Networks of monitoring stations have been set up in many European countries to detect the passage of a radioactive cloud. The layout and spatial density of these networks differs from country to country. Germany and the Netherlands decided to set up relatively dense networks for the detection of weak radioactive plumes. As a test case the existing sampling design of the Dutch and German networks with 193 sensors in an area of 200 km around the nuclear power plant near the city of Lingen (Emsland) in the German federal state of Lower Saxony has been selected. For a hypothetical accident scenario 292 radioactive plumes have been simulated which are shaped by recorded weather conditions of the year 2007. Simulation results show that 95% of the plumes are detected within 4 h after the release. Only in a joint network of German and Dutch sensors all simulated plumes triggered an alarm. This result encourages efforts of close international collaboration, e.g. between EU member states, in network design and operation. The assessment criteria can be used for a revision of existing networks or for planning purposes in countries such as those applying for EU membership.