We can’t rule out leakage, but it’s rare with Vapor Pin® sampling device, and if you detect helium at multiple sample points, it might be caused by false positives from methane. Most helium detectors respond positively to methane. Similarly, high concentrations of C5-C12 hydrocarbons in soil gas have been reported to cause false positives in helium detectors. Methane generation is common when oxygen is depleted by high concentrations or large sources of hydrocarbons, especially in petroleum products containing ethanol. This is one of the reasons that Cox-Colvin encourages leak testing via mechanical means, as described in our SOP Leak Testing the Vapor Pin® sampling device via Mechanical Means (located under our Resources Page), and as discussed in the Interstate Technology & Regulatory Council (ITRC), 2014 Petroleum Vapor Intrusion guidance. If you do use a helium leak detector, we recommend using a model that does not respond to methane, and test the soil gas for false positives before applying helium.