Acid sulfate soils in Western Australia |
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Acid sulfate soils in Western Australia commonly occur in low lying wetlands, back-swamps, estuaries, salt marshes and tidal flats, though are not constrained to coastal regions.
Low-lying land fringing estuaries - typically grey silty or sandy sediments of alluvial origin commonly occurring in low-lying areas adjacent to estuaries. These sediments may locally contain significant amounts of sulphides (up to 5% oxidisable sulphur). Sands in particular are very reactive, and can begin to oxidise within a few hours on exposure to air. Groundwater dependent wetlands - Typically peaty and sandy sediments are associated with some wetlands on the Swan Coastal Plain. Pyrite in the sediments can acidify the wetland if the water table falls well below the base of wetland due to dry weather or excessive groundwater pumping. Although acid sulphate soils on the east coast of Australia generally only occur at elevations of less than 5 m above sea level, sulphidic sediments associated with wetlands may occur at elevations of up to 70 m above sea level near the crest of the Gnangara groundwater mound and other smaller ground-water systems on the Swan Coastal Plain. Similar acid sulfate soil materials are also likely to occur in wetlands on the South Coast. Former sea shores - Pyrite often occurs with heavy-mineral accumulations associated with former sea shores. These sea-shores may occur several kilometres inland from the current sea shore. Inland acid sulfate soils -There are inland forms of acid sulfate soils not associated with coastal soils and sediments commonly occurring in agricultural areas well inland from the coast. These soils appear to be forming in response to rising water tables and land salinisation in southern WA. They have the potential to cause significant down-stream environmental problems if these soils are drained. MappingDEC has compiled maps of Acid Sulfate Soil (ASS) risk areas for several regions of Western Australia, which provide a broad-scale indication of the areas where ASS are most likely to exist. The majority of these ASS risk maps are based on reviews of existing geomorphological, geological and hydrological information. Important note: The ASS risk maps are designed to be used for broad-scale planning purposes and are not intended to provide site specific ASS information, so are not appropriate for use at an individual property level. Consequently, the information derived from the maps cannot be relied upon to determine whether ASS management will be required for a particular development. The maps should be read at the scale of their intended use, 1:50,000. When using ASS risk maps, please keep the following in mind:
Maps of the State's ASS risk areas can be found at WA Atlas via Landgate's SLIP Enabler (Shared Land Information Platform) https://www2.landgate.wa.gov.au/idelve/bmvf/app/waatlas/ For access to diagnostic analytic detail users can use the interest inquiry feature at www.landgate.wa.gov.au . Select the "My Landgate" link in the top right hand corner to gain access and obtain a user id. The maps can also be viewed on DEC's Geographic Data Atlas. The ASS datasets are listed under the folder "Geoscientific Information". (Note - the map can only be viewed at large scales and will not be visible at scales below 1:50 000 (as displayed next to the distance scale at the bottom of the spatial data viewer).) The GIS datasets can be directly downloaded (with metadata) from the http://www.asris.csiro.au/index_ie.html.
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Policy Position - Acid Sulphate Soils and the Contaminated Sites Act 2003 
