Isotope and geochemical tracing for acid mine drainage impacts in coal mines areas of Pakistan

Groundwater in coal mining regions is highly vulnerable to contamination from Acid Mine Drainage (AMD), posing significant environmental and public health risks. This study applied combined hydrogeochemical and stable/isotopic analyses to assess AMD impacts and recharge mechanisms in the active Pail-Padhrar coal mining area, Chakwal, Pakistan. Water samples were collected from mine sumps, surface bodies, and boreholes (purged prior to sampling), with field measurements of pH, electrical conductivity, and dissolved oxygen. Cations, anions, and trace metals were analyzed using AAS, ICPOES, and UV-visible spectrophotometry, while δ18O, δ2H, δ34S, and δ18O of sulfate were measured to trace recharge and geochemical processes. AMD-impacted waters were characterized by SO42-–Cl-–Na+–Ca2+ hydrochemical types, high TDS, low pH, and signatures of sulfide oxidation, evaporation, and silicate weathering. Non-AMD-impacted waters exhibited SO42-–Na+–Ca2+ to Na+–Ca2+–HCO3 types, dominated by rock weathering, mineral dissolution, and ion exchange. Isotopic data confirmed precipitation as the primary recharge source, with d-excess values distinguishing rainwater mixing, evaporation, and AMD influence. Sulfate isotopes revealed pyrite oxidation and gypsum dissolution as major sulfate sources, supported by iron oxyhydroxide presence. These findings highlight the spatial heterogeneity of groundwater processes and provide a comprehensive framework for understanding AMD impacts on aquifer chemistry, essential for sustainable groundwater management in coal mining regions.