Uranium spatio-temporal variability in groundwater : an environmental risk assessment case study

Por razões relacionadas com direitos de autor, só está disponível o resumo e os metadados.Uranium in the environment results from natural geochemical processes and human actions. The discharges of uranium and associated radionuclides as well as metals and metalloids from waste and tailing dumps in uranium mining areas and processing sites expose the target area to risk of contamination, concerning surface and groundwater. Uranium is one of the most widespread contaminant in mining areas. Uranium and associated trace elements spatial distribution patterns, in groundwater, within the transboundary watershed of the Águeda River (Portugal-Spain) is the main purpose of the herein work. Uranium minerals and associated sulphides occur distributed along the all area and are a potential source of contamination. These mineral resources were exploited in the past and were abandoned without any monitoring or remediation processes. Seventy-five groundwater samples were selected, georeferenced and collected during June of 2012. Each water point was analysed each water point were analysed “in situ” parameters such as: temperature, pH, electrical conductivity, Eh, dissolved oxygen. Trace elements contents such as uranium, were determined by inductively coupled plasma coupled mass (ICP-MS). Groundwater’s Uranium distribution was obtained thorough a spatial statistics approach were simulated scenario, for Uranium spatial distribution (Sequential Gaussian Simulation) were discussed and considering the average map and the associated spatial uncertainty, for each was determined the standard deviation of a hundred simulations. In a second step Local G clustering was performed in order to obtain Uranium’s hot-spots distribution. Uranium hot spots are located preferentially in the central area of the Águeda watershed and clearly associated with the proximity to the mineralization and overlapping the old mine site. In the northern and southern regions it is possible to identify clusters of moderate to high Uranium contents. High spatial uncertainty of associated though, which indicates the need of future detailed monitoring. The obtained results demonstrate that the old U-mining activities are nevertheless a serious environmental risk factor in the survey region. Finally, intrinsic vulnerability of groundwater was assessed by the calculation of the DRASTIC index. The results allow the identification of the areas with higher risk of contamination and works as a tool for the definition of effective groundwater systems’ management and exploitation policies