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As one of the globally largest cities suffering from severe water shortage, Beijing is highly dependent on groundwater supply. Located northeast of Beijing, the Pinggu district is an important emergency-groundwater-supply source. This area developed rapidly under the strategy of the integrated development of the Beijing–Tianjin–Hebei region in recent years. It is now important to evaluate the spatiotemporal variations in groundwater quality. This study analyzed groundwater-chemical-monitoring data from the periods 2014 and 2017. Hydrogeochemical analysis showed that groundwater is affected by calcite, dolomite, and silicate weathering. Self-organizing map (SOM) was used to cluster sample sites and identify possible sources of groundwater contamination. Sample sites were grouped into four clusters that explained the different pollution sources: sources of industrial and agricultural activities (Cluster I), landfill sources (Cluster II), domestic-sewage-discharge sources (Cluster III), and groundwater in Cluster IV was less affected by anthropogenic activities. Compared to 2014, concentrations of pollution indicators such as Cl−, SO42−, NO3−, and NH4+ increased, and the area of groundwater affected by domestic sewage discharge increased in 2017. Therefore, action should be taken in order to prevent the continuous deterioration of groundwater quality.

Goaf water in mining areas is widely found in China's coal mines. To clarify the hydrogeochemical characteristics of goaf water and the influence mechanism of water-rock interaction and further reveal microbial action on the formation of goaf water quality, the goaf water in the Menkeqing coal mine was taken as the object, and physical modeling was used to simulate the process of the real goaf changing from an oxygen-sufficient environment to an anoxic environment with the rise of groundwater level in this work. The experimental results showed that the water-rock interaction in the goaf was mainly the dissolution-precipitation of minerals in the rocks of the caving zone and fracture zone, cation exchange, and oxidation of pyrite in the coal layer. The primary sources of Na + and K + in the goaf water were the dissolution and reverse ion exchange of silicate minerals such as albite and potassium feldspar, while Ca 2+ and Mg 2+ mainly from the dissolution of minerals such as calcium feldspar, calcite, and chlorite. The oxidation of pyrite in coal was the main reason for the increase in SO 4 2- concentration, the enhancement of reduction, and the decrease in pH and DO (dissolved oxygen) in the goaf water. Relative abundance of sulfate-reducing bacteria (SRB) in goaf (e.g., Desulfosporosinus, Desulfobacterium, etc.) increased gradually, inhibiting the increase in SO 4 2- concentration in goaf water through the devulcanization of SRB. The inverse hydrogeochemical modeling was performed using PHREEQC for two stages of the simulation experiment: 0-30 days and 30-300 days. The simulation results show that the water-rock action in the formation of goaf water mainly occurred in the simulation experiment's early stage (0-30 days), and the mineral dissolution is dominant throughout the experimental stage. The results of the study provide a theoretical reference for the prediction of highly mineralized water pollution in goaf and its prevention and control.

• Investigation into eastern Himalayan syntaxis geothermal field in southern Tibet. • This geothermal field is a typical high-temperature magmatic geothermal field. • Seven conceptual patterns of the evolution of geothermal waters were established. • Brittle tensional faults cross-cutting the IYSZ control hydrothermal activity. • Hydrothermal activity is closely related to Cenozoic magmatic activity. The eastern Himalayan syntaxis is the easternmost end of southern Tibet and undergoing the continental Indian-Eurasian collision. The occurrence of large amounts of geothermal waters with high temperatures along the regional active faults is a clear manifestation of an abnormal thermal structure of the crust. In order to further complement the distribution characteristics of hydrothermal activity in southern Tibet, geothermal waters were collected and the hydrochemical characteristics and genetic mechanisms were analyzed. In the eastern Himalayan syntaxis geothermal field, geothermal waters show different compositional features. The major ions are Na+, Ca2+ and HCO 3 −, SO 4 2−, which are mainly controlled by water-rock interaction. Two peculiar hydrochemical characteristics of geothermal waters are proposed: ⅰ) the Cl− concentration of three water samples is abnormally high due to the likely contribution of magmatic water; ⅱ) the other three have a lower Cl− concentration but higher temperature because of flashing steam heating. The positive correlations between B, Li and Cl concentrations indicate that the geothermal waters originate in a parent geothermal liquid. The enthalpy-chloride diagram shows that the Cl− concentration and the enthalpy of the parent geothermal liquid are 283 mg/L and 1732 J/g (matching a temperature of 413.74 °C), respectively. Four cooling processes for the geothermal waters which ascend from reservoirs to surface were suggested, i.e., conductive cooling, adiabatic cooling, mixing with cold groundwater and the combination of these processes. The partial melting derived from crustal anatexis or crust-mantle mixing is the heat source for this geothermal field. The oxygen and hydrogen isotopic ratios indicate that the geothermal waters are meteorically-fed. The meteoric waters infiltrate via brittle tensional small-scale faults. According to the results of hydrochemical analysis, the evolution patterns of geothermal waters have been further summarized into seven patterns. Except for Pattern g, Patterns a to f are associated with the parent geothermal liquid. [ABSTRACT FROM AUTHOR]

As one of the globally largest cities suffering from severe water shortage, Beijing is highly dependent on groundwater supply. Located northeast of Beijing, the Pinggu district is an important emergency-groundwater-supply source. This area developed rapidly under the strategy of the integrated development of the Beijing–Tianjin–Hebei region in recent years. It is now important to evaluate the spatiotemporal variations in groundwater quality. This study analyzed groundwater-chemical-monitoring data from the periods 2014 and 2017. Hydrogeochemical analysis showed that groundwater is affected by calcite, dolomite, and silicate weathering. Self-organizing map (SOM) was used to cluster sample sites and identify possible sources of groundwater contamination. Sample sites were grouped into four clusters that explained the different pollution sources: sources of industrial and agricultural activities (Cluster I), landfill sources (Cluster II), domestic-sewage-discharge sources (Cluster III), and groundwater in Cluster IV was less affected by anthropogenic activities. Compared to 2014, concentrations of pollution indicators such as Cl−, SO42−, NO3−, and NH4+ increased, and the area of groundwater affected by domestic sewage discharge increased in 2017. Therefore, action should be taken in order to prevent the continuous deterioration of groundwater quality. [ABSTRACT FROM AUTHOR]