Erosion Risk Assessment of the Jabiluka Mine Site, Northern Territory, Australia

This research utilizes Monte Carlo simulations of soil loss and runoff equations to assess impacts of the Jabiluka Uranium Mine site on Ngarradj, the downstream waterway. Ngarradj, a stream of high conservation value, debouches into wetlands of international importance within Kakadu National Park. The stream has a low background mean annual suspended-sediment concentration of 5.2mgL-1 (S=1.2mgL-1) determined through monitoring. Erosion modeling indicated that a mean suspended-sediment increase of about 17.3mgL-1 (S=14.1mgL-1) was expected from construction of the Jabiluka site's waste rock dumps at Year 30 of the operation. The model indicated that the probability that the Jabiluka site activity would result in exceedence of the water-quality guideline for stream suspended sediment was 0.98 for that year. The evaluation was able to reach this conclusion based on 5 years of stream suspended-sediment concentration data and is highly conservative as a 1:1 sediment delivery ratio is assumed. Application of the simple methodology here not only enabled greater certainty concerning the risks of downstream sediment impact, but also identification of important management strategies.