Acid Sulfate Soils

What are Acid Sulfate Soils

Acid sulfate soils are the common name given to soils containing iron sulfides. In Australia the acid sulfate soils of most concern are those which formed within the past 10,000 years, after the last major sea level rise.

Acid sulfate soils occur naturally in both coastal (tidal) and inland or upland (freshwater) settings. Left undisturbed, these soils are harmless, but when excavated or drained, the sulfides within the soil react with the oxygen in the air, forming sulfuric acid. These soils include those that are producing acid (actual acid sulfate soils) and those that could become acid producing (potential acid sulfate soils).This acid, together with associated toxic elements (heavy metals and other contaminants), can kill plants and animals, contaminate drinking water and food such as oysters, and corrode concrete and steel.

Where Acid Sulfate Soils can be Found

Acid sulfate soils are typically found in low-lying areas near the coast generally where surface elevation is less than five metres above mean sea level. They are still being formed today in mangrove forests and salt marshes, estuaries and tidal lakes.

Parts of the Newcastle local government area are impacted by acid sulfate soils. Acid Sulfate Soils Maps have been prepared as part of the Newcastle Local Environmental Plan 2012. This map identifies five classes of land, with Class 1 having the highest risk for acid sulfate soils.

Acid Sulfate Soils and Development

Certain works on land Classed 1 to 5 on the Potential Acid Sulfate Soils Maps (particularly works which disturb soil or are carried out below the water table) may have the potential to cause environmental impacts if not properly managed.

Works on land affected by acid sulfate soils for which development consent is required may not be issued with consent without Council first being provided an Acid Sulfate Soils Management Plan undertaken in accordance with the Acid Sulfate Soils Manual (PDF).

An Acid Sulfate Soils Management Plan may not however be required if a Preliminary Assessment of the proposed works has been undertaken in accordance with the Acid Sulfate Soils Manual indicating that the proposed works will not require the preparation of an acid sulfate soils management plan in accordance with the Acid Sulfate Soils Manual.

Acid sulfate soils table

Class of Land

Works which may require a Management Plan or Preliminary Assessment prior to development consent being issued

1

Any works

2

Works below the ground surface
Works by which the water table is likely to be lowered

3

Works more than 1 metre below the natural ground surface
Works by which the water table is likely to be lowered more than 1 metre below natural ground surface

4

Works more than 2 metres below the natural ground surface
Works by which the water table is likely to be lowered more than 2 metres below natural ground surface

5

Works within 500 metres of adjacent Class 1, 2, 3 or 4 land that is below 5 metres Australian Height Datum and by which the water table is likely to be lowered below 1 metre Australian Height Datum on adjacent Class 1, 2, 3 or 4 land




Note: Council defines 'works' to mean any disturbance of more than one tonne of soils, the construction or maintenance of drains, extractive industries, dredging, the construction of artificial water bodies (including canals, dams and detention basins), the construction of footings or erection foundations, flood works, or any other works that are likely to lower the water table.