Bentofix® Geosynthetic Clay Liner Safeguards WA’s Roebuck Bay

Project snapshot

Situated on the southern coastline of the Broome Peninsula, the WA Water Corporation’s southern wastewater facility has been under the spotlight in recent years following reports of contamination of the sensitive Roebuck Bay Marine Park.

Outbreaks of blue-green algae in the bay have been linked to excessive nutrient levels, possibly caused by groundwater pollution in the vicinity of the wastewater treatment ponds (WWTPs).

To rectify this, the Water Corporation has taken progressive steps to mitigate any risk associated with the WWTPs including:

• Environmental studies under the direction of the Department of Water and Environmental Regulation (DWER)

• Modification of Broome’s wastewater processing, and

• Relining one of the main waste ponds

It is the waste pond relining project that Global Synthetics got involved in, offering a Geosynthetic Clay Liner solution for challenging soil conditions at the site.

The challenges

Utilising Geosynthetic Clay Liners (GCLs) as a barrier system for wastewater treatment ponds is nothing new to the Water Corporation, but the Broome South location presented concerns around pre-existing groundwater chemistry.

Water Corporation engineers insisted on using a GCL capable of providing uncompromised sealing capabilities in the presence of calcites with high electrical conductivity.

This is because GCLs carrying low-grade sodium bentonite generally suffer elevated ionic exchange in such soil conditions which in turn leads to high permeability or poor sealing potential.

Bentofix® GCLs carry high-grade sodium bentonite which has been tested in chemical solutions with electric conductivities of up to 10.000 μS/s - much higher than those levels found at the Broome site - without any significant increase in permeability.

It is widely accepted that GCLs with ‘enhanced or altered’ bentonites have no track record of long term performance in benign environments let alone those exhibited at Broome wastewater treatment ponds.

Standards and regulatory bodies such as GRI and EPA publish warnings in relation to the use of modified bentonites in applications requiring long term performance.

The solution

Installation of approximately 30,000m2 of Bentofix® NSP 5100 was completed at Broome South by lining experts under a subcontract arrangement to a local energy services group.

Third-party testing of the Bentofix® GCL was completed by an independent body and all rolls passed independent quality assurance and were subsequently approved for installation by the project’s quality auditors.

Bentofix® GCL features a nonwoven cover geotextile and woven carrier geotextile, sandwiching a layer of bentonite clay. The exceptional, immediate swelling characteristic of powdered sodium bentonite provides a long-term barrier that can self-seal and rehydrate to renew the barrier, even if it has been exposed to desiccation.

The highly engineered geotextile outer layers provide outstanding protection against piping of the bentonite, durability to resist damage, and strength to manage the challenges inherent in barrier designs, such as for security on slopes and against fluctuating heads.