Thermodynamics and Hydrogeochemical Evolution of the Shallow Aquifer in Enugu Urban, Southeastern Nigeria

The shallow aquifer system in Enugu Urban, southeastern Nigeria, represents a critical groundwater resource but is increasingly affected by complex hydrogeochemical and thermodynamic processes driven by rapid urbanization, lithological heterogeneity, and climatic variability. This study integrates field-based hydrochemical investigations (via groundwater sampling and laboratory analysis), graphical and statistical tools, and thermodynamic modeling using PHREEQC to elucidate the key controls on groundwater chemistry, mineral stability, and water–rock interactions. Results reveal a dominance of the Na-HCO₃ water type, coupled with active cation exchange and extensive silicate weathering. Thermodynamic indices indicate that calcite, dolomite, and gypsum are predominantly undersaturated, with spatial and seasonal variations reflecting the interplay between geogenic factors and anthropogenic influences, particularly from land use changes and urban development. These findings underscore the aquifer’s limited buffering capacity and its vulnerability to quality degradation, with significant implications for groundwater management and aquifer sustainability in rapidly urbanizing settings. The study provides a scientific basis for informed decision-making aimed at preserving groundwater quality and ensuring long-term water security in Enugu.