An Assessment of Groundwater Contamination Risk with Radon Based on Clustering and Structural Models

Abstract

There is currently some controversy in the scientific community regarding the efficiency of the water–rock interaction process in the contamination of radon in groundwater. In this study, some difficulties were found in the sampling phase. Many of the water collection points are used for human consumption. As such, some municipalities did not want to collaborate. When this natural contaminant is undetectable to the human sense and may cause pulmonary neoplasms in the long term, it is difficult to obtain collaboration from the municipalities concerned. To overcome this controversy, it is important to understand that geogenic, climatic, hydrological, and topographic features may contribute to the effective transfer of radon from rocks to groundwater. In brief, this new approach combines the radon transfer from the geological substrate to the groundwater circulation through hierarchic agglomerative clustering (HAC) and partial least squares-path modeling (PLS-PM) methods. The results show that some lithologies with higher radon production may not always contribute to noticeable groundwater contamination. In this group, the high-fracturing density confirms the recharge efficiency, and the physical-chemical properties of the hydraulic environment (electric conductivity) plays the main role of radon unavailability in the water intended for human consumption. Besides, the hydraulic turnover time of the springs can be considered an excellent radiological indicator in groundwater. In the absence of an anomalous radioactive source near the surface, it means that the high-turnover time of the springs leads to a low-radon concentration in the water. Besides linking high-risk areas with a short period required to free local flow discharges, this study exposes the virtues of a new perspective of a groundwater contamination risk modeling.

Path Modelling Analysis of Natural Radioactivity in Drinking Water and Public Health Impacts

“…For instance, when there is not mobilization of radon from rocks to water, it becomes crucial to understand which factors may be preventing this transfer process. Previous studies in fractured aquifer systems have reported that there is not a direct relationship between high-radon contents in rocks and the significant contamination of groundwater [2], [6], [7]. Then, how is it justified when in this comparison there is a high-radon production in rocks and a reduced radon concentration in groundwater?…”

“…Radon contamination in drinking water is invisible to human sense, and as such, should be given particular attention when a high radioactive exposure in drinking water occurs. For a practical assessment of aquifer contamination risk, it is useful to establish a conceptual model that explains the production and transport of radon from rocks to drinking water [2]- [5]. For instance, when there is not mobilization of radon from rocks to water, it becomes crucial to understand which factors may be preventing this transfer process.…”

“…Then, how is it justified when in this comparison there is a high-radon production in rocks and a reduced radon concentration in groundwater? A study by Martins et al [2] shows that a high-emanation or high-radon production in rocks may not always represent an efficient transport into the intergranular space and consequently an increased risk of groundwater contamination. For the assessment of the risk of groundwater contamination, it is crucial to conduct a survey about the connection between several factors that may increase the radon diffusion from rocks to the water such as, the weathering rate of U-bearing minerals under certain specific pH conditions [8]- [13], rock hydraulic diffusivity [14]- [16], and the emanation coefficient [17].…”

“…For the assessment of the risk of groundwater contamination, it is crucial to conduct a survey about the connection between several factors that may increase the radon diffusion from rocks to the water such as, the weathering rate of U-bearing minerals under certain specific pH conditions [8]- [13], rock hydraulic diffusivity [14]- [16], and the emanation coefficient [17]. Several environmental studies used the structural equation modelling-partial least squares (SEM-PLS) models to establish common approaches in large flood management [18], ecological surveys [19], [20], and radiological impact in groundwater [2]. The application of cluster analysis with complex structural models was previously performed by Martins et al [2] to study the effect of some factors on radon contamination in the aquifer system.…”

“…Several environmental studies used the structural equation modelling-partial least squares (SEM-PLS) models to establish common approaches in large flood management [18], ecological surveys [19], [20], and radiological impact in groundwater [2]. The application of cluster analysis with complex structural models was previously performed by Martins et al [2] to study the effect of some factors on radon contamination in the aquifer system. This study aims to develop a simpler structural model, although much more robust than the previous one [2].…”