When using a utility locate service to identify underground lines, you need to contact 811 at least two to three business days before any digging begins. This free national service connects you with your local one-call center, which notifies every utility company with infrastructure in your area. Locators then visit your site and mark the approximate location of buried lines using color-coded paint, flags, or stakes so you know exactly where it’s safe to dig.
How the Locate Process Works
The process starts with you, not the utility companies. Before calling 811 or submitting an online request, you’re expected to “white line” your dig area. This means marking the boundaries of your planned excavation in white paint, flags, or stakes so locators know exactly where to focus. If standard white paint markings might confuse pedestrians or drivers (near a crosswalk, for example), you can use alternative methods like flags or stakes, but you should notify your local one-call center about the substitution.
Once you submit your locate request, the one-call center generates a ticket and notifies every utility operator with lines in the vicinity. Each company then sends a locator to mark their specific infrastructure. The typical turnaround is two to three business days, though exact timelines vary by state. You’ll receive a ticket number to track the request.
A locate ticket doesn’t last forever. In most states, tickets are valid for about 21 consecutive calendar days from the start date. If your project runs longer than that, or if the markings become hard to see from weather or construction activity, you need to request a renewal ticket before continuing work.
What the Color-Coded Markings Mean
Every color on the ground corresponds to a specific type of utility, following a standardized system developed by the American Public Works Association. Here’s what each one indicates:
- Red: Electric power lines, cables, and conduit
- Yellow: Gas, oil, steam, or other hazardous materials
- Orange: Communications, cable TV, alarm, or signal lines
- Blue: Potable water lines
- Purple: Reclaimed water, irrigation, and slurry lines
- Green: Sewer and drain lines
- Pink: Temporary survey markings
- White: Your proposed excavation route (placed by you, not the locator)
These markings appear as spray paint lines, small flags, or sometimes both. The paint is designed to fade naturally with rain and sunlight, and flags are typically collected once the project wraps up. If you need to mow your lawn while flags are in place, you can briefly lift them and set them back in the exact same spot, but don’t move or remove them permanently until all digging is complete.
The Tolerance Zone Around Each Mark
The painted line on the ground isn’t the edge of the utility. It’s an approximation of the center. Every marked line has a “tolerance zone” extending 18 to 24 inches on each side, depending on your state’s law. The Common Ground Alliance defines this zone as the width of the utility itself plus 18 inches measured from its outer edge in both directions.
Within this tolerance zone, you cannot use mechanical equipment like backhoes, trenchers, or augers until the utility has been physically exposed and visually confirmed. The only permitted methods are hand tools: blunt or rounded shovels used at a 45-degree angle, stopping as soon as you see the pipe coating or cable sheathing. Once you’ve confirmed the utility’s exact position and protected it, mechanized digging can resume outside the confirmed location. This rule exists because even small deviations between the marked line and the actual pipe can lead to a gas leak, severed fiber optic cable, or electrocution.
How Deep Utilities Typically Sit
Depth varies by utility type, soil conditions, and local codes, so locate markings only show horizontal position on the surface. They don’t tell you how deep something is buried. As a general reference, New York state code requires buried service lines to have at least 18 inches of cover, and most residential gas, water, and electric lines fall somewhere between 18 and 36 inches deep. Sewer and water mains often run deeper, sometimes four to six feet or more.
These are installation standards, not guarantees. Erosion, landscaping changes, and previous construction can shift the actual depth considerably. Lines installed where underground obstacles prevented standard depth may be shallower than expected, though they’re required to have additional protection in those cases. This is why hand digging within the tolerance zone matters so much: you can’t assume a line is deeper than your shovel just because the code says it should be.
How Locators Find Non-Metallic Lines
Metal pipes and cables are relatively straightforward to find. Locators send an electromagnetic signal along the line and trace it with a receiver at the surface. The challenge comes with non-metallic materials like PVC water pipes or plastic gas lines, which don’t conduct electromagnetic signals.
For these, locators often rely on tracer wire, a thin metallic wire buried alongside the plastic pipe during installation specifically so it can be located later. When tracer wire is present, the process works much like locating any metal line. When it’s missing or broken, locators turn to ground-penetrating radar, which sends electromagnetic pulses into the soil and reads the reflections that bounce back from buried objects.
Ground-penetrating radar works well for materials that are electrically distinct from the surrounding soil. But PVC has a dielectric constant around 3, while common soils range from 4 to 30, meaning the signal bouncing off a PVC pipe can be weak or nearly indistinguishable from the soil around it. Small-diameter plastic pipes are especially difficult to detect. According to the Federal Highway Administration, locating plastic and PVC lines remains a significant challenge, with success depending on soil conditions, pipe size, and how much signal processing the data requires. This is one reason why locate services include the caveat that not all utilities may be marked, and why careful hand digging near known utility corridors is critical even when no markings are present.
What Locate Services Don’t Cover
The 811 system notifies utilities that are members of your regional one-call center, which typically includes gas, electric, water, sewer, and telecommunications providers. It generally does not cover privately owned lines on your property. If you had a sprinkler system, septic tank, propane line, or private well line installed, those are your responsibility to identify. Landscape lighting wiring, invisible pet fences, and private drainage systems also fall outside the scope of a standard locate.
If you’re unsure whether private utilities exist on your property, a private utility locating company can sweep the area using the same electromagnetic and radar tools the public locators use. This is an out-of-pocket expense, but it’s worth considering for larger excavation projects on properties with older or undocumented infrastructure.