I get calls almost every week from people who want to know what this or that colored mark they found on the ground means. After spending more than two decades in the underground utility protection business, I sometimes forget that not everyone understands what each of the various colors we use to designate buried facilities mean.
The American Public Works Association (APWA) has developed a color code for marking underground utilities that is accepted and used by most locating companies and other related industries across the United States. Using this standard keeps us all on the same page and makes the world a little bit safer for everyone.
The most common colors most people regularly see on the ground are orange, red, and blue. Orange paint or flags represent communications facilities such as telephone or cable television services, but can also include cables carrying traffic, railroad, or other signaling device information as well. Almost all fiber optic cables fit into this category.
Red paint or flags represent underground electrical circuits carrying power to lights, homes, or other structures where electricity is in use. A red mark on the ground can represent power ranging from low voltage decorative lighting to high voltage distribution systems. You should always use extreme caution around any facilities designated as underground electrical wiring.
Potable or drinking water should always be marked with blue paint or flags, though some companies also use this color to designate irrigation piping as well. This includes the water mains delivering municipal water to your home or business as well as water from wells used for human consumption.
The next most common marking color most people encounter is probably yellow, used to designate petroleum products in either liquid or gaseous form, as well as pressurized steam pipelines. Natural gas and propane are probably the two most common petroleum products found in residential and commercial settings. Cross country petroleum pipelines are also usually marked in this color, and it is a felony to deface temporary or permanent pipeline markings.
Green paint or flags typically indicate the presence of underground sewage pipelines or other drain lines such as storm water management systems. Some sewage systems include pressurized pipes commonly called forced mains. These systems depend on mechanical pressure to move waste water from one place to another, rather than relying on gravity to get the job done. You do not want to be present if one of these pipelines is ruptured.
The final three elements of the APWA color code are pink, purple, and white. White markings should be reserved only for designating proposed excavation routes or areas. Pink paint is reserved for temporary survey markings, though some utility contractors use it to differentiate lines they have marked for their own use from those marked by other locators. I often use pink paint for my initial survey of a work site, placing dots along underground utility routes until I am able to determine exactly what type of utility I’ve found and mark each facility appropriately.
The color purple is, in my experience, the least common color used to mark underground facilities and indicates reclaimed or grey water, irrigation, and slurry pipelines. Again, some irrigation systems may be found marked with blue paint, especially if they are served from a municipal supply line.
Regardless of what colored lines you see on the ground, you should always treat every mark as an unknown until you have physically verified the utility beneath. Professional locators do our best to provide accurate surface information to excavators and others who utilize our work, but even the most experienced technician can be mistaken and mislabel utilities he or she cannot see. Personally, I’d rather mislabel a facility than leave it completely unmarked.
For more information about the color code or what the marks on the ground mean, please visit the American Public Works Association or Common Ground Alliance. Respect the marks and dig safely, because the life you save could be your own.