Acid Sulfate Soils (ASS)
Summary
Acid sulfate soils (ASS) are naturally occurring soils or sediments that contain sulphide minerals. When these materials are disturbed and exposed to oxygen, they can generate sulphuric acid. This process can significantly affect soil, groundwater, surface water and infrastructure if not properly managed.
ASS are a common environmental constraint in coastal, estuarine and low-lying areas of Australia. Identification and management of ASS is an important part of environmental site assessment, contaminated land investigations, earthworks planning and development approvals.
Definition
Acid sulfate soils are soils or sediments containing reduced inorganic sulphur, typically in the form of iron sulphides such as pyrite. When these materials are excavated, drained or otherwise exposed to air, oxidation can occur and sulphuric acid may be produced.
The generation of acid can lower soil and groundwater pH, mobilise metals and cause damage to infrastructure and the surrounding environment.
Why Acid Sulfate Soils Matter
From a practical environmental consulting and planning perspective, acid sulfate soils present a risk that needs to be understood early.
Disturbance of ASS can result in acidification of soil and groundwater and the release of metals such as aluminium, iron and arsenic. These impacts can extend beyond the site boundary, affecting drainage lines, wetlands and downstream waterways.
Acidic conditions can also attack concrete, steel and other construction materials. This has implications for foundations, buried services, retaining structures and long-term asset performance.
ASS is also a recognised regulatory issue. In many jurisdictions, planning authorities and environmental regulators require investigation and, where necessary, formal management measures before works commence. If ASS is not addressed early, it can delay approvals or result in additional conditions being imposed late in the project.
ASS risk commonly overlaps with other site constraints such as contaminated land, groundwater management, geotechnical conditions and soil reuse. For larger developments or remediation projects, it is often assessed alongside these issues rather than in isolation.
When Acid Sulfate Soils Are Typically Assessed
Consideration of ASS is generally required where proposed works involve:
Excavation or drainage in low-lying coastal, estuarine or floodplain areas
Works below the groundwater table, including basements, piling or service trenches
Bulk earthworks or changes to groundwater levels that may expose sulfidic soils
Redevelopment of land identified as having potential ASS risk under state mapping
Development consent or approval conditions that specifically reference ASS
Legislative and Regulatory Context
Management of acid sulfate soils is addressed through a combination of environmental legislation, planning controls and technical guidance.
In New South Wales, ASS considerations are captured through planning instruments, EPA guidance and associated contaminated land and waste management frameworks. Other states, including Queensland and Western Australia, have specific ASS policies and technical manuals that set investigation thresholds and management requirements.
At a national level, the National acid sulfate soils guidance: a synthesis document provides overarching principles that inform state-based approaches.
How We Can Help
Confluence Environmental provides acid sulfate soil services as part of broader contaminated land, remediation and environmental assessment projects.
Our work typically includes:
Desktop screening and review of ASS risk mapping and site history
Design and oversight of ASS investigations, including soil and groundwater sampling
Interpretation of laboratory results and assessment of ASS risk
Preparation of Acid Sulfate Soil Management Plans where required
Integration of ASS management with remediation strategies, earthworks planning and monitoring programs
ASS management is most effective when addressed early and aligned with the overall site assessment and approval strategy.
Related Terms and Concepts
Acid Sulfate Soil Management Plan
Contaminated Land
Environmental Site Assessment
Preliminary Site Investigation
Detailed Site Investigation
Remediation Action Plan
Soil Classification
Waste Classification
Groundwater Investigation
Groundwater Monitoring Wells
Geotechnical Investigation
Site Validation