Are GCLs keeping pollutants in check?

Image credit: User: Wisconsin Department of Natural Resources

An international team led by environmental engineers from the University of Sydney are investigating whether geo-synthetic clay liners (GCL) are appropriate for protecting groundwater from highly-saline water.

Image credit: User: Wisconsin Department of Natural Resources
Image credit:
User: Wisconsin Department of Natural Resources

According to the latest media release issued by the University of Sydney, enormous amounts of high-salinity water are said to be produced by coal seam gas mining, which can result in unwanted groundwater contamination.

Abbas El-Zein, Associate Professor in environmental engineering at the University’s Faculty of Engineering and Information Technologies said recent application of GCL in the coal seam gas mining process has yet to be tested appropriately, despite the fact that a number of extraction, mining and waste industries in Australia and overseas are said to rely on GCL to prevent pollution.

“GCL is a bentonite clay, sandwiched between geotextiles, and engineered to have very low hydraulic conductivity, which means it can help contain contaminants and prevent them from causing damage to the environment,” explained Professor El-Zein.

The GCL’s performance is said to depend on numerous environmental and design factors such as the manufacturing process, the degree of hydration, the degree of grip between the GCL and the geo-membrane and chemical compatibility with the contaminant.

“Its use in landfills is accepted as best practice worldwide. But the conditions to which it is exposed at the base of a landfill are different to, and not as harsh as, those below a brine pond related to coal seam gas mining.”

According to El-Zein, GLCs have been used in landfills where waste places high downward pressures on the GCLs (in excess of 150 kPa), thus preventing desiccation and cracking. Also, landfills temperatures do not usually exceed 60oC, which is not the case for GCLs used on coal seam gas sites.

“In the brine ponds typically found at coal seam gas sites, there is very little pressure on top, temperatures can be as high as 90°C and salt can reach levels that are a few times higher than those found in the ocean. How does the GCL actually perform under such conditions? We need to find the answers,” he added.

Thanks to an Australian Research Council Discovery grant, Professor El-Zein and colleagues Professor Malek Bouazza at Melbourne’s Monash University and Professor Kerry Rowe at Queen’s University in Canada can now initiate a project based on research in unsaturated soil mechanics.

“Our team is conducting theoretical, experimental and computational research on the unsaturated behaviour of GCLs, which will give us a much better appreciation of the risks involved and, possibly, lead to new GCLs that can do a better job under such extreme conditions,” concluded the Professor.