Identifying enhanced radon homes on the geological and physical basis in selected regions in poland

In Poland as in many other countries regulations limiting permissible level of radon concentrations indoors are in force. It implies a need for a methodology of searching for houses with elevated radon concentration. Since it was discovered that the bedrock was the most powerful source of radon indoors it has been observed by many researchers that homes with enhanced radon concentrations occur more frequently in particular areas. Thus it may be expected that determining radon-prone areas followed by intensive local monitoring allows for more effective finding of individual high-radon houses. Our investigations of radon concentrations in soil gas and in houses were performed in 2 regions selected by geologists as untypical for Poland. One of them Wa?brzych and Jelenia Gra region lies in the Karkonosze-Izera Block within south-western Sudety Mountains and is dominated by Precambrian and Palaeozoic magmatic and metamorphic rocks with numerous indices of uranium mineralization. In this region there were uranium mines and concentration of radium in the soil is highest in Poland (Radiation Atlas of Poland). The other region is the Upper Silesian Coal Basin with mining-related subsidence fissures that could be radon conduits. U-enriched rocks are found locally in some sedimentary units along local tectonic structure in this area. Measurements of radon concentrations in soil gas sampled at the depth of 75 cm were conducted by means of Lucas cells. Measurements of radon indoors were made in two groups of houses which differ from each other with the way of selection. Houses in group A were selected randomly and in group B they were pointed out by geologist, who selected them searching for enhanced radon levels, taking into account high soil radon and the type of geological bedrock. The method of track detectors CR-39 was applied in group A and charcoal detectors and liquid scintillation counter (PicoRad) were used in group B. In this group radon concentrations in household water was also determined. Within both groups influence of the presence/absence of cellar beneath the house was analysed. The results revealed that the Karkonosze-Izera Block can be consider radon potential with averages of radon concentrations in soil gas reaching 300 kBq/m3. In this region in 40% of homes in the group B radon concentration is greater than 200 kBq/m3, which is set up an action level in new built houses in Poland, whereas in the group A only 6% of cases exceeds this limit. In the Upper Silesian Coal Basin, where radon concentration in soil gas is much lower (averages values below 65 kBq/m3), percentage of cases above 200 kBq/m3 is 5% in the group B and 2% in the group A, what is typical of the whole country. In the Karkonosze-Izera Block results of radon concentration in water exceed level of 50Bq/l in 68% of houses reaching maximum value of 1400 Bq/l and in Upper Silesian Coal Basin all values are below this level with maximum equal to 32 Bq/l.