History of Groundwater Chemistry Changes (1979–2001) at the Nabarlek Uranium Mine, Australia

The Nabarlek uranium mine is located in the Alligator Rivers Region of the Northern Territory of Australia. The site lies in the wet/dry topics with an annual rainfall of about 1400mm, which falls between October and April. The site operated as a “no release” mine and mill between 1979 and 1988 after which time the facility was mothballed until decommissioning was required by the Supervising Authorities in 1994. The dismantling of the mill and rehabilitation earthworks were completed in time for the onset of the 1995–96 wet season. During the operational phase accumulation of excess water resulted in irrigation of waste water being allowed in areas of natural forest bushland. The practice resulted in adverse impacts being observed, including a high level of tree deaths in the forest and degradation of water quality in both ground and surface waters in the vicinity. A comprehensive environmental monitoring programme was in place throughout the operating and rehabilitation phases of the mine’s life, which continues, albeit at a reduced level. Revegetation of the site, including the former irrigation areas, is being observed to ascertain if the site can be handed back to the Aboriginal Traditional Owners. A comprehensive review of proximal water sampling points was undertaken in 2001 and the data used to provide a snapshot of water quality to assist with modelling the long term prognosis for the water resources in the area. While exhibiting detectable effects of mining activities, water in most of the monitoring bores now meets Australian drinking water guideline levels. The paper reviews the history of the site and examines the accumulated data on water quality for the site to show how the situation is changing with time. The paper also presents an assessment of the long term future of the site in respect of water quality.