Parametric assessment of groundwater vulnerability to pollution within an open pit reclaimed by gangue

The use of post-mining wastes in the reclamation of an open pit may act as a source of pollution that has a very strong impact on the groundwater environment. One such facility in Poland is the CTL Maczki-Bor S.A. sand mine filled with waste rock from hard coal mines. The current hydrodynamic conditions in the Quaternary aquifer causes that the wastes are in the bottom part of the open pit under the constant influence of groundwater. Due to the sub-level nature of the pollution source, the author of the study modified the classic rank-weight method of assessing the groundwater vulnerability to pollution in order to adapt it to the atypical type of the pollutant emitter. An individual approach was proposed by modifying the range of parameters as well as the assigned ranks and weights. Six key parameters were indicated, i.e. the thickness of the aeration zone, the thickness of the saturation zone, the filtration coefficients of the deposits in both of these zones, the recharge of the aquifer and the surface topography. The correctness of weight selection was verified by sensitivity analysis in the sensitivity variant of one parameter. It has been proposed to classify the groundwater vulnerability to 5 classes from moderately high to extremely high. For theoretical and effective weights, the obtained values of the index of groundwater vulnerability to pollution allowed to divide the area of the reclaimed open pit into two zones with high and very high groundwater vulnerability to pollution.