Australasian Science: Australia's authority on science since 1938

Is Coal Seam Gas Polluting Groundwater?

Protesters called for no further expansion of coal and coal seam gas.

Protesters called for no further expansion of coal and coal seam gas outside the Gunnedah Basin Coal and Energy Conference held in Newcastle on 25 June 2012. Photo: Kate Ausburn

By Kate Osborne

Landholders are adamant that coal seam gas is contaminating their groundwater, but natural geological processes make their accusations difficult to prove. Now science is starting to fill in the cracks.

Brian Monk calls himself a coal seam gas refugee. At a protest rally in October 2011 he described the series of events that led him to conclude that his drinking water had been contaminated by coal seam gas activity.

He says the first thing that happened was his grandchildren started crying in the bath one night. “We hoicked them out of the bath and they had a ring around them. Everything that had been in the water was red like a burn, a scald. We stopped using the water for everything but washing clothes. Shortly after that, the stock (cattle) stopped drinking the water. Then a few months ago, the frogs that were happily living in the tank we pump the water from died.”

Brian’s water comes from a registered freshwater bore on his property. He claims there is a lot of gas suspended in the bore water: “We were lighting the gas from the bore... You don’t need to see it. You can feel it. Hold onto the inch-and-a-half pipe and you can feel the gas bubbling through.”

As the coal seam gas industry begins to ramp up production, the views of supporters and those opposing the industry have become increasingly polarised. Supporters believe the industry is safe and will create jobs, diversify rural economies and bring prosperity through mining royalties and investment. Detractors believe the industry will put Australia’s food security at risk, destroy rural communities and lead to pollution and depletion of underground aquifers, including Australia’s largest water resource, the Great Artesian Basin.

Landowners are understandably worried about any changes to water supply and water quality. Without access to underground water many rural townships, properties and industries will not survive.

Monk lives near Kogan in the Surat Basin in Queensland, in the middle of a giant gas field. The only thing he is certain of is that he can’t trust the quality of the water in his well. He doesn’t trust the Queensland regulators and thinks the coal seam gas industry is going to pollute the air and pollute the water. Whether or not coal seam gas is responsible for declining water quality in his well, Monk and others like him are looking for some certainty in their relationship with the coal seam gas industry.

A fundamental requirement for predicting the impacts of coal seam gas on groundwater is knowledge of where the water has come from, where it is being transported to and a pathway or mechanism for how that is happening. The main tool for determining the patterns of underground water flows is a groundwater model. For each location where gas extraction will occur, the underlying stratigraphy is mapped and the rates and quantities of water movement between the layers of rock and sediments is estimated. Predicted values are compared with observed values, and over time the model is gradually refined. For each water bore, the groundwater model aims to predict the extent that water levels will be reduced by changes in underground pressure gradients due to coal seam gas extraction.

Prof Chris Moran of the University of Queensland is a hydrologist on the expert panel advising the federal government on major coal seam gas projects. He says that the current state of knowledge about how water moves through coals is less well-understood than sandstones and soils, where traditional research efforts have been strong. He says, however, “that over large areas the exchange between stratigraphic layers is very minor”. In locations where coal formations are well separated from aquifers being used for water supplies, or where the layers are isolated from each other due to low permeability, groundwater models should provide good predictions of aquifer drawdown as long as the mapping and characterisation of the hydrological properties of the underlying stratigraphy is accurate.

In 2011 the Surat Basin was declared a Cumulative Management Area, which meant the Queensland government assumes responsibility for groundwater modelling and monitoring. It has defined a 2–5 metre reduction in water bore levels as the trigger for a “make good” agreement for the gas extraction companies to compensate bore owners for water loss. Of 21,000 bores, more than 500 are expected to trigger “make good” agreements.

The plan provides a framework with which landowners can evaluate the impact on their own water bore and see how that fits into the regional context. Early groundwater models produced by the gas extraction companies had errors of up to 50%, so validation processes such as bore monitoring not only help validate the model but give more certainty to landowners. Recognition that cumulative impacts on groundwater levels can occur, and need to be addressed through a managed and integrated framework, is a step forward for those affected by coal seam gas extraction in the Surat Basin.

The process for dealing with well contamination is managed within a similar framework, but is less transparent. A Department of Environment and Heritage investigation into Monk’s bore “revealed that there were narrow coal beds in the Kumbarilla Beds that (his) bore uses as an aquifer. As the water level in the aquifer decreases, the pressure also decreases releasing methane gas held in the coal seams. The investigations indicated that the decrease in water level in the aquifer was not caused by CSG activities in the area.”

Water testing of his bore identified high levels of hydrogen sulphide, a corrosive chemical that could have caused the children’s burns. Hydrogen sulphide can be released from coal or can be a product of decomposition of organic matter.

Monk’s experience bears some striking similarities to a scene in the 2011 movie Gaslands. The controversial documentary made by Josh Fox interviews people directly affected by water contamination and exposure to chemicals from the natural gas industry in the United States. In one scene, a contaminated water bore leads to a build-up of gas in the household pipes. When a cigarette lighter is held next to the stream of water from the tap, the gas explodes. Investigations by environmental agencies concluded that oil and gas activity were not responsible and that the gas was naturally occurring.

Where coal is close to or is a water-holding aquifer, or where the process of drilling has created a connection between previously isolated stratigraphic layers, a potential pathway exists for aquifer contamination. However, the proximity of coal and freshwater also increases the likelihood that an exchange of fluid or gas occurs naturally as conditions underground fluctuate, particularly if water is removed from the aquifer.

When incidents of water contamination and gas migration into household wells have been investigated in the United States, it has rarely been found that oil and gas activity was responsible due to a lack of baseline data defining “natural conditions” and difficulties to prove the pathway or mechanism that the contaminants have taken to reach the aquifer. In Garfield County in Colorado, for example, investigators agreed that saltier water from deep coal formations had mixed with the shallower freshwater and contaminated aquifers. The first study attributed causation to oil and gas activity as it found a correlation between increasing levels of salt and methane and the number of gas wells through time. A subsequent review did not agree, claiming the correlation was not statistically significant. The source of methane was also disputed, and there was insufficient evidence to establish pathways of transport.

For Australian scientists and regulators, the experience from the United States points to data gaps that can help avoid problems here, in particular, collecting adequate baseline data and using smart science to uniquely identify water from different stratigraphic layers and any pathways between them.

Constructing geochemical and isotopic fingerprints for water within coal measures and aquifers used for water resources is one method that can potentially distinguish between impacts from gas operations and “natural” processes. In Australia, fingerprinting has been used in a pilot study demonstrating the degree of connectivity between shallow aquifers and deep coal aquifers for a gas operation near Broke in NSW. The monitoring study combined standard hydro-geochemical analysis with analysis of stable isotopes (oxygen-18, deuterium and carbon-13) and radiogenic isotopes (carbon-14 and tritium). It found clear differences in the geochemical properties, water age and isotopic signatures of deep coal aquifers and shallow alluvial aquifers.

The methods used in Broke increase the lines of evidence available to investigators when existing hydrological or hydro-geochemical methods are inconclusive, as is commonly the case when coals and freshwater are in close proximity. Tracers can also be added to the fluids used for drilling to eliminate, if necessary, chemicals added during drilling as a source of contamination. However, site-specific baselines need to be established before oil and gas activity commences.

In the Surat Basin, baseline testing of water bores was introduced in 2010 when the Surat was already the largest producer of coal seam gas in Australia. The main target for coal seam gas, the Walloon Coal Measures, is also a target for water extraction and is directly in contact with or adjacent to the Condamine Alluvium.

Water levels in the Condamine Alluvium have been declining for decades due to unsustainable levels of water extraction for agricultural, domestic and industrial uses. The depletion of the aquifer through water extraction for agriculture and other uses is a “natural” explanation for the release of methane from the coal seam, so without detailed baselines the chance that Monk can establish a causal link with coal seam gas operations is slim.

A submission made to the United States EPA study on well construction and operation in 2011 said that wells within or adjacent to good quality water “can be made safe by careful planning, additional geological study, and close attention to fracture procedures. However, each well field must be considered on an individual basis.” The submission said that the only true evaluation was the relative value of hydrocarbons and water, and to date operators have been free to go after “cheap gas” regardless of the environmental cost.

The direct proximity of fresh water and coal is relatively uncommon. However, gas in the US is extracted from shale that is normally much deeper than the aquifer, while in eastern Australia the coals being targeted for coal seam gas are relatively shallow.

With tens of thousands of wells to be drilled in Queensland and NSW there is a risk of aquifer contamination every time a gas well is drilled through an aquifer to reach a coal deposit. If the construction of the drilled well is structurally poor there can be an exchange of fluids or gas along the drilling profile or well casing.

Problems with well or casing integrity can occur throughout the process of exploration, gas production and well abandonment. The most common faults are structural failure of the cement that maintains the isolation of stratigraphic layers, and failure of the joints between sections of metal casing.

Gas leakage from a the Argyle 2 exploration well drilled by Queensland Gas Company is an example of a failure of casing integrity. The well was first repaired in 2005, and then again in 2010 and 2011. According to QGC: “This well was drilled in 2001 and would have been constructed with much greater rigour had we applied today’s standards”.

New guidelines were introduced in Queensland in January 2012 for casing design and monitoring. It is unclear, however, what time frame applies to the gas company’s responsibility to seal the well or how long the seals are intended to last.

Queensland government regulators use a process known as adaptive management to help decision-making where there is a lot of uncertainty, or if the risks and facts are not fully known. As coal seam gas is a new industry, adaptive management principles are used in virtually every facet of the industry.

The processes that guide adaptive management are improved knowledge but also failures. Where failures are in the public eye or have an economic cost for the gas companies they are likely to be addressed quickly. This may not be the case if they affect only a few individuals, or if they are not easily detected and measured.

A good example is the potential threats to the biodiversity of the largely unexplored groundwater systems in Queensland. Dr William Humphreys of the Western Australian Museum is an authority on the biology of subterranean faunas, including those in groundwater. He says that the process of drilling can directly affect the properties of aquifers and bores. The drill profile, whether or not it is cased, can act as a conduit for organic matter to the groundwater. Cross-contamination of microbes between aquifers at different depths is likely to be pervasive, and there is a high risk of transferring microbiota.

The age of water in some deep aquifers is of the order of 105 years, and the overlying aquitards contain short range endemic species. As demonstrated by the more common threats of aquifer contamination, a lack of baseline data is a major weakness for any kind of impact assessment deemed necessary in the future.

Environmental regulation of the coal seam gas industry is a mammoth task. It is unprecedented in Australia for a new extractive industry of such large scale to unfold so rapidly. The challenge for scientists is large, but so are the opportunities to develop new methods and models that will help safeguard the environment and guide industry practice.

Kate Osborne is an ecologist and science writer.