Acid Sulphate Soil Monitoring & Assessment

What are Acid Sulphate Soils?

Acid Sulfate Soils (ASS) are naturally occurring soils and sediments containing iron sulfides, primarily pyrite (FeS2).  In an undisturbed and reduced (i.e. waterlogged) condition they are relatively harmless and pose little to no risk to the environment. However, when disturbed and exposed to air, either directly (e.g. excavated) or indirectly (e.g. in response to groundwater dewatering), they can oxidise to produce a variety of iron compounds and sulfuric acid (H2SO4). The release of the H2SO4 causes the pH of the soil, and associated soil solution and/or groundwater, to decrease to levels that may result in the release and subsequent mobilisation of salts and metals and metalloids, resulting in the generation of metalliferous drainage.

Acid sulphate soils typically occur in recent (Holocene; last 10,000 years) estuarine sediments along the current coastline. However, as significant marine regression and transgression events have occurred since the Eocene period (56 – 34 million years ago), which have shaped the Australian coastline, ancient marine shorelines can occur inland up to an elevation of 330m AHD, resulting in a more widespread distribution of acid sulphate soil within Australia.  In addition, there is a growing realisation that acid sulphate soils occur extensively within inland regions, associated with wetlands, current river systems, paleo-drainage channels and other more permanent surface water bodies.