INTEGRATED CHEMICAL, RADIOLOGICAL AND BIOLOGICAL MONITORING FOR AN AUSTRALIAN URANIUM MINE - A BEST PRACTICE CASE STUDY

摘要

The Australian Government's Supervising Scientist Division (SSD) is the entity responsible for the independent supervision, monitoring and audit of uranium mines in the Alligator Rivers Region (ARR) of Australia's Northern Territory. The Ranger uranium mine, one of the world's largest producers of uranium oxide (5,000 tpa or 10% of world production), is located here. The mine lease is surrounded by the World Heritage-listed Kakadu National Park and is situated only several kilometres upstream of the Ramsar-listed Magela Creek wetlands. This location imposes especially stringent requirements on water management and, in particular, on the extent of permissible impact on receiving waters downstream of the mine.The objective of SSD's aquatic monitoring program, which is the focus of this paper, is to provide independent assurance to the Australian community that the aquatic environment remains protected from detrimental impacts from current and past uranium mining-associated activities in the ARR. The aquatic monitoring program is a best practice multiple lines of evidence approach comprising grab sampling for chemical and radiochemical analysis, continuous monitoring of pH, EC and turbidity, sentinel in situ toxicological monitoring, bioaccumulation (body burdens) of radionuclides in freshwater mussels and ecosystem biodiversity assessment.The techniques and indicators used in the monitoring program satisfy two key requirements for environmental protection assessment: (i) the early detection of significant changes to minimise the potential for broader scale ecosystem impacts; and (ii) the use of biodiversity indicators to provide ongoing information about the status of the aquatic ecosystems so as to be able to distinguish any impacts of mining from the effects of other regional ecological stressors.The past 25 years of independent monitoring conducted by the SSD has not shown any environmentally significant impact on the aquatic ecosystems downstream of the mine. Detailed radiochemical investigations have shown that the mine lease accounts for only a very small proportion of the ~(226)Ra found in downstream freshwater mussels.Current work is focused on developing a water quality guidelines framework that addresses the dynamic nature of variation in water quality parameters as revealed by the continuous measurements of physicochemical parameters. In particular, the relevance of management guidelines derived from ecotoxicological testwork using chronic 3-6 day exposure periods to pulse exposures that may be only several hours in duration is being investigated.