Mechanism of groundwater inrush hazard caused by solution mining in a multilayered rock-salt-mining area: a case study in Tongbai, China

Abstract

Abstract. The solution mining of salt mineral resources may contaminate groundwater and lead to water inrush out of the ground due to brine leakage. Through the example of a serious groundwater inrush hazard in a large salt-mining area in Tongbai County, China, this study mainly aims to analyse the source and channel of the inrushing water. The mining area has three different types of ore beds including trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, with the formula Na2CO3 × NaHCO3 × 2H2O, it is a non-marine evaporite mineral), glauber (sodium sulfate, it is the inorganic compound with the formula Na2SO4 as well as several related hydrates) and gypsum (a soft sulfate mineral composed of calcium sulfate dihydrate, with chemical formula CaSO4 × 2H2O). Based on characterisation of the geological and hydrogeological conditions, the hydrochemical data of the groundwater at different points and depths were used to analyse the pollution source and the pollutant component from single or mixed brine by using physical–chemical reaction principle analysis and hydrogeochemical simulation method. Finally, a possible brine leakage connecting the channel to the ground was discussed from both the geological and artificial perspectives. The results reveal that the brine from the trona mine is the major pollution source; there is a NW–SE fissure zone controlled by the geological structure that provides the main channels through which brine can flow into the aquifer around the water inrush regions, with a large number of waste gypsum exploration boreholes channelling the polluted groundwater inrush out of the ground. This research can be a valuable reference for avoiding and assessing groundwater inrush hazards in similar rock-salt-mining areas, which is advantageous for both groundwater quality protection and public health.