Investigation of tailings water leak at the Ranger uranium mine

Supervising Scientist, 2000

Supervising Scientist Report 153
ISSN 1325-1554
ISBN 0 642 24356 5

Separate sections

About the report

During the 1999-2000 Wet season, a leak occurred in the tailings water return pipe at the Ranger uranium mine in the Alligator Rivers Region of the Northern Territory. The first indication to the authorities that a leak had occurred was in a facsimile message from Energy Resources of Australia (ERA), the mine operator, to the Office of the Supervising Scientist (oss) on the afternoon of Friday 28 April 2000. This message advised that approximately 2000 cubic metres of tailings water (process water) had leaked from a pipe in the Tailings Dam Corridor of the Ranger site between late December 1999 and 5 April 2000. The facsimile message was also sent by ERA to the Northern Territory Department of Mines and Energy (NTDME), Northern Land Council (NLC) and the Department of Industry, Science and Resources (DISR).

Water in the tailings dam at Ranger is pumped from the dam back to the mill through the Tailings Water Return Pipeline for use in the process plant. The primary containment system is the pipeline itself. A secondary containment system is in place to protect the environment from any adverse effects arising from a failure anywhere along the pipeline. This secondary containment system consists of a bunded roadway that collects any spilled water and directs it to a sump, the Tailings Dam Corridor Sump. Water that is collected in this sump is returned to the mill water management system. Should both the primary and secondary containment systems fail, a third barrier for the protection of the environment is in place in the form of constructed wetland filters which are designed to partially remove contaminants from the water as it passes through the filter system.

Although a leak had been reported, no indication was given that the secondary containment system may have been breached. Indeed, the report stated that no infringement of the Ranger General Authorisation had occurred. On receipt of the facsimile, the oss contacted ERA to clarify the circumstances surrounding the incident. The Department of Industry, Science and Resources also sought advice from ERA on the nature and the timing of the leak. During telephone conversations between oss and ERA staff, information on water quality at a number of sites was provided which indicated that a proportion of the process water had entered the Very Low Grade Corridor Road Culvert (VLGCRC) built under the Tailings Dam Corridor, and hence had escaped the secondary containment system consisting of bunds and a sump, designed to collect any spillages from the pipes in the tailings corridor.

Based on this information, the Supervising Scientist concluded that a breach of the Environmental Requirements had occurred and immediately notified the office of the Minister for the Environment and Heritage. On Sunday 30 April, the Supervising Scientist provided a formal brief to the Minister on the incident. Following receipt of this brief, the Minister requested that the Supervising Scientist investigate the incident and provide a report to him. A similar request was received from the Minister for Industry, Science and Resources who is responsible for the administration of the Atomic Energy Act 1953 under which approval has been given for ERA to operate the Ranger Mine. This report is in response to these requests.

In preparing this report, the Supervising Scientist has consulted all the major stakeholders including ERA, NTDME, NLC and the Gundjehmi Aboriginal Corporation. On technical aspects of the assessment, a report was prepared by ERA in close cooperation and consultation with staff of the Supervising Scientist and the NTDME. In addition ERA commissioned a report from a specialist pipeline inspection company, Intico, on the condition of pipes in the Tailings Corridor and the Supervising Scientist commissioned a review from Sinclair Knight Merz on the adequacy of the design, operation and maintenance of the tailings corridor system. NTDME also prepared a report on the incident.

The issues that needed to be addressed were:

  • The origin of the leak and the adequacy of remediation measures taken to prevent similar occurrences in the future;
  • The extent to which the people and the environment of Kakadu National Park have been adversely affected by the leak;
  • The extent to which Energy Resources of Australia has complied with the reporting requirements specified in the Environmental Requirements that apply to the Ranger operation.

A number of other issues arose in the course of the investigation.