Defining achievable rehabilitation standards will ensure that the legacy from mine sites will not become a burden on stakeholders
Mine rehabilitation has been covered by an increasing number of newspaper articles in recent years showing that the topic is one of growing public concern (eg Slezak and Robertson, 2016). These articles suggest there is a growing sense of unease amongst the public that the industry is not taking rehabilitation as seriously as it should. Recent legislation such as the ‘Chain of Responsibility’ legislation that passed into law in Queensland this year indicates this unease has also passed to the political sphere as well (State of Queensland, 2016).
The issue of perhaps most immediate concern to the public is that many mines are not undertaking progressive rehabilitation. This increases the risk that the community may be left to do the job when these mines close. In the case of Queensland, this concern is amplified by the fact that, in the decade since progressive rehabilitation certification legislation was established, there has been only one case of rehabilitation sign off and this was for land impacted by longwall subsidence (Dale, 2015). There have been no cases involving areas of rehabilitated spoil or tailings landforms.
But it also seems there is considerable variation in the quality of mine rehabilitation now being undertaken, with some examples of very good outcomes and others where the outcomes are much less satisfactory. This suggests there is uncertainty concerning just what rehabilitation standards should be and, hence, what must be done before the legal requirements for mine closure can be met. This makes it difficult for the industry to fulfil its obligations as well as for regulators to confirm that they have done so.
The most widely used aspirational objectives are that rehabilitation after mining should leave sites safe, stable, sustainable and non-polluting to enable some ‘agreed post-mining land use is established to the satisfaction of the community and government’ (Commonwealth of Australia, 2006).
Two things can be said about this. The first is that these are important but ultimately vague objectives that are difficult to quantify. Without national protocols on how to measure these in some way, and integrate community approval and accurately monitor the degree of ‘satisfaction’, it is difficult to evaluate rehabilitation and determine whether it has been successful or not. Moreover, they leave open the possibility that the ‘bar’ for rehabilitation, particularly in outback Australia where the population is sparse and there are few local stakeholders, will gradually fall to a very low level at which point future land use options may be substantially reduced.
Secondly, it seems that in practice the actual rehabilitation targets are often being established late and towards the end of a mine’s life during a process of negotiation with regulators over mine closure. That is, they are not clearly defined – at least in quantitative terms – before mining commences.
Achieving acceptable rehabilitation
There are a number of rehabilitation issues deserving some more explicit prescriptions to provide guidance for both miners and regulators. The most obvious of these is defining the precise nature of the rehabilitation target. This is clearly dependent on the pre-mine condition and the relationship this has with what land uses are possible after mining. From our perspective, sites that remove natural vegetation should restore the pre-mine ecosystems. There has been some success at doing this (eg Koch and Hobbs, 2007) although it is unclear how many sites have set this standard as an objective (or have reached it). It is likely that most of the places where this is possible are those with relatively reliable rainfall. However, it is clear this objective will not always be possible or appropriate. For example, it will always be more difficult in drier, inland locations that have sporadic rainfall and may be inappropriate for landscapes that have been extensively modified prior to mining (eg grazing land dominated by fast-growing pasture species). Newly created landforms, such as rock dumps or tailings dams, will also require other targets when they are rehabilitated.
Some issues needing resolution
Mining frequently generates new topographies and landforms. Just what are the most appropriate design standards for features such as rock dumps or tailings dams (eg how steep? how high?) and how will these dictate rehabilitation objectives? But other topographic legacies, such as voids, pose arguably even greater dilemmas. These voids include large trenches, kilometres in length and having steep vertical faces (‘highwalls’) like those left at the cessation of open cut mining for coal. Some pits may end up being more than 300 m deep and extend below the natural water table. See, for example, the recent approval in Queensland for final mine voids of these dimensions in the Environmental Impact Assessment for the proposed Carmichael mine (State of Queensland, 2014). How should these be treated?
A major concern is the impact these voids have on water resources. Sometimes this can be beneficial, such as when voids are left to fill with water and thereby contribute to improving regional recreation opportunities. But what of those where any water becomes contaminated by salinity or toxic materials? Should such voids be refilled irrespective of their size and the considerable expense this will entail? How many Australian companies have budgeted for such expenses and how many performance bonds allow for this cost? In this context it is worth noting that there has been a requirement in the US since the 1970s for all final voids left after coal mining to be backfilled. The Surface Mining Control and Reclamation Act of 1977 determined that ‘all surface coal mining operations backfill, compact (where advisable to insure stability or to prevent leaching of toxic materials), and grade in order to restore the approximate original contour of the land with all highwalls, spoil piles, and depressions eliminated’ (SMCRA, 1977).
The objective of rehabilitation, and hence the type of revegetation undertaken, is a particular issue at sites where something other than the original ecosystem is being established. Just how many plant species should be re-established at such sites, what types of species should be used (natives or exotics?) and what proportions of each species should be added? It may be easy to quickly establish some kind of vegetative cover by relying on just one or two easily established and fast-growing species. But this can be risky: these may not be able to survive stresses of degraded topsoils with poor water holding capacity and subject to droughts or wildfire. How well will they be able to persist in the longer term?
A related question concerns just how much vegetative cover should be sought. Vegetation tends to be sparser and patchily distributed in drier landscapes, but how might a regulator decide on the difference between an appropriate level of plant cover for a particular site (for which there is no undisturbed reference site or benchmark) and a site where rehabilitation at that site has been attempted but been relatively unsuccessful?
Whatever the objective, the primary aim of all rehabilitation is to establish a successional trajectory where species are eventually regenerating by themselves and the new ecosystem is self-sustaining. This would indicate that legal responsibility for the site can then be relinquished. But the time this might take is unclear, especially in drier landscape where regeneration opportunities are only episodic (eg following rainfall that is enough to trigger germination and also sufficient to allow the new seedlings to grow and persist at the site). One obvious indicator is that there are multiple age classes of each species (ie there has been successive regeneration events after the initial rehabilitation program). Another might be that wildlife species are beginning to re-occupy the site. But evidence that an appropriate successional trajectory has been established is likely to be specific to each site, the species being used and the ecosystem being targeted by rehabilitation. It may also take some years. What is a reasonable time for monitoring to take place? A summary of these issues is given in Table 1.
Some in the industry might welcome the lack of prescriptions and argue that this uncertainty is only to be expected given the variety of environmental situations being faced and the different types of mining being conducted. But each of the questions in Table 1 have significant financial implications, and the public’s growing interest in mine rehabilitation and concern about who pays the costs probably means it is time to rethink the whole issue of appropriate post-mining rehabilitation standards.
As noted earlier, broad principles to guide mine site rehabilitation are well-known (Commonwealth of Australia, 2006). But it is also clear that these are not as widely followed as might be expected (Lamb et al, 2015; Roche et al, 2016). Part of the problem is that the principles outlining best-practice were not complemented by the development of a set of national rehabilitation standards, since this was seen as a state responsibility. An attempt to promote standards for ecological restoration within Australia has recently been published by the Society for Ecological Restoration Australasia (2016). These allowed for a graduated level of achievement (‘one star’, ‘two star’, ‘three star’, etc) reflecting the fact that funding or environmental circumstances might mean it can sometimes take time to achieve full ecological restoration and that incremental achievements should be recognised. The standards were not specifically designed for the mining industry but could be useful in developing appropriate mine rehabilitation standards.
The Society for Ecological Restoration Australasia standards prefer defining a target based on a nearby natural reference or benchmark site, but they also recognise that this is not always possible. This means other targets may be more appropriate provided these generate as wide a range of ecosystem services as is possible. Some of the criteria they suggest using to define and assess restoration success are the physical conditions at the rehabilitated site (topography, soil physical properties, etc), the species composition, community structure, functional attributes of the new ecosystem, exchanges with the surrounding landscape and the ability to control threats (eg wildfires, grazing animals).
Translating these criteria into elements of a checklist can be difficult. For example, it would be quite inappropriate to specify that a particular number of species must be established at a particular site given the variety of environmental conditions at different mine sites. On the other hand, it would also be inappropriate to leave the issue undefined until rehabilitation commenced and then argue that the standard was whatever had then been achieved. A more appropriate approach would be to establish standards before mining commenced based on knowledge of pre-mining climatic conditions and the types of soils and landscapes generated by mining. These would then lead to the formulation of some quantitative targets and a timeline.
When is ‘success’ achieved?
Successional trajectories towards a self-sustaining state are often disrupted by unexpected events. These can make it difficult for regulators to be certain that rehabilitation has been successful. Defining the various desirable states to be progressively reached along a timeframe helps indicate whether the ecosystem has deviated from an appropriate trajectory and identifies what management actions might be needed. Analyses of this type mean that managers (and regulators) must know the type of new plant community that is being targeted and the quantitative indicators of success at different stages of the post-mining succession. These indicators need to be based on credible evidence, and this means there must be agreement on what this might be, the thresholds that must be exceeded at different stages and how it might be established that the new ecosystem is self-sustaining.
The current objective of much contemporary post-mining rehabilitation of providing a safe, stable and non-polluting site able to be used for an agreed post-mining purpose is an important, though poorly defined, target. But even that is not being delivered, at least in Queensland, where not a single example of spoil or tailings rehabilitation has been recognised so far by regulatory agencies as having reached this supposed standard. Equally disturbing is the fact that there is no publicy accessible state or national database where we can determine how much land has been disturbed by mining, how much of this has been rehabilitated and just how successful the rehabilitation has been. We know the accumulated area is large and that many mines have the potential to severely pollute waterways and ground water. But we don’t know what ‘rehabilitation’ means or how functionally effective previous efforts have been. It is time these uncertainties are addressed at a national level in order to meet the Minerals Council of Australia target of providing ‘leadership in environmental practices and performance based on continual improvement and excellence’ (Minerals Council of Australia, 2016).
Commonwealth of Australia, 2006. Mine Rehabilitation; Leading Practice Sustainable Development Program for the Mining Industry. Department of Industry, Tourism and Resources, Canberra.
Dale N, 2015. The progress of rehabilitation. Environment Institute of Australia and New Zealand Inc. https://www.eianz.org/document/item/2938
Koch J M and Hobbs R, 2007. ‘Synthesis: Is Alcoa Successfully Restoring a Jarrah Forest Ecosystem after Bauxite Mining in Western Australia?’ Restoration Ecology, 15 (Supp 4), S137-S144. 10.1111/j.1526-100X.2007.00301.x
Lamb D, Erskine P E and Fletcher A, 2015. Widening gap between expectation and practice in Australian minesite rehabilitation. Ecological Management and Restoration. 16: 186-195