Radon concentration in soil gas: a comparison of the variability resulting from different methods, spatial heterogeneity, and seasonal fluctuations

From the end of 1996 through March 1999, the spatial and the temporal variability of the soil 222Rnconcentration was investigated at a 20m x 20m test field with porous soil in 0.5 m and 1.0 m depth atnine positions each and at 1m x 1m plots at four positions each. For this, soil gas was collected weeklyinto evacuated scintillation cells and was analysed subsequently for radon activity. In the 20m x 20mfield the spatial variability is characterised by coefficients of variation (C.V.) of 26% at 0.5m, and13% at 1.0 m depth. Within the 1m x 1m plots the C.V. Were 4% and 2%, i.e. Within the uncertainty ofthe method. Time series analysis (TSA) of the soil radon data shows seasonal variations withmaximum concentrations in the winter months. Radon concentrations ranged from 6 to 50 kBq m-3 in0.5 m depth, and from 8 to 34 kBq m-3 in 1.0 m depth. Mostly, the concentrations were higher in 0.5depth than in 1.0 m depth. However, seasonal variation of the 0.5m to 1.0 m concentration ratio hasbeen verified by TSA. To test the variability resulting from different methods, additional proceduresand instruments were investigated at the 20m x 20m field and at a second test field with a different soiltype. Soil gas sampling into evacuated scintillation cells was selected as the reference procedure. Soilradon concentrations obtained with the different sampling procedures and detection methods at the20m x 20m field essentially agreed within the limits of uncertainty of the methods tested. At thesecond test field, i.e. In a largely impermeable soil, deviations up to a factor of two related to thereference procedure were observed.