Radioactive and radiogenic isotopes in Ngarradj (Swift Creek) sediments: a baseline study

Department of the Environment and Heritage, 2003

Internal Report 404
Bollhöfer A & Martin P
Supervising Scientist Division

About the report

In 1977, the Australian Government authorised the mining and export of uranium in the Alligator Rivers Region. This included the mining leases at Ranger, approved in 1977, Jabiluka, approved in 1998, and Koongarra. The environmental protection plan for the mining leases had three essential elements:

  • the granting of land to Traditional Owners,
  • the establishment of Kakadu National Park and
  • the establishment of a Supervising Scientist.

After the implementation of the Environmental Protection Plan, mining and milling of uranium at the open-cut Ranger Mine commenced in 1981 and will probably be completed by 2007 (Johnston and Prendergast, 1999). Decline and underground works at the underground mine Jabiluka commenced in 1998 and the first stage of the development was finished in 1999. Currently, the Jabiluka Project is on a standby modus.

There are two alternatives for the milling of the Jabiluka uranium ore. One possibility is to mine and mill the ore on the Jabiluka mine site. This would involve the storage of waste rock and ore on the surface of the mine and 25% of the tailings would be stored in a large tailings dam, whereas the other 75% would be stored as cement paste in the voids of the mine. The second possibility is to transport the uranium ore via a haul road from Jabiluka to Ranger mine and use the existing milling facilities at Ranger to process the Jabiluka ore. ERA was proposing to mine and mill the ore at Jabiluka, which has been approved, based on all the tailings being eventually returned to the underground mine voids. Regardless which milling alternative is chosen, waste rock and ore stockpiles will be stored on the surface of the mine lease.

Approximately 90% of the rainfall falling onto Jabiluka becomes runoff (Chiew and Wang, 1999). The legislative requirements are such that runoff, erosion products and surface water that was in contact with the stockpiles will have to be contained in the retention pond and are not meant to leave the Total Containment Zone (TCZ). Whereas surface waters from the Mine Valley, above Jabiluka ore body 2, drain towards the west into Magela floodplain, surface water on the eastern side of the topographic divide, including Jabiluka mine, drain into the Ngarradj (Swift Creek) catchment and finally into the Magela Creek floodplain several kilometres north of the ore body.

Fears have been expressed by Traditional Owners and environmental organisations that the development of the Jabiluka project might have an adverse effect on Kakadu National Park, although Rio Tinto, who now own Energy Resources Australia (ERA), have announced a 10 year moratorium on the mining of Jabiluka (an announcement made at the company's Annual General Meeting on April 12, 2001, in London). However, the Jabiluka lease, with an area of 73 km² at the edge of Kakadu National Park, might be sold by Rio Tinto or economic developments might make the mining of uranium at Jabiluka more profitable. Therefore, a baseline dataset is needed to be able to assess impacts of mining of uranium at the Jabiluka mine should this occur.

Baseline studies investigating radionuclide and heavy metal concentrations in surface waters and biota have previously been conducted. The present study aims to produce a baseline dataset for sediments of the Ngarradj catchment to be able to estimate a possible impact of erosion from the Jabiluka mine site on the composition of sediments of the Ngarradj catchment. The current report focuses on a chemical and radiochemical dataset relevant to sediments from the Ngarradj catchment.