Trace gas leak detection is a method used to locate hidden underground pool plumbing leaks. A safe tracer gas -- commonly a low-concentration hydrogen and nitrogen mixture -- is introduced into an isolated plumbing line that has already failed a pressure test. A gas detector is then used above ground to find where the gas escapes through soil, pavers, or deck.
Trace gas is a locating method, not a confirmation method. It is used after pressure testing confirms which line is leaking -- to help find exactly where before deciding where to excavate.
What Trace Gas Leak Detection Does
Trace gas testing answers one question: where is the underground pipe leaking? It is not usually the first test. The technician pressure tests the pool plumbing first. If a line fails, trace gas may be used to help locate the leak without opening large areas of deck, soil, or landscaping unnecessarily.
The gas escapes from the leak opening and migrates upward through soil, pavers, or cracks in the deck. The detector reads the gas concentration at the surface. The highest reading helps identify the leak area.
Trace gas does not replace pressure testing, dye testing, hydrophones, or judgment. It is one tool in a complete leak investigation -- used at the right stage of a systematic diagnostic process.
How Trace Gas Testing Works -- Step by Step
Isolate the suspected plumbing line
The line must be properly isolated before gas is introduced. Testing an unisolated line produces unreliable results -- gas can travel to unrelated areas and create misleading surface readings.
Confirm the line is leaking with pressure testing
Trace gas should only be used after pressure testing confirms a specific line has failed. Using trace gas before confirming a leak wastes time and can create false conclusions.
Introduce tracer gas into the line
Using a regulator and injection rig, introduce the tracer gas at a controlled rate. The exact gas mixture, pressure, and handling requirements depend on the equipment, supplier, and applicable local regulations. Always follow manufacturer safety instructions.
Allow time for gas to escape and migrate
Gas needs time to travel from the leak point through the soil or substrate to the surface. Rushing this step produces incomplete readings. Soil conditions, depth, and substrate type all affect how long migration takes.
Scan the surface above the pipe route
Scan systematically along the known pipe route -- not randomly across the yard. Knowing where the pipe runs is essential. Scanning the wrong area wastes time and produces false conclusions.
Mark the strongest reading and confirm before excavation
The highest surface reading helps identify the leak area. It is not always directly over the break -- gas can migrate sideways through soil, voids, or expansion joints. Confirm the reading before recommending excavation.
What Gas Is Used?
The most commonly used tracer gas for pool leak detection is a low-concentration hydrogen and nitrogen mixture. The hydrogen content is typically formulated to be non-flammable when mixed with nitrogen as the balance gas. This makes it significantly safer than using pure hydrogen.
The exact product, concentration, and handling requirements depend on the specific equipment, supplier, and local regulations. Always follow the manufacturer's safety instructions for the tracer gas system being used. Pure hydrogen should not be used casually or without proper training and equipment.
When Trace Gas Works Well -- and When It Struggles
- Line has already failed pressure test
- Line can be isolated and cleared
- Leak is under pavers or deck
- Acoustic listening is unclear
- Leak is too quiet to hear
- Pipe route is known
- Soil is not saturated
- Line cannot be isolated
- Line cannot be cleared for gas movement
- Soil is saturated or waterlogged
- Leak is very deep
- Wind affects surface readings
- Gas migrates sideways significantly
- Multiple leaks exist in the line
How Trace Gas Compares to Other Detection Methods
Pressure Testing
"Is this line leaking?"
Confirms whether a specific plumbing line holds pressure. The foundation of every underground leak investigation. Always comes first.
Acoustic / Hydrophone
"Where is the leak sound strongest?"
Listens for leak sounds when the line is pressurized. Often faster when the leak creates a clear audible signal. May struggle with quiet leaks or deep lines.
Trace Gas
"Where does the gas escape?"
Locates quiet leaks, deep leaks, and leaks under surfaces where sound is unclear. Used after pressure testing confirms the line is leaking.
Neither acoustic tools nor trace gas replaces the other. A professional chooses the tool based on the situation -- and uses both when needed to increase confidence before recommending excavation.
Equipment Used in Trace Gas Detection
Common Beginner Mistakes
Where Trace Gas Fits in the H.U.N.T.E.R. Method™
LBA Resources for Advanced Leak Detection
Jeff David's Perspective
Trace gas is one of the most powerful tools available to a pool leak detection professional -- and one of the most misunderstood. I see two common mistakes. The first is using it too early, before pressure testing has confirmed which line is actually leaking. The second is trusting the reading without understanding how gas travels through soil.
Gas does not always come straight up. It can migrate sideways through expansion joints, voids, and loose substrate. The highest reading is a starting point -- not always a precise coordinate. A confident excavation decision comes from combining the gas reading with everything else you know about the pipe route, the pressure test result, and the site conditions.
-- Jeff David, Founder | Leak Business Academy, LLC | Leak and Subsurface Locators, LLC
Trace Gas Locates the Leak -- After Pressure Testing Confirms It
Trace gas leak detection is a professional method for locating hidden underground pool plumbing leaks. A tracer gas is introduced into an isolated line that has already failed a pressure test, and a detector is used above ground to find where the gas escapes.
Trace gas does not replace pressure testing, dye testing, hydrophones, or judgment. Used correctly -- after the leaking line is confirmed and the pipe route is known -- it can significantly reduce unnecessary digging and help locate difficult underground leaks more accurately.
Learn Advanced Pool Leak Detection Methods
Leak Business Academy, LLC teaches trace gas detection, acoustic listening, pressure testing, and the complete H.U.N.T.E.R. Method diagnostic process for underground pool pipe leaks.