Hydrochemical assessment of environmental status of surface and ground water in mine areas in South Korea: Emphasis on geochemical behaviors of metals and sulfate in ground water

In this study, hydrochemistry of ground and surface water collected around six metalliferous mines and one coal mine in South Korea was investigated to evaluate the status of mining-related impact and pollution. Groundwater system under the mine impact shows varying degrees of immobilization and retardation of heavy metals during the flow. SO₄^{2 -} is shown to be the most reliable indicator of the mining impact on groundwater, as it reflects the degree of initial sulfide oxidation even after subsequent removal of metals; SO₄^{2 -} is also less prone to sorption, precipitation, and geochemical reduction. A good correlation between the concentrations of SO₄^{2 -} and the sum of Ca and Mg is observed, indicating that SO₄^{2 -} represents the degree of dissolution of Ca- and Mg-bearing carbonates and silicates (i.e., neutralization of acidic water to circumneutral pH) by generated H⁺ that is proportional to SO₄^{2 -}. The higher Zn/Cd ratios of ores and water than those of tailings and precipitates indicate a more preferential immobilization of Cd, and this ratio also reflects the inherent composition of each ore. The modified HPI (Heavy Metal Pollution Index) consisting of the measured concentrations and respective environmental standards of Fe, Mn, Al, Zn, Pb, Cd, Cu, As, and SO₄^{2 -} is suggested as MPI (Mine Pollution Index) to overall reliably evaluate the status of mining-related water pollution. The plot of SO₄^{2 -} versus MPI is very effective to identify the contaminated mine water and its evolution, including the source and the pathways consisting of immobilization (precipitation, sorption) and dilution of contaminants in groundwater system. This study shows that a careful examination of the relationship between MPI and SO₄^{2 -} can be very useful to identify diverse geochemical processes occurring in groundwater affected by mine drainage.