Environmental Impacts of Unconventional Gas
- Contamination of groundwater and surface waters from fracking and drilling fluids (which contain toxic chemicals) and from waste/produced water.
- Contamination of water from methane.
- Impacts to water systems where water is extracted for use in gas production.
- Impacts to rivers and groundwater levels due to dewatering.
- Methane contamination of soil, leading to anoxic conditions.
- Air pollution from gas emissions.
- Emission of greenhouse gases, particularly methane, contributing to climate change.
- Extensive habitat disturbance and land use.
- The creation of earthquakes from fracking.
The techniques involved in the extraction of unconventional gas, particularly hydraulic fracturing, have a high potential to create major environmental impacts, including:
- The diffuse nature of unconventional gas throughout the rock, which requires a much more invasive and larger scale of operation compared to conventional gas.
- The need for many more drilling wells (often >1 well per km2) compared to conventional gas extraction (<1 well per 10km2).
- The need for an energy intensive industrial process.
- The use of hydraulic fracturing (essential for tight gas and shale gas operations) which has many potential environmental impacts.
- The use of toxic chemicals during hydraulic fracturing and drilling, including known carcinogens.
- The large volumes of water needed for hydraulic fracturing.
- The extraction of water (dewatering) from the coal-bed during coal seam gas production to depressurise the seam and allow for gas flow; this extracted water, known as produced water, is highly saline and can contain trace elements and organic compounds.
- The disposal of large volumes of waste water and produced water which can contain fracking chemicals, salts, metals and other organic compounds.
- The disposal of waste salts produced as a by-product.
- The risk of blowouts from wells (eruption of high pressure gas during drilling causing fluids to be expelled), which can cause contamination and potentially cause fires.
The risk of water contamination from unconventional gas production is one of the most serious environmental concerns. Water contamination can occur to both surface waters, including rivers, creeks, and lakes, and groundwater systems, affecting aquifers and drinking wells.
Contamination can be from fracking fluids, drilling fluids, methane, waste water, and solid wastes. Studies have shown contamination of waterways from these sources causes death or serious health impacts to aquatic and terrestrial wildlife, livestock and vegetation, and can cause serious health impacts for people in surrounding communities. As fracking fluids can contain hundreds of chemical additives, many of which are known to cause cancer in humans, the contamination from this source is particularly concerning.
Water contamination can occur due to spills at the surface, leaking of fracturing fluids or wastewater from wells and pipes, discharge of insufficiently treated waste water, or direct movement of methane, fracturing fluids or wastewaters upwards through the rock body.
Potential sources of water contamination that can arise from unconventional gas extraction
In the US, where the unconventional gas industry has the longest history, the contamination of water systems surrounding gas developments is well documented. In Australia, evidence of water contamination from unconventional gas operations has also been growing.
Methane contamination of water is a serious environmental hazard which has been well documented, particularly in surrounding water wells in settlements nearby gasfield operations. Methane levels in drinking water have been found to be high enough to be an explosion hazard, and can be set alight. River systems kilometres away from areas of gas production have also been found to be contaminated with methane. For example, in the Condamine River in Queensland, which runs through the most developed coal seam gas fields in the Surat basin, the bubbling of methane gas has been observed in at least three different locations.
The disposal of wastewater, which can contain toxic chemicals, high salt loads and toxic heavy metals, is extremely problematic, and often leads to the contamination of surrounding waterways. In many cases, wastewater is directly discharged into surface waters. There is no safe way of disposing wastewater. In the Bohena Creek in the Pilliga, water sampling found elevated levels of seven compounds where treated wastewater was discharged, including significantly elevated levels of ammonia, cyanide, and boron. A biodiversity survey linked the pollution of streams from the discharge of treated wastewater to the deaths of aquatic vertebrates.
Surface spills of wastewater, fracturing fluids and other substances are well documented in the US and worldwide. For example, in the Pilliga, many spills of toxic fluids into waterways have been documented, including 10,000L of wastewater, 250L of algaecide from a ruptured pipe, and major spills from storage ponds.
Sedimentation of waterways from unconventional gas production is another major recognised threat to aquatic ecosystems. Increased sedimentation in rivers and streams surrounding gas developments can result from construction activities and the altering of system flows. In Australia, many streams are already been heavily impacted by sedimentation, and the worst affected rivers are those in agricultural areas where the major gas developments are operating. The added sediment loads from gas operations could therefore be a significant threat to already stressed systems.
Over-consumption of water
The production of unconventional gas requires the consumption of huge amounts of water, particularly during fracking. Each well may consume up to 5 million gallons of water (almost 19 million L). This water can come from surface waters such as streams and rivers, or from boreholes that draw from underground aquifers.
The large amounts of water consumed in CSG production can significantly affect surrounding water sources and ecosystems. Extraction from streams can adversely affect biodiversity through lowering water quantity and impacting hydrological flows, at regional and local scales. The water table can also be significantly lowered if extracting from groundwater sources. The extraction of ‘produced water’ from coal seam beds during production can also have a large impact on water levels and hydrology, and has been shown to result in the depletion of aquifers. Surrounding springs and aquifers are also affected by water extraction, including overlying and underlying aquifers. For instance, in the Surat Basin in Queensland, studies have modelled that aquifers surrounding coal seam gas operations will be significantly impacted, and that large ‘de-pressurised’ zones will be created.
The impacts of over-consumption and depletion of water are of particular concern for Australia, where we already face water shortages and major issues of over-extraction. All of the major coal seam gas operations across the country occur in areas where water resources are already stressed.
Greenhouse gas emissions
Gas has widely been considered to be a “cleaner” fossil fuel compared to coal, largely due to lower emissions of carbon dioxide. However, the level of overall greenhouse gas emissions is a source of active debate among scientists. Some scientists consider that greenhouse gas emissions from unconventional gas have been significantly underestimated, and that the full life cycle emissions could be comparable with or even higher than coal.
Fugitive emissions, or unintentional emissions, of methane can occur from several sources, and are often unaccounted for or underestimated. For instance, the diffuse release of methane through the soil can be large, but is generally discounted by the industry. Official industry estimates of fugitive emissions are therefore thought to be extremely underestimated.
Recent scientific studies in Tara, Queensland, have found fugitive methane emissions to be high, which significantly increases the GHG footprint.
The exact composition of hydrocarbon concentrations in unconventional gases can also vary significantly and is generally unquantified. Therefore, greenhouse gas emissions from the end-use combustion of that gas can vary significantly, and the GHG footprint may be significantly higher than industry statements.
Accurate estimation of the overall greenhouse gas emissions from unconventional gas is constrained by uncertainties.
Unconventional gas developments impact habitats and biodiversity through the direct clearing of land, habitat fragmentation, the potential spread of invasive species, and an increased risk of fire. Unconventional gas developments have a larger scale of industrial operation and land use compared to conventional gas. Access roads, pipelines, wells and other infrastructure require the clearing of large tracts of land. Unconventional gas requires a large number of drilling wells, with often more than one well per km2. The negative impacts of habitat destruction and habitat fragmentation are well documented, and remain one of the leading causes of biodiversity loss globally.
An Australian report suggests that the impacts of coal seam gas developments on terrestrial habitats could be severe, with particularly bad impacts on landscapes where extensive vegetation clearing and fragmentation have already occurred, such as in many of the rural areas of CSG operation. Areas of high conservation value are also under threat from developments, such as the Pilliga forest, which is a national biodiversity hotspot and provides habitat for 48 threatened species. During the exploration phase, 150 ha of native vegetation was cleared and 1,700 ha of native vegetation was heavily fragmented, and the full production phase would involve the clearing of at least 2,400 ha of native vegetation, and the fragmentation of an area of 85,000 ha.
Coal seam gas development in Queensland, showing the high number of drilling wells and resulting habitat fragmentation
The ABC Four Corners program provides a good introduction to the issue in Australia:
The attached PDF (below) provides a summary of the potential environmental impacts arising from unconventional gas extraction, and the state of knowledge and research relating to these risks.