Before any excavation: call 811 (One Call) at least 3 business days before digging; wait for all utilities to be marked; require private locates for utilities not covered by 811 (irrigation, fiber, private electric). Pothole (hand-expose) any utility that your excavation will come within 18 inches of horizontally or 6 inches vertically. Utility locate marks are approximations — the excavated depth and horizontal position can vary significantly from the mark.
811 and the One Call System
In the US, 811 is the national one-call system. Calling 811 at least 3 business days before excavation is required by law in all 50 states. The one-call center notifies all registered utility operators in your area. Each operator sends a locator to mark their facilities with APWA color-coded paint or flags. The system covers: electric, gas, water, sewer, telephone, cable TV, and fiber optic utilities owned by regulated utilities.
What 811 does NOT cover: private utilities installed by property owners (irrigation, private electric feeds, private fiber), utilities on private property not connected to public infrastructure, and utilities from operators who did not respond to the locate request (always verify all operators responded).
APWA Color Codes
| Color | Utility Type |
|---|---|
| Red | Electric power, lighting |
| Yellow | Gas, oil, petroleum, steam |
| Orange | Telephone, CATV, fiber optic |
| Blue | Potable water |
| Green | Sewer, storm drain |
| Purple | Reclaimed water, irrigation |
| Pink | Temporary survey markings |
| White | Proposed excavation area |
When to Pothole (Hand-Expose)
Potholing means hand-excavating (by hand shovel or vacuum excavation) to physically expose and verify the exact location and depth of an existing utility. Pothole when:
- Your excavation will come within 18 inches horizontally or 6 inches vertically of a locate mark
- The utility depth is unknown (locates do not provide depth information)
- The utility type is high-risk (gas main, high-voltage electric, fiber serving a data center)
- You are installing a crossing or a connection to an existing utility
- Historical plans show a utility that was not located or marked
Vacuum excavation (hydrovac) is the fastest and safest potholing method — it exposes utilities without the strike risk of a backhoe bucket.
Minimum Clearances
| Utility Type | Typical Min Separation from New Utility |
|---|---|
| Gas main | 12 inches horizontal; 6 inches vertical (varies by utility) |
| Water main (potable) | 10 ft from sewer; 18 inches from other utilities |
| High-voltage electric (>35 kV) | 3–5 ft (varies by NESC and local utility) |
| Fiber optic | 6 inches minimum; 12 inches preferred |
All clearances are minimums — always verify the applicable utility owner’s standards before finalizing the design and before beginning excavation.