Approach for the development of a radon potential map for the Darmstadt area

Radon (Rn)is a naturally occurring, radioactive gas that is considered an indoor air pollutant. Due to its negative effects on human health, a Germany-wide "Radon Potential Action Plan" was implemented based on the European Directive for Radiation Protection (2013/59/Euratom). As part of this action plan, areas with high geogenic Rn potential (GRP) need to be determined and surveyed. GRP is based on the measured soil gas Rn concentration and the soil gas permeability indicating higher availability of Rn and hence, a higher potential for elevated indoor Rn concentration. Based on former studies of the Federal Office for Radiation Protection, a medium-to low GRP for the state of Hesse was estimated. Locally high variations in the south are found, primarily due to the Odenwald-Mountain-Range. Based on the geological diversity and its major impact on the GRP, this study tried to include geological small-scale variations, to estimate an urban GRP map for Darmstadt. For this, 134 measurements of soil gas Rn concentration were used as well as a soil gas permeability map with a resolution of 100 km2. The geological classification is based on the Hessian geological map 1:25 000, showing 55 petrographic classes for Darmstadt, from which 16 are represented by GRP calculations showing the highest GRP for silt with 41.39. The other classes are following the tendency that acidic plutonic rocks show higher GRP (18.4), metamorphic rocks medium (10.1), and clastic sediments lower GRP (6.1).