Geochemical assessment of water and sediment quality at an abandoned coal mine site, Alabama, USA

This study presents a pre-reclamation geochemical assessment of a 67-acre abandoned coal mine site in the upper Hurricane Creek watershed, eastern Tuscaloosa County, Alabama. Reclamation is planned for Fall 2024 under the USDOI/DOL Abandoned Mine Land Economic Revitalization (AMLER) Program. Over a two-year period (June 2022–May 2024), monthly surface water (SW1–SW10) and quarterly sediment samples (SS1-SS10) were collected from the same ten monitoring stations to evaluate spatial and seasonal contaminant dynamics. Upstream sites (SW1–SW6) exhibited circumneutral pH (7.0–8.3), high conductivity (600–1800 µS/cm), and elevated sulfate concentrations (100–1200 mg/L), with evidence of seasonal dilution during winter months. In contrast, retention pond sites (SW8–SW10) displayed persistent acidity (pH 3.0–3.5) and elevated trace metal concentrations. Site SW7, hydrologically disconnected from acid mine drainage sources, showed lower conductivity and higher pH values. Inductively coupled plasma–optical emission spectrometry analysis revealed elevated aluminum, manganese, nickel, and iron concentrations at SW8–SW10, regularly exceeding drinking water standards with peak concentrations of >4, 29, 0.2, and 2 mg/L, respectively. Sediment particle size analysis classified sediments collected at SS1–SS6 and SS8 as sand-dominated, whereas SS7, SS9, and SS10 were silt-dominated. Microwave nitric acid digestion (EPA 3051 A) indicated highest total iron concentrations at SS10. Metal extractability exhibited grain-size dependence, with sand-dominated sediments showing higher extractable iron, manganese, and nickel, while silt-sized sediments showed higher extractable aluminum, due to mineralogical controls. These findings highlight chronic acid mine drainage impacts at SS8–SS10 and provide baseline geochemical data to inform targeted remediation and post-reclamation monitoring under the AMLER Program.