Locating method
Subsurface Utility Engineering
ASCE 38 quality levels, sealed and survey-grade.
Subsurface Utility Engineering investigates and depicts existing utilities to ASCE 38-22, classifying every segment by quality level from records research (QL-D) up to physically verified position at a test hole (QL-A). The deliverable is a sealed, surveyed drawing used for design, not marks on the ground.
What Subsurface Utility Engineering is
Subsurface Utility Engineering is a branch of engineering practice, not a single instrument, and in North America it is governed by ASCE 38-22 (published as ASCE/UESI 38-22). The standard defines how existing utility information is investigated, how confident you are allowed to be in it, and how it must be depicted. Its central idea is the quality level: every utility segment shown on the drawing carries a letter, QL-D, QL-C, QL-B, or QL-A, that states exactly how that segment was determined and therefore how much a designer may rely on it. Because the levels are assigned per segment rather than per project, one plan routinely carries all four, with QL-A only at the points where a conflict had to be resolved. The finished product is signed and sealed by a licensed professional engineer, with the survey components under a licensed surveyor where state law requires it, which is what separates SUE from every other service in this catalog.
How it works
QL-D is records research: utility owner atlases, as-builts, permit files, GIS layers, and interviews are collected and plotted, with no field verification, so completeness is unknown. QL-C adds a field survey of visible above-ground appurtenances, meaning manholes, valve boxes, meters, pedestals, risers, and vaults are surveyed to project control and correlated against the QL-D records, which still leaves what happens between those points an inference. QL-B is designating: surface geophysics, typically electromagnetic pipe and cable locating supported by ground penetrating radar, magnetometers, and occasionally acoustic methods, establishes the existence and approximate horizontal position of a line, and those marks are surveyed to project control before they wash away. QL-A is locating: a test hole, almost always cut by vacuum excavation, physically exposes the utility at one point so a surveyor can record precise horizontal position and elevation on the top of the pipe or conduit, along with material, outside diameter, condition, encasement, and pavement thickness. All four levels are compiled into a CAD or GIS deliverable in which the quality level travels with each segment, and the accompanying report states what was investigated and what could not be resolved.
When to choose Subsurface Utility Engineering
Choose SUE when a design decision, not a dig, depends on the answer: setting a profile, fixing a bore path, sizing a relocation agreement, or building a utility conflict matrix before a project goes to bid. It is the standard scope on DOT roadway, interchange, and bridge work, on rail and transit corridors, and on water and sewer trunk main design, where an unknown line found during construction becomes a change order or a claim. Congested urban corridors and campus, airport, and industrial sites benefit most, because that is where records are thinnest and the cost of being wrong is highest. It also pairs naturally with ASCE 75-22 (published as ASCE/UESI/CI 75-22), the companion standard for recording and exchanging utility infrastructure data, when the project has to hand back usable as-built records at the end. If what you actually need is marks on the ground before a crew digs next week, private utility locating or line marking is the faster and more appropriate service.
What SUE is used for
- DOT roadway, interchange, and bridge design
- Utility conflict matrices and relocation agreements
- Rail, transit, and light-rail corridor design
- Water, sewer, and trunk main alignment studies
- Trenchless bore and directional drill path design
- Airport, campus, and industrial plant expansions
- QL-A test hole programs at foundations and crossings
What SUE cannot do
QL-B inherits every weakness of the instruments behind it. Non-metallic water, gas, and sewer lines with no tracer wire give an electromagnetic locator nothing to induce a signal onto, ground penetrating radar is badly degraded in wet clay, saline ground, and other high-conductivity soils, and in congested corridors an applied signal can couple onto adjacent metallic lines and produce a mark over the wrong pipe. QL-B is a horizontal answer: any depth read from an electromagnetic locator is an estimate affected by signal distortion, and ASCE 38 does not treat it as verified. Only a QL-A test hole gives a verified elevation, and it is valid at that hole only, because the line can rise, dip, or deviate between test holes. Abandoned lines, unmapped private services, and non-conductive laterals with no surface appurtenance can go undetected at every level, which is why the standard requires the report to state the limits of the investigation, and why blank space on an SUE plan is not evidence that nothing is buried there. Test holes also carry real cost and schedule: permits, traffic control, utility owner coordination, and pavement restoration, which is why full QL-A coverage of an entire corridor is rarely justified. Finally, an SUE deliverable is a design document with a shelf life, and it never satisfies the legal requirement to file a one-call ticket before excavation.
What Subsurface Utility Engineering finds
Looking for one specific line rather than a technique? Each of these covers what the utility is, why it is hard to find, and what one-call does and does not mark.
- Water Line LocatingFind the water line before the excavator does.
- Gas Line LocatingThe highest-stakes line on the property.
- Electrical Line LocatingLive power is easy to find. Dark conduit is not.
- Sewer & Septic LocatingLaterals, tanks, and drain fields with no map.
- Fiber & Telecom LocatingGlass carries no signal. Locate before you bore.
Questions
Subsurface Utility Engineering FAQ
What do the SUE quality levels mean?
ASCE 38-22 defines four. QL-D is information from existing records and interviews with no field verification. QL-C surveys the visible above-ground features, such as manholes, valve boxes, and pedestals, and correlates them to the records. QL-B uses surface geophysics to establish that a line exists and where it sits horizontally, surveyed to project control. QL-A physically exposes the line at a test hole so its horizontal position and elevation are measured directly, along with size, material, and condition.
Does an SUE survey replace calling 811 before we dig?
No, and it is not meant to. One-call is free, required by law before excavation in most jurisdictions, and marks the public utilities up to the meter with a ticket that is only valid for a limited window. An SUE plan is an engineering deliverable produced during design, often months or years before a shovel moves, so you still file a one-call ticket every time you dig. What SUE adds is the private and on-site lines past the meter that one-call does not own or mark, plus verified depths and a sealed record that paint marks never provide.
Do we need QL-A on every utility in the corridor?
Almost never, and a firm that proposes it is usually overselling. Normal practice is QL-B designation across the corridor to establish what is there and where it runs horizontally, then QL-A test holes only at the points where the design actually conflicts, such as crossings, proposed foundations, and bore entry and exit points. Scope is written per project and quoted per project, so describe the corridor length, the design stage, and how many test holes you expect, and local firms will price their own approach so you can compare.
How is SUE different from standard private utility locating?
Private utility locating puts marks on the ground so a crew can dig safely, usually same week, with no surveyed or sealed record afterward. SUE runs the same field geophysics but ties every mark to project survey control, adds records research and test hole verification, and delivers a signed and sealed drawing where each segment carries its own quality level. Many companies offer both, so if you are unsure which the job needs, say what the data is for: digging soon points to private locating, designing a project points to SUE.
Find Subsurface Utility Engineering by state and province
- Alabama568 cities
- Alaska249 cities
- Arizona388 cities
- Arkansas506 cities
- California1461 cities
- Colorado407 cities
- Connecticut200 cities
- Delaware76 cities
- District of Columbia55 cities
- Florida941 cities
- Georgia619 cities
- Hawaii251 cities
- Idaho206 cities
- Illinois1364 cities
- Indiana657 cities
- Iowa869 cities
- Kansas551 cities
- Kentucky541 cities
- Louisiana469 cities
- Maine429 cities
- Maryland739 cities
- Massachusetts501 cities
- Michigan690 cities
- Minnesota820 cities
- Mississippi356 cities
- Missouri898 cities
- Montana304 cities
- Nebraska447 cities
- Nevada110 cities
- New Hampshire247 cities
- New Jersey616 cities
- New Mexico377 cities
- New York1391 cities
- North Carolina735 cities
- North Dakota240 cities
- Ohio1175 cities
- Oklahoma637 cities
- Oregon361 cities
- Pennsylvania1819 cities
- Rhode Island59 cities
- South Carolina386 cities
- South Dakota284 cities
- Tennessee436 cities
- Texas1608 cities
- Utah325 cities
- Vermont172 cities
- Virginia562 cities
- Washington610 cities
- West Virginia391 cities
- Wisconsin792 cities
- Wyoming157 cities
- Alberta30 cities
- British Columbia28 cities
- Manitoba18 cities
- New Brunswick14 cities
- Newfoundland and Labrador12 cities
- Nova Scotia13 cities
- Northwest Territories5 cities
- Nunavut4 cities
- Ontario40 cities
- Prince Edward Island8 cities
- Quebec32 cities
- Saskatchewan20 cities
- Yukon4 cities