What is utility locating?
Utility locating is the process of determining where buried infrastructure runs before ground is disturbed. It supports excavation, construction, maintenance, design, investigation, and mapping, and the output is a position — an alignment on the surface, a set of recorded points, or an exposed pipe — rather than a yes-or-no answer about whether something is down there.
Three related words get used interchangeably and should not be. Locating is the field work that determines where a utility runs. Marking is the temporary surface record of that determination, usually paint and flags in standardized colors. Mapping is the durable record — coordinates, drawings, or a GIS layer — that survives after the paint weathers off. A site can be located and marked without ever being mapped, and a mapped record can be years out of date. The broader engineering practice that manages utility risk across a project is subsurface utility engineering, which FHWA characterizes as a process rather than a technology.
The person who does the field work is a utility locator; what a utility locator is and what they do covers the role, the equipment, and the split between a one-call response and a private locate.
What types of underground utilities can be located?
Almost any buried service can be located under the right conditions, but detectability depends less on what a utility carries than on what it is made of and what it is connected to. A continuous metallic line with an accessible connection point is a straightforward target; a bare plastic pipe with no tracer wire and no way in is one of the hardest problems in the field.
| Utility | What typically provides the signal | Where it gets difficult |
|---|---|---|
| Electric | Conductive cable, often carrying a passive signal as well as an applied one | De-energized or unloaded cable, shared trenches, bonded metal paths |
| Natural gas | Metallic pipe, or tracer wire installed with plastic pipe | Plastic pipe with missing, broken, or unreachable tracer wire |
| Water | Metallic pipe with an accessible fitting, or tracer wire | Plastic pipe; a live pressurized main is no place for a sonde |
| Sanitary sewer | A sonde advanced through the pipe from a cleanout or manhole | No access point, blockages, and pipe carrying no signal of its own |
| Storm drainage | Access through inlets and structures, or radar where conditions allow | Large, shallow, irregular structures that behave unlike round pipe |
| Communications and fiber | Metallic conductors, duct tracer wire, or a rod pushed through duct | All-dielectric fiber with no metallic component and no duct access |
| Irrigation and site lighting | Conductive control wiring running near the pipe or fixture runs | Shallow plastic pipe with no wire, and undocumented later additions |
| Private and abandoned facilities | Whatever the installer left behind — often nothing designed for locating | No records, no operator, no load, and frequently outside the one-call response |
How are underground utilities located?
There is no single procedure every locator follows, but most investigations move through the same stages, and each narrows the problem for the next. The value of the sequence is that it puts the cheap, non-invasive work first and reserves the intrusive work for the points that justify it.
1. Review available records
Site plans, as-builts, permits, GIS layers, facility records, and prior repair documentation.
2. Walk the site
Establish what is visible, what the ground and surface conditions are, and what access exists.
3. Identify access points
Meters, valves, pedestals, cleanouts, manholes, and service entrances anchor the buried network.
4. Select methods to suit the targets
Material, access, and site conditions decide which techniques are even candidates.
5. Apply and trace signals
Energize what can be energized, follow it from the surface, and note where confidence drops.
6. Sweep for what records missed
Search the work area for additional responses rather than only confirming known lines.
7. Mark or map the findings
Paint and flags for immediate work, recorded positions where the result must outlast them.
8. Verify the critical points
Expose the utility where horizontal position, depth, or identity has to be certain.
Underground utility locating methods
The seven methods below are the working toolkit. Most sites need more than one, because each answers a different question and each fails in a different way. The limitations column is the more useful half of the table.
| Method | Best used for | Main limitation |
|---|---|---|
| Electromagnetic locating | Conductive lines with an accessible connection point | Needs a conductive path; signal can couple onto neighboring utilities |
| Tracer wire | Nonmetallic utilities installed with a locating conductor | The wire must exist, be continuous, and be reachable |
| Sonde | Nonmetallic pipe and duct that can physically be entered | Requires an access point and a passable line |
| Ground penetrating radar | Targets with no conductor and no access, plus unknown anomalies | Soil, moisture, depth, target size, and interpretation govern results |
| Records and as-builts | Narrowing the search area before any field work | May be schematic, outdated, or never have matched construction |
| Visual site investigation | Anchoring the network to real, verifiable surface features | Shows endpoints and access, not the alignment between them |
| Physical verification | Confirming horizontal position, depth, and identity | Intrusive and slow, so it is used at selected points only |
1. Electromagnetic utility locating
Electromagnetic locating uses a transmitter to put a signal onto a conductive utility and a receiver to follow the electromagnetic field that signal produces. What the receiver detects is a field around a conductor — not the pipe, not the soil, and nothing non-conductive nearby. That single fact explains most of what the method can and cannot do.
There are three normal ways to get a signal onto a line. A direct connection clips the transmitter to an accessible conductive point, which FHWA calls conduction and which is generally cleanest because it puts the signal where you intend it. An induction clamp goes around an accessible cable. Induction sets the transmitter on the ground above a suspected line and couples a signal into it without contact — useful when nothing can be reached, and less selective about which conductor it energizes. Passive locating uses signals already present, and Vivax-Metrotech is explicit that passive signals should never be used to identify which line is being located.
The limits are common and practical. A poor ground return weakens the signal. In a congested corridor the signal couples onto parallel utilities and produces a confident trace of the wrong line. Bonded metallic paths inside a building carry the signal somewhere unintended. Damaged tracer wire ends the trace at the break rather than the utility's end. And nothing at all happens on bare plastic — FHWA's guidance notes that conduction does not detect abandoned utilities or non-conductive materials such as PVC and fiberglass, and that nearby utilities interfere with the signal.
2. Tracer wire locating
Because plastic pipe carries no signal, some nonmetallic utilities are installed with a tracer wire — a conductor laid in the trench alongside the pipe for the sole purpose of making it findable later. Plastic gas and water services, irrigation runs, and some duct systems are the common examples. Where a wire exists, is continuous, and terminates somewhere reachable, a transmitter energizes it and the route is traced exactly as a metallic line would be.
The word doing the work there is “where.” Installations predating the practice have no wire. A break stops the trace at the damage rather than the end of the pipe, and nothing about the receiver announces that this is what happened. Corroded splices and poor terminations distort the signal, and a wire never brought up to an accessible point cannot be energized without excavating to reach it. The wire is also not the pipe — it was laid beside it, so its position approximates the utility's rather than measuring it.
3. Sonde locating
A sonde is a small self-contained transmitter physically introduced into a pipe or duct and tracked from the surface. Vivax-Metrotech describes sondes as battery-powered transmitters inserted and propelled into pipes, drains, or ducts, and notes that for CCTV inspection work a sonde is frequently built into the camera head itself. It can also ride on a push rod or duct rodder.
The distinction from line locating is worth being precise about. Electromagnetic line locating follows a signal running along a whole conductor, so the receiver sees a continuous line. A sonde is a point source: the receiver finds one position at a time, directly above the transmitter, and a route is built by marking successive positions as it advances. That is slower, and it follows the actual pipe — bends included — through material carrying no signal of its own.
It applies wherever a line can be entered: sewer laterals and site drains from a cleanout or manhole, storm structures, empty conduit, and nonmetallic pipe with a usable opening. The constraints follow from the same fact. There has to be an access point; the line has to be passable, so a blockage, collapse, offset joint, or tight bend ends the trace where the equipment stops; signal strength falls with depth; and Vivax-Metrotech notes that low-frequency sondes work in cast iron up to about three meters but cannot be used in ductile iron or steel pipe.
4. Ground penetrating radar
Ground penetrating radar transmits radar pulses into the ground and records reflections where electrical properties change. Because it needs neither a conductor nor an access point, it is often the only remaining option for bare plastic pipe with no tracer wire — and it is the method most often described inaccurately.
Radar does not display labelled utilities. It produces subsurface responses that an operator interprets, using depth, geometry, site context, records, and connection points to decide what a reflection probably is. Pipes, conduits, vaults, voids, backfilled trenches, and other disturbances can all generate responses, and two competent operators can read the same data differently. That interpretive step is part of the method, not a caveat attached to it.
Whether a given target is detectable depends on its size and material, its depth, the contrast against surrounding ground, soil type and moisture, the surface above it, congestion, and antenna frequency. Conductive and clay-rich soils attenuate the signal quickly; FHWA notes that effectiveness reduces in clay-rich soils and that utilities beyond roughly two to four feet may be undetectable in those conditions, while other ground supports far greater depth. This is why radar usually runs alongside electromagnetic locating rather than instead of it: the two fail under different conditions.
Two guides go further: GPR utility locating covers what radar can and cannot resolve, and how deep ground penetrating radar can see covers why no single penetration figure applies to every site.
5. Utility records, maps, and as-builts
Records are the cheapest way to reduce a search area and should be gathered before anyone walks the site: civil and site plans, construction drawings, as-builts, utility company maps, municipal GIS layers, connection permits, facility records, prior repair invoices, and — often the single most valuable document a property owner has — a photograph taken while a trench was open.
None of it is field verification, and treating it as such is the most common failure in this whole subject. Crews route around obstacles that were never redrawn, repairs are made on new alignments, sections are abandoned in place and stay on the drawing, and private facilities frequently appear on no plan at all. Plans are often schematic, so a straight line on paper can be a pipe that bends twice. FHWA puts records at the bottom of its confidence scale for exactly this reason: quality level D is information from existing records or verbal recollections, which it describes as typically unreliable sources.
6. Visual site investigation
Buried networks surface somewhere, and every point where they do constrains where the buried part can run. Meters and meter pits, valves and valve boxes, hydrants, curb stops, transformers and pad-mounted equipment, pedestals and cabinets, poles and riser conduits, cleanouts, manholes, catch basins, vault lids, irrigation heads, service entrances, and building penetrations are all anchors — as are the softer clues: settled trench lines, differential vegetation, patched pavement running straight, and old markings that have not fully weathered.
In FHWA's framework, surveying visible features and correlating them with records is quality level C — better than records alone, still short of any field determination of where the utility actually runs. Two anchors tell you a pipe probably runs between them; they do not tell you it runs straight, or that it is the only thing in that corridor. A settled line is a lead worth recording, not a located utility.
7. Physical verification and potholing
Every method above infers a position from the surface. Exposure observes one. Careful hand digging, vacuum excavation, and hydro excavation open a small hole down to the utility so its horizontal position, depth, and identity can be recorded rather than estimated. FHWA calls this quality level A — the precise plan and profile information obtained through nondestructive exposure, and the only level at which anyone actually sees the thing.
It is used selectively, where being wrong is expensive: a bore crossing a live service, a tight vertical clearance, a tie-in, a footing over an unknown line. Utility potholing is a scope to arrange, not a technique to improvise around energized or pressurized infrastructure. And a verified position is verified at the hole — it establishes that utility at that point, and says nothing certain about the same line fifteen feet away.
Utility locating equipment
The equipment list follows directly from the methods. What matters when comparing providers is not brand but which of these actually arrive on site, because a crew carrying only an electromagnetic set cannot investigate bare plastic pipe, and a crew carrying only radar cannot confirm which conductor it is looking at.
| Equipment | What it does | Common uses | Major limitation |
|---|---|---|---|
| Transmitter | Applies a locating signal by direct connection, clamp, or induction | Energizing metallic lines, tracer wire, and inserted conductors | Needs a conductive target and, ideally, an accessible connection point |
| Receiver | Detects the field around an energized conductor and estimates depth | Tracing and marking line positions from the surface | Distortion and coupling can produce a confident trace of the wrong line |
| GPR system | Transmits radar pulses and records subsurface reflections | Nonmetallic targets, unknown anomalies, and sweeping for missed lines | Soil, moisture, depth, and target size govern results; output needs interpretation |
| Sonde | Transmits from a point inside a pipe so a surface receiver can find it | Nonmetallic sewer, drain, and duct where an access point exists | Needs a passable line; unsuitable for ductile iron and steel pipe |
| Inspection camera | Records the interior of a pipe, frequently with a sonde in the head | Sewer and drain work where condition and route are both wanted | Blockages, collapses, and tight bends stop the run part-way |
| Push rod or duct rodder | Carries a sonde, or introduces a conductor into a nonconductive line | Empty conduit, drains, and short nonmetallic runs | Limited reach, and it still requires a way into the line |
| Tracer wire accessories | Connection, grounding, and splice hardware for energizing a wire | Nonmetallic utilities installed with a locating conductor | Useless where the wire is missing, broken, or never brought to grade |
| GNSS or survey positioning | Assigns coordinates to located points instead of paint on the ground | Utility mapping deliverables and records that outlast the marks | The record cannot be more accurate than the locate it is based on |
| Vacuum excavation equipment | Removes soil to expose a utility without striking it | Confirming horizontal position, depth, and identity at chosen points | Intrusive and slow, so it is applied at selected points only |
Locating underground electrical lines
Buried electrical cable is conductive, which makes it one of the more tractable electromagnetic targets, and energized loaded cable can often be picked up passively on a receiver's power mode. That convenience carries a warning: FHWA notes that an energized line carrying no load may produce no detectable passive signal while remaining very dangerous, so the absence of a passive response proves nothing.
Electrical distribution is also frequently bonded and grounded in ways that give an applied signal several paths to travel, and cable often shares a trench with communications. Both conditions produce traces that look clean and are not. Applying a transmitter to energized electrical equipment is qualified work; if you are not that person, the correct move is a notification ticket for operator-owned facilities and a private locate for anything downstream of the demarcation point.
Locating underground gas lines
Steel and other metallic gas piping is conductive and can generally be traced electromagnetically where a connection point is available. Plastic gas piping is not, and locating it depends on a tracer wire installed with the service — with the same failure modes: no wire on older installations, breaks that silently truncate the trace, and terminations never brought somewhere reachable.
Gas belongs in a different consequence category from most buried services and should be treated that way regardless of how confident a locate looks. The notification obligation before excavation exists largely because of facilities like these, and the U.S. Department of Transportation's damage-prevention material is built around contacting the one-call center before digging. Where excavation is planned near a gas service, a marked line is a starting point and exposure establishes position — this is not a category to investigate with improvised equipment.
Locating water, sewer, and communications lines
Water services split along material. Metallic pipe can often be traced electromagnetically where a fitting, valve, or meter provides a connection point; plastic pipe depends on tracer wire, radar where conditions allow, or narrowing the corridor from records and the building entry point and confirming by exposure. A live pressurized service is also no place for a sonde. Treat the meter-to-house shortcut with scepticism — the pipe between two known endpoints need not run straight between them. How to find a water line underground works through that in full.
Gravity sewer laterals are the classic hard case: PVC, ABS, and clay carry no signal, and tracer wire is far less common on gravity lines than on pressurized services. What makes them tractable is that they can be entered, so the access point tends to decide everything — see how to find a sewer cleanout, then how to locate a sewer line underground for the trace itself and how deep are sewer lines for the separate question of burial depth.
Communications is where an assumption commonly breaks down. Copper cable is conductive and traces like any metallic line, but optical fiber is glass and carries no locating signal at all — what gets traced is whatever metallic component accompanies it, such as armoring, a strength member, duct tracer wire, or the duct bank's reinforcement. All-dielectric cable with no metallic element and no accessible duct offers an electromagnetic locator nothing. Communications also shares trenches with electric more often than any other pair of services, which makes coupling and mis-identification routine rather than exceptional.
How to locate underground pipes
For pipe specifically, material decides the method before anything else does, so establishing material early — from records, from the age of the installation, or from what a camera shows once it is inside — usually saves more time than any equipment choice. None of the rows below is a guarantee: site conditions decide whether the listed approach works on a particular pipe.
| Situation | Usual approach | What can go wrong |
|---|---|---|
| Metallic pipe with an accessible fitting | Direct electromagnetic connection and surface tracing | Discontinuity at a repair, bonding onto other metal, coupling in congested ground |
| Plastic pipe with tracer wire | Energize the wire and trace it as a conductive line | Wire missing, broken, corroded, or never brought to an accessible point |
| Accessible sewer or drain | Camera or push rod carrying a sonde, traced from the surface | No access point, or a blockage that ends the run part-way |
| Empty or rodded conduit | Push a sonde or conductive rod through and trace it | Occupied duct, tight bends, and limited reach |
| Nonconductive pipe with no access | Radar, combined with records and connection points | Clay, saturated soil, depth, and small diameter can leave no usable response |
| Any critical crossing | Physical exposure at the point that matters | Confirms that point only; the same pipe elsewhere remains unverified |
How deep are underground utilities?
There is no universal depth, and installation standards are a poor proxy for what is in the ground. Depth varies with utility type, the jurisdiction and standard in force when the line was installed, its age, the grade at the time, subsequent regrading and erosion, later construction over the top, ownership, and every repair since. A minimum cover requirement is a floor for new work, not a description of an existing line — and the same line is frequently at more than one depth along its length.
Two consequences follow. Depth reported by a locating receiver is an estimate derived from signal geometry, so it is a planning input rather than a measurement; where exact depth matters, exposure establishes it. And shallow excavation is not automatically safe, because irrigation, low-voltage lighting, communications drops, and private feeds are often the shallowest things on a property. For the sewer case specifically, how deep are sewer lines covers what governs burial depth in more detail.
Can you locate underground utilities yourself?
You can do a real and useful share of the work, and it is mostly the part that happens before any equipment comes out. Gather the property records, plans, permits, and past repair documentation. Identify and photograph the visible features — meters, valves, cleanouts, pedestals, service entrances, building penetrations. Note where each service enters the structure, and write down what you know about private facilities a previous owner installed. Then submit the applicable excavation notification and read every operator response on the ticket rather than only the marks on the lawn.
What that does not get you is a located utility. Consumer metal detectors respond to buried metal generally and cannot identify a service or its depth, phone applications do not detect anything underground, probing blind finds shallow utilities the hard way, and connecting locating equipment to energized or pressurized infrastructure is qualified work. The gap is widest exactly where it matters most: utilities that are privately owned, unrecorded, abandoned, nonconductive, missing their tracer wire, or mapped inaccurately are the ones a property owner is least equipped to find and most likely to hit.
811 and private utility locating
In the United States, an excavation notification to the applicable one-call center asks participating facility operators to respond and mark the facilities they own or operate. It is the legal starting point for excavation in most circumstances, it generally carries no direct fee to the person digging, and a private locate does not replace it. The U.S. Department of Transportation's damage-prevention program is built around contacting the center before digging, and the Common Ground Alliance publishes the industry best practices most state programs draw on.
What that response covers varies. Publicly owned mains and operator-owned services are generally inside it; facilities owned by the property or facility owner frequently are not. Indiana 811 notes that some utilities are privately owned and are not marked by its members. Colorado 811 states that private lines are not registered with the notification center, are not part of an 811 request, and must be located at the owner's expense. Tennessee 811 lists customer-owned lines its operators may not locate, and Virginia 811 describes specific points of consumption beyond which a facility will not be marked.
Do not convert any of that into a national rule in either direction — coverage depends on the facility, the operator, the service agreement, the property, and the state's one-call law, and it is not universally “the meter.” The facilities most often outside the response are the ones a site owner installed: private electric feeds, site lighting, private water services, irrigation, private gas, site communications, sewer laterals, and campus infrastructure generally, though whether any particular example is excluded still depends on where it is and who owns it. Check the official one-call resource for the state where work will occur, and see 811 vs. private utility locating and what are private utilities for the ownership boundary in detail.
Underground utility marking colors
Marks are made in standardized colors so anyone on site can read them. The American Public Works Association publishes the uniform color code that U.S. one-call programs generally follow, using ANSI Z535.1 safety colors, and encourages agencies, utilities, and contractors to adopt it.
Two things matter more than the colors themselves. Marks show approximate horizontal position, not exact position and not depth. And APWA describes a tolerance zone within which excavation is done with non-powered hand tools or a non-invasive method until the facility is exposed — the width of the facility plus eighteen inches measured horizontally from each side, unless law or code specifies otherwise. Some jurisdictions specify more: Indiana 811 refers to a mandated two-foot tolerance zone around all marked utilities. Follow the requirement that applies where the work is happening.
| Color | What it designates |
|---|---|
| Red | Electric power lines, cables, conduit, and lighting cables |
| Yellow | Gas, oil, steam, petroleum, or gaseous materials |
| Orange | Communication, alarm or signal lines, cables, or conduit |
| Blue | Potable water |
| Green | Sewers and drain lines |
| Purple | Reclaimed water, irrigation, and slurry lines |
| Pink | Temporary survey markings; some centers also use it for unidentified facilities |
| White | Proposed excavation — the location, route, or boundary of planned work |
Limitations of underground utility locating
The persistent misconception in this subject is that some device can be walked across a site to reveal everything beneath it. Nothing does that. Every method detects a specific physical property under specific conditions, and a competent locate is an accumulation of partial answers, each with its own failure mode.
The recurring gaps are worth naming, because they are what a scope conversation with a provider should cover: missing or schematic records; undocumented private and site utilities; abandoned facilities with no operator, no load, and no record; broken or absent tracer wire; nonconductive pipe with no way in; signal coupling in congested corridors; multiple utilities sharing a trench; targets deeper than a method's practical range; clay-rich and saturated soils that attenuate radar; reinforcement and surface conditions that mask responses; electromagnetic interference; inaccessible connection points; and changes made after the last drawing was produced. A locate reduces uncertainty. It does not eliminate it, and an honest deliverable states where confidence is lower.
When should you hire a private utility locator?
Private locating is worth arranging when the facilities that matter fall outside the operator response, when the answer needs to be more precise than marks on a lawn, or when a record has to outlast the paint. Scope varies a great deal — a single-line residential trace, a full site sweep, a mapped deliverable, and potholed verification points are different jobs at different prices, so define what you need before requesting quotes. Private utility locating cost covers how scope drives a quote, and utility mapping and subsurface utility engineering cover the deliverable end of the range.
Excavation on private property
Work inside a site's own network, where operator-owned facilities are only part of the picture.
Commercial sites and campuses
Multiple buildings, site utilities, and several eras of construction records at once.
Records are missing or unreliable
Nothing shows what was installed, or the drawings clearly do not match what is visible.
Nonconductive utilities are involved
Plastic pipe with no tracer wire needs methods a standard locator set does not provide.
Boring or a critical crossing
Directional drilling and tight clearances are where estimated positions stop being adequate.
A mapped record is required
Design, asset management, and future work need coordinates rather than temporary marks.
Common questions
Frequently asked questions
How do you locate underground utilities?
By combining methods. A typical investigation reviews records, walks the site for visible features and access points, applies electromagnetic locating to conductive lines, uses tracer wire or a sonde where a nonmetallic utility allows it, adds ground penetrating radar where conditions support it, and exposes the utility where position has to be certain.
What is utility locating?
The process of determining where buried infrastructure runs before ground is disturbed. Locating is the field determination, marking is the temporary surface record of it in standardized colors, and mapping is the durable record of coordinates or drawings. They are separate steps, and a site can receive one without the others.
What equipment is used to locate underground utilities?
Electromagnetic transmitters and receivers, ground penetrating radar systems, sondes, inspection cameras, push rods and duct rodders, tracer wire connection hardware, GNSS or survey positioning for mapped deliverables, and vacuum excavation equipment for physical verification. Which of these actually arrive on site is worth confirming before booking a provider.
Can all underground utilities be detected?
No. Abandoned facilities, undocumented private lines, nonconductive pipe with no tracer wire and no access point, and targets beyond a method's practical range can all go undetected. Congested corridors, clay-rich or saturated soil, and shared trenches add further uncertainty. Locating reduces risk rather than eliminating it.
Can plastic pipes be located underground?
Not directly with electromagnetic equipment, because plastic carries no signal. It is located through a tracer wire installed alongside it, a sonde or conductive rod introduced where access exists, radar where soil and depth allow, or by narrowing the corridor from records and confirming position by exposure.
Can GPR locate underground utilities?
It can detect many of them, including nonmetallic targets, but it does not identify utilities by itself — it records subsurface reflections that an operator interprets. Detectability depends on target size and material, depth, soil type and moisture, congestion, and antenna frequency. FHWA notes effectiveness reduces in clay-rich soils.
How do you locate underground pipes?
Material decides the method. Metallic pipe with an accessible fitting can be traced electromagnetically; plastic pipe with tracer wire is traced through the wire; an accessible sewer or drain is traced with a sonde; nonconductive pipe with no access falls to radar and records. Critical crossings are confirmed by exposure.
How deep are underground utilities?
There is no universal depth. It varies with utility type, the standard in force when the line was installed, age, grading and erosion, later construction, and repairs — and a single line is often at different depths along its length. Installation minimums are floors for new work, not descriptions of existing lines.
Can I locate underground utilities myself?
You can gather records, identify and document visible features, note where services enter the building, and submit the required excavation notification. What you cannot do reliably is find nonconductive, unrecorded, abandoned, or private facilities — consumer metal detectors and phone apps do not locate utilities, and connecting equipment to live infrastructure is qualified work.
Does 811 locate private utilities?
Often not. Colorado 811 states private lines are not part of an 811 request and must be located at the owner's expense, and Indiana 811 notes some utilities are privately owned and not marked by its members. Coverage depends on the facility, operator, and state law, so confirm with your state's center.
How accurate is underground utility locating?
Accuracy depends on the method and the conditions, which is why subsurface utility engineering grades information rather than treating it as uniform. FHWA's quality levels run from records at the least reliable end, through surveyed visible features and surface geophysics for horizontal position, to nondestructive exposure for precise plan and profile data.
Do utility locators determine depth?
Receivers commonly report an estimated depth, derived from the shape and strength of the detected field rather than measured directly. Signal distortion, coupling, congested ground, and targets near the equipment's range limit all degrade it. Where depth has to be exact, physical exposure is what establishes it.
Official and technical references
- APWA: Uniform Color Code and guidelines for temporary marking
- FHWA: Site Characterization and Utility Locating
- FHWA: Subsurface Utility Engineering
- Common Ground Alliance: Best Practices Guide
- U.S. DOT PHMSA: Call Before You Dig
- Vivax-Metrotech: utility locating FAQ (sondes, non-metallic pipe, depth accuracy)
- U.S. EPA: Ground Penetrating Radar
- Indiana 811: homeowner FAQs (private facilities and the tolerance zone)
- Colorado 811: private underground utility information
- Tennessee 811: private locating information
- Virginia 811: private utilities explained