14-Month Water Quality Investigation of Coal Mine Discharge on Two Rivers in NSW, Australia: Implications for Environmental Regulation

Ineffective environmental regulation of effluent discharged from an underground coal mine operation has enabled water pollution within two highly valued Australian rivers. This study investigated the impacts on water chemistry of the Bargo and Nepean rivers as a result of the continuous disposal of mine effluent from Tahmoor Colliery over a 14-month period. Coal mine effluent was saline (2180 μS/cm) and alkaline (8.7 pH), and strongly modified the ionic composition within both rivers. Ecologically hazardous concentrations of several metals were found in mine effluent, including aluminium (858 μg/L), arsenic (59.7 μg/L), nickel (60.7 μg/L), and zinc (49.4 μg/L). The effluent also contained elevated total nitrogen (2.89 mg/L) and the waste discharge contributed 67% of the median flow volume in the Bargo River below the discharge point. The plume of saline- and metal-enriched contamination extended at least 9 km downstream past the discharge point, impairing water quality in both the Bargo and Nepean rivers. This study reveals more than a decade of ineffective regulatory and governance systems that enable Tahmoor Colliery to continually release inadequately treated mine effluent.