What Do Green Utility Flags Mean?

Call Before You Dig is a free service across the U.S. funded by its utility members to help prevent you from punching through natural gas, electric lines, or other underground infrastructure during your yard project, which could include tasks like digging a fence post hole. The national phone number for Call Before You Dig is 811. When you or your contractor calls this number, utility locators will come and mark out any underground lines for you, using flags or stakes in an array of colors following the American Public Works Association Uniform Color Code. This color code system is also used in Canada. Red flags mean electric cables, yellow is for gas, and so on. If you see any green flags, this does not mean “go.” Instead, Green indicates that there are sewer or drain lines underneath the soil you need to avoid. 

You have to avoid digging both on top of the area marked, plus a buffer zone (varying in size based on your state’s laws) from the marked line of the flags. This buffer zone reflects how the colored flags mark approximate locations rather than exact areas. For projects like installing a pond or digging a trench for a French drain, you would need to avoid machine digging within the buffer zone and instead dig by hand. If you are planting a garden or doing surface-level work, don’t assume you are ok above any drainage lines, as the depth of these pipes is often shallow, from one to up to six feet on average. Additionally, this depth can change throughout your yard as the line carries sewage or stormwater away from your home.

It is critical to note that public utility marking only applies to publicly owned pipes and lines. Many drainage and sewer lines on your property are actually private. For example, the line that connects your toilet to the main sewer system is private and won’t be marked with green flags if you call 811 to your property. If you have a septic system, it has private drain lines from your house to the tank and then out to a septic field. Things like privately installed perforated drainage pipes are also important to mark, but are not public utilities. If you will be digging in an area that you suspect has any of these private drainage lines, you’ll need to call a private utility locator service to mark them. But don’t worry, a private locator company also follows the same color coding system, so green flags and paint will be used by them as well.

Considering the hefty fines for not submitting a public or private locate request and damaging underground utility lines, it is always a good idea to call ahead and have them marked. Damaging a sewer, septic, or drain line could cause flooding, release toxic sludge into your yard, and pose a hefty repair bill. Ultimately, fixing a damaged underground pipe, like a sewer line, is a headache that is best avoided by following those little green flags.