Assessment of the impact of a non-operational municipal landfill site on groundwater quality: a case study from southwestern Poland.

Groundwater and leachate quality tests were carried out in 2023-2024 at a closed landfill site in southwestern Poland. This novel study aimed to identify the variability in their compositions, taking into account physicochemical, microbiological, and toxicological tests on the site two decades after its closure. The impact of the closed landfill site on the groundwater environment during its non-operational phase was assessed. The results show that waste deposited in 1974-2001 caused a deterioration in the quality of the aquatic environment, as indicated by high values of various indicators, e.g. bicarbonates (1290.67 mg/L), electrolytic conductivity, ammonium ions, ammonium nitrogen, total inorganic carbon, free carbon dioxide, E. coli, and coliform bacteria, and luminescence inhibition. Wide range is a new approach to identifying the impacts of non-operational landfill sites on the aquatic environment. Particular deterioration in the groundwater and leachate quality was noticeable in the third and fourth quarters of 2023. The activity of the non-operational landfill site confirms the impact of the leaky subfloor on the significant deterioration of groundwater quality in its vicinity, taking into account seasonality. It is necessary to introduce additional inorganic and biological indicators for quarterly monitoring of the aquatic environment. Moreover, a vertical geomembrane screen must be incorporated to protect against the impact of the old landfill on groundwater until the end of its environmental activity.