Precision Locating locates gas leaks (above and below ground).Below ground gas leaks are located by introducing helium into the system. Helium, being lighter than air, rises up through the soil, and is detected above ground using a helium leak detector. For above ground leaks, we use ultrasonic leak detection, helium, or propane as a trace gas. Propane is detected with a combustible gas analyzer. We have the experience and equipment to quickly and accuratly locate all types of gas, air or vacuum leaks.