Before driving a mechanical auger, post-hole digger, or shovel into your yard, contacting 811 is a legal requirement in all 50 US states. Even a standard residential fence post requires digging 24 to 48 inches deep. That is more than deep enough to strike buried electrical feeders, high-pressure natural gas lines, fiber optic cables, or water mains.
Striking a buried line carries severe risks, including electric shock, gas explosions, regional service blackouts, and hefty repair bills that can reach thousands of dollars.
Here is how the 811 notification process works, what the color-coded paint marks signify, and how to safely dig fence posts inside designated tolerance zones.
How the 811 Notification Process Works
Contacting 811 is free and straightforward for both homeowners and contractors.
- Pre-Mark Your Proposed Fence Line in White: Walk your perimeter and outline the exact fence post locations or post run using white spray paint or white survey flags. This tells locating technicians exactly where you plan to excavate.
- Submit Your Request 2 to 3 Business Days Ahead: Call 811 or submit an online locate request through your state 811 notification center (such as Texas 811, Sunshine 811, or Dig Safe). The waiting period excludes weekends and state holidays.
- Receive Confirmation and Ticket Numbers: You will receive an official ticket number listing every utility company notified in your area (electric, gas, telecommunications, water, sewer).
- Inspect the Marks Before Digging: Before starting work, confirm that every utility company listed on your ticket has either painted markings on the ground or sent positive notification that the area is clear.
Understanding the APWA Utility Color Code
Locating technicians mark underground infrastructure following the American Public Works Association (APWA) uniform color code:
- Red: Electric power lines, cables, conduit, and lighting cables
- Yellow: Gas, oil, steam, petroleum, or gaseous materials
- Orange: Communication, cable TV, alarm, fiber optic, or signal lines
- Blue: Potable water lines
- Green: Sewers and drain lines
- Purple: Reclaimed water, irrigation, and slurry lines
- White: Proposed excavation boundary (marked by you)
- Pink: Temporary survey markings
The “Tolerance Zone” and Safe Digging Rules
Utility markings do not indicate exact burial depth. Erosion, grade changes, and tree roots can cause pipes or wires to sit just inches below the grass. Furthermore, markings indicate the approximate horizontal center of a utility run, subject to a legally mandated “tolerance zone”.
In most jurisdictions, the tolerance zone extends 18 to 24 inches outward from either side of the outer edge of the marked utility.
- Never use power equipment inside the tolerance zone: Do not use gas-powered augers, skid-steer trenchers, or mechanical diggers within 18 to 24 inches of any utility mark.
- Hand-dig or pothole to expose lines: Use a blunt hand shovel, garden trowel, or vacuum excavation to verify line depth before installing nearby fence posts.
- Adjust your post spacing if needed: If an electric or gas line intersects an intended post hole, shift your post spacing by 6 to 12 inches to clear the line entirely.
What 811 Does NOT Mark: Private Utilities
The 811 service only notifies public utility operators. They do not locate privately installed lines downstream of the utility meter, such as:
- Underground power lines to detached garages, sheds, or workshops
- Low-voltage landscape lighting wiring
- In-ground sprinkler pipes and irrigation control valves
- Propane tank supply lines from private tanks to the home
- Septic tanks, drain fields, and private sewer laterals
- Pool filtration lines and electric heat pump connections
You must locate these private lines yourself or hire a private utility locating contractor before drilling post footings.
Project Planning and Material Takeoffs
Plan post depths and calculate exact concrete quantities based on your yard layout:
- Size post holes and concrete volume with our fence post concrete calculator.
- Determine proper footing depths below regional frost lines with the fence post depth calculator.
- Read our technical breakdown on how deep should a 6-foot fence post be.
- Learn how to set uprights safely in setting fence posts in dirt vs concrete.
- Consult boundary rules in our property line and setback guide.