Acid Sulfate Soils

Acid sulfate soils is the common name given to naturally occurring soil and sediment containing iron sulfides. When disturbed and exposed to air these sulfides can release acid, which damages structures and waterways and harm animals and plants.

One tonne of iron sulfides can produce about 1.5 tonnes of sulfuric acid when oxidised.

The most common activities that can trigger acid sulfate soils to oxidise and produce acid are:

  • agricultural activities
  • infrastructure works
  • construction
  • extraction.

Acid sulfate soils occur in low-lying areas near the coast where the surface elevation is less than five metres above mean sea level. They occur in every coastal estuary in NSW.


Acid sulfate soil risk maps are available to identify potential acid sulfate areas. The maps predict the distribution of acid sulfate soils and are based on landform assessment, extensive fieldwork and laboratory testing.

Acid sulfate soils are classified based on the likelihood of the soils being present in certain areas. There are five classifications:

  • Class 1: likely to be found on and below the natural ground surface
  • Class 2: likely to be found below the natural ground surface
  • Class 3: likely to be found beyond one metre below the natural ground surface
  • Class 4: likely to be found beyond two metres below the natural ground surface
  • Class 5: not typically found in class 5 areas. Areas classified as class 5 are located within 500 metres on adjacent class 1, 2, 3 or 4 land.

You can look up the acid sulfate soil maps for your area:

Please note: As of 1 December 2021, a reference to an Environment Protection Zone E1, E2, E3 or E4 in a document should be taken to be a reference to a Conservation Zone C1, C2, C3 or C4. For further information, please see the Department of Planning, Housing and Infrastructure's 'Standard Instrument (Local Environmental Plans) Amendment (Land Use Zones) Order 2021'.

Developing in an acid sulfate soil area

You may need development consent if you carry out works in an acid sulfate soils area, depending on the class of land where the works are being carried out and the type of work. Clause 6.3 of the Eurobodalla Local Environmental Plan 2012 explains what considerations or investigations are necessary.

If your development is in a class 1, 2, 3, 4 or 5 acid sulfate soils area, and is likely to impact on acid sulfate soils and trigger clause 6.3 of the Eurobodalla Local Environmental Plan 2012, you will need to appoint a qualified environmental scientist to test your soils in the area of potential disturbance. This testing should be carried out in according to the Acid Sulfate Soils Manual and the National Acid Sulfate Soil Guidance 2018.

The Acid Sulfate Soils Manual forms part of an ‘all of government’ approach to the management of acid sulfate soils in NSW. For information about development consent refer to Section 2: Assessment Guidelines and Section 3: Management Guidelines. You will need to prepare an acid sulfate soils management plan to carry out works before consent is granted.

Note that the Laboratory Methods Guidelines (2004) replaces the Laboratory Methods in the Acid Sulfate Soils Manual (1998).

Management and treatment

National guidance documents provide clear advice for managing acid sulfate soils based on current scientific knowledge.

If you need to transport and treat acid sulfate soils offsite, you should apply the EPA Waste Classification Guidelines.

More information

Contact us

For more information about whether you need development consent for your works, or if you have any further queries about acid sulfate soils, contact our Development Help Desk: