What has caused the groundwater contamination?
Acid sulfate soils, which are soils that contain iron sulphides, are found naturally in the Stirling/Balcatta area. When exposed to air, iron sulphides oxidise and produce sulfuric acid. The soil itself can neutralise some of the sulfuric acid but the remaining acid moves through the soil, acidifying the soil, groundwater and eventually surface water. Areas where iron sulphide layers occur are waterlogged. Drainage and excavation of these areas expose the iron sulphide layers to air, which accentuates the rate of oxidation, and this concentrated acid can overwhelm the natural ability for the environment to neutralise it. This is what appears to have happened in the Stirling/Balcatta area. Lowering of the water table and sulphide soil disturbance has resulted in an increase in sulphuric acid in the groundwater. How long as the groundwater been contaminated? It is possible that there has been an acidic water issue in the area for at least the last 12 months. Water and Rivers Commission i
