Risk assessment for the prevention of managed aquifer recharge (MAR) facility failure during the operation and the expansion phases

Abstract

This comprehensive risk assessment, done for a MAR facility in Tarnów, southern Poland, covers two MAR techniques: infiltration ditches and induced bank filtration during the operation and planned potential expansion phases. Two methods were applied: the semi-quantitative risk assessment matrix and the probabilistic risk assessment – fault tree analysis (PRA-FTA), and their advantages and limitations analysed. Both methods examine a range of technical and non-technical risks that may pose a threat to the efficient functioning of the MAR facility in Tarnów, which supplies about 25% of the city’s population with drinking water. It was found that 34 of the 65 risks analysed could pose a low to high risk for the Świerczków well field. The predominant risks potentially reducing MAR efficiency or leading to MAR failure are technical ones. According to the PRA-FTA method, if no preventive measures are taken, there is a 99.5 and 99.3% probability of the MAR system failing during the operational and expansion phases, respectively. The results indicate that the most serious risk is associated with the insufficient initial removal from the recharge river water of suspended solids, which clog infiltration ditches. The risks scored as medium relate to the threat of groundwater inflow from an extensive industrial zone, lying to the east of the well field, and to climate change negatively affecting the quantity of groundwater resources. This is the first example in Poland of a risk assessment for an existing MAR facility and its expansion, based on a broad spectrum of technical and non-technical risks present at the Świerczków well field, using two methods: the risk assessment matrix and PRA-FTA. This case study is a practical example of how to perform a risk analysis for a MAR site. It can make an important contribution to existing knowledge in this field and enrich the subject literature, a particularly relevant aspect given the widespread use of MAR techniques in Central Europe for the supply of drinking water to the public.