A cost-effective method for assessing groundwater well vulnerability to anthropogenic and natural pollution in the framework of water safety plans

Water abstraction is a key aspect when performing drinking water risk assessment within the scope of Water Safety Plan (WPS). In this context, evaluating aquifer vulnerability could be not exhaustive. Care must be taken to consider the well structure and dynamic behavior that can determine different water quality and vulnerability than those of the tapped aquifer. Here, a methodological approach to assess well vulnerability to natural and anthropogenic pollution is proposed. A data-driven hydrogeochemical conceptual modeling was performed through cluster analysis, supporting the identification of the main features determining well vulnerability. Well vulnerability was then assessed through a semi-quantitative method based on a well-specific analysis of the tapped aquifer type, water table depth, vadose zone permeability, natural redox conditions, and qualitative classification of the tapped groundwater age, considering evidence of mixing processes induced by the well dynamic behavior. Each feature was categorized into several classes, and a score was associated with each class according to the vulnerability induced by that specific condition. The method was applied to a dataset of ∼200 wells, in northern Italy. Each well was classified, and its vulnerability was assessed. The method was validated by analyzing the distribution of wells affected by natural or anthropogenic pollution in each of the vulnerability classes. Results of the chi-square test showed that the distribution of the polluted wells was associated with vulnerability classes, which is evidence of the robustness and reliability of the proposed method. This method was developed exploiting only hydrogeological information and raw water quality data, largely available to water managers from routine monitoring, which makes this approach widely applicable and cost-effective.