CAT Scan vs Trial Hole: Do You Need Both?

CAT scanning and trial holes are both used to find buried services before digging, but they work in completely different ways — and in many cases, you need both, not one or the other.

What a CAT Scan Does

A CAT (Cable Avoidance Tool) scan uses a handheld detector to locate buried metallic services and signals from live cables, without digging anything. It’s fast, non-invasive, and the standard first step before any excavation.

What a Trial Hole Does

A trial hole is a physical excavation that exposes the ground directly, confirming exactly what’s there — depth, position, and condition of services and ground layers — in a way a scan alone can’t.

Why a Scan Isn’t Always Enough

CAT scanning has real limitations: it struggles with non-metallic pipes (like some plastic water or gas pipes), can’t always distinguish between services running close together, and gives an estimated position rather than a confirmed one. A scan tells you where something probably is — a trial hole confirms it.

When You Need Both

• Before any excavation near suspected services — scan first to identify likely locations, then trial hole to confirm before digging through
• On sites with non-metallic pipework — scanning alone may miss these entirely, making a trial hole essential
• Where scan results are unclear or congested — multiple services close together often need physical confirmation
• For formal documentation — a trial hole produces a verifiable record; a scan reading typically doesn’t carry the same weight in a report

The Safe Sequence

The standard safe approach is: scan first to identify likely service locations, then hand-dig a trial hole at those points to confirm exactly what’s there before any machine excavation begins nearby.

Recording the Findings

Once a trial hole confirms what’s underground, getting it documented properly matters just as much as the digging itself. Trial Trench Surveys captures trial hole findings on site — plan position, depth, photos — and produces a finished report without manual write-up afterward.