Radon and tectonics in an urban area – case study Bad Nauheim (Hesse, Germany)

Inspired by the new Radiation Protection Act (2013/59/EURATOM), which entered into force at the end of 2018, the city of Bad Nauheim in southern Hesse has been chosen for measurements of soil air radon and CO2. In doing so, the focus is on the variability of concentrations in the area of tectonic features (normal faults), which are hosted in Devonian rocks, overlain by Tertiary and Quaternary unconsolidated sediments (Schäffer & Sass, 2016). Some of the faults, which are trending N-S and W- E respectively, are supposed to be active, enabling the migration of mineralized waters towards the surface. Within a first measuring campaign, 231 soil air measurements were carried out, following transects that cross tectonic faults perpendicular. Results confirm advective radon anomalies with concentrations of up to 2000 kBq/m³, guided by a positive correlation between radon and CO2. At the same time, this correlation is diminishing with increasing distance to the faults (Möll 2018). Based on the outcomes a second measuring campaign is on the way, addressing the following questions: 1) Are measured radon and CO2 concentrations reproducible? 2) How much radon is exhalating into buildings located near faults? Works are focusing on two faults, which are located close to the so called “Sprudelhof” (fountain court), a bath house in the city center, and include both active (Saphymo AlphaGUARD) and passive (Exposimeter) soil air measurements as well as repeated indoor measurements (also active and passive) in the basement of the “Sprudelhof”.