Mine operators have proposed nine major new coal mines for the Galilee Basin in central Queensland. Those proposals currently being assessed by the Queensland government could significantly impact water resources on a regional scale. But they are not being assessed as a whole.
Already some projects have received approval, though there has been no co-ordinated assessment of their combined effects on groundwater and surface water. This is a major oversight that has gone unchecked because of flaws in the way mining projects have been assessed to date in Australia.
The Independent Expert Scientific Committee appointed by the Federal Government to look at new major coal and coal seam gas projects found there has been inadequate examination of cumulative impacts of multiple mining operations – as are proposed in the Galilee – on water resources.
This includes both groundwater and surface water. These are the lifeblood of agriculture and the environment, and are part of an interconnected system. Impacts in one area cannot be isolated from others.
The proposed Galilee projects include the Alpha mine and at least eight others under assessment or approved. They cover a stretch of land hundreds of kilometres long parallel to the Queensland Great Divide. Both open cut and underground longwall mining are proposed.
Both inevitably require high levels of interference with water – particularly, groundwater. In open cut mining, groundwater levels must be reduced by pumping to allow mining. If the Galilee mines go ahead, groundwater levels would need to be depressed in places by tens of meters at each site. In combination, this would likely create drawdown cones (regions where groundwater heights decline due to pumping), covering thousands of square kilometres.
Proponents of some mines acknowledge that after the mines are closed, recovery of water levels will be slow – in the order of centuries – and may never occur completely.
Longwall coal mining also fundamentally changes geological structure by inducing fracturing, which increases permeability and increases water leakage between layers. It can potentially cause serious land subsidence, and irreversible impacts on surface water and shallow groundwater. This has been extensively documented in New South Wales' Hunter Valley.
In the Galilee Basin, the proposed mines are close to areas where much of the recharge to the Great Artesian Basin is thought to occur. There may be effects on the groundwater flow field (the pressures controlling direction and rate of groundwater flow), that extend into these areas.
Shallower local aquifers are also important water supplies for agriculture, and are in many places connected to surface water resources. These would also be affected on a large scale across the region.
The projected total water consumption of the mines is tens of thousands of megalitres per year, but the estimates from individual mines are uncertain. In light of these issues, it is extremely concerning that cumulative impacts on water – that is, the combined impact of the full set of proposed mines – have to date not been examined.
Groundwater’s response to pumping depends on the properties of the geological materials in which it is stored, which can vary greatly. An aquifer’s response has no regard for the boundaries of a mine lease area – drawdown can and often does extend well beyond areas of pumping.
Many of the mines proposed are close together (including Alpha, South Galilee, Kevin’s Corner and China First). This raises the prospect of creating interfering and overlapping areas of drawdown, which could cause regional changes to groundwater flow. It makes no sense to assess impacts on a mine-by-mine basis, without examining combined effects of all proposed mines operating in concert.
We have the modelling tools to assess cumulative impacts of mining on groundwater. However, we need more data on the degree of connectivity between individual aquifer layers and their key hydraulic properties to run them effectively. Without this data, and unless we model the strata as a connected system that is simultaneously affected by combined stresses, the real impacts can’t be accurately captured.
The mining sector is increasingly affecting Australia’s precious water. Communities are reasonably concerned about long-term effects on livelihoods, the environment and our capacity to produce food. The federal government’s introduction of a better assessment process for coal and CSG impacts on water makes sense. But the process is clearly not working if individual mines in an area of intense new development can be approved on a staggered basis without a regional, cumulative assessment of total impact.
Everyone involved, from federal and state government, to the mine proponents and investors, should respect that this needs to be part of a proper assessment process. Statements about 'unnecessary green tape' by politicians are counter-productive to such a process, which is required in order to safeguard some of our most important national assets.
Matthew Currell is a lecturer in the RMIT in the School of Environmental Engineering, undertaking teaching and research predominantly in the fields of hydrogeology and environmental geochemistry.