Determination of radon prone areas by probabilistic analysis of indoor survey results and geological prognostic maps in the Czech Republic

Abstract

The determination of radon prone areas is usually based on indoor radon surveys and prognoses of occurrence of houses above action level [CRP Publication 65, Protection against Radon at Home and at Work]. The sample of houses in the survey must be representative and large enough, if accurate results are to be obtained. However, even if such condition are fulfilled, inaccuracy in prediction of number of houses above action level may occur, if local information (especially local geological structure or building types) were not taken into account. Uncertainties and inaccuracies of radon risk prediction depend on the type of mapping process and map scale. The finer the map scale, the more complex geological structure and radon risk areas are found. An important but not easy task is to link indoor radon data to geological (geochemical and geophysical) parameters. Such relation is useful not only for planning of indoor radon survey in areas, where indoor measurements were not carried out yet, but mainly for prediction of radon risk for new buildings. This relation between geology and indoor radon can be studied by mathematical models, in situ experiments, or by statistical analysis of large data sets. Because a lot of parameters are influencing radon transport (some of them are not completely understood yet), only a “probabilistic” indoor-geology relationship can be found. Nevertheless, it can be useful in the process of derivation of “radon potential” area and in decision making on radon risk for new types of buildings in practice. Empirical transfer factors T f defined as ratio of indoor/soil radon concentration are analysed. It is shown that lognormal distribution of T f can be used to derive a relationship between geological parameters and probability of exceeding indoor radon concentration level.