In June 2018 radioactive (37Ar and 127Xe) and stable (SF6) tracers were injected into the chimney of the Disko Elm underground nuclear explosion, located in the U-12p tunnel complex. After the injection sampling was performed from locations within the tunnel, a borehole drilled from the surface, and from the surface of the mesa. Additionally, the 127Xe activity within the chimney was continuously monitored for two months after the injection. While none of the injected radiotracers were detected in the monitoring borehole, elevated levels of 39Ar (an activation product produced by underground nuclear explosions) were detected and quantified in each sample.