Abstract
Employing unmanned aerial vehicles (i.e., drones) for water sampling of pit lakes offers a range of benefits that contribute to safer, more efficient, accurate, and environmentally conscious monitoring and management of these unique aquatic systems. A Mavic Matrice 300 drone was used to access eleven pit lakes at a remote iron ore mine site in the Pilbara region of Western Australia for depth profiling, in-situ water quality parameter measurement, and collection of surface water samples (bailers) and at various depth intervals through the water column (with Hydrasleeves®) for laboratory analysis. The objectives of the study were to: i) characterise the water quality of each pit lake with depth, ii) determine whether stratification had developed in any of the pit lakes, and iii) predict future pit water quality through geochemical modelling in combination with the acquired pit lake data, geological models and hydrologic models to inform site water management and rehabilitation. Results from the pit lake water characterisation revealed five distinct water quality groups which were defined based on pH, salinity and metal(loid) content; these groups were i) neutral to alkaline fresh and non-metalliferous, ii) neutral to alkaline fresh and metalliferous, iii) alkaline brackish and non-metalliferous, iv) alkaline brackish and metalliferous, and v) acidic fresh to brackish and metalliferous. Results from the PHREEQC water quality modelling (of pit lakes with moderate to high data confidence) indicated that the most significant water quality changes were predicted for pit lakes modelled as hydrogeological sinks due to evapoconcentration.