What Is a Utility Survey? A Plain-Language Guide

The design is 60% done. The alignment is set, the drainage works, the client has signed off on the plan sheets. Then the field crew digs its first test hole and finds the gas main four feet from where the drawings show it, because the design started before a real utility survey did. Now the team is reworking sheets, the schedule is slipping, and everyone is asking how nobody knew.

Here's what a utility survey is, how it differs from the other ways people find buried lines, and how the process works from the first records request to the last test hole.

What is a utility survey?

A utility survey is the process of finding, identifying, and mapping the utilities on or under a site so a project can be designed and built around them. It records where each line is, what it is, and how reliable that information is.

A complete one typically captures:

• Location: geographical position, and depth where it's been measured
• Type: gas, electric, water, sewer, storm, telecom, fiber, and so on
• Attributes: size, material, and condition where they can be observed
• Owner: the utility or agency responsible for each line
• Reliability: a quality level for each segment, so designers know which information was confirmed in the field and which came from records

That last item is what separates a professional survey from a sketch of where people think things are. A line drawn from a 1970s as-built and a line exposed and measured last week can look identical on a plan sheet. They don't deserve the same trust. That isn't to say that the as-built is inaccurate, just that the accuracy should be confirmed in the field before ground is broken. Moreover, retrieving that record provides a lot of value in determining where a survey should take place.

What types of utilities are found with a utility survey?

A utility survey finds every type of buried or overhead utility that could affect a project: electric lines, natural gas and petroleum pipelines, water mains, sanitary sewers, storm drains, and telecom, cable, and fiber optic lines. It also picks up what an 811 locate often misses, like abandoned lines, private service lines, irrigation, and conduit for traffic signals and street lighting. Some are harder to find than others. Metal pipes and live cables carry a signal that electromagnetic locators can follow, while plastic, clay, and concrete pipes often need ground penetrating radar or a test hole (also known as a pothole) to confirm.

Utility survey vs. 811 locate vs. SUE

These three terms are sometimes used interchangeably, but they shouldn't be.

• An 811 locate is the free, legally required notification you make before digging. Member utilities send locators to paint or flag their lines on the ground. It exists to prevent damage during excavation, and the marks are temporary. They don't give you depth, and they don't cover facilities owned by non-members.
• A utility survey maps utilities for planning and design. It pulls together records, field observations, and measurements into a drawing the design team can work from.
• Subsurface Utility Engineering (SUE) is the formal engineering practice behind a rigorous utility survey. Under the ASCE 38-22 standard, a SUE provider assigns a quality level to each utility segment and delivers sealed drawings and a utility report. The Federal Highway Administration describes the practice of SUE here.

In short: 811 marks lines so you can dig safely, while a utility survey maps them so you can design around them. SUE is how you make that map defensible. However, as always, doing an 811 locate is necessary before you break ground: CALL BEFORE YOU DIG

The four utility quality levels (ASCE 38-22)

Utility quality levels are a rating system, defined in ASCE 38-22, for how trustworthy a piece of utility information is. From least to most certain:

• QL-D: information from existing records, such as utility maps, as-builts, and permit drawings. QL-D tells you what should be there and where to look.
• QL-C: visible surface features such as manholes, valve boxes, and poles are surveyed and matched against the QL-D records. Discrepancies get resolved.
• QL-B: geophysical tools detect buried lines and mark their horizontal position on the surface. This is often called designating.
• QL-A: the utility is physically exposed and measured, giving precise horizontal and vertical position plus size, material, and condition. This is often called locating.

QL-D is the starting point, not the endpoint. It's essential for early planning, scoping, preliminary designing, and for deciding where field work should happen, but it isn't enough on its own to confidently dig. Most projects need a mix of levels, with QL-A reserved for the spots where an error would be costly.

How a utility survey works, step by step

Most utility surveys follow the same sequence, whether the site is a single intersection or a 20-mile corridor.

1. Records research. Gather maps, as-builts, and GIS data from every utility and agency with facilities in the project area. This produces the QL-D picture and can be the slowest step, because records live with dozens of separate owners.
2. Site walk and surface features. Survey visible structures and tie them to the records (QL-C). Mismatches here are early warnings.
3. Designating. Sweep the site with geophysical equipment to trace buried lines and mark their horizontal position (QL-B).
4. Test holes. Excavate small holes at critical points to expose utilities and measure them directly (QL-A). This can also be known as potholing.
5. Mapping and deliverables. Compile everything into utility drawings and a report, with each segment labelled by the quality level it achieved.

Electromagnetic (EM) locating

Electromagnetic (EM) locators detect the signal carried by, or induced onto, metallic and conductive lines. It's the most common everyday method, and it works well for pipes and cables that conduct a signal.

Ground penetrating radar (GPR)

Ground penetrating radar (GPR) sends radar pulses into the ground and reads the reflections. It can detect non-metallic lines, such as plastic pipe, that EM can miss. Results depend heavily on soil conditions.

Vacuum excavation

Vacuum excavation uses pressurized water (hydro excavation) or air to loosen soil while a vacuum removes it. It exposes utilities without a bucket or blade that could cut a line, which is why it's the standard way to dig test holes.

What are those small holes in the street?

If you've seen a crew with a truck-mounted vacuum digging a small, neat hole in a road or sidewalk, then filling it back in the same day, you've probably watched a test hole being dug. It's sometimes called potholing or daylighting.

A test hole is a small excavation made to expose a buried utility so it can be measured directly. The crew isn't fixing anything. They're confirming exactly where a pipe or cable sits and how deep it is, usually because a new project is being designed nearby.

Crews use vacuum excavation instead of a backhoe because it's far less likely to damage the line they're looking for. Once the measurement is recorded, the hole is backfilled and the surface is patched. A few small holes now can prevent a damaged gas line, a service outage, or a torn-up street later.

When do you need a utility survey?

If your project involves digging, boring, or building where utilities could be, you need some level of utility survey. How much depends on the stakes. It's especially important for:

• Linear projects: pipelines, fiber runs, water and sewer mains, and roadway widening, which cross many owners' facilities
• DOT and highway work, where the Federal Highway Administration has long promoted SUE to reduce utility conflicts and delays
• Utility capital programs, such as replacements, undergrounding, and new service
• Dense urban and brownfield sites, where decades of abandoned and undocumented lines accumulate

If you're scoping a utility survey, three decisions shape the cost and the result:

• Timing: start records research at project kickoff, not after design is underway. Early QL-D data tells you where field work will pay off.
• Quality levels: specify which areas need QL-B coverage and where QL-A test holes are required, rather than one level for the whole site.
• Deliverables: agree up front on file formats (DWG, DGN, SHP) and how quality levels will be shown on the drawings.

If you own utilities: the records request is step one

Every utility survey begins with someone asking a utility owner for records. If you work in records, mapping, or GIS at a utility or agency, those requests are the first link in the chain that keeps your assets from being struck.

A good records request names the project, defines the area precisely, and states what the records will be used for. The faster accurate records reach the design team, the earlier conflicts with your facilities show up on paper instead of in the field.

What you get at the end

A finished utility survey usually includes:

• Utility drawings showing each line's position, type, size, and owner, with the quality level labelled for each segment
• A utility report describing methods, sources, conflicts found, and recommendations, sealed by the responsible engineer when the work is done as SUE
• CAD and GIS files the design team can load straight into its base map

Where utility surveys lose time, and how CivilGrid helps

The field steps get the attention, but records research is where schedules frequently slip. Engineers spend days identifying which agencies to contact, sending requests, waiting on replies, and reconciling PDFs and paper as-builts drawn to different conventions. We call this the pre-construction research tax, and every project pays it.

CivilGrid handles that step for you. The team sources maps and as-builts directly from the utilities, municipalities, and agencies that own them, and every record comes with chain of custody documentation. The result is a QL-D base map, aligned with ASCE QL-D guidelines, that shows utility density and congestion before a crew mobilizes. Survey and SUE teams can then target fewer, better-placed test holes.

In the field, the CivilGrid mobile app puts that map on site, logs test hole findings with location-pinned photos and notes, and works offline, syncing back to the shared project map.

CivilGrid doesn't replace SUE, field survey, or 811. It gives them a better starting point.

"CivilGrid's data specialists are top notch. They are always ready to answer questions, lend assistance, and make product changes to help us work better." — Robert Lundeen, Survey Technician, Mark Thomas

Utility survey FAQ

Who performs a utility survey?

A utility survey is usually performed by a SUE provider, a land surveying firm, or both. Surveyors map surface features and tie in field marks; SUE professionals designate buried lines with geophysical tools, dig test holes, and seal the utility deliverables.

Is a utility survey the same as calling 811?

No. Calling 811 is required before any digging and gets member utilities to mark their lines for safe excavation. A utility survey maps utilities for design, includes non-member facilities, and documents how reliable each piece of information is. You still call 811 before you dig.

How accurate is a utility survey?

It depends on the quality level achieved. QL-D records can be off by a few feet, while QL-A test holes measure position and depth directly. A McKissock guide to ASCE 38-22 puts QL-A accuracy at 0.1 ft vertically and 0.2 ft horizontally.

How long does a utility survey take?

It depends on the site's size, the number of utility owners, and the quality levels required. Field work for a small site can take days. Records research is often the longest step, because it depends on how quickly each owner responds.

See it on your next project

Want to see what's under your next site before the first test hole? Book a demo, or browse our glossary of preconstruction terms and Safe Site Data to learn more.

The short version

• A utility survey finds, identifies, and maps the utilities on a site, and records how reliable each piece of that information is.
• It isn't the same as calling 811: 811 marks lines so you can dig safely, while a utility survey maps them so you can design around them.
• Every good utility survey starts with records research, the QL-D step, and that's where most projects lose time.