Subsurface utility engineering (SUE) is the process of finding, mapping and documenting buried utilities — water, sewer, gas, power and telecom lines — before design or construction work disturbs them.
The Federal Highway Administration describes it as a combination of civil engineering, surveying and geophysics, and says it has become a routine requirement on highway projects in many states.
This page explains the field itself: how a SUE project runs and who does the work.
What is SUE?
SUE is an engineering process for establishing what lies beneath a project site and how much confidence a design can place in that picture.
FHWA describes it as combining civil engineering, surveying and geophysics, drawing on technologies that include vacuum excavation and surface geophysics.
FHWA's reading of the current standard is blunt: SUE is a process, not a technology.
The process is written down.
The current standard is ASCE/UESI/CI 38-22, "Standard Guideline for Investigating and Documenting Existing Utilities," which ASCE released in July 2022.
It replaced ASCE 38-02, which carried the earlier title "Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data."
ASCE issued a companion standard at the same time: ASCE 75-22, "Standard Guideline for Recording and Exchanging Utility Infrastructure Data."
Its purpose is as-built and as-constructed records, so that utilities added or relocated during a project carry accurate, usable records of their location and attributes going forward.
What makes SUE distinct is how it grades its own answers.
FHWA's summary of ASCE 38 recognizes four quality levels of utility information, from QL-D (the lowest) to QL-A (the highest).
Each level states how a piece of data was obtained — which is also a statement of how far it can be trusted.
The ladder runs from paperwork to steel.
QL-D comes only from existing utility records or verbal recollections.
QL-C adds a survey of visible above-ground features — manholes, valve boxes, hydrants — correlated with those records.
QL-B applies surface geophysical methods to record approximate horizontal positions, the activity FHWA calls "designating," and that data is surveyed to project control.
QL-A physically exposes the utility by non-destructive soft digging — vacuum excavation or hand digging — for precise horizontal and vertical positions, which FHWA calls "locating."
For anyone planning a career, that control clause matters.
Designating data is surveyed to project control, and QL-C is surface survey work, so both run on the fundamentals a survey crew already carries: instruments, control, notes and documented positions.
The field role this cluster covers is the SUE technician — the SUE technician career guide covers the job itself, its duties and how crews run the work.
How does SUE differ from 811 locating?
Start with 811, the national call-before-you-dig number: a caller is connected to their state 811 center, receives a ticket number, and utilities send locators to mark the approximate locations of buried lines with paint or flags.
The one-call system runs on its own clock.
Call811 says response times are set by state law — generally a few days — and that the digger must confirm that all utilities have responded before digging.
The marks are approximate, and the system treats them that way.
CGA Best Practice 5-19 sets an excavation tolerance zone around a marked facility: the facility's width plus 18 inches on either side of the outside edge, and states may specify more.
SUE answers a different question.
A dig ticket protects one excavation; a SUE investigation produces an engineering record of a corridor's buried utilities, delivered at a quality level the project owner dictates (CGA Best Practice 2-14).
Designating positions are surveyed to project control, and test holes expose the line itself for precise horizontal and vertical measurement.
Then there is the vocabulary collision.
In one-call work, "locating" means an approximate paint or flag mark made for digger safety.
In FHWA's SUE vocabulary, "locating" is the QL-A activity — physically exposing the line.
An 811 mark and a surveyed, vacuum-exposed test hole are different products carrying different certainty — and the quality levels are how SUE records that difference.
For the job-to-job comparison — an 811 locator's week next to a SUE technician's — the SUE technician career guide keeps the two roles side by side.
What happens on a SUE project?
Scope comes first, and the owner holds the pen.
Per CGA Best Practice 2-14, the project owner dictates the required quality levels and the amount of effort the SUE provider spends on each.
A planning study and a deep excavation beside live ducts do not buy the same levels.
The work then climbs the ladder.
Records research and interviews with knowledgeable utility personnel establish the QL-D base.
Surveying the visible above-ground features — manholes, valves, hydrants — and correlating them with the records brings a corridor to QL-C.
Designating comes next where the owner has called for QL-B.
Surface geophysical methods — electromagnetic locating instruments, ground penetrating radar, radar tomography, metal detectors and optical instruments — record approximate horizontal positions (and, in some cases, vertical ones), and the information is surveyed to project control.
Where the owner calls for QL-A, the crew exposes selected utilities by non-destructive soft digging — vacuum excavation or hand digging — to capture precise horizontal and vertical positions.
Where test holes go is a scope decision — it follows from the quality levels and the amount of effort the owner dictates.
Soft digging is still digging, and OSHA's excavation standard is the rule set for that work: under 29 CFR 1926.651(b), the estimated location of underground utilities must be determined before an excavation is opened, and the utility owners must be contacted.
OSHA adds a timing rule: if a utility owner cannot respond within 24 hours — unless state or local law allows longer — the employer may proceed with caution using detection equipment.
What comes out the other end is a documented picture: records correlated with observed features, designating lines with approximate positions on project control, and test holes with measured horizontal and vertical values.
For utilities that are new or relocated, the companion ASCE 75-22 standard carries accurate, usable location and attribute records forward.
Who works in SUE?
FHWA's three-part description — civil engineering, surveying and geophysics — is also a hiring map.
The field mixes crew specialists who run the instruments and the vacuum rig with the engineering and surveying disciplines FHWA says the process combines.
On the crew side, the field work divides along the quality levels: records research, feature surveying, geophysical designating and vacuum-excavated test holes.
Designating data is surveyed to project control, and feature surveying is surface survey work — both run on fundamentals a survey crew already knows.
That overlap is the door between the two fields for technicians and party chiefs.
Titles vary.
The same family of names — SUE technician, utility designating technician, SUE field technician, utility locator — can cover very different scopes, so read the duties, not the label.
What separates the jobs is the quality-level work each one actually performs: records, feature survey, designating or exposure.
Training has a recognized frame.
CGA Best Practice 4-5 says locators should be trained, with the training documented: locating theory, equipment, plant recognition, OSHA safety, written and field testing, and annual retesting.
It names NULCA's Locator Training Standards and Practices as an accepted industry model.
The role-level detail — duties, the skills to build, and how crews run the work — lives in the SUE technician career guide, and current openings are on the SUE technician jobs board.
What drives demand for SUE work
The policy driver is explicit.
FHWA has encouraged the use of SUE on Federal-aid and Federal Lands Highway projects since 1991 as an integral part of the preliminary engineering process, and costs for SUE services are eligible for Federal participation.
FHWA also describes SUE as having become a routine requirement on highway projects in many states — a statement about project practice, not about any single instrument.
The reliability gap pulls the other lever.
FHWA calls QL-C probably the most commonly used level of information, and cautions that at that level it is not unusual to find many utilities omitted or wrongly plotted.
A project that decides records alone are not enough to build on adds designating and test holes.
The standards are a third driver.
ASCE reissued the SUE standard as ASCE/UESI/CI 38-22 in July 2022 and added ASCE 75-22 so that new and relocated utilities carry accurate, usable records forward.
Current standards give owners and engineers precise language for scoping the work — and scoping language is what turns a process into line items.
The field's own framing protects the work from gadget cycles, too.
FHWA's reading of ASCE 38-22 — SUE is a process, not a technology — means demand follows a project's need for documented, quality-leveled utility data.
Instruments change; the process deliverable does not.
If the combination appeals — records, geophysics, survey control and careful excavation — the titles above are the ones to search, and current openings are on the SUE technician jobs board.
Career information, not legal, tax or licensing advice. Standards, policies and safety rules change — confirm the current requirements with the bodies named here: ASCE, the Common Ground Alliance, FHWA and OSHA.