Assessment of the Slaná River contamination impact on groundwater quality

In February 2022, the siderite mine in Nižná Slaná (Slovakia) was flooded. Because of this accident, mine water with an enormously high content of iron, manganese, arsenic, nickel and sulfates began to flow into the Slaná River and ferrous ocher with a high content of arsenic was precipitated. It caused intense turbidity of water and deterioration of the ecological status of the Slaná River.

For representative assessment of the impact of this accident on groundwater quality, the results of groundwater quality monitoring in 18 sampling sites (groundwater wells) of the State Hydrological Network were assessed for selected determinants (iron, manganese, arsenic, antimony and nickel), which could have impact on the deterioration of the groundwater status in the interested area. The area where the contamination impact was investigated was the area from the Nižná Slaná River to the state border with Hungary.

The assessment was based on long-term results of groundwater quality monitoring since 2000. We focused mainly on assessment of quality change in 9 sampling sites located directly in alluvial sediments of the Slaná River.

From the total number of 7,587 measurements since 2000, the worst groundwater quality was in Betliar, where the highest concentrations of manganese, iron and arsenic were measured. However, we should note, that in comparison with the previous monitoring period of sites in alluvial sediments of the Slaná River, above – limit concentrations were repeatedly determined even in the period before the accident of the siderite mine in Nižná Slaná.

Despite the results of the monitoring so far, there is still a risk of pollution caused by the flooding of the former siderite mine, and it is therefore necessary to continue to pay increased attention to this area and further monitoring of the impact of pollution of the Slaná River on groundwater quality.