Coastal Acid Sulfate Soils (CASS)
Coastal acid sulfate soils (CASS) occur naturally and have been present for thousands of year. These soils are harmless if left undisturbed. However, increased human activity in coastal regions has lead to increased risk of disturbance of CASS. Disturbance of CASS can cause impacts on the environment, intrastructure and human health. CASS-related incidents are often difficult and costly to mitigate and damage is irreversible.
For these reasons coastal acid sulfate soils, which exist along Victoria's coasts and estuaries, are the focus of a new strategy released by the Department of Sustainability and Environment.
On this page:
- The Victorian Coastal Acid Sulfate Soils (CASS) Strategy
- What are Coastal Acid Sulfate Soils?
- Where are CASS found in Victoria?
- Existing management of CASS in Victoria
- Further information
- Frequently asked questions
Victoria's CASS strategy aims to protect the environment, humans and infrastructure from the effects which can occur if CASS is disturbed. The emphasis of the strategy is on avoiding the disturbance of CASS. The strategy is available below. Please note: the file size is large and may take some time to download.
 | The strategy explains why CASS is a management issue in Victoria and promotes a risk identification and assessment process. It aims to build the capacity of land owners and land and water managers to identify areas where disturbance of CASS is best avoided. Coastal Acid Sulfate Soils Strategy (PDF - 3.0 MB).The strategy includes:
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What are Coastal Acid Sulfate Soils (CASS)?
CASS are naturally occuring soils containing iron sulfides. CASS underlie large areas of Australia's low lying coastal areas. In a water-logged state these soils are harmless but, when exposed to air, the iron sulfides can oxidise producing acid which can then leach into the environment.
Natural setting: PASS insulated from exposure to oxygen by watertable. Waterway well flushed, mitigating impact from incidental, acid discharge events.
Post Drainage: Lowered water table exposes PASS soils to oxygen. Increased drainage density and volume leads to increased acid export.
The effects of acidic water include:
- death and bleaching of vegetation
- unusually clear or milky, blue-green drainwater within or flowing from the area
- extensive iron stains on drain or pond surfaces; or iron-stained water and ochre deposits
- corrosion of concrete and/or steel infrastructure
- skin irritation after exposure to acidic water
- loss of water quality
- dead fish
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Where are CASS found in Victoria?
CASS are generally found in low lying areas within coastal plains.
Prospective maps of areas where coastal acid sulfate soils (CASS) are likely to occur have been prepared and are available on the Department of Primary Industries' Victorian Resources Online (VRO) website.
Soil investigations were conducted as part of the Victorian Coastal Acid Sulfate Soils (CASS) Strategy in order to increase the accuracy and quality of mapping of areas identified as being at high risk in the event of soil disturbance from development and land use change.
Existing management of CASS in Victoria
The strategy has recognised and builds upon a number of CASS management tools already existing in Victoria. These include:
- A key action in the Victorian Coastal Strategy 2008
- Recent amendments to the State Planning Policy Framework and the Environment Effects Act Guidelines which have highlighted the need to consider CASS in development planning or planning scheme amendment processes.
- Prospective risk mapping showing the prospective ditribution of CASS in Victoria (2009) - see Victorian Resources Online
- EPA's industrial waste management guidelines, developed under the Environment Protection Act 1970. This policy deals with CASS after it has been disturbed.
- Best practice management guidelines from other jurisdictions that can be adapted for Victorian circumstances.
Further information
- Acid Sulfate Soil and Rock (EPA Publication No:655)
- Soil analysis and sampling analysis guidelines and publications from the Queensland Acid Sulfate Soils Investigation Team (QASSIT)
- National Atlas and CASS knowledge initiative.
Frequently asked questions
What are Coastal Acid Sulfate Soils (CASS)?
CASS form naturally when sulfate rich water (sea water, sewerage or mine waters) mix with soils that contain iron and organic matter. Most soils with the potential for CASS found in Victoria were formed within the last 10,000 years, after the last major sea level rise.
Why are CASS a problem?
If CASS is not disturbed, it presents no problem. If disturbed, CASS can create an acidic environment, which can adversely affect:
- human health, including skin and eye irritations and burns
- drinking water which can become contaminated
- occupational health & safety
- the ecology of wetlands and shallow freshwater and shallow aquifer systems by degrading water quality, habitat and dependant ecosystems
- commercial and recreational fisheries and rural productivity
- concrete and steel infrastructure by corroding culverts, pipes and bridges
CASS are generally found in low lying areas within coastal plains and along the edges of water bodies. This includes flood plains and lower slopes, abandoned river meanders and oxbow lakes, swamps, morasses, beaches, coastal dunes and swales and tidal flats. Tidal influence can also extend CASS inland.
Areas in Victoria with potential for CASS cover approximately 250,000 ha of land. The majority of land with potential for CASS surrounds Port Phillip Bay and east to the Gippsland lakes. However environmentally sensitive areas are scattered along the entire coastline of Victoria. To view the map of potential CASS in Victoria, please visit the DPI website.
How do I know if CASS is on my property?
If any of the following signs are present on your property, CASS should be considered if proposing land use changes:
- Do the maps in the Strategy indicate that the area has potential to contain CASS?
- Is the area low lying, swamp or estuarine?
- Is the vegetation coastal or estuarine in nature? Are Mangroves, Melaleuca or Casuarina species present?
Soil investigations are necessary to identify risks and impacts. Once risks are identified, avoidance or a low risk solution can be planned. If you suspect that CASS may be present, and may be a risk to your proposed activity then soil tests should be undertaken.
Where do I go to get my soils tested for CASS?
Soil sampling and assessment should be carried out by a suitably qualified and experienced professional. The latest sampling and analysis schedule for Victoria is found in the EPA’s Waste Acid Sulfate Soil and Rock Publication 655 at www.epa.vic.gov.au. Soil samples should be analysed by an accredited NATA laboratory. For a list of accredited laboratories visit the Yellow Pages or NATA websites.
The results should then be interpreted and a report produced by a qualified and experienced consultant.
Can I develop my land if CASS is identified?
Yes, land with CASS left undisturbed can be developed. Soil investigations should identify the locations of CASS and the potential risks if that soil is disturbed. Development that avoids disturbing CASS is the most cost effective strategy. Managing, mitigating or remediating the adverse impacts once CASS is disturbed is generally difficult and expensive.
What activities/ land use changes may disturb CASS?
Activities that may cause the disturbance of CASS include:
- excavating
- filling land
- moving CASS horizontally or vertically
- temporarily or permanently dewatering soil containing CASS
- causing CASS to be temporarily of permanently bathed in oxygenated water
- agricultural activities that cause land drainage particularly deep drainage
- dredging
- drilling for bores
- extractive industries;
- infrastructure works – flood management, drainage works, road, railway and water and sewerage pipe installation
- land use changes that may alter water tables
- urban and tourism development
- water extraction.
Signs of CASS disturbance include:
- Water with pH less than 4
- Dead fish in the area
- Death and bleaching of vegetation
- Unusually clear or milky blue-green drainwater within or flowing from the area
- Extensive iron stains on drain or pond surfaces, or iron-stained water and ochre deposits
- Corrosion of concrete and/or steel structures
- Skin irritation after exposure to water.
If indicators are present, coastal communities should report to their local municipal authority, DSE office or local Catchment Management Authority.
What does the Victorian Strategy for Coastal Acid Sulfate Soils do?
The strategy aims to protect the environment, humans and infrastructure from the harmful effects which can occur if coastal acid sulfate soils are disturbed. The strategy explains why CASS is an issue in Victoria and outlines actions to address these issues. Maps which identify areas with the potential to contain CASS can be viewed on the DPI website.
The Strategy implements a key action in the Victorian Coastal Strategy 20088 and meets Victoria’s national obligations to implement appropriate plans and strategies for managing CASS
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