In all sectors of society and the economy, contaminated sites, human health issues, environmental litigation and enormous cleanup costs have heightened the awareness of environmental issues relating to contaminated properties.

Contaminated soil, sediment or groundwater in prime real estate and sensitive ecological locations has resulted in the loss of irreplaceable environmental habitats and cost millions of dollars in lost development opportunities and in remediation efforts to address ineffective management and control of environmental pollutants. Heggies brings the highest standards of investigation, mitigation design and remediation management of contaminated properties.

Acid sulphate soils are the common name given to soils containing iron sulphides. In Australia, the acid sulphate soils of most concern are those which formed within the past 10,000 years, after the last major sea level rise. When the sea level rose and inundated land, sulphate in the seawater mixed with land sediments containing iron oxides and organic matter. The resulting chemical reaction produced large quantities of iron sulphides in the waterlogged sediments. When exposed to air, these sulphides oxidise to produce sulphuric acid, hence the name acid sulphate soils.

The iron sulphides are contained in a layer of waterlogged soil. This layer can be clay or sand, and is usually dark grey and soft. The water prevents oxygen in the air reacting with the iron sulphides. This layer is commonly known as potential acid sulphate soil (PASS) because it has the potential to oxidise to sulphuric acid. When the iron sulphides are exposed to air and produce sulphuric acid, they are known as actual acid sulphate soils. The soil itself can neutralise some of the sulphuric acid. The remaining acid moves through the soil, acidifying soil water, ground water and, eventually, surface waters.

Iron sulphide layers were formed under tidal conditions, so they are found in low-lying areas near the coast. They are still being formed today in mangrove forests and salt marshes, estuarine and tidal lakes. In general, we expect to find iron sulphide layers where the surface elevation is less than five meters above mean sea level.

In Australia iron sulphide layers are found along the coastlines of the Northern Territory, Queensland and New South Wales. They are also found along the northern coastline of Western Australia, and around Perth, Adelaide and Westernport Bay near Melbourne. Scientists have estimated that there are more than two million hectares of acid sulphate soils in Australia containing about one billion tonnes of iron sulphides. One tonne of iron sulphide can produce about 1.5 tonnes of sulphuric acid when oxidised.

Ecology

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