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Tailings storage facilities
Tailings are by-products of processed ore minerals.
Depending on the type of ore and the method of processing, tailings could contain toxic and environmentally harmful substances or could be totally benign.
Tailings are stored in different types of tailings storage facilities (TSFs), with the most common TSFs having embankments to contain the tailings. Mined-out open pits are also used as TSFs with no containment embankments. Tailings are also stored within mine waste rock dumps.
Regardless of being toxic or benign, sudden release of tailings could cause significant safety, health and environmental hazards. Such incidents could occur if the TSF embankments are not designed, constructed, operated and closed to comply with acceptable standards.
In other countries, several catastrophic failures of TSF embankments have occurred and have destroyed lives, property and the environment.
TSF with an embankment
Department of Mines, Industry Regulation and Safety
In-pit TSF with no embankment
Department of Mines, Industry Regulation and Safety
TSFS in Western Australia
There are about 500 TSFs in Western Australia, with the majority located on relatively flat ground in low rainfall regions of the State. The flat topographic and dry climatic conditions reduce the potential for sudden failures of TSFs.
Nonetheless, minor failures in the form of embankment erosion and overtopping (where material flows over the embankment) have occurred without causing much damage. To reduce the risk of TSF failure, a stringent regulatory process is followed in Western Australia.
The process includes:
thorough scrutiny of the design proposals for any new TSFs and any changes to existing TSFs, before granting approval for construction
enforcement of the construction quality control measures to ensure compliance with the approved design and relevant standards
mandatory twice daily inspection, plus ongoing maintenance and record keeping by nominated mine site personnel during TSF operation
mandatory periodic review and audit of the TSF performance by third party experts
regular inspections and audits by safety, health and environment regulators
enforcement of stringent closure requirements before the TSF operation is ceased permanently.
The process in WA
Design
For regulatory approval, the design process must begin by assigning a hazard rating (high, medium or low) to the TSF.
The hazard rating reflects the potential impact on safety, health and the environment in the event of TSF failure, and takes into account the location, ground conditions, tailings tonnage, type of tailings, deposition method, surface water bodies, rainfall runoff, groundwater conditions, and the surface area of the TSF.
TSFs are then categorised into 1, 2 and 3.
All TSFs with a high hazard rating fall into Category 1. Any TSF with an embankment higher than 15 metres, regardless of its hazard rating, also falls into Category 1.
Only the TSFs with a low hazard rating and less than five metres in height fall into Category 3. Other TSFs will be Category 2.
TSF designs must be supported with details of technical data, analyses, construction method, quality control and operation procedures.
Category 1 requires the highest level of details, followed by Category 2 and 3. The details must conform to the Department's Tailings storage facilities in Western Australia – code of practice published by the Department and TSF guidelines published by the Australian National Committee on Large Dams (ANCOLD).
Before being approved, the designs are thoroughly scrutinised by the Department to ensure regulatory compliance. TSF proposals are also reviewed by the Department of Water and Environment Regulation and other relevant government agencies.
Construction
During construction, suitably qualified and experienced specialists are engaged for construction quality control. The specialists prepare a detailed report confirming compliance with the approved design and relevant standards and then submit the report to the Department for review.
Non-compliance with the approved design and the relevant standards could result in the annulment of the approval for TSF operation.
Operation
Operation of TSFs comply with the approved operating conditions, specified at the time of the design approval. Failure to comply could result in the issuance of directives to cease the TSF operation.
Closure
The closure requirements include third party review of the TSF status, and site rehabilitation measures such as reshaping, capping, runoff control and revegetation.
These measures take into account the chemical and physical stability of the TSF and future land use of the area. The performance of these measures are monitored for an extended period, before accepting the closure and relinquishment of the TSF sites.
Introduced in early 1990s, the requirements have been continuously improved through a proactive consultation between the industry, researchers and regulators. This process has been recognised as one of the best in the world.
