The APWA color code chart is a national system that assigns one color of paint or flag to each type of buried utility, so a red mark always means electric, yellow always means gas or other flammable material, and so on down the list. The American Public Works Association standardized eight colors: six for actual underground facilities and two for planning and survey work. Once you can read them, you can walk any marked dig site and know what’s under your feet before a shovel moves.
The Eight APWA Colors and What They Mark
Six colors identify buried infrastructure. Two exist only to guide the locating and construction process and do not indicate any hazard beneath the surface.
- Red — Electric. Power lines, cables, conduit, and lighting cables. Contact can be fatal.
- Yellow — Gas, oil, steam, petroleum. Any flammable or gaseous material. A ruptured yellow-marked line carries the highest explosion risk on any site.
- Orange — Communication, alarm, and signal lines. Includes fiber optic and cable television conduit. No energy hazard, but damage can knock out service for a whole neighborhood.
- Blue — Potable water. Drinking water supply lines only.
- Green — Sewers and drain lines. Hitting one creates contamination rather than an immediate safety emergency.
- Purple — Reclaimed water, irrigation, and slurry. Purple warns the liquid inside is not safe to drink, keeping these systems visually distinct from blue potable water.
- White — Proposed excavation. Painted or flagged by the person planning the dig to show locators where work will happen. Not a utility.
- Pink — Temporary survey markings. Used by surveyors for property boundaries, benchmarks, and reference points. Not a utility.
The chart is aligned with ANSI Z535.1 safety color standards, which is why the same red, yellow, and orange you see on hazard signage carry over to the ground.1American Public Works Association. Uniform Color Code
Reading the Letters, Arrows, and Offsets
Field marks usually carry more than color. Locators paint short letter codes next to their marks to specify the facility type. You’ll commonly see:
- E — electric
- G — gas
- W — water
- S — sewer
- SD — storm drain
- FO — fiber optic
- TEL — telephone
- TV — television
- STM — steam
- LPG — liquefied petroleum gas
When those letters appear in the matching APWA color, they confirm the facility type. Directional arrows show where a line changes course or where a lateral branches off. Vaults, inlets, and lift stations get outlined to their full buried footprint so you know the real clearance, not just the visible lid. Dead ends are marked so no one assumes the line continues past where it actually stops.2Common Ground Alliance. Guidelines for Operator Facility Field Delineation
Sometimes the mark isn’t directly over the line. When site conditions make that impractical, locators place offset marks to one side in the correct color, with arrows pointing toward the true location and the distance noted. If you see a paint stripe with a number and arrow next to it, that number is telling you how far over the actual utility sits.
How the Marks Get There: 811 and White-Lining
The colors only appear on the ground after somebody requests them. Calling 811 connects you to your state’s one-call notification center, which alerts every registered utility operator with infrastructure near your dig site. The service is free, and federal law requires anyone planning to excavate near pipeline facilities to contact the appropriate one-call system before breaking ground.3Office of the Law Revision Counsel. 49 USC 60114 – One-Call Notification Systems
Most states require you to submit a locate request at least two full working days before your planned start date. You provide the address, the type of work, expected depth and duration, and a description of the dig boundaries. You can file by phone or through your state 811 center’s website.4811 Before You Dig. 811 Before You Dig – Every Dig, Every Time
Before locators arrive, you’re expected to outline your dig area in white paint or white flags. This is called white-lining or pre-marking, and it tells locators where to focus so they aren’t marking an entire property when you only need a ten-foot trench. For rectangular areas, use a continuous white perimeter, dashes at each corner, or a dashed line around the boundary. For curves, use white dots at close intervals. Very small sites with a radius of 50 feet or less can be marked with a single white stake at the center, labeled with your company name and the work radius. Include something identifying you on the marks, whether a printed flag or your name written in paint.
Locate tickets expire. Some states allow as few as 15 calendar days; others give 20 to 25. If your project runs past the expiration or the marks fade, call 811 again and request a remark before continuing. Faded or lost marks account for roughly 2 percent of reported utility damages each year, which translates to thousands of preventable strikes.5Common Ground Alliance. 2024 DIRT Report
The Tolerance Zone Around a Marked Line
A color on the ground isn’t a green light to run a backhoe through it. Every marked utility has a tolerance zone: a buffer where mechanical excavation is restricted. APWA guidelines recommend a zone equal to the width of the facility plus 18 inches measured horizontally from each side.6American Public Works Association. APWA Guidelines for Uniform Temporary Marking of Underground Facilities
State law may set different dimensions. Some states use 18 inches, others 24 inches from the outer edge of the facility, and a few calculate the zone based on pipe diameter. The principle holds everywhere: inside the tolerance zone, you must expose the utility by careful means before any powered equipment goes near it.
Approved methods within the zone include hand digging with non-powered tools, vacuum excavation, potholing (a small test hole to visually confirm the utility’s exact position), pneumatic hand tools, and soft digging. Power equipment can remove pavement, but once you’re into the soil within the tolerance zone, switch to gentler methods. Other mechanical approaches may be acceptable if the utility operator specifically approves them.7Common Ground Alliance. Excavation within Tolerance Zone
Potholing deserves special attention. Surface marks show approximate horizontal location, but they tell you nothing about depth. A few minutes potholing at key points along your trench can prevent a strike that shuts down the project for days.
What 811 Will Not Mark
A common assumption is that calling 811 gets every buried line on your property flagged. It doesn’t. The 811 system only notifies utilities that own public infrastructure, and those operators only mark their facilities up to the point where their responsibility ends, usually at the meter or the connection on the side of your building.
Everything past that point is a private line, and locating it is on you. Lines that 811 will not mark include:
- Water service lines from the meter to the house
- Sewer laterals from the cleanout to the main
- Electric, gas, or water lines running to detached garages, sheds, or workshops
- Sprinkler and drainage lines, pool heater connections, and outdoor lighting wiring
- Septic tanks and drain field piping
- Propane tanks and buried supply lines
- Invisible pet fence wires
If you suspect private lines in your dig area, hire a private utility locator. They use ground-penetrating radar, electromagnetic locating equipment, or both to find what the public system won’t touch. Residential jobs typically run a few hundred dollars depending on property size and complexity.
If You Hit a Line Anyway
Strikes happen even with proper marking, and the first few seconds decide how bad it gets.
Gas (Yellow)
The most dangerous scenario. If you smell gas, hear hissing, or see dirt blowing from the ground, stop equipment and evacuate on foot. Do not start vehicles, use cell phones, or operate anything that could spark. First responder guidance recommends an initial evacuation of at least 330 feet in all directions, extending to half a mile downwind for larger leaks. Call 911 from a safe location, then contact the gas company.
Electric (Red)
If your equipment contacts a buried power line, stay in the cab. The machine may be energized, and stepping off creates a path to ground through your body. If fire or another immediate threat forces you out, jump clear without touching the machine and the ground at the same time, then shuffle away with small steps to avoid voltage differences in the soil. Call 911 and the electric utility.
Water, Sewer, and Communication (Blue, Green, Orange)
Water breaks can flood a trench and undermine adjacent structures. Shut off any accessible valve and call the water utility. For sewer strikes, stop work and stay clear because of contamination. Communication damage should be reported to 811 and the affected provider; there’s no physical danger.
Reporting
Every state requires you to report utility damage. Pipeline operators have federal reporting obligations to the National Response Center at 1-800-424-8802 for hazardous material releases. Report the damage to 811 as well so the affected utility can dispatch repair crews and update the locate ticket.8Pipeline and Hazardous Materials Safety Administration. Incident Reporting