September 1996, updated March 1999

ENVIRONMENTAL MANAGEMENT AND REHABILITATION
OF THE NABARLEK URANIUM MINE

The Nabarlek uranium orebody was discovered in 1970 by Queensland Mines Ltd (QML, now Queensland Mines Pty Ltd) in Arnhem Land in the Northern Territory, approximately 270 km east of Darwin. It was the first of the "new generation" of uranium mines to commence operations, the first to finish and the first to be rehabilitated.

Environmental protection was stressed at Nabarlek since before mining commenced, and everything proceeded with eventual rehabilitation very much in mind. During the life of the mine, QML worked together with Commonwealth and NT governmental agencies, the Northern Land Council (NLC) and Aboriginal land owners to ensure a high standard of environmental management, culminating in its decommissioning and rehabilitation.

It appears that QML has been able to achieve an excellent quality of rehabilitation, underlining the importance of prior planning. Although it will be some years before the revegetation reaches a state of maturity, the various governmental agencies, NLC and the land owners have expressed satisfaction with the process and its outcomes.

The cost of the work was about one third that of Mary Kathleen's rehabilitation (per tonne of U production in constant dollar terms). The project exemplifies the truism that mining is a temporary land use, and the company is confident that in the medium term the mine site will be virtually indistinguishable from the surrounding bushland.

The Nabarlek pit (right of centre) in February 1999,
with the waste rock dump site on the left, looking west.

In the EIS, QML proposed to mine the Nabarlek orebody in a period of about 6 months, stockpile the ore, construct a treatment plant at the minesite and to process the ore over a period of 8 to 10 years after mining was completed.

Measures for the protection of the physical environment included:

• containment of all contaminated waters,
• treatment of tailings waters by neutralisation and barium chloride,
• minimisation of land to be cleared and used,
• return of tailings direct to the open pit,
• ultimate backfilling of the open pit with waste rock, and
• landscaping and revegetation of disturbed areas on completion of operations.

Uranium mining in the Northern Territory is regulated by the NT Government under the Uranium Mining (Environment Control) Act 1979, which extends to control of water, vegetation and landscape protection and environmental monitoring.

The Commonwealth is able to keep an overview of the NT uranium mining operations through the Office of the Supervising Scientist. OSS functions involve research, the development of environmental standards and restoration measures, the communication between concerned parties and the provision of advice to the Commonwealth Minister for the Environment.

Planning for decommissioning started before the project commenced and continued throughout the life of the mine. From the beginning (1979) there was an obligation to plan the decommissioning and rehabilitation of the project and to document these plans. The first Decommissioning Proposal was completed and submitted to the governmental authorities at the end of 1981. Each year all rehabilitation matters were updated and it was furthermore necessary to have "detailed specifications" approved by the governmental authorities before any rehabilitation work could be undertaken.

In-Pit tailings Disposal
Nabarlek was the first open cut mine to have its tailings placed directly in the pit from which the ore was won. This was possible and appropriate due to:

• Precise definition of the small and high-grade orebody before mining commenced.
• The small size of the orebody enabled it to be mined out in one dry season.
• The Fox Inquiry recommendation for below ground storage of tailings.

• The tailings are almost as secure physically as the original orebody.
• There is no hydraulic head due to the position of the tails being below ground and thus less prospect of pollutants being leached.
• A greater depth of cover is more easily achieved, ensuring radiological safety.
• The tailings do not need double handling as they are deposited in their ultimate resting place.

The drains were inserted after the completion of ore treatment in 1988. Following heap leaching in 1989, some 150,000 tonnes of below ore-grade material was added. The remaining waste rock was then emplaced in layers. Significant consolidation was thereby achieved before and during the final stage of filling the pit in the 1995 dry season. The new surface was sown with seed in December 1995 and minor subsequent settlement was even.

Revegetation
Studies of old mine sites in the region made it clear that trees will reestablish over time. Thus, in scientific terms, the mine revegetation program is essentially one of speeding up a natural process; although in political terms it is much more. With this in mind, QML implemented much practical research, reinforced by the progressive rehabilitation and revegetation of disturbed areas no longer in use, during the production phase.

Before the commencement of the actual rehabilitation phase, QML had a revegetation plan which addressed all the above parameters and which was approved by governmental agencies and the NLC. Amongst the features of the final revegetation were:

• The preparation of the seed bed by ripping with a winged tyne of the type developed in Western Australia.
• The preferential use of waste rock instead of stored topsoil as the seed bed. This was due to the recognition that grasses and weeds tended to grow on the topsoil stockpiles in contrast with the waste rock dumps which supported a prolific variety of volunteer shrubs and trees.
• The use of a local seed collection contractor to obtain, mix and sow the specific seed mixes for the mine site. The mixes were determined after surveying numbers and concentrations of plant species in the Nabarlek area.
• The incorporation of the results of QML's germination rate test work in the determination of the seed mixes.
• The exclusive use of direct seeding, as QML's trials of tube stock had indicated a poor survival rate.
• The pre-treatment of hard-coated seeds by various methods.
• Two applications of fertiliser: the first with the seeding and the second later in the wet season.

Water Management
During the initial planning of the water management system, radium and heavy metals were viewed as the main solutes of concern. These were treated by neutralisation and, in the case of radium, precipitation by barium chloride. These processes worked well and metals were never of concern to the system. All contaminated waters were fully contained.

Water management during the decommissioning phase was complicated by both the volume of waters in the system and the presence of ammonium and sulphate in them. An extra effort was made to increase evaporative surfaces, by means of irrigation on the walls of the pit and within the ponds. This was successful and enabled evaporation to dryness in the ponds. The salt and sediment on the pond floors were then scraped up and placed in the pit. Thereafter, the clean rainwater which fell in the ponds was allowed to overflow. Despite the fact that Nabarlek experienced the highest recorded rainfall in the year of decommissioning (1995), the contaminated water was all successfully disposed of by evaporation.

The Nabarlek plant, evaporation pond and ore stockpile site in February 1999

Dismantling and Removal of Equipment
QML had to ensure the radiation cleanliness of items from the dismantled Nabarlek mill which were for sale. To this end the company, together with its consultant, devised a procedure of decontamination, registration and certification of radiation safety for every item which left the site. These procedures and certification were endorsed by the NT Departments of Health and of Mines and Energy.

All items from the dismantling of the mill were either placed in the pit (prior to filling with waste rock) or decontaminated and removed. No item left the site without a certificate of radiation safety.

Conclusion
QML believes that the success of the decommissioning and rehabilitation program at Nabarlek is a function of the time and resources devoted to planning.

Being the first of the new generation of uranium mines established at a time of high environmental expectations and not a little antipathy from some sectors of the public resulted in the imposition of a very high level of regulatory control. This included the requirement for decommissioning and rehabilitation to be planned before the project started and updated annually throughout the life of the mine. Involvement of a number of different government agencies and the NLC was also required.

QML found that holistic rehabilitation planning combined with clearly focussed and co-operative involvement of the other parties was both beneficial and cost effective in that the work, when actually carried out, went smoothly and below budget.

URANIUM INFORMATION CENTRE Ltd.
A.C.N. 005 503 828

GPO Box 1649N, Melbourne 3001, Australia
phone (03) 9629 7744
fax (03) 9629 7207