Mapping the geogenic radon potential in Germany

Mapping the geogenic radon potential in Germany is a research project initi ated by the German Federal Ministry for the Environment, Conservation and R eactor Safety. The project was aimed to develop a standard methodology for the estimation of a geogenic radon potential and to apply this method to ma p the region of Germany as an overview for planning purposes. The regionali sation results from a distance-weighted interpolation of the site-specific values of radon concentration in soil gas and in situ gas permeability of s oils on a regular grid considering the corresponding geological units. The map of Germany in a scale of 1:2 million is based on the radon concentratio n in soil gas as an estimator of the geogenic radon potential assuming the 'worst case' of uniform highest permeability. The distribution is subdivide d into categories of low(< 10 kBq/m(3)), medium (10-100 kBq/m(3)), increase d (100-500 kBq/m(3)) and high (> 500 kBq/m(3)) radon concentration. High va lues occur especially in regions with granites and basement rocks of Paleoz oic age, and are proven by measurements in 0.03% of the total area. Many of these regions are also known for their enhanced indoor values. The class w ith increased values takes a portion of 7.86% and likewise occurs mainly in regions with outcrops of folded and metamorphic basement, but also of some Meso- and Cenozoic sediments with increased uranium contents and/or higher emanation coefficients. For 67.3% of the country, the radon concentration is classified as 'medium', and an assignment to specific geological units c annot be made at the map scale considered. Low radon contents, where protec tive measures against radon are usually not considered, are found in the ge ologically rather homogeneous part of northern Germany with unconsolidated Cenozoic sediments, covering approximately 25% of the total country. It is of course not possible to predict the indoor radon concentration of single houses from these maps, because construction type and structural fabric of houses are essentially governing the extent to which subsoil radon potentia l affects the indoor concentration. Besides this, in places with site speci fic geochemical, structural and soil-physical properties, local radon anoma lies may occur which were not recorded in the course of the wide-meshed scr eening study. (C) 2001 Published by Elsevier Science B.V. All rights reserv ed.