The migration of pesticide residues in groundwater at a bank filtration site (Krajkowo well field, Poland)

River bank filtration systems are widely used for water supply purposes. Using these systems, the movement of water over short distances between the river bottom and extraction wells can decrease the concentrations of some contaminants. Such systems are especially important for the removal of specific micro-pollutants that seasonally appear in river water. In this article, pesticides migration at the Krajkowo well field is analysed based on different water extraction schemes. The water is extracted by two groups of wells (one located 60–80 m from the Warta River, and the second located more than 400 m from the river) and by a horizontal well with radial drains located 5 m below the river bottom. Based on this scheme, the rate of pesticide residues removal was analysed in wells located at different distances from the river channel. The results of the three sampling campaigns conducted in summer and autumn 2017 and winter 2018 indicate the presence of pesticide compounds in the Warta River (max. total concentration of 0.171 μg/l). The pesticides were also present in the horizontal well (max. total concentration of 0.137 μg/l). Much smaller concentrations (max. 0.064 μg/l) were observed in vertical wells located 60–80 m from the river. Additionally, in the well located 250 m from the river, only two pesticide constituents were detected (at concentrations just above the detection limit), and in a well located 680 m from the river, the concentrations of pesticide residues were below the detection limit (excluding isoproturon, which was slightly above the detection limit). This research illustrates the effectiveness of pesticides removal by river bank filtration.