Influence of underground mining on the geogenic radon potential

Different aspects of the geogenic radon potential in a coal mining area in south-western Germany arediscussed. Due to the rather low specific radium activities of rocks and soils varying between 10 and70 Bq/kg a low geogenic radon potential can be expected. Radon concentrations in soil gas inabandoned mining areas are characterized by a lognormal distribution with a median value of 20kBq/m3. In the neighboring area with deep mining generally younger than two years, radon contentsincrease up to a median value of 38 kBq/m3. The radon background in mining areas can besuperimposed by an advective, structurally controlled component. Actually, narrow mining inducedfracture zones constant in time and adjacent to the mining area often show radon peaks in soil gas fourto five times higher than the background reaching values of more than 100 kBq/m3. A positivecorrelation between methane and radon at methane degassing spots is probably caused by a CH4 flow,which collects radon from the soil and carries it up to the surface. Indoor measurements in about 100houses over a period of three months were conducted. The radon concentrations on ground floor arenot influenced by the mining activities. In the basement, however, higher radon concentrations weredetected. A time-dependent spatial shift of high indoor values following the direction of undergroundcoal mining can be explained by the disturbance of the rock system strength in the subsurface leadingto tectonic movements just above the recent mining area.