Introduction

Acid Sulfate Soils can present serious risks to infrastructure development – especially in regional and coastal areas of New South Wales. Without proper investigation and planning, these soils can trigger environmental damage, corrode materials and delay project delivery.

This article will discuss common questions about managing acid sulfate soils in infrastructure projects and highlight how environmental consultants add value through proactive acid sulfate soil assessment and risk mitigation.

What Are Acid Sulfate Soils and Why Are They a Concern in Infrastructure Projects?

Acid sulfate soils are naturally occurring soils that contain iron sulfides, typically in the form of pyrite. When these soils are disturbed and exposed to air – during excavation, dewatering or drainage – the sulfides oxidise and form sulfuric acid.

This acidic runoff can:

• Damage concrete and steel infrastructure
• Leach heavy metals into waterways
• Cause long-term degradation of soil and groundwater quality

For infrastructure projects involving bulk earthworks or drainage modifications, the presence of acid sulfate soils must be identified early and managed effectively to avoid structural and environmental consequences.

Where Are Acid Sulfate Soils Commonly Found in New South Wales?

In NSW, acid sulfate soils are widespread in low-lying coastal and estuarine areas. Regions where Acid sulfate soils are commonly encountered include:

• Northern Rivers (Richmond, Clarence and Tweed catchments)
• Mid-North Coast (Macleay and Hastings valleys)
• Hunter and Central Coast
• Parts of the Illawarra and Shoalhaven floodplains

These areas often support infrastructure upgrades such as stormwater basins, transport corridors, housing developments and recreational spaces – all of which require careful soil assessment during planning and design.

What Problems Can Arise if Acid Sulfate Soils Are Not Managed Properly?

Neglecting to manage Acid sulfate soils can result in:

• Corrosion of buried infrastructure, such as sewer mains and stormwater Acid sulfate soil sets
• Release of toxic metals into wetlands, rivers and groundwater systems
• Increased remediation costs, particularly when contamination spreads offsite
• Compliance breaches, leading to delays or regulatory enforcement

Projects that fail to identify Acid sulfate soils early may also face difficulties obtaining planning approval, as councils and the NSW EPA require Acid sulfate soils risk to be addressed in environmental documentation.

What Strategies Help Mitigate Risks During Construction on Affected Sites?

Best-practice management of acid sulfate soils includes:

• Pre-construction soil sampling and classification, guided by the NSW Acid Sulfate Soils Manual
• Development of an Acid Sulfate Soil Management Plan 
• Treatment of excavated soils using neutralising agents (e.g. lime)
• Controlled dewatering processes that avoid the spread of acidity
• Onsite monitoring of pH and redox conditions, especially during ground disturbance

These strategies are integrated into broader environmental and soil management plans to ensure regulatory compliance and construction efficiency.

How Have Consultants Added Value in Managing Acid Sulfate Soils in Real Projects?

At Raw Earth Environmental, we’ve supported several complex infrastructure projects involving acid sulfate soil-affected land.

One example is our work on the Riverstone Stormwater Management Basin, where construction was planned across a site containing known contamination, including non-friable asbestos and acid sulfate soils.

Our team provided:

• Detailed soil assessment to identify and classify acid sulfate soils
• Development of a Remediation Action Plan and acid sulfate soil mitigation measures
• Ongoing monitoring and environmental supervision throughout excavation
• Coordination of disposal pathways for affected material

By integrating these services into the construction planning process, we helped ensure environmental compliance, protected nearby ecosystems and safeguarded critical infrastructure – including a sewer main beneath the excavation zone.

Conclusion

Infrastructure projects in coastal and low-lying areas demand careful planning to manage acid sulfate soil risks. With the right approach, these risks can be mitigated – and long-term environmental and structural integrity protected.

Whether you need sampling, planning or on-site monitoring, we deliver solutions that protect both your project and the environment. Get in touch today.