Higher-than-average acidity in soils and water can cause significant problems such as degradation of the natural environment, loss of land productivity and damage to infrastructure. Find out what the City of Stirling is doing to manage this issue.

What are acid sulphate soils?

Acid sulphate soils are naturally-occurring soils containing iron sulphides, typically formed in water-logged soils such as peat.

These soils are harmless until they are exposed to air, through activities such as excavating or dewatering that can disturb the soil, which causes these sulphides to produce sulphuric acid.

This acid can then release heavy metals (including, arsenic, aluminium and iron) and other contaminants that can cause significant problems such as degradation of the natural environment, loss of land productivity and damage to infrastructure.

Since the problem was first identified in 2001, the City of Stirling has undertaken significant research into nature, extent and remediation of acid sulphate soils.

For an explanation of the 2 classes of acid sulphate soils and how to manage them, download the Acid sulphate soils information sheet (PDF) .

For more information on acid sulphate soils, please contact the Department of Environment and Conservation on (08) 6364 6500.

Development applications

Where development applications are submitted for sites identified as containing acid sulfate soils, the City of Stirling may request the applicant submit and Acid Sulfate Soils Applicant Self-Assessment Form. Refer to the Planning and Development section of this website for more information.

Acid lakes bioremediation

To reduce acidity in our water and soil, the City of Stirling has partnered with Edith Cowan University and installed a groundwater treatment system on an island in the southern lake at Spoonbill Shearwater Reserve.

The higher-than-average acidity soils have been caused by land development in the area, releasing previously stable soil minerals, including iron and arsenic, into local groundwater.

The innovative groundwater treatment system uses a combination of liming technology developed by Curtin University and biological remediation technologies developed by Edith Cowan University. This is a pilot project and the first of its kind in the Perth metropolitan tegion.

The treatment process follows 3 principal phases:

1. Neutralisation
The acidic water is neutralised as it passes through a vat where lime (sodium hydroxide) is added, and then clarified in a settling tank.

2. Bioreactors
The neutralised water then passes through 2 organic bioreactors to lower the oxygen levels of the water and to convert heavy metals and arsenic into stable minerals. Essentially, this phase reverses the oxidation process that formed the acids in the first place. The bioreactors are stimulated with rotting potatoes and hardwood mulch from tree pruning.

3. Aerobic filtration
The treated water is re-aerated by biofiltration using native reeds and rushes of the lake. 2,500 plants were purchased by the City of Stirling and planted by students from Edith Cowan University for this purpose.

Results so far indicate that the system successful, with lake water readings changing from highly acidic to slightly alkaline. Additionally, sulphate concentrations have been reduced by 90%, nitrate concentrations by 73% and arsenic concentrations by 40%.