Hydrochemical characteristics and quality assessment of deep groundwater from the coal-bearing aquifer of the Linhuan coal-mining district, Northern Anhui Province, China

There is little information available about the hydrochemical characteristics of deep groundwater in the Linhuan coal-mining district, Northern Anhui Province, China In this study, we report information about the physicochemical parameters, major ions, and heavy metals of 17 groundwater samples that were collected from the coal-bearing aquifer. The results show that the concentrations of total dissolved solids, electrical conductivity, and potassium and sodium (K++Na+) in most of the groundwater samples exceeded the guidelines of the World Health Organization (WHO) and the Chinese National Standards for Drinking Water Quality (GB 5749-2006). The groundwater from the coal-bearing aquifer was dominated by the HCO3 center dot Cl-K+Na and HCO3 center dot SO4-K+Na types. Analysis with a Gibbs plot suggested that the major ion chemistry of the groundwater was primarily controlled by weathering of rocks and that the coal-bearing aquifer in the Linhuan coal mining district was a relatively closed system. K and Na+ originated from halite and silicate weathering reactions, while Ca2+ and Mg2+ originated from the dissolution of calcite, dolomite, and gypsum or anhydrite. Ion exchange reactions also had an influence on the formation of major ions in groundwater. The concentrations of selected heavy metals decreased in the order Mn> Zn> Cr> Cu > Ni> Pb. In general, the heavy metal concentrations were low; however, the Cr, Mn, and Ni concentrations in some of the groundwater samples exceeded the standards outlined by the WHO, the GB 5749-2006, and the Chinese National Standards for Groundwater (GB/T 14848-93). Analysis by various indices (% Na, SAR, and EC), a USSL diagram, and a Wilcox diagram showed that both the salinity and alkalinity of the groundwater were high, such that the groundwater could not be used for irrigating agricultural land without treatment. These results will be significant for water resource exploiting and utilization in coal mine area.