Increased soil gas radon and indoor radon concentrations in Neoproterozoic olistostromes of the Teplá-Barrandian unit (Czech Republic)

Abstract

The Neoproterozoic olistostromes were first distinguished as a special geological unit in a generalised geological map of the Czech Republic on a scale 1:500,000. The olistostromes represent a tectonic melange or subaquatic continental slope-slides formed by a mixture of black shales, greywackes, carbonates and shales, forming an extremely inhomogeneous geological environment. The extreme over-limit values of indoor radon (Rn, 222Rn) were first detected during check measurements performed for final building approval by team of the National Radiation Protection Institute in a house situated on bedrock of black shales—lithological component of olistostromes north-eastward from Plzeň. Additional measurements of soil gas Rn performed by the Czech Geological Survey were oriented to cover the whole olistostrome belt extending over 65 × 25 km area NE of Plzeň–Prague general direction. The increased concentrations both of soil gas and indoor Rn were confirmed in the whole extent of Neoproterozoic olistostrome belt compared to neighbouring geological units (Neoproterozoic metasediments on NW and Cambrian Palaeovolcanites and Ordovician sediments on SE). This observation lead to increasing the radon index of olistostromes to medium radon category (from the low one) both in general and detailed Rn index maps. Drawing the attention to this lithological type enables to improve the radon risk prevention for newly built houses and interest of remediation of existing houses not only in the specific area of the Czech Republic, but also in other European countries, where Neoproterozoic olistostromes form the geological basement.