Quality of water from subsidence area: a case study in the Luling coal mine, northern Anhui Province, China

Quality of water in the subsidence area related to coal mining is important for water usage in the coal mining areas. In this study, forty-two samples from the subsidence pools in the Luling coal mine, northern Anhui Province, China have been collected and measured for their major ion concentrations, and the data have been applied for quality evaluating of drinking and irrigation purposes. The results suggest that the water samples from different pools have different concentrations of major ions and all of them can be classified to be Na-HCO₃ type. According to the results of water quality index, all of them are suitable for drinking (considering only about the major ion concentrations). However, sodium absorption ratio (SAR) and residual sodium carbonate (RSC) give different answers about irrigation purpose, the water can be used for irrigation according to SAR whereas cannot be used according to RSC, and can be attributed to the high concentrations of CO₃²⁻ and HCO₃⁻. Gibbs diagrams and relationships between Na⁺ normalized Ca²⁺, Mg²⁺ and HCO₃⁻ suggest that different extents of contributions from weathering of silicate, dissolution of carbonates and evaporates are the main mechanism controlling the major ion concentrations of water from the subsidence areas in this study, which is related to the natural conditions of the pools.