visible and measured.
Where PIX4Dcatch + RTK fits
The PIX4Dcatch + Emlid RTK trench-scan methodology Easepect deploys produces QL-A records on every newly installed utility. The trench is open, the utility is visible, the photogrammetry capture is geo-anchored to centimetre RTK accuracy, and the resulting 3D record is timestamped, vectorised in PIX4Dsurvey, and signed off in partnership with a licensed surveyor.
This methodology is now in production with the Singapore Land Authority — read the SLA case study.
GPR for QL-B, PIX4Dcatch for QL-A — both, not either
The two technologies solve different problems and most mature subsurface programmes deploy both:
- Ground Penetrating Radar (GPR) — detects what is buried under intact ground. Output: QL-B records. Used to investigate before excavation.
- PIX4Dcatch + RTK — documents what is visible in the open trench during installation or service work. Output: QL-A records. Used to capture the new network at construction.
A utility-authority programme that combines both ends up with a digital network record where every existing asset is at QL-B (located but not exposed) and every newly built asset is at QL-A (exposed and measured). Over time, as the network is rebuilt, the QL distribution shifts toward QL-A.
What the deliverable actually contains
For a PIX4Dcatch + RTK trench-scan QL-A record, Easepect delivers:
- Georeferenced 3D point cloud of the trench (LAS / LAZ).
- Orthophoto of the open trench (GeoTIFF).
- Vectorised pipe centreline and joints (Shapefile / DXF / IFC).
- Attribute table — pipe size, material, depth, surveyor sign-off.
- Timestamped capture metadata for the audit trail.
Bottom line
If your utility programme is producing QL-D records (paper drawings) or QL-C records (sketches with manhole correlations), the path to QL-A is open-trench digital capture during installation. PIX4Dcatch + RTK is the methodology Singapore agencies have adopted. Get a quote for the kit, training and surveyor partnership.