Development of an indoor radon risk map of the Walloon region of Belgium, integrating geological information

A radon risk map for the Walloon region of Belgium, based on the two databases available, has been calculated and is presented in this work. The data are organized into geological units. For each unit, an average logarithmic standard deviation is calculated, after correcting the higher variability of short term data. The region is divided with an 1-km grid. For each node, the local geological unit is determined, as well as the corresponding logarithmic standard deviation. The logarithmic mean is evaluated by smoothing the data belonging to the same geological unit as the node. Assuming a log-normal distribution, a map that shows for each node the predicted percentage of buildings with an indoor radon concentration above the Action level (400 Bq/m3) is constructed. This is the first radon risk map for this region that fully takes into account the geological information.