Combining Predictive Modeling and a Full-Scale Analog to Reduce Uncertainty

A proposed project in the Northern Territory, Australia, involves a partially developed open pit filled with water that needs dewatering before future operations can commence. The water quality in the pit lake is poor, and predictive modeling suggests that the pit walls may result in acid rock drainage and metal leaching during operations and post-closure, necessitating treatment of the collected water. To facilitate safe discharge of the dewatered water, in-pit treatment using micronized lime was initiated in 2012, aiming to raise the lake water pH above 7.0 to precipitate essential metals from solution. This treatment has successfully produced circum-neutral water and decreased metal concentrations, enabling dewatering to move forward and safe discharge to local rivers without adverse impacts. Despite five years of pumping, the pit lake level remains sufficiently high that potentially acid-generating rock units remain submerged under oxygen-limited conditions. Ongoing monitoring and water quality data collection have confirmed the effectiveness of this in-situ treatment approach, reinforcing the reliability of predictive modeling for successfully implementing closure options.