When one of Australia’s largest landfills sought to expand, engineers were concerned about the potential impact on groundwater, as well as the overall site’s integrity. The new cell would need to be asymmetrical and utilize a steep-slope footprint, which presented challenges for designing in a secure barrier system and proper drainage management.
The South Cardup Landfill’s operator is Western Australian Landfill Services (WALS), a joint venture between SITA Environmental Solutions and Pioneer. Stringent environ-mental monitoring would be used in the construction of Cell 7. WALS turned to Golder Associates for design of the new cell; and Golder turned to NAUE’s geosynthetics.
South Cardup is a successful, energy-generating landfill with a history of strong environmental performance. It was one of the first landfill facilities in the world to sell carbon credits. Methane generated in the waste is harvested and converted to power. Annually, this process prevents the release of roughly 115,000 tonnes of CO2 – a dramatic number that is equivalent to removing more pollution than that generated by 31,000 cars. And the site provides power equivalent to 355,000 barrels of oils per year. Approximately 22,000 litres of leachate are collected.
For the new cell with its unusual shape, a double-liner system was selected to provide the best protection and maximize environ-mental functionality. Golder’s rigorous design calculations and testing led to the specification of a combination barrier system utilizing Carbofol® geomembranes and Bentofix® geosynthetic clay liners.
Due to the long, steep slopes, a high-friction angle was required for the primary geomembrane liner. A 2 mm, structured Carbofol® MegaFriction geomembrane was the right choice, due to its unique, embossed surface. The structured, uniform studs provide excellent contact with the slopes to prevent liner movement.
Bentofix ® BFG 5000 was selected for its robustness and high-swelling bentonite. It provides efficient, easy-to-install rolls, thus lowering both delivery and installation costs; and the self-sealing bentonite and strong shear resist-ance of the geotextile outer layers provide extraordinary durability for long-term barrier performance. Bentofix® BFG 5000 features a cover nonwoven geotextile that has been uniformly impregnated with a second layer of sodium bentonite powder, which can help the installation proceed more efficiently versus installations where the overlaps must be sealed with additional bentonite. Secured with NAUE’s containment technologies, the South Cardup site continues in its role as an exemplary installation in Australia and as an environmental leader in the global waste management industry.