# The Relationship between Radon and Geology: Sources, Transport and Indoor Accumulation
## 4 Risk Assessment and Mitigation
### Geographical and Seasonal Variations in Radon Concentration  
#### 4.2.1 Geographic Variations  
As previously stated, the concentration of radon in soil and air is strongly influenced by local geology. Areas with higher concentrations of uranium and thorium in rocks and soils tend to have higher concentrations of radon. For example, granite regions and areas with igneous and metamorphic rocks rich in uranium and thorium generally have higher concentrations of radon. In addition, the permeability of soil and rocks also influences the concentration of radon, with more permeable soils facilitating the movement of gas through the subsurface. Understanding these geological factors is important for identifying areas of high radon concentration and developing effective mitigation strategies. [PERSON] et al. (2005) examined the application of seasonal correction factors to indoor radon concentrations in the UK, with a particular focus on the role of geology [34]. The intricacy of the UK's geological terrain, which is likely the most intricate in terms of both solid and surficial characteristics across short distances, was emphasised by the authors as a crucial reason for high indoor radon levels. The National Radiological Protection Board amassed a sizable database on which the study was based, which included information from small-scale surveys that started in 1976 and proceeded with a larger-scale survey in 1988. These studies have unequivocally demonstrated that indoor radon levels vary seasonally. However, the use of a seasonal adjustment factor may occasionally overstate or underestimate radon levels due to the wide range in the permeability of underlying materials and the complexity of the UK's geology. As a result, the authors propose using either seasonal adjustment factors with extreme caution or never using them at all. The case studies from the Northamp-tonshire area served as the basis for this study, which also included comparisons to other permeable geologies in the UK. The results raise concerns about the effectiveness of using seasonal correction factors uniformly across various geological landscapes and emphasise the necessity of taking local geological diversity into account when assessing indoor radon levels. In addition, [PERSON] et al. (2020) conducted a comprehensive study to explore the various factors contributing to indoor radon accumulation, examining 100 case studies in Romania [184]. They confirmed that the geological characteristics of bedrock strongly influence radon emissions, yet noted that other factors, including permeability, building and architectural features, ventilation, and occupation patterns, also significantly determine radon's in-soil transport and indoor entry paths. The researchers found that the geological foundation could largely account for the majority of the radon values recorded in both soil and indoor air, thus emphasising the influence of geology on radon levels. The study also revealed intriguing correlations with housing characteristics. Older houses, particularly those built with earth-based materials, were found to be highly permeable to soil radon, potentially leading to higher indoor radon concentrations. Conversely, energy-efficient houses were found to have a higher predisposition to indoor radon accumulation, largely due to their design which often disregards the radon potential of the geological foundation. This oversight can lead to a decrease in the general indoor air quality. The findings from this study underscore the multifaceted nature of radon accumulation indoors and the need to consider a broad spectrum of natural and man-made factors in its assessment and mitigation.