Monitoring acid sulfate soils (ASS) is essential to prevent environmental degradation and ensure compliance with regulatory standards.
Effective monitoring is rooted in specific indicators that signal changes in soil and water chemistry.
Over 13 years of operation, the team at West Soil & Water has been able to whittle down the vast array of indicators to find those that are most effective in the unique environment of Western Australia.
This article outlines what those signals are and how they work. If you would like assistance in managing ASS on your site and would like to speak with one of our environmental consultants, you can contact WSW at sam@westsoilandwater.com.au or on 0424 021 264.
ASS are naturally occurring soils and sediments that contain iron sulfides, primarily pyrite. These soils are typically found in WA’s low-lying coastal areas and wetlands. In their undisturbed state, ASS are harmless, as the sulfides remain stable under waterlogged, oxygen-free conditions.
However, when disturbed through activities such as excavation or drainage, the iron sulfides are exposed to oxygen. This exposure triggers a chemical reaction that produces sulfuric acid, with that acidity leading to environmental and structural issues including:
Soil Degradation: The acidic conditions lower soil pH, reduce fertility and mobilise toxic metals like aluminium and iron.
Water Contamination: Acid runoff can pollute nearby waterways, harming aquatic ecosystems and degrading water quality.
Infrastructure Damage: Sulfuric acid can corrode concrete and steel, compromising the integrity of buildings, pipelines and other structures.
Due to these risks, early identification of ASS, followed by stringent management and treatment, is essential to prevent long-term environmental damage and ensure regulatory compliance during and after development.
At WSW, we find the following indicators to be the most reliable in revealing the presence of ASS.
Soil pH measures the acidity or alkalinity of the soil. A decline in pH would indicate increased acidity and a presence of the ASS on site. Regular pH monitoring helps detect early signs of acidification, allowing for timely intervention.
TAA quantifies the soluble and exchangeable acidity in the soil, including hydrogen ions and loosely bound aluminium and iron ions. Elevated TAA levels suggest active acidification and ASS presence, necessitating intervention.
PSA assesses the amount of oxidizable sulfur present in the soil, measured as reduced inorganic sulfur compounds (primarily pyrite). High PSA values indicate a significant risk of future acid generation should the soil be disturbed and exposed to oxygen.
ANC measures the soil’s ability to neutralise acidity, typically enabled by the presence of carbonates and other organic matter. A low ANC implies that the soil lacks sufficient buffering capacity, increasing vulnerability to acidification.
RA represents the acidity stored in sparingly soluble sulfate minerals like jarosite and schwertmannite. These minerals can slowly release acidity over time, leading to prolonged growth of ASS and subsequent environmental impacts.
EC indicates the soil’s salinity levels. In potential ASS landscapes, increased EC can be caused by the mobilisation of salts due to acidification. This may affect plant growth and soil structure.
Monitoring levels of iron, aluminum and heavy metals is crucial. Soil acidification can mobilise these elements, leading to potential contamination of groundwater and surface water.
Identifying minerals like pyrite and jarosite provides insights into the soil’s acid-generating potential and the effectiveness of remediation strategies.
Regular monitoring of these indicators enables proactive management of ASS, helping to mitigate environmental risks and ensure sustainable land use.
It allows quick intervention should acidification begin but also helps construct effective treatment strategies should ASS already be present.
Regularly assessing these indicators can prove the difference in whether your site is adversely affected by acid sulfate soils.
Engaging experienced environmental consultants, such as West Soil & Water, helps you identify ASS before they can cause damage your site and the surrounding areas. Backed by over 13 years of experience, our services will ensure site safety, environmental protection and compliance.
Our full list of services includes acid sulfate investigations, management plans (ASSMPs) and treatment. If you are worried about the presence of ASS on your site and would like to speak with a member of our team, you can contact WSW at sam@westsoilandwater.com.au or on 0424 021 264.
