Since January 1959, Health Canada has monitored environmental levels of radioactive fallout, to ensure the health and well being of Canadians. This work has evolved to include explosion verification for the Comprehensive nuclear-Test-Ban Treaty by monitoring the concentration of radioxenon in the atmosphere. Detection of Xe at Yellowknife by the monitoring system of Health Canada combined with the atmospheric transport and dispersion models (ATDM) of Environment Canada and seismic timing data have shown that the source of this Xe was most likely from the North Korean nuclear test of October 9th, 2006. Historical and real time monitoring data on the distribution of Xe releases from Chalk River Labs, the major source of anthropogenic background to Yellowknife were studied. Careful review of other large Xe-133 measurements at Yellowknife with ATDM was used to understand the October 2006 measurements of Xe. This allowed us to conclude that the Xe-133 detected at Yellowknife could be attributed to a release from the October nuclear test in North Korea. Health Canada and Environment Canada have demonstrated that Xe detection combined with ATDM is a viable technology for treaty verification.