Determination of spatiotemporal variations and mixed patterns for a multi-aquifer system in the Sulin mining area based on analyses of hydrochemical and isotopic characteristics

Determining the hydrochemical variations and groundwater mixing is crucial for mining safety and water resource management in the Sulin mining area in North China, especially after mining activities. In this study, 94 groundwater samples were collected from the main aquifers in the Sulin mining area during the early and late stages of mining. Water-rock interactions, spatiotemporal variations in hydrochemistry, and groundwater level characteristics during the early and late stages of mining were determined by analyzing data on major ions, hydrogen and oxygen isotopes, and groundwater level. Analytical methods included Piper diagram, principal component analysis, ionic ratio analysis, and Kriging interpolation. A comprehensive conceptual model was proposed to describe the spatiotemporal variations and mixed patterns of the multi-aquifer systems. Results showed that groundwater level in the study area remained relatively consistent before and after mining, with no significant changes observed. The distribution of regional geological structures significantly affects on the groundwater distribution characteristics, which, in turn, determines the spatial variations in groundwater hydrogeochemistry and mixing patterns of groundwater under natural conditions. Moreover, there was significant temporal variation in hydrochemistry in areas of strong drainage. Mining activities led to a decrease in groundwater level, resulting in regional differences in water-rock interactions and groundwater mixing patterns. The Bayesian isotope mixing model (MixSIAR) and the hydrogeological conceptual model can be applied to quantitatively verify the groundwater mixing and the hydrogeochemical process. The study offers insights into the spatiotemporal variations and mixing patterns of groundwater under the impact of exploitation.