J. Kania1, T. Michalczyk1, S. Witczak1, D. Bar-Michalczyk1, K. Rozanski2, M. Dulinski2, J. Najmann3
1 AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, al. Mickiewicza 30, Krakow, Poland
2 AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, Krakow, Poland
3 Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, Krakow, Poland
The fissured-porous karstic aquifer located in southern Poland is the main source of potable water for ca. 300000 inhabitants of the Częstochowa city and the surrounding villages. The aquifer belongs to the category of Major Groundwater Basins in Poland (GZWP 326). Annually, approximately 7.8∙106 m3 of water is pumped annually from the aquifer. In the mid 1980s nitrate levels exceeding 50 mgNO3/L began to appear in wells located in the southern part of the aquifer. By the early 2000’s all major exploitation wells were affected by high nitrate levels. In 2006, a denitrification plant reducing nitrate levels in water to ca. 10-15 mgNO3/L has been build and put in operation, thus allowing local Waterworks Company to keep nitrate levels in potable water supplied to the clients below 50 mg NO3/L. Since the mid 2000’s the nitrate levels in major groundwater intakes remain roughly constant in the range between ca. 30 and 70 mgNO3/L (Michalczyk et al., 2016).
The presentation summarizes results of comprehensive modelling efforts aimed at reproducing time series of nitrate concentration in major exploitation wells of GZWP 326, available for the period since 1985. The approach consists of two major steps: (i) assessing input function of nitrate to groundwater using historical data on nitrate sources at the ground surface and modelling of nitrate percolation through the soil column with the aid of NLES 4 model (Højberg et al., 2015) combined with assessing time lag of nitrate transport through unsaturated zone using water balance approach (Wachniew et al., 2016), (ii) modelling of nitrate transport in the aquifer using 3D flow and transport model, calibrated with time series of environmental tritium. The degree of nitrate reduction in the aquifer was assessed through measurements of gaseous nitrogen excess in groundwater.
The modelling framework outlined above allows to quantify time lags associated with transport of nitrate through the unsaturated and saturated zones. It also allows to identify zones on the surface which contribute most to the nitrate load observed in the aquifer.
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