Evaluation of surface water quality after mine closure in the coal-mining region of Guizhou, China

In this study, we used pollution evaluation indices, principal component analysis (PCA), and hierarchical cluster analysis (HCA) to assess the pollution status of surface water systems after mine closure in an intensive coal-mining area of Guizhou. The concentrations of Fe, Al, Mn, Hg, total nitrogen, volatile phenols, sulfide, and petroleum in most of the water samples exceeded the limits set by China and the World Health Organization. The surface water in this region was characterised as near-neutral-high metals and near-neutral-low metals. The metal elements showed high spatial variability as inferred from their high variation coefficients. In contrast, most non-metallic pollution elements were not considered dominant polluters and generally showed low spatial variability. Modifications to the existing heavy metal pollution index and degree of contamination scheme showed comparable results to that of the heavy metal evaluation index, where 76.92%, 7.69%, and 15.38% of the water samples showed low, medium, and high pollution, respectively. Combined, the results of the HCA, PCA, and pollution indices inferred highest surface water contamination at sites closest to the coal mines (G1, G4, G9), while distal sites were less contaminated. Our results highlight the need to assess the pollution status of surface water systems after mine closure in intensive coal-mining areas in order to prevent severe ecological and environmental degradation.