PSK Environmental is an expert in the assessment, management and treatment of Acid Sulfate Soils. We’ve worked on small to large-scale infrastructure projects. Our extensive knowledge and experience garnered from over 20 years of research and consultancy means that you can trust us to get the most cost effective, low risk environmental outcomes for your project.
What are Acid Sulfate Soils?
Acid Sulfate Soils are naturally occurring soils, sediments or organic substrates (e.g. peat) that contain elevated levels of pyrite (FeS2). Pyrite is formed by sulfate reducing bacteria in low energy environments under waterlogged conditions. Acid Sulfate Soils are therefore typically encountered in alluvial soils and sediments at less than 5m AHD and at the bottom of deep drains in the form of Monosulfidic Black Ooze (FeS).
Acid Sulfate Soils is a general term that may include both Potential Acid Sulfate Soils (PASS) or Actual Acid Sulfate Soils (AASS). Potential Acid Sulfate Soils are generally located below the water table. Undisturbed, PASS are harmless. However, if PASS are drained, excavated or exposed to air by a lowering of the water table, the pyrite reacts with oxygen to generate acidity in the form of sulfuric acid. This oxidised, acidified layer is referred to as AASS.
What are the potential impacts of Acid Sulfate Soils
Sulfuric acid, if left untreated, can harm the environment through the acidification of soil and groundwater and can corrode infrastructure including pipes, roads, bridges, and building foundations.
The acid also attacks soil minerals, releasing metals like aluminium and iron. Rainfall can then wash the metals, and acid, from the disturbed soil into the surrounding environment.
How do you manage Acid Sulfate Soils?
Typical measures to manage ASS include the application of agricultural limestone (‘Aglime’) to soils. Aglime and hydrated lime are commonly used to treat surface water as they raise the pH from acidic to neutral and encourage the precipitation of metals. Commonly, groundwater and surface water monitoring is required following treatment with lime products to monitor the effectiveness of the acid sulfate soil treatment efforts. There are a number of methods to manage ASS and ASS-impacted groundwater and surface water and site-specific approaches often need to be developed, particularly for complex sites. Management measures should therefore be designed by a Certified Professional Soil Scientist.
As industry leaders in Acid Sulfate Soils, the PSK team specialises in management and treatment of ASS to comply with relevant guidelines. Our team can develop a site-specific ASS Environmental Management Plan (ASS EMP) that addresses the legislative requirements.
For project examples, head to our Projects page or to discuss your project with one of our team, click here.
What are the requirements in Queensland?
Current Queensland legislation, the State Planning Policy (April 2016), requires that ASS investigations be undertaken where there is a proposed disturbance to all land that is at or below five metres (AHD) and the disturbance will involve:
1) Works (not associated with a material change of use) on land below 5 meters Australian Height Datum (AHD), where such works involve either:
∙ excavating or otherwise removing 100 cubic metres or more of soil or sediment, or
∙ filling of land involving 500 cubic metres or more of material with an average depth of 0.5 metres or greater.
2) Works (not associated with a material change of use) on land between 5 metres and 20 metres AHD where such works involve excavating or otherwise removing 100 cubic metres or more of soil or sediment at or below 5 metres AHD.
3) Material changes of use on land within the overlay area where any associated works as described by 1 and 2 above are a component of the use.