Derivation of radon potential of the building site from indoor radon data

The definition of radon prone area based on indoor radon survey and the statistical analysis of data (ICRP65) is a well known process. Such a definition of radon area involve all parameters that influence radon concentration in dwellings (geology, building technology, user habits, ventilation, etc.) and is useful especially for planing targeted Rn survey and remedial measures in existing houses. However, from the point of Rn protection of new modern buildings, the approach based on "Rnpotential" (geological parameters) seems to be more useful for delineation of radon area. The key problem is, how to reasonably define "Rn potential", otherwise how to link geology parameters of the area (Rn-222, Ra-226 in the soils, permeability, local tectonics) with building technology and indoor radon concentration. The study of this relation is based either on theoretical or experimental modelling of radon transport from soil to the building, or on statistical analysis: correlation of indoor - bedrock Rn data with respect to other geology parameters. In this work the classification of area is based on a probabilistic approach. The radon transfer factor defined as T = (indoor radon concentration) /(soil gas radon concentration) is discussed with respect to spatial variation of radon concentration in the dwelling and validity of Rn soil gas measurement. The statistical distribution of this transfer factor (approximately log-normal) is studied for different geological parameters (permeability) and different parts of dwellings. The statistical parameters of the distribution (mean and variance) depend mainly on the type of the new building technology (due to the variation in radon ingress, ventilation, etc.), slightly on other geological parameters (permeability etc). It seems to be practical and useful to define the "standard house" as a "set of houses of specific type" characterised by parameters of the distribution of Rn transfer factors. These parameters depend on geological parameters of the area and on specific building technologies used in the area. If this statistics is known, it can be used as a basis for practical derivation of the "radon potential" of the area (or of the building site). If we define the radon potential of the area as the risk (i.e. probability) that Rn concentration in the house built on this area will be above the limit, than geological parameters (Rn soil concentration) corresponding to this risk can be derived from known parameters of the above log-normal distribution. If category of low radon risk of building site is defined as the site where < 1 % of new houses is above limit and category of high radon risk as the site with > 10 % of new houses above limit, corresponding limits for geological classification can be derived. Because of existence of differences in building technology, this procedure ought to be carried out for specific building technology separately. Because of influence of other geological parameters (permeability etc.), the procedure ought to be performed for different geological parameters, too. From this follows that Rn potential of the area derived by this way is generally not one value but set of values corresponding to different building technologies that are used in the country. This methodology was studied on the set of 90 Czech modern houses. Indoor Rn concentrations were measured (one year measurements by STTD) in all rooms, the building technology and technical conditions were investigated and the geological parameters of building sites (Rn in the soil, permeability, etc.) were measured. [1] Kemski, J. Siehl, A. Valdivia M, Lehmann, R., Comparision of radon concentration in buildings in Oberfranken with geogenic radon potential. The Fourth International Workshop on the Geological Aspect of Radon Risk Mapping, Praha 1998.