Different hydrogeological characteristics of springs associated with abandoned coal mines in well-developed karst area

Karst groundwater is an important part of human drinking water sources. However, mining operations have resulted in the continuous discharge of acid mine drainage (AMD) in the karst region, which has the potential to negatively impact the quality and safety of the karst groundwater. In order to investigate the pollution process of karst aquifer caused by abandoned coal mines, multilayer karst system was taken into account to discuss the hydrogeological behavior of adjacent karst springs to reveal the mechanism of AMD pollution to different karst springs. Hydrologic monitoring and hydrochemical analysis revealed that the adjacent karst springs had an independent karst system during the dry season and were connected during the wet season. The carbonate strata above and below the coal seams of Permian Liangshan formation in the study area had developed waterconducting karst systems. The pollution levels and time stages of the perennial and seasonal springs were identified, providing a timetable for possible active and/or passive remediation. Water isotopes data showed that atmospheric rainfall was the main source of groundwater recharge, while AMD-contaminated karst springs were enriched in stable isotopes, showing obvious rain water, surface water, groundwater, and AMD mixing effect. Finally, six groundwater flow patterns represented were summarized, namely, the dominant fissure flow model, dominant conduit flow model, goaf-channel flow model, fissure-goaf overflow model, intermittent conduit-goaf overflow model, and interconnected fissure-goaf-channel flow model. The findings of this study provide a reference for ecological restoration and water resource managers to solve the problem in AMD pollution of karst springs associated with abandoned coal mines.