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Coal seam gas water leaks could be a problem for decades

Coal seam gas landscape in New South Wales, showing ponds holding wastewater. Jeremy Buckingham MLC/Flickr, CC BY

Coal seam gas water leaks could be a problem for decades

Recently reported leaks of water containing high levels of radioactive uranium from a coal seam gas (CSG) wastewater pond operated by Santos in New South Wales put the spotlight on an industry already wracked by controversy. Most concerns over CSG have to date focused on “fracking” — fracturing deep rock strata to get at gas in coal seams — but as the incident shows, waste produced by CSG wells and brought to the surface is another major environmental issue.

Contamination risk

According to the NSW Environment Protection Authority, the groundwater aquifer downstream of the leak contained 20 times the acceptable level of uranium for drinking water. This is concerning given the long timescales and effort involved in groundwater clean-up, and the fact that the region affected is an area of recharge for the Great Artesian Basin.

The type of water that resulted in contamination in this case (called “produced” or “co-produced” water) is generated in large quantities by all CSG wells, and it is usually of poor quality, containing potentially harmful levels of salt, radionuclides, metals and other contaminants. It appears that in this case such water was inappropriately stored in a leaky dam, allowing it to infiltrate and migrate into the underlying aquifer.

A 2011 study in the Queensland Murray-Darling basin projected that the amounts of additional salt brought to the surface by CSG wastewater were of similar quantity to all combined salts added from conventional groundwater irrigation and natural sources. If all this salt was allowed into waterways, it would effectively double the amount of salt entering the landscape.

Managing produced water and the salts and contaminants dissolved in it is therefore major issue for the CSG industry. It can be treated and reused for irrigation or industry, re-injected underground, or released into waterways following treatment. Treating CSG wastewater usually involves reverse osmosis, which produces “clean” water, but also concentrates contaminants in brine, which requires safe disposal. Some contaminants (such as boron) are hard to remove and are retained in the treated product water. In some cases methane can also remain in water after it leaves the treatment plant, adding to concerns over fugitive emissions.

All of these strategies involve technical challenges, and none are without risk. Most produced water management is conducted on a local scale, increasing the potential for small scale contamination if something goes wrong. Hence, the highest protocols of safety, risk management and monitoring need to be observed.

Trouble with regulating

Monitoring and management of produced water is not a simple task when considering the number of gas wells (at least 5,000) currently operating and under development around Australia. While policy on CSG wastewater has rapidly developed, there are still gaps. It is dealing with the rapid expansion of the industry that is the biggest challenge for managing water.

For instance, originally CSG operators were allowed to dispose wastewater in “evaporation dams” — now the practice is prohibited. We also still lack a rigorous and consistent method to asses environmental impacts of discharging treated water into streams — another strategy attractive for operators. In many cases the “clean” water produced by reverse osmosis treatment does not match the natural characteristics of stream water required for proper ecosystem functioning. The cost and technical challenges of reinjecting water back into wells has also proved prohibitive in some cases.

Then there is the problem of disposing the waste brine produced by water treatment plants. Currently locally managed, on a large scale this will be a major undertaking. Disposing waste brine from a few CSG wells may have little impact; but many thousands may well be highly significant. This underscores the importance of assessing the cumulative impacts of CSG (and indeed of all mining).

Mistakes do happen

The recent contamination issue highlights that mistakes can and do happen.

In this specific case there should be particular concern. The shallow aquifers in the area are important recharge area on the margin of the Great Artesian Basin. To date a relative lack of any major polluting land-use activities in the area has meant that the shallow groundwater is of high quality – and thus it is worthy of the highest levels of protection.

According to the Environment Protection Authority the pollution isn’t moving further into groundwater, which is encouraging. Monitoring and remediation will be required of Santos. However it must be understood that groundwater systems such as the one exposed here are slow to respond. In most settings groundwater is unlikely to migrate far within a period of months, or even years. Only after years of monitoring will be able to tell whether contamination is moving, diluting or breaking down.

We need CSG operators and environmental regulators to commit to monitoring local and cumulative effects, not just in the immediate aftermath of publicised incidents, but for decades, given the slow response of natural groundwater systems. Only then will we ensure the safety of our precious water in the long term.

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