SPATIAL SAMPLING DESIGN FOR THE GEOGENIC RADON POTENTIAL SURVEY IN SLIVEN PROVINCE, BULGARIA

The development of a methodology for the geogenic radon potential (GRP) mapping based on soil gas radon and soil gas permeability field measurements is among the main objectives in the determination of "radon priority areas" in Bulgaria. One of the key elements of the methodology is to define as accurately as possible, areas of risk for the presence of radon gas (222Rn) on the map. This study presents an approach to spatial sampling for the geogenic radon potential survey in Sliven Province, Bulgaria. The district is characterised by its very complex geological settings, represented by rocks of different age and mineral and chemical compositions. The proposed methodology defined a sampling frame of province radon map, prepared on the base of indoor radon measurement and the complex sampling scheme of random points. The parcel-level GIS was used for establishing the sample frame of 5x5 km polygons on the territory of the province. The IBM SPSS Complex Samples Module was applied for planning the survey's polygons by drawing sample units according to the spatial design. The spatial relationship between indoor radon concentration and geological information was analysed for the sampling scheme construction by the polygons. The latter serve as sampling units, allowing both indoor radon concentration and geological data to be linked. The results show that the applied spatial sampling approach allows controlling the specific environmental conditions, in terms of their specificity, variability, and distribution.