Calculating groundwater mixing ratios in groundwater-inrushing aquifers based on environmental stable isotopes (D, 18O) and hydrogeochemistry

Conventional hydrogeochemical data and environmental stable isotopes are used to identify the recharge sources and the water-rock interactions in the groundwater-flowing direction within the multilayer groundwater system of the Sulin coal-mining district in the north Anhui province in China. delta D and delta O-18 of groundwater in the mining district decrease along the groundwater-flowing direction in the recharge areas, yet in the runoff or discharge areas, they rise and fall along average delta values (delta O-18 = -8.68 aEuro degrees, delta D = -67.4 aEuro degrees), which are lower than average delta values of local atmospheric precipitation (delta O-18 = -7.80 aEuro degrees, delta D = -52.4 aEuro degrees). Principal component analysis is used to analyze the conventional hydrogeochemical data (K+ + Na+, Mg2+, Ca2+, Cl-, SO4 (2-), HCO3 (-), CO3 (2-)) in the groundwater. The first and second principal components have large variance contributions, and represent "pyrite oxidation or groundwater hardening" and "desulfurization or cation exchange and adsorption," respectively. From conventional hydrogeochemical data and environmental stable isotopes, it is demonstrated that groundwater of the Sulin coal-mining district is characterized by a mixing type, which is confirmed by three recharge end-members: fresh groundwater, leaching groundwater, and retained groundwater. By means of a sample dot-encompassed triangle in the scatter diagram of load scores for Component 1-Component 2, whose vertexes stand for the three end-members, a model for calculating groundwater mixing ratio is established and applied successfully to the evaluation and management of groundwater hazards in the coal-mining districts.