Relevance Between Hydrochemical and Hydrodynamic Data in a Deep Karstified Limestone Aquifer: a Mining Area Case Study

Abstract

Safe coal mining in a karst region requires that mining operations assess any disturbances in the hydrogeological functioning of local aquifers and flow systems, and determine if disruptions are likely in the mine. We studied the geologic, hydraulic, and geochemical characteristics of the deep Ordovician karstified aquifer in the Xinglongzhuang and Dongtan mines of the Yanzhou coal mining district (China). The presence of a 100 m deep research borehole in the Ordovician limestone aquifer nearby facilitated hydrochemical and hydrodynamic data collection. The buried depth affected karst rock porosity, and the reduced porosity increased karst development. This, in turn, affected the abundance of water in the karst fissure. In addition to calcite and dolomite, the Ordovician limestone contains gypsum, which dissolves to form sulfate ions. Hydraulic data revealed that the water abundance in the research area is comparatively low, except for the C8 syncline zone. The Ordovician strata in this area is located in the deep, slow-flow zone of a vertical karst aquifer system, and the drilling unit water inflow is very low, which could represent the water abundance of the aquifer. Understanding this complex flow system is critical to appropriately assess the area’s deep groundwater resources and guide decision making regarding coal extraction.