Shutdown & Rehabilitaiton
The ability to successfully rehabilitate mined areas is fundamental to the industry’s social licence to operate.
THE USE of land for mining stretches back to the 1840s in Australia.
From the early silver discoveries in South Australia to the gold rushes of Victoria and the recent WA boom – mining has always been a feature of the country’s economic landscape and a significant contributor to its wealth.
Mining continues strongly today, however one element has only recently achieved prominence: the issue of how to rehabilitate the land.
In February this year, research by a Melbourne public policy think tank suggested that there were more than 60,000 abandoned mines in Australia, with only a handful ever being completely rehabilitated.
As the recent mining boom draws to a close, environmental issues become further entrenched in political agendas and the everyday lives of people and business.
Mining companies are increasingly beginning to factor in both the necessity and costs how to restore the land to an acceptable standard once all resources have been extracted.
Although most States have their own legislative requirements that encourage this aim, no uniform laws exist at present and this can result in uneven restorative outcomes.
According to an industry report commissioned by the Minerals Council of Australia last year, the ability to successfully rehabilitate mined areas is fundamental to the industry’s social licence to operate and a foundation for demonstrating the industry’s commitment to operating responsibly.
“During development and operation, mines bring significant benefits to regional areas through economic development, capacity building and infrastructure.
However, mining operations are finite in nature and mining is only one of many alternative land uses over time,” the report stated.
“The Australian minerals industry recognises its responsibility as a temporary custodian of land to contribute to sustainable land use outcomes.
“It is the industry’s goal that previously mined land is available for future economic activity, conservation or community use.”
Similarly, according to the Federal Government’s Mine Rehabilitation Handbook, mine site rehabilitation should now be viewed as an integral component of a mining company’s sustainable development strategies and considered a key performance indicator against which the company’s environmental performance is judged.
The handbook states any mine site rehabilitation plan should be designed to meet three key objectives:
1) the long-term stability and sustainability of the landforms, soils and hydrology of the site.
2) the partial or full repair of ecosystem capacity to provide habitats for biota and services for people.
3) the prevention of pollution of the surrounding environment.
Engagement with landholders, local communities and other stakeholders is essential in the development, implementation and review of mine closure and rehabilitation strategies for mining companies.
Community input helps shape final land use objectives for closed mines.
From site closure to rehabilitation
According to the Fraser Institute the mine closure process typically consists of several steps:
Shut-down:
Once production stops, the number of workers is reduced, and only a small labour force is retained to permanently shut down the mining equipment.
In some cases, the mining company may provide re-training or early retirement options to their workers before the mine is closed.
Decommissioning:
Small crews or contractors decommission or take apart the mining processing facilities and equipment.
Pipelines are drained, equipment and parts are cleaned and sold, buildings are repurposed or demolished, warehouse materials are recovered, and waste is disposed of.
Remediation/reclamation:
The objective of reclamation is to return the land and watercourses to an acceptable standard of productive use, ensuring that any landforms and structures are stable, and any watercourses are of acceptable water quality.
Reclamation typically involves a number of activities such as removing any hazardous materials, reshaping the land, restoring topsoil, and planting native grasses, trees, or ground cover.
Post-closure:
Monitoring programs are used to assess the effectiveness of the reclamation measures and to identify any corrective action that may be needed.
In addition, mines may require long-term care and maintenance after mine closure such as ongoing treatment of mine discharge water, periodic monitoring and maintenance of tailings containment structures, and monitoring any ongoing remediation technologies used such as constructed wetlands.
Perth-based Griffin Coal follows a four step process that involves “returning the land to its natural state post-mining through strict, well researched strategies of revegetation and the regeneration of natural ecosystems”.
Work to restore disturbed areas is carried out progressively as soon as practicable with the objective to create a structurally stable landform capable of future productive use.”
Rehabilitation involves a comprehensive process of classifying overburden material; land recontouring, seeding and regeneration as follows:
Overburden Material Classification:
Overburden material is classified according to its potential to cause geochemical impacts (acid rock drainage) on the environment.
Dumping of waste material is undertaken so the best materials end up near the surface of waste landforms and the other material is encapsulated in the middle.
Land Recontouring:
When landforms are no longer needed for mining or dumping purposes the slopes are recontoured to around 10 degrees to control surface runoff and to ensure a stable slope.
Topsoil is then spread to a depth of 150 millimetres before the area is contour ripped, fertilised and seeded with local natives.
Seeding:
Rehabilitation areas are seeded at the break of the winter rainy season, and can initially be susceptible to erosion damage until germination and root development occurs.
Regeneration:
As native species do not germinate and develop until the following spring, native bush species comprising grasses; groundcovers, shrubs and trees, are sown together with a “nurse” crop of cereal rye.
The cereal rye germinates quickly and stabilises the surface through the winter and the natives then emerge the following spring.
The seed mix includes Jarrah, Wandoo, Flooded Gum, numerous Acacias and understorey species.
Hazelwood Rehabilitation Project
The owner of Victoria’s recently closed brown coal Hazelwood power station and mine in the La Trobe Valley – French global energy provider ENGIE – has revealed the rehabilitation of the mine is expected to cost $439 million, with the cost for remediation on the power station site $304m.
It will be the first mine in Australia of its type and size to be rehabilitated and is expected to take a number of years to complete.
Current rehabilitation work at the site includes continued overburden stripping in the Northfield with the bucket wheel excavator, Dredger 25.
This overburden is being relocated to cover coal and also to place up against the existing batters to assist the long term stability.
Dredger 25 is operational and rehabilitation of the eastern batters is continuing with the cutting down of the coal batters, reshaping and re-profiling them to a 3:1 gradient.
The company is also in the process of removing redundant infrastructure and erecting new infrastructure, which includes relocating roads and powerlines.
ENGIE will be providing an exclusive update and interview in The Australian Mining Review in the first half of 2018.