The CSG industry is governed by stringent water management regulations and legislation designed to safeguard landholders’ water supplies.
The industry has invested heavily in water studies. In 2016 it had more than 1100 water monitoring bores in place.
Independent studies conducted by the Queensland Water Commission and the NSW Government on the Namoi valley catchment area show natural CSG activity would have little impact on underground water supplies in most regions.
A report released by the Queensland Water Commission (QWC) in July 2012 shows previously reported figures on CSG-related water drawdown need to be revised down.
It finds that 97.5 per cent of the 21,000 bores in the Surat Basin will not see any impact arising from coal seam gas activity that could pose a risk to groundwater supply from a bore.
Out of 21,000 bores in the study area, 528 are forecast to see falls in water levels over and above the seasonal or climatic water level fluctuations and those caused by non-CSG activities.
The Great Artesian Basin
The Great Artesian Basin covers more than 70 per cent of Queensland and about one-fifth of Australia’s landmass. It contains several layers of sandstone alternating with layers of mud, siltstone and rocks. The water is held in the sandstone and there are three or four main aquifer systems within the Great Artesian Basin.
Water held in the Great Artesian Basin totals about 65 million gigalitres – equivalent to about 130,000 Sydney Harbours. It is estimated that CSG operations’ total water extraction in the Surat Basin portion of the Great Artesian Basin will average about 75GL a year over the next 20 years. Other areas of CSG production will have considerably lower water production than the Surat.
Gas is held in coal seams by burial pressure and water. When water is pumped out of the coal seam, total pressure falls and the gas begins to be released. Generally, gas production cannot begin until depressuring of a coal seam has begun.
Water in coal seams typically lies 200 metres or more below the water table used for stock and domestic purposes. It is distinct from water found in other non-coal seam aquifers and has different properties to normal artesian water. CSG production water tends to be relatively saline (usually it is brackish, like estuarine water).
CSG production extracts water from coal seams rather than from normal aquifers. But producing water from the coal seams will change the pressure balance between water in those seams and the water in overlying and underlying aquifers. This could induce some water flows between these aquifers and the coal seams, but intervening mud and siltstone formations will impede and limit any such flows.
The distance between coal seams targeted for CSG production and overlying aquifers used for cropping and drinking water is between 200 and 800 metres. In some areas where the impact could be considerable, the uppermost coals would not be tapped for CSG production.
Interconnection between coal seams and other aquifers is often very slight. But there could be localised effects on aquifers and bores in some parts of the Surat Basin where about half of this extraction is expected to occur. In some cases, some aquifers could be depleted by 6 to 20 metres.
Queensland CSG companies are legally required to make good any depletion of bore-water that could affect landholder activities.
Any measure taken to deal with the problem must be by agreement with the landholder.
In Queensland, every CSG company must also produce an Underground Water Impact Report that identifies likely impacts of its operations over the coming three years. The company is legally required to take action to deal with these projected impacts on landholders before the impacts actually occur. Government and industry will not wait to see a drop in water levels before taking action.
If a sudden change in water levels occurs, the Department of Environment and Heritage Protection can compel a CSG company to make good any impacts as quickly as possible. The government can also undertake work itself and bill the CSG company.
The burden of proof rests on the government and the CSG company, not the landholder. The priority is reinstating water supply in the shortest possible time.
CSG production is not expected to affect groundwater quality
CSG production is not expected to have a detrimental effect on groundwater quality, including salinity. A strenuous assessment process identifies any potential for CSG activities to affect groundwater quality. Under the Environmental Protection Act, if any concerns or impacts are found, companies will be required to take action to rectify these.