Geological controls to the indoor radon distribution in southern Belgium

Variability of indoor radon concentration in UK homes

This study investigated the variability of indoor radon concentrations in 518 100 homes in the UK. The statistical analysis included measurements in 395 720 homes with downstairs living rooms and upstairs bedrooms. The radon concentration in these bedrooms was found to be on average 63% of the living room value. The analysis of 122 380 homes with living rooms and bedrooms situated on the same floor found that there is a small difference in radon concentration of 9% between the two rooms. The results showed that the ratios of the living room to bedroom radon concentrations were approximately lognormally distributed. The geometric mean of the ratio was found to be 1.6 for rooms situated on different storeys and 1.1 for rooms situated on the same floor. It was found that house characteristics and energy efficiency measures affect the distribution of radon within homes. Detached houses and those with suspended floors had higher radon levels in their upstairs bedroom, 66.7% and 76.9% of the downstairs living room values, respectively. For homes built between 1993 and 2007, the bedroom to living room ratio increased from 58.8% to 76.9% due to the increased airtightness and improved energy performance of the modern buildings. Homes with installed wall and loft insulation had much higher bedroom to living room ratio (76.9%) than those without energy efficiency measures (52.6%).

Qualitative overview of indoor radon surveys in Europe

The revised European Directive from 2013 regarding basic safety standard oblige EU Member States to establish a national action plan regarding the exposure to radon. At the same time, International Atomic Energy Agency started technical projects in order to assist countries to establish and implement national radon action. As a consequence, in recent years, in numerous countries national radon surveys were conducted and action plans established, which were not performed before. In this paper, a qualitative overview of radon surveys performed in Europe is given with a special attention to the qualitative and conceptual description of surveys, representativeness and QA/QC (quality assurance/quality control).

Distance to faults as a proxy for radon gas concentration in dwellings

This research was done to demonstrate the usefulness of the local structural geology characteristics to predict indoor radon concentrations. The presence of geologic faults near dwellings increases the vulnerability of the dwellings to elevated indoor radon by providing favorable pathways from the source uranium-rich bedrock units to the surface. Kruskal-Wallis one-way analyses of variance by ranks were used to determine the distance where faults have statistically significant influence on indoor radon concentrations. The great-circle distance between the 640 spatially referenced basement radon concentration measurements and the nearest fault was calculated using the Haversine formula and the spherical law of cosines. It was shown that dwellings located less than 150 m from a major fault had a higher radon potential. The 150 m threshold was determined using Kruskal-Wallis ANOVA on: (1) all the basement radon measurements dataset and; (2) the basement radon measurements located on uranium-rich bedrock units only. The results indicated that 22.8% of the dwellings located less than 150 m from a fault exceeded the Canadian radon guideline of 200 Bq/m(3) when using all the basement radon measurements dataset. This percentage fell to 15.2% for the dwellings located between 150 m and 700 m from a fault. When using only the basement radon measurements located on uranium-rich bedrock units, these percentages were 30.7% (0-150 m) and 17.5% (150 m-700 m). The assessment and management of risk can be improved where structural geology characteristics base maps are available by using this proxy indicator.

Hierarchical modeling of indoor radon concentration: how much do geology and building factors matter?

Radon is a natural gas known to be the main contributor to natural background radiation exposure and only second to smoking as major leading cause of lung cancer. The main concern is in indoor environments where the gas tends to accumulate and can reach high concentrations. The primary contributor of this gas into the building is from the soil although architectonic characteristics, such as building materials, can largely affect concentration values. Understanding the factors affecting the concentration in dwellings and workplaces is important both in prevention, when the construction of a new building is being planned, and in mitigation when the amount of Radon detected inside a building is too high. In this paper we investigate how several factors, such as geologic typologies of the soil and a range of building characteristics, impact on indoor concentration focusing, in particular, on how concentration changes as a function of the floor level. Adopting a mixed effects model to account for the hierarchical nature of the data, we also quantify the extent to which such measurable factors manage to explain the variability of indoor radon concentration.

A statistical evaluation of the influence of housing characteristics and geogenic radon potential on indoor radon concentrations in France

Radon-222 is a radioactive natural gas produced by the decay of radium-226, known to be the main contributor to natural background radiation exposure. Effective risk management needs to determine the areas in which the density of buildings with high radon levels is likely to be highest. Predicting radon exposure from the location and characteristics of a dwelling could also contribute to epidemiological studies. Beginning in the nineteen-eighties, a national radon survey consisting in more than 10,000 measurements of indoor radon concentrations was conducted in French dwellings by the Institute for Radiological Protection and Nuclear Safety (IRSN). Housing characteristics, which may influence radon accumulation in dwellings, were also collected. More recently, the IRSN generated a French geogenic radon potential map based on the interpretation of geological features. The present study analyzed the two datasets to investigate the factors influencing indoor radon concentrations using statistical modeling and to determine the optimum use of the information on geogenic radon potential that showed the best statistical association with indoor radon concentration. The results showed that the variables associated with indoor radon concentrations were geogenic radon potential, building material, year of construction, foundation type, building type and floor level. The model, which included the surrounding geogenic radon potential (i.e. the average geogenic radon potential within a disc of radius 20 km centered on the indoor radon measurement point) and variables describing house-specific factors and lifestyle explained about 20% of the overall variability of the logarithm of radon concentration. The surrounding geogenic radon potential was fairly closely associated with the local average indoor radon concentration. The prevalence of exposure to radon above specific thresholds and the average exposures to radon clearly increased with increasing classes of geogenic radon potential. Combining the two datasets enabled improved assessment of radon exposure in a given area in France.

A geostatistical approach to assess the spatial association between indoor radon concentration, geological features and building characteristics: the case of Lombardy, Northern Italy

Radon is a natural gas known to be the main contributor to natural background radiation exposure and second to smoking, a major leading cause of lung cancer. The main source of radon is the soil, but the gas can enter buildings in many different ways and reach high indoor concentrations. Monitoring surveys have been promoted in many countries in order to assess the exposure of people to radon. In this paper, two complementary aspects are investigated. Firstly, we mapped indoor radon concentration in a large and inhomogeneous region using a geostatistical approach which borrows strength from the geologic nature of the soil. Secondly, knowing that geologic and anthropogenic factors, such as building characteristics, can foster the gas to flow into a building or protect against this, we evaluated these effects through a multiple regression model which takes into account the spatial correlation of the data. This allows us to rank different building typologies, identified by architectonic and geological characteristics, according to their proneness to radon. Our results suggest the opportunity to differentiate construction requirements in a large and inhomogeneous area, as the one considered in this paper, according to different places and provide a method to identify those dwellings which should be monitored more carefully.

Health implications of radon distribution in living rooms and bedrooms in U.K. dwellings--a case study in Northamptonshire

Environmental radon exposure of residents of domestic premises in the United Kingdom (UK) and elsewhere in Europe is estimated on the basis of the measured radon concentrations in, and the relative occupancies of, the principal living room and bedroom. While studies on radon concentration variability in the individual units in apartment blocks in various countries have been described, little data has been reported on variability in two-storey single-family dwellings, and the majority of extant studies consolidate living room and bedroom data early in the analysis. To investigate this further, detailed analysis was made of radon concentration data from a set of thirty-four homes situated in areas of Northamptonshire known to exhibit high radon levels. All homes were of typical UK construction of brick/block/stone walls under a pitched tile/slate roof. Approximately 50% of the sample were detached houses, the remainder being semi-detached (duplex) or terraced (row-house). Around 25% of the sample possessed cellars, while 12% were single-storey dwellings (bungalows), reflecting the typical incidence of this type of dwelling in England. In the two-storey homes, all monitored bedrooms were on the upper floor. Distribution of the ratios of bedroom/living room radon concentrations (BR/LR ratio) in individual properties was left-skewed (mean 0.67, median 0.73, range 0.05-1.05) with a tail extending to just above 1.0. The mean is consistent with the outcome of earlier extensive studies in England, while the variability depends principally on the characteristics of the property, and not on seasonal factors. In a small set of homes, the BR/LR ratio was anomalously low, (mean 0.3). BR/LR ratios in single-storey homes clustered around a value of 1.0, indicating that house design, rather than lifestyle, is the dominant factor in determining bedroom radon concentrations. Homes with higher mean annual radon concentrations showed lower BR/LR ratios, supporting our proposal that, in some homes, radon emanation from building materials may comprise a significant component of the overall radon level.

Mapping soil gas radon concentration: a comparative study of geostatistical methods

Understanding soil gas radon spatial variations can allow the constructor of a new house to prevent radon gas flowing from the ground. Indoor radon concentration distribution depends on many parameters and it is difficult to use its spatial variation to assess radon potential. Many scientists use to measure outdoor soil gas radon concentrations to assess the radon potential. Geostatistical methods provide us a valuable tool to study spatial structure of radon concentration and mapping. To explore the structure of soil gas radon concentration within an area in south Italy and choice a kriging algorithm, we compared the prediction performances of four different kriging algorithms: ordinary kriging, lognormal kriging, ordinary multi-Gaussian kriging, and ordinary indicator cokriging. Their results were compared using an independent validation data set. The comparison of predictions was based on three measures of accuracy: (1) the mean absolute error, (2) the mean-squared error of prediction; (3) the mean relative error, and a measure of effectiveness: the goodness-of-prediction estimate. The results obtained in this case study showed that the multi-Gaussian kriging was the most accurate approach among those considered. Comparing radon anomalies with lithology and fault locations, no evidence of a strict correlation between type of outcropping terrain and radon anomalies was found, except in the western sector where there were granitic and gneissic terrain. Moreover, there was a clear correlation between radon anomalies and fault systems.

Mitigation of a radon-rich Belgian dwelling using active subslab depressurization

In a radon prone area in Belgium, a dwelling with high indoor radon concentrations was identified through a passive measurement. Next, a continuous, active radon monitoring device was installed for one month. A 20-a retrospective radon assessment was also performed. The house was subsequently mitigated through active subslab depressurization with a radial fan. Afterwards the dwelling was actively monitored for several more months to observe the effects of the mitigation and to study the effect of reducing the fan power. Dose evaluations were made to evaluate the health benefit of the mitigation. It was seen that the results of the three measuring techniques before mitigation all yielded between 1700 and 2000 Bq/m3. Clear diurnal radon variations showed up only after mitigation. After mitigation, the average radon concentration fell to less than 200 Bq/m3. The yearly average dose was reduced from potentially 45 mSv/y to less than 4.5 mSv/y through mitigation. Reducing fan power to 50% did not clearly influence the amount of radon entering into the dwelling.

Radon risk mapping in southern Belgium: an application of geostatistical and GIS techniques

A data set of long-term radon measurements in approximately 2200 houses in southern Belgium has been collected in an on-going national radon survey. The spatial variation of indoor Rn concentrations is modelled by variograms. A radon distribution map is produced using the log-normal kriging technique. A GIS is used to digitise, process and integrate a variety of data, including geological maps, Rn concentrations associated with house locations and an administrative map, etc. It also allows evaluation of the relationships between various spatial data sets with the goal of producing radon risk maps. Based on geostatistical mapping and spatial analysis, we define three categories of risk areas: high risk, medium risk and low risk area. The correlation between radon concentrations and geological features is proved in this study. High and medium Rn risk zones are dominantly situated in bedrock from the Cambrian to Lower Devonian, although a few medium risk zones are within the Jurassic. It is evident that high-risk zones are related to a strongly folded and fractured context.