Indoor radon risk mapping of the Canary Islands using a methodology for volcanic islands combining geological information and terrestrial gamma radiation data

Within the framework of the recent approval of the National Plan Against Radon by the Council of Ministers of the Spanish Government, one of its five axes focuses on the delimitation of priority action areas. In line with this objective, this paper presents the indoor radon risk maps of the Canary Islands. Due to the volcanic origin of the Canary Islands, there is a great deal of geological heterogeneity in the soils on which buildings settle, making it very difficult to delimit radon-risk areas in the process of creating maps. Following a methodology developed in previous works for a study area formed of a set of representative municipalities, this paper presents radon risk maps of the Canary Islands based on lithostratigraphic information and high-resolution terrestrial gamma radiation maps. The goodness of fit of these maps is verified based on a statistical analysis of indoor radon concentration measurements carried out at representative building enclosures. In order to analyse the level of risk to the population, these maps were combined with built up areas (urban fabric) maps and estimations of the annual effective doses due to radon was obtained by applying a dosimetric model. This methodology improves the capability to delimit indoor radon risk areas, with a greater margin of safety. In this respect, it is estimated that areas classified as low risk have indoor radon concentrations 41 % below the current reference level of 300 Bq/m3 established by national regulations in compliance with the precepts laid down in the European EURATOM Directive.

Multiparametric analysis for the determination of radon potential areas in buildings on different soils of volcanic origin

The transposition of the European EURATOM directive into the regulations of the different member states of the European Union involved governments making great efforts to define priority action maps against indoor radon exposure in buildings over a short time period. In Spain, the Technical Building Code established 300 Bq/m³ as a reference level and set up a classification of municipalities in which remediation measures should be adopted for radon exposure in buildings. Oceanic volcanic islands, such as the Canary Islands, present high geological heterogeneity in a small space due to their volcanic origin. This variability poses a challenge to the elaboration of radiological risk maps, which makes it necessary to have a high density of data to collect local variations. This paper presents a methodology to obtain accurate radon risk maps based on geological criteria and terrestrial gamma radiation. The predictive efficiency of these maps is statistically verified using indoor radon concentration data measured in buildings. Other radiological variables, which are commonly used as criteria for radon risk prediction found in the literature, were also applied, such as the geogenic radon potential and the activity concentration of natural radioisotopes in soils. The higher resolution of the maps obtained allows for a more detailed classification of radon risk zones in the study area than the current risk maps published in the Spanish building regulations.

Methodology for determination of radon prone areas combining the definition of a representative building enclosure and measurements of terrestrial gamma radiation

The recommendations of the European Atomic Energy Community (EURATOM) have recently been incorporated into Spanish regulations in the Basic Document of Health Standards of the Technical Building Code (CTE), section HS6, on protection against radon exposure. This further accentuates the need to delimit radon prone areas as a strategy to address measures which minimise the effects of this gas on the population. In this research, measurements of terrestrial gamma radiation and indoor radon of dwellings have been carried out in the same location to delimit these risk areas. A new methodology has been developed including a definition of a Representative Building Enclosure (RBE) and it is proposed a Building Storey Index (I_BS) which allows normalizing measurements of indoor radon activity concentration taken in different levels from the ground to the RBE. The results show the need to consider the type of contact that exists between the building and the ground as a determining factor of radon risk. Terrestrial gamma radiation is used as a proxy for radioisotopic composition of soils to characterise the indoor radon risk at different geological formation.