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

Abstract. The solution mining of salt mineral resources may contaminate groundwater and lead to water inrush out of the ground due to brine leakage. Taking a serious groundwater inrush hazard in a large salt mining area with three different types of ore beds which are trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3 · NaHCO3 · 2H2O, is a non-marine evaporite mineral), glauber (sodium sulfate, is the inorganic compound with formula Na2SO4 as well as several related hydrates) and gypsum (a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4 · 2H2O) in Tongbai County of China as an example, this paper mainly aims to analyse the source and channel of the inrush water. Based on the understanding of geological and hydrogeological conditions, the study obtained hydrochemical data of groundwater at different points and depths first; and then analysed the pollution source and pollutant component from single or mixed brines by both physical-chemical reaction principle analysis and hydrogeochemistry simulation method; finally possible leakage brine conducting channel to the ground had been discussed from both geological and artificial aspects. The results reveal that the brine from the trona mine is the major pollution source; the fissure zone in NW–SE direction controlled by the geological structure provides the main channels for the leakage brine to flow into the aquifer around the water inrush regions, and a large number of waste gypsum exploration boreholes are the channels that supply the polluted groundwater inrush out of the ground. The research can offer a valuable reference for avoiding and assessing groundwater inrush hazard in similar rock salt mining area, which is advantageous for both groundwater quality protection and resident health.