It has been known for a long time that houses built over certain geologies, notably granite, black shale or permeable rock or sediments are prone to elevated e sometimes indeed very high e indoor Rn concentrations. Other geological grounds, typically most limestone (except karst), sandy alluvial sediments or sandstones not bearing organic matter are usually low in Rn. Much literature (not to be reviewed here because of its sheer amount) deals with the relation between geology and Rn related quantities. The reason for this interest is that geological information about an area is easily available in most instances, and it can serve as a “cheap” predictor
of the presence of a Rn hazard. (Here the term geology is used in a wider sense, including base rock and overburden, and possibly soil properties or even tectonic and geo-hydrological features. In the context of the example discussed here, however, the available geological information has been derived from a base rock map.)