What is potholing, and why is it done before boring or trenching?

An 811 locate gives you paint and flags. Potholing gives you a measurement. The two work together, and one does not replace the other.

State law requires an excavator to find out where underground facilities are before digging in a public street, alley, right-of-way or public utility easement. Under A.R.S. 40-360.22, the operator then marks its lines, and the marking "is valid for fifteen working days from the date of the marking." The statute also lists the ways an operator may mark a line, and one of them is "Manual location techniques, including pot-holing."

So potholing is part of the toolbox the law itself names. But a mark is still a mark. The paint shows where the locator believes the line runs, and it says little about depth. A second statute, A.R.S. 40-360.23, makes the point that getting that information "does not excuse any person making any excavation from doing so in a careful and prudent manner." The excavator still owns the job of not hitting anything.

Think of the paint as a map and the pothole as stepping out to look at the road.

A pothole turns a guess into a fact. Federal highway engineers rank utility information in four quality levels. The highest, Quality Level A, is described by the Federal Highway Administration as the "Precise horizontal and vertical location of utilities obtained by the actual exposure and subsequent measurement of subsurface utilities, usually at a specific point." Potholing is the usual way to get it.

What you get from one hole:

• Depth. Surface marks do not give it. A bore path or trench depth can be set against it.
• Exact position. The pipe's actual centerline, not the marked estimate.
• Pipe type and size. Material, diameter and condition, which tells you what you are crossing.
• Conflicts. Whether the new line clears the old one, or the design has to change before anyone breaks pavement.

How big is the hole? ADOT's permit guidelines define a pothole as "A hole cut in the surface within the right-of-way with a maximum size of 300mm x 300mm to access underground utility facilities." That is about a foot square. Small, then patched.

Not as one blanket rule. Potholing shows up through permits, plan review and fee schedules, and what is required depends on the agency and the job. Here is what the primary sources show.

• It can be its own permit. Avondale's engineering permit list includes a "Potholes" item described as a "Permit for utility potholing in right-of-way." Digging the test hole in the street is itself work in the right of way.
• It counts as pavement disturbance. Mesa's code defines its pavement restoration fee as the fee "required by the City when a permittee cuts into, excavates, opens, bores, trenches, potholes, damages, or disturbs pavement in the right-of-way." Mesa treats a pothole like any other opening.
• State highways run it through a permit. ADOT's guide says its utilities staff may contract with a utility-locating contractor "to verify location, elevation and potential conflicts" on a highway project, and that "The utility locating contractor shall apply for an Encroachment Permit."

The pattern: if the hole is in the public street, plan on a permit and a patch standard, even for a hole a foot wide. If the plan reviewer or the permit conditions ask for potholes at crossings, that is a condition of the permit, and it will be in writing on your plans or comments.

Ask for potholing at the spots where a miss would be expensive. Those are crossings, tie-ins and any place where records are old or missing.

1. 1Bore paths. A directional bore cannot see what it hits. Exposing the utilities at the crossing points before the bore is the safest way to avoid a strike.
2. 2Tie-ins to an existing main or lateral. You need the real depth and pipe material before you order fittings.
3. 3Older lines. For a facility installed before 1989 the statute says the operator "may refer to installation records or other records relating to the facility to assist in locating the facility." A record is not a measurement, and a pothole is.
4. 4Congested corridors. Streets and alleys with gas, electric, communications, water and sewer stacked together.
5. 5Shared or unknown laterals. When nobody can say which property a line serves, exposing it settles the question. For who owns it once you find it, see who repairs a sewer line that runs through an easement behind your building.

A one-call ticket does not shift the risk away from the person digging. The statute says the information does not excuse an excavator "from liability for any damage or injury resulting from their negligence."

Spell potholing out so everyone prices and schedules it. Name the locations, who digs them, who patches them, and what permit covers the holes in the street. Then check these items:

• A current 811 ticket, and a fresh one if the marks pass fifteen working days.
• The pothole locations drawn on the plans, with the depth you expect to find.
• Traffic control if the holes sit in a travel lane, which ties into who handles traffic control when plumbing work closes a lane.
• Restoration of each hole to the agency's standard, since it is still a pavement cut. See who restores pavement after a water or sewer repair.

For the full Arizona 811 process, read what Arizona 811 requires before a commercial excavation. For when the street itself needs a permit, see whether commercial plumbing work in the street needs a right-of-way permit.

If the question on your site is a failing sewer line, HQ Plumbing & Air can run a camera through the line and repair it, with upfront pricing and free estimates. Work that reaches into the street is governed by the city, county or ADOT permit rules covered on this site, so confirm what applies to your address before you schedule it.

This page explains how the rules work and is not legal advice. Agencies change their requirements, so confirm the current rules with the permitting office before you dig.