Uranium, radium and radon are usually found in groundwater, as moving groundwater interacts with its environment, it can mobilise, transport and accumulate these isotopes similarly to other chemical substances. As groundwater represents the main source of public drinking water supplies in many regions (EU 75%, Hungary 88%), presence of natural radioisotopes in groundwater may pose a hazard factor to the public. However, in accordance with Council Directive 96/29/EURATOM, the risk from ionising radiation must be kept as low as reasonably achievable. The Council Directive 2013/51/EURATOM, therefore, lays down requirements for the protection of the health of the general public with regard to radioactive substances in water intended for human consumption. This was implemented in Hungary in 2015. Thus, nation-wide overview of the radioactivity of drinking water in Hungary became available only recently, since waterworks and authorities are measuring and generating data only in the last three years. Based on the results 11% of the measured gross-alpha and 3% of gross-beta values are above the threshold values. This indicates that in areas where elevated gross values are found natural radionuclides may pose a health risk to the public.
In general, however, there is no apparent relationship between the type of rock constituting the water-bearing formation and the observed activity concentration levels of the radionuclides, since wide ranges of activity concentrations of the radioisotopes are observed within the same aquifer. The theory of regional groundwater flow, however, puts previous observations in a different context. In case of redox-sensitive parameters, such as the uranium or radium, understanding groundwater flow systems is especially important. Areas of different hydraulic regimes – recharge, throughflow and discharge – as well as different order flow systems – local, intermediate, regional – even within the same aquifer are characterized by different geochemical environment. Groundwater flow system evaluation thus contributes to the understanding of the measured radioactivity in drinking water by providing explanation of the origin and transport of radionuclides. Furthermore, it helps to successfully predict favourable conditions for elevated radionuclide content enabling efficient and successful decision-making, resource management and involvement. Presented case studies based on the combination of flow system evaluation and nuclide specific analyses support the applicability and significance of this approach.
This study was supported by the ÚNKP-17-4 and ÚNKP-18-3 New National Excellence Programs of the Ministry of Human Capacities. This topic is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.