This article is the third article of the “Mining and the Environment Series” released by Global Road Technology. In the first article we identified the range of effects that mining practices have had on the environment in the past in general. The second article focussed on real life cases where the environmental impact of mining practices and lack of rehabilitation were extreme. This article will conclude the series, and will focus on real life cases where rehabilitation has been successful. This article will provide a guide as to the various methods available for different environmental issues, which can be implemented to rehabilitate the over 50,000 mines that have been currently abandoned in Australia.
Alcoa rehabilitates approximately 600 hectares each year at its Huntley and Willowdale Bauxite mine, with their superior knowledge on mine rehabilitation.
Since the beginning of the Alcoa mining operation, one of the major objectives of the mining program, was to restore 100% of the environment that was to be disturbed as a result of the mine. The first rehabilitation program was completed in 2001 when over 101% of botanical species returned to the rehabilitated area. Yes 101%, on top of the fact that every species that was cleared at the beginning of the operation, returned after the rehabilitation program, and there was evidence of new native species inhabiting the area.
However, to achieve such a high-rehabilitated floral recovery percentage, Alcoa had to invest and develop a range of innovative techniques, which included their own nursery-grown plants from seeds, cuttings and tissue culture. The nursery utilised a computer controlled air-seeding machine that efficiently spread seeds into freshly cut soil for superior germination rates.
Initially, a study was performed prior to the mines establishment to understand the dynamic and state of the environment in the area. The conclusions of the study found that the area has difficulty in producing viable seeds, and even if the seeds are viable, there are challenges to effective germination. These plants are referred to recalcitrant species, however, they have been found to play an essential role in the forests ecosystem.
From cuttings alone, there have been over 50 000 plants that have grown from the seed cultures each year. Annually, a population of fresh plant seeds are taken from the area and are stored in their facility to assist in floral propagation during the winter. We see the effective technique that Alcoa utilised involves consistent monitoring, recording data on environmental state throughout the project, and planning for the future. In the figure below we see the summary of the project.
Planning for rehabilitation for the Coal and Allied Mine began in 1990 in the Hunter Valley, which is before mining operations even began. Over 165 hectares of farming land was mined over the course of the mines working life.
Prior to active mining practices, there was a mapping of the soil profile, which was carried out on the topsoil and subsoil profile, which were both stockpiled separately. As an area was completed with mining practices, rehabilitative measures occurred immediately. By 2003, backfilling of the eastern section of the alluvial land was complete and rehabilitation commenced. The rehabilitation technique utilised in the area included returning of the stockpiled subsoil and topsoil which were replaced to a depth of 1.5m to accommodate crops with deep roots.
Furthermore, there were metrics put into place to ensure that rehabilitation was not only completed, but also valid over a long term. Coal and Allied mine were required to demonstrate that the rehabilitation of the area was rehabilitated long term, by producing an equivalent production yield for three consecutive years, and they were to be compared to production yields prior to the mines establishment. The metric test found that the post mining operation crop yields were above average for three consecutive years, compared to the yields prior the mines establishment.
Throughout the rehabilitation there was scheduled and consistent surveys to ensure progress was gradual and consistent. What is evident in this case is that throughout the entire life of the mine the state of the environment was a high priority. In the photos below we see the extent of regeneration and rehabilitation.
The Renison Tin Mine has been mined since 1890. The challenges of this particular mine were the tailings comprised of a liquid slurry of fine sediment particles, and was produced as a by-product of processing minerals. The major threat that it poses is that these by-products can oxidise in the presence of air and water, resulting in a concentrated acid. This acid that is produced as a result is very harmful to the biosphere.
The major environmental issue at the Renison Bell Tin Mine was the water quality in Lake Pieman. It was recorded at various times throughout the operation of the mine of considerably high levels of sulphuric acid. Rehabilitation was achieved when CSIRO, and Renison collaborated to restore the area to its original state, which occurred after the mine was exhausted.
The objective in this case was to turn the post mining area into a wetland, to allow the natural restoration of nutrients in the water. The rehabilitation objective was achieved by identifying a suitable capping material that were able to be separated during the mineral processing. This material was spread across the beaches affected by tailing. Grasses and rushes were subsequently planted on these beaches to further stabilise the soil structure, and initiate the gradual development of a self-sustaining wetland.
The sulphate levels that originated from the mine were found to be over 1500mg/L in 2002 at Lake Pieman, which was prior to the rehabilitation project. However, the post rehab concentration levels were found to have fallen to 70g/L by 2006, at which they were sustained until 2013. In 2014, the concentration levels of sulphates had dropped by 90% since the 1994 level, and were as a result deemed acceptable for discharge. The metrics in this case involved consistent monitoring of the wetland to ensure growth was occurring, as well as filed test data of the nutrients at the wetland. In the photos below we see the changes in the environment over the course of the introduction of, usage of and post rehabilitation of the mining operations. This is followed by a summary of the land uses and key success factors.
The Ginkgo Mine was a mine based in the Murray Darling, the rehabilitation methods utilised here are similar of that found at the Coal and Allied Mine. Initially, the topsoil was directly removed into stockpiles when the mine was established. The timber vegetation that was cleared was stockpiled for re-use as faunal habitat and to stabilise sloping landforms.
Initially, vigorous research was undertaken to understand the areas habitat, and climate. It was identified that the area suffers from heat of over 40 degrees over the summer and only approximately 270 mm of rainfall over the year. They found a fragile nature of overburden materials, which were prone to tunnelling and erosion, which ultimately hindered stability and regrowth of vegetation.
Cristal mining engaged into the early stages of rehabilitation by modelling erosion and landform design to create a short and long term plan to minimise environmental impact through the extent of the mining operation. The next phase of research was initiated to identify the most effective seed mixes, and most effective techniques as well as seeding locations for optimal vegetative propagation. The data from these tests were utilised to identify the optimal soil depths for the re-establishment of soil profiles.
The rehabilitation profiles were specifically designed to correct the gradient of the land to minimise erosion rates. The timber and topsoil that were initially cleared for the mine site, were then utilised to create a growth medium and protective microclimate for the seeds to propagate. Any larger flora, such as trees, are re-seeded standing to re-establish lost habitat for fauna in the area.
The challenges of this rehabilitation were unexpected storm events, such as severe rainfall, extreme drought, bushfires and locusts plagues, which caused flooding and erosion. However, the rehabilitation process was already in progress whilst these events were occurring, therefore the damage from the events were heavily minimised.
Due to the harsh conditions of the environment, at first there were difficulties in seed propagation. All flora that was replanted had difficulties re-establishing itself. The company altered its strategy by focussing on planting smaller stands of tube stock that can be manageably watered in a dry and arid environment.
The primary metrics for this project was consistent monitoring of the entire area, and consistent field-testing to ensure that the environment is able to sustain itself. There have been yearly observation studies that evaluated the germination of the flora in the area. It has been recorded that annually the regeneration rate is actively rising, due to the harsh conditions, the propagation is occurring gradually. These metrics have played a key role in assisting and ensuring in long term success of the rehabilitation of the Ginkgo Mineral Sands Mine.
For more information, refer to the reference and reading list provided below.
References and Further Reading:
All photos source:
Mattiske Andrew, 2016, Mine Rehabilitation in the Australian Minerals Industry, Minerals Council of Australia, https://minerals.org.au/sites/default/files/MCA%20Publications/Mine%20rehabilitation%20in%20the%20Australian%20minerals%20industry%2025%20Feb%202016.PDF
Primary Information Source: https://minerals.org.au/sites/default/files/MCA%20Publications/Mine%20rehabilitation%20in%20the%20Australian%20minerals%20industry%2025%20Feb%202016.PDF
OTHER References:
https://minerals.org.au/sites/default/files/Mine%20rehabilitation_Update%20AUG%202018_FINAL.PDF
https://www.tandfonline.com/doi/full/10.1080/14615517.2016.1176407
https://www.mining-technology.com/features/australian-mine-rehabilitation/
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