Assessment of Surface Water and Groundwater Quality Impacts at Iduapriem Mine, Tarkwa, Southwestern Ghana Approaches for Decommissioning of a Tailings Storage Facility

This study evaluated the hydrochemistry, surface water and groundwater quality, potential impacts, and decommissioning strategies for the Tailings Storage Facility (GTSF) at Iduapriem Mine in Tarkwa, Ghana, focusing on compliance with Ghana's Minerals and Mining Regulations (L.I. 2182). The research spanned from 2011 (baseline pre-operational year) through 2023 and aimed to assess water quality evolution, identify hydrochemical processes, and develop effective TSF closure strategies. Hydrochemical analysis was conducted on 46 sampling points comprising decant water (1), topliner sumps (19), underliner sumps (10), deep boreholes (7), shallow boreholes (7), and surface water sites (2). Results showed that multiple physical (pH, TSS, turbidity), chemical (potassium, free cyanide, nitrite, nitrate, ammonia), and trace metal (arsenic, lead, iron, copper, manganese, magnesium) parameters exceeded Environmental Protection Agency (EPA), Ghana Standards Authority (GSA), and World Health Organization (WHO) permissible limits in both surface and groundwater systems. Groundwater and surface water chemistry were predominantly characterized by Ca-HCO₃ facies, driven by carbonate and silicate mineral weathering processes. Nine distinct hydrochemical facies were identified, with Ca-HCO₃ (26%) being the most prevalent, followed by Mg-SO₄ (23%) and Ca-SO₄ (13%). Gibbs diagrams confirmed rock-water interaction as the primary controlling mechanism for water chemistry. Principal Component Analysis (PCA) identified pH, electrical conductivity, total dissolved solids, nitrate, nitrite, ammonia, iron, manganese, sulphate, and cyanide as dominant parameters contributing to hydrochemical variability. Bivariate plots revealed strong positive correlations (r = 0.996–0.999) between major ions, confirming the concurrent influence of silicate weathering and carbonate dissolution. Hydrochemical facies correlation analysis revealed significant geochemical interactions among topliners, underliners, shallow and deep boreholes, and surface water, indicating hydraulic connectivity and seepage migration pathways between the TSF and surrounding aquifers. Based on these findings, six integrated decommissioning approaches are recommended: systematic dewatering and water management, advanced multi-stage water treatment, recycling and controlled discharge, encapsulation with 500 mm topsoil cover, establishment of vegetated buffer zones around surface water bodies, and implementation of long-term monitoring and maintenance programs to ensure environmental protection and regulatory compliance.