Utility locating and call before you dig: the 811 ticket, the marks, and digging safe

Utility locating and call before you dig

Utility locating is the work of finding and marking buried lines before anyone digs, and call-before-you-dig is the system that triggers it. You contact 811, the national three-digit number that routes to your state one-call center, and the center notifies every utility that has lines in your dig area. Each owner sends a locator who marks the approximate path of their buried facilities with paint and flags in a standard color. Then you dig around the marks, by hand where you have to.

That is the whole arrangement. You give notice, they mark, you respect the marks and verify them. The call is free. In every state it is also the law, written into a one-call or underground-damage-prevention statute, and the specifics of the wait time, the tolerance zone, and the marking rules belong to that state law and the authority having jurisdiction.

What gets buried under a site is rarely just one line. A single lot can carry gas, electric, fiber, water, sewer, cable, and street lighting, stacked and crossing at different depths. Hit the wrong one with a bucket and the consequence is not a repair bill. It can be a funeral. This guide covers finding and respecting buried lines before you open the ground; building and proving the structure under the pavement once the ground is clear is covered in the base and subgrade compaction and subgrade stabilization guides cross-linked here.

What a struck line actually does

A struck line is not a paperwork problem. It is the fastest way to kill someone on a dig.

Gas is the one that makes the news. Tear open a gas main and the escaping gas finds an ignition source, an engine, a spark, a cigarette, and the explosion levels the trench and everything near it. Electric is quieter and just as deadly. A bucket or a hand tool through an energized cable puts fault current through the operator, and the arc burns at temperatures that do not give second chances. Fiber and communication lines do not kill the operator, but cut the wrong one and you can take down a 911 center, a hospital's data link, or a city block's phone and internet for days.

Then there is the money. A damaged line means the repair, the restoration, the downtime claims from everyone the outage touched, and a fine from the state for digging without a valid ticket or without respecting the marks. The liability runs to the excavator who put the steel in the ground, and it follows the company long after the trench is closed. That is why it is the law, and why the call is the cheapest insurance on the job.

Who has to call 811?

Everyone who disturbs the ground has to call, not just the crews running big iron. The law is written around excavation, and excavation in a one-call statute is broad. It covers any operation that moves earth. That sweeps in trenching and grading, but also augering a fence post, setting a sign, planting a tree, driving a stake, and pulling a stump.

The size of the job is not the test. Depth is not the test either. Gas services and communication drops are often shallow, sometimes less than a foot down, exactly where a post-hole digger or a hand auger lands. Some of the worst strikes come off the smallest jobs, because the operator decided a quick hole did not need a ticket.

Homeowner or contractor, the obligation is the same, though the procedure and the narrow exemptions vary by state. If you are not sure whether your work counts, the safe read is that it does. Call, get the marks, and dig clean. The exception that lets you skip the call is defined by your state law, not by your judgment on the day.

How long before you dig do you call 811?

Call several business days ahead, commonly two to three, and the exact lead time is set by your state one-call law. Most states count business days and exclude the day of the call, weekends, and holidays, so a request placed Friday afternoon may not come due until the middle of the next week. Plan the locate into the schedule, not the morning you want to dig.

The clock matters in both directions. Call too late and you have a crew standing around waiting on marks. Call too far ahead and the marks may fade or get destroyed before you reach that part of the site, and the ticket may expire before you finish.

Put the request in as soon as the dig area is known. You can mark the area and file the ticket while other trades are still working, so the locate runs in parallel and the marks are fresh when you break ground. The wait time is a floor, not a target. You do not start when the clock runs out. You start when every utility has responded.

The locate ticket and how to describe the dig

The locate request, the ticket, is the document that starts everything and the record that protects you later. You file it with the one-call center by phone or online, and the center issues a ticket number that ties to your dig. Keep that number. It is your proof that you gave notice and the key to checking responses.

The ticket lives or dies on the dig-area description. The locator is not reading your mind. They are reading your text. Give the address, the cross street, and a clear account of where on the property you are working: the back forty feet, the east side from the corner to the driveway, the full lot. Mark the limits on the ground too, so the words and the paint agree.

A vague ticket gets a vague locate. Say the whole site when you mean one corner and the locator may mark the easy frontage and miss the run you actually care about. Describe too small an area and lines just outside it never get marked, and you dig into them with a clean conscience and a struck line. Match the words on the ticket to the white lines on the ground and to the work you are about to do.

White-lining the dig area

White-lining is pre-marking the outline of your dig with white paint, flags, or stakes before the locator arrives, and it is the single best thing you can do to get an accurate locate. White is the APWA color for proposed excavation. When the locator sees a white box on the ground, they know exactly where to put their effort instead of guessing from a text description.

On anything but a small, obvious dig, white-line it. A long trench, a scattered set of pier holes, a dig that does not match the parcel lines, all of it locates better when the area is drawn on the ground. Some states and some one-call centers require pre-marking for larger or complex jobs, so check what your law and the center expect.

The payoff is fewer missed lines and fewer re-marks. The locator marks what is inside your white lines and a margin around them. Draw the box where the work is and the marks land where you need them.

What do the utility marking colors mean?

The marks follow the APWA Uniform Color Code, a national standard so a locator's paint reads the same to any crew. Red is electric. Yellow is gas, oil, steam, and petroleum. Orange is communication, alarm, and signal lines, which takes in most fiber and cable. Blue is potable water. Green is sewer and drain. Purple is reclaimed water, irrigation, and slurry. Pink is temporary survey marking. White is the proposed excavation you outlined.

Learn the colors cold, because they drive how you dig. Red and yellow are the two that kill. When you see red or yellow paint, the digging discipline tightens before the steel moves.

The color code is a convention, not a law of physics, and adoption can vary, so confirm the scheme your locators and your AHJ use, especially on older sites where markings may predate the current standard. The paint also carries more than color. Locators write the line size, the owner, and sometimes the number of lines, so read the whole legend, not just the stripe.

What is a positive response, and why wait for it?

A positive response is each utility's posted answer to your ticket, telling you whether they marked, found no conflict, or need more time. You do not dig when the wait time runs out. You dig when every utility on the ticket has responded and the area is clear.

Most one-call centers run a positive-response system you check online or by phone using your ticket number. It lists each notified utility and what they reported: marked, clear, or not complete. A missing or no-response entry is not permission. It means a line owner has not confirmed, and a line owner who has not confirmed is a line you cannot see and cannot trust.

This is where strikes hide. The crew sees paint on the ground, assumes everyone marked, and digs while one utility is still pending. The paint they saw was the gas company. The one still pending was the fiber. Confirm that every member responded, in writing, before the bucket moves. Many states make checking positive response a legal step, not a courtesy, so treat a complete response as the real start line.

What is the tolerance zone?

The tolerance zone is the band on each side of a mark where you treat the line as present even though you cannot see it, and where mechanical digging is off the table. A common figure is 18 to 24 inches measured out from each side of the marked line, but the exact width is set by your state law, so confirm it.

Inside the zone you dig by hand or with vacuum excavation, never with a backhoe, trencher, or auger, until the line is exposed and you can see it. The marks are approximate, so the zone is the margin that covers the slop in the mark plus the width of the line itself.

The rule that gets crews hurt is treating the paint as a hard edge and running a machine right up to it. The line is not under the paint to the inch. It is somewhere in the zone. Hand-dig the tolerance zone, expose the line, and only then bring the machine back to work outside it. This is one of the three habits that keep a dig safe, and it is the one operators skip when they are behind schedule.

Potholing and daylighting: expose before you trust

Potholing, also called daylighting, is digging a careful hole by hand or with a vacuum truck to expose a buried line and see its exact location and depth before you work near it. The marks give you horizontal position and nothing about depth. Potholing is how you turn an approximate stripe into a known pipe.

Do it wherever your work crosses or runs parallel and close to a marked line, and especially before any boring, trenching, or machine excavation that will pass through the tolerance zone. Vacuum excavation is the cleanest method, soft and fast, and it does not nick coatings the way a shovel can. Where you hand-dig, use a blunt tool, work parallel to the line, and let the shovel slide off the pipe instead of stabbing into it.

A line you have daylighted is a line you can dig around with confidence. A line you have only seen as paint is a guess. On a crossing of an energized or pressurized line, the pothole is not optional caution. It is the step that tells you whether your trench clears the pipe or hits it.

The marks are approximate, not as-built

Locate marks show the approximate horizontal location of a line and nothing more. They are not survey-grade, they do not give depth, and they can be wrong. Treat them as a strong hint, not a guarantee, and the rest of the procedure follows from that.

Several things move a line off its paint. The locator's signal can wander where lines run parallel or cross, where the soil is wet, or where a second line couples onto the one being traced. Depth changes along a run as the grade changes, so a line two feet down at one end can be six inches down at a low spot. And lines get missed entirely: an abandoned service with no current on it, a line with no tracer wire, a private line the one-call locator never touches.

That is why the tolerance zone and potholing exist. The system assumes the mark is off by some amount and builds the safety margin in. The crew that gets in trouble is the one that reads the paint as an as-built drawing. It is not. It is the best guess of where to start looking.

Private utilities that 811 will not mark

811 marks the utility-owned lines up to the meter or the service connection, and it stops there. Everything on the customer side of the meter is private, and the one-call locators do not mark it. That gap is where a lot of strikes live, because the private lines are often the ones running across the part of the site you are digging.

The list is long on a developed property. A gas line from the meter to a pool heater or a detached garage. The electric feed to a sign, a gate, or site lighting. Irrigation mains and laterals. A private water or sewer line between buildings. A propane line from a tank. Data and security conduit between structures. None of it comes up on the public ticket.

To find it, hire a private locator. They run the same electromagnetic and ground-penetrating-radar tools as the public locators, but they work for you and they mark the customer-side lines the one-call center leaves out. On any site with buildings, site lighting, or irrigation, plan and budget the private locate. The public ticket is half the picture. Private utilities need a private locator, and that is the third habit that keeps a dig safe and the one most often forgotten.

How the locator actually finds a line

Most locating runs on electromagnetic induction. The locator applies a signal to a conductive line, directly with a clamp or connection or indirectly by inducing it, and walks the receiver over the ground to trace the field the line radiates. Anything metallic carries it well: copper, steel pipe, an electric cable, a tracer wire.

The problem is everything that is not metallic. Plastic gas pipe, PVC water and sewer, fiber with no metallic element, none of it carries the locator's signal on its own. That is what tracer wire is for, and it is why a plastic line without tracer wire is close to invisible to a standard locate.

Where the electromagnetic method cannot see, ground-penetrating radar fills part of the gap. GPR reads changes in the soil and can pick up non-metallic and abandoned lines a signal locator misses, but it needs a skilled operator to interpret and it struggles in wet clay and some soils. No single tool finds everything. A good locator switches methods based on what is in the ground and what the records say should be there.

Tracer wire on your own plastic utilities

If you install a plastic utility, install tracer wire with it. A bare plastic pipe carries no signal, so the next crew that calls 811 gets no mark for your line, and your line becomes the unlocatable one that someone digs into years later. The tracer wire is a continuous conductor laid in the trench with the pipe and brought up to an accessible point so a locator can connect to it.

This is the part of damage prevention that is on you, not the one-call center. Every plastic gas, water, sewer, irrigation, and conduit run you put in the ground is a future locate, and whether it can be found depends on the wire you did or did not install. Use the gauge and material the spec calls for, keep it continuous, test continuity before backfill, and tie it off where it can be reached.

A buried plastic line with a broken or missing tracer wire is a strike waiting to happen on someone else's clock. Spend the wire now and the line stays findable.

What do you do if you hit a line?

If you strike a line, the response depends on what you hit, and on gas and electric the first move is to get people away, not to assess the damage. Stop work, keep the crew clear, and do not try to fix it yourself.

For a gas strike, treat it as a leak even if it looks minor. Shut down equipment, evacuate the area upwind, keep all ignition sources away, no engines, no phones, no switches at the trench, and from a safe distance call 911 and the gas utility's emergency line. Do not try to crimp, plug, or backfill the line. Get clear and let the responders work.

For electric, do not touch the cable or anything it contacts, and keep everyone back. An energized cable can charge equipment and the ground around it. Call the electric utility and 911.

Report every contact, even a nick. A scrape on a coating or a dent in a pipe weakens it and fails later, and most damage-prevention laws require you to report any contact or damage to the line owner, not just a full break. The small one you do not report is the leak that shows up next month.

Ticket expiration and re-marks

A locate ticket does not last forever. It is valid for a set number of days, often around two weeks but set by your state law, and after that the marks are considered stale and the ticket has to be renewed before you keep digging. Long jobs need a plan for keeping tickets and marks current.

Marks fade and disappear too. Rain, traffic, grading, and time erase paint and pull flags, and a mark you cannot read is a mark you cannot trust. If the marks are gone or unclear and you are still digging, request a re-mark before you continue, even if the ticket itself is still inside its window.

Renew the ticket for the next stage before the current one lapses, the same way you placed the first request, so the locate stays ahead of the work. Confirm the renewal interval and the re-mark procedure with your one-call center, because both vary by state. The expired ticket and the faded mark are quiet, common causes of a strike, because the crew is sure they did everything right, weeks ago.

Emergency locates

There is a faster track for true emergencies. When there is a danger to life, health, or property, a broken water main flooding a street, a gas leak, a downed line, the one-call center runs an emergency locate with a much shorter response than the normal wait. You still call first. You do not skip the system because it is urgent.

Use it for what it is for. An emergency locate is for an actual emergency, not a way to jump the line because the schedule slipped. The definition of an emergency is set by your state law, and abusing the emergency track is itself a violation. When it is real, call, say it is an emergency, and the response comes fast.

Documenting the locate

The locate is only as good as the record you can produce when there is a claim. If a line gets hit on or near your dig, the question is whether you called, waited, and respected the marks, and the only thing that answers it is documentation. Build it as you go, not after the phone rings.

Photograph the marks before you dig and again before you backfill, with something in frame for scale and location. Keep the ticket number, the list of notified utilities, and the positive-response confirmation showing every member responded. Log the dates, the white-lining, any re-marks, and the depth and location of anything you potholed. If you damage a line, document the contact and the report you made.

A field tool such as FieldOS makes this hold up, because the photos, the ticket, and the positive response are stamped with time and location and tied to the job instead of scattered across phones. When a claim lands a year later, the crew that kept the record walks away and the crew that did not pays for a line nobody can prove they protected.

Training the crew to respect the marks

The locate fails at the shovel if the crew does not respect it. The operator on the machine is the last line of defense, and the rules only work if everyone on the dig knows them and follows them when the foreman is not standing there.

Train the crew on the short list. What the colors mean. Where the tolerance zone starts. That machines stay out of it. That plastic without tracer wire may not be marked. That any contact gets reported. Make it normal to stop and pothole rather than push a bucket toward fresh paint. The pressure on a job is always to keep moving, and the strike happens in the moment someone decides the marks are close enough.

Most damage-prevention programs expect a competent, trained excavator running the work, and some states require specific training or certification. The crew that treats the marks as real, hand-digs the zone without being told, and reports a nick instead of burying it is the crew that stays off the DIRT report.

CGA best practices and the DIRT report

The Common Ground Alliance, the CGA, publishes the consensus best practices the damage-prevention world works from, and most state one-call laws line up with them. The framework is the one this guide follows: notify the one-call center, wait and confirm positive response, respect the marks, dig carefully in the tolerance zone, pothole to verify, and report damage.

The CGA also runs the DIRT report, the Damage Information Reporting Tool, which collects utility-strike data across North America every year. The value of DIRT is the pattern it shows. A large share of damages trace back to the same few causes: no notification made, digging before marks were confirmed, and not respecting the marks that were there. The strikes are not random. They are the predictable result of skipping a known step.

The CGA best practices are guidance, and your state one-call law and the AHJ are what actually bind you. Where the law is silent, the CGA practice is the defensible standard of care. Where the law is stricter, the law wins. Read both for the jurisdiction you are working in.

Field checklist

Common mistakes

• Not calling 811 at all because the job seemed too small to need a ticket.
• Digging before every utility posted a positive response.
• Running a machine inside the tolerance zone instead of hand-digging it.
• Trusting the marks as exact and skipping the pothole.
• Forgetting private utilities on the customer side of the meter.
• Working on an expired ticket or over faded marks without a re-mark.
• Failing to report a nick or scrape, so the slow leak surfaces later.

Standards and references

The binding rule is your state one-call or underground-damage-prevention law. It sets who must call, the advance notice, the wait time, the width of the tolerance zone, the positive-response requirement, and the penalties, and these vary state to state, so read the statute and confirm the details with the authority having jurisdiction. The 811 number and the one-call center are how you comply with it.

The CGA best practices give the national consensus the state laws are built on, and the APWA Uniform Color Code is the marking standard the locators use. Confirm the colors and the practices your locators and AHJ actually follow. On the federal side, OSHA's excavation rules in 29 CFR 1926 Subpart P require that underground installations be located and protected before excavation, alongside the trench-protection rules. Pipeline damage prevention is reinforced under the federal pipeline safety regulations in 49 CFR, which drive the state one-call programs that govern digging near gas and hazardous-liquid pipelines.

Three habits carry the most weight. Call 811 and wait for a positive response from every utility. Hand-dig the tolerance zone and pothole to verify before you trust a mark. And get a private locator for the lines past the meter that 811 will not mark. Proving the structure under the pavement, covered in the base and subgrade compaction and the subgrade stabilization guides cross-linked here, is the next concern once the ground is clear of lines.

Units, terms, and conversions

Damage prevention has its own vocabulary, and the same idea goes by different names across states and centers.

Call-before-you-dig, one-call, and 811 all name the same notification system. The locate request is also called the ticket. Positive response is the posted confirmation that a utility has answered the ticket. Daylighting is another word for potholing. The tolerance zone is sometimes called the approximate location zone or the safety zone. Tolerance-zone width is given in inches in the US, commonly 18 to 24 inches each side, and in millimeters in metric sources. Depth of cover, once a line is exposed, reads in inches or feet here and in meters elsewhere.

811 / one-call

The three-digit number and the center that notify utilities to mark their lines before you dig

Locate ticket

The request you file; its number is your proof of notice and your key to checking responses

Positive response

Each utility's posted answer confirming whether it marked the dig area or found no conflict

APWA color code

The national color standard for utility marks, from red electric to white proposed excavation

Tolerance zone

The hand-dig band on each side of a mark, commonly 18 to 24 in but set by state law

Potholing / daylighting

Hand or vacuum digging to expose a line and verify its exact location and depth

Tracer wire

A continuous conductor laid with plastic pipe so the line can be located later

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