Acid Sulfate Soil Disposal in NSW: What Builders and Civil Contractors Need to Know

Acid sulfate soils are a common consideration for construction and civil projects across coastal New South Wales, particularly where works involve excavation, drainage, dewatering or disturbance of low-lying land.

For builders, developers and civil contractors, identifying acid sulfate soil can affect how excavated material needs to be handled, treated, transported and disposed of.

Planning for acid sulfate soil before excavation begins can help avoid delays, unexpected disposal costs and environmental compliance issues once earthworks are underway.

What Are Acid Sulfate Soils?

Acid sulfate soils (ASS) are naturally occurring soils and sediments containing iron sulfides.

While these soils remain undisturbed and waterlogged, they generally present little risk. Problems can arise when excavation, drainage or other activities expose the sulfides to oxygen.

This oxidation can produce sulfuric acid.

If not appropriately managed, disturbed acid sulfate soil can create environmental risks for surrounding soil and waterways and may also contribute to corrosion of infrastructure such as concrete and steel.

Where Are Acid Sulfate Soils Found in NSW?

Acid sulfate soils are widespread along the NSW coastline and have been identified in every coastal estuary in New South Wales.

They are commonly associated with low-lying coastal environments including floodplains, estuaries, wetlands, mangroves, saltmarshes and former tidal areas.

This makes acid sulfate soil an important consideration for construction and civil projects throughout Newcastle, the Hunter, Central Coast and Greater Sydney.

NSW Acid Sulfate Soil Risk Maps can be used as an initial tool to identify the probability of ASS occurring in an area, its estimated depth and the potential environmental risk associated with disturbing it.

Where acid sulfate soil may be present, appropriate investigation and testing may be required before excavation or disposal decisions are made.

What Happens When Acid Sulfate Soil Is Excavated?

Identifying potential or actual acid sulfate soil does not necessarily mean excavation cannot proceed.

It does mean the material needs to be appropriately assessed and managed.

Depending on the site and project requirements, management may involve:

• soil investigation and laboratory testing

• classification of excavated material

• preparation or implementation of an Acid Sulfate Soil Management Plan

• controlled excavation and stockpiling

• treatment and neutralisation

• validation testing

• transport and haulage

• off-site management or disposal

• documentation of the treatment and disposal process.

The correct pathway will depend on the characteristics of the soil, the proposed works and the environmental and regulatory requirements applying to the project.

Can Acid Sulfate Soil Be Taken Off Site?

Yes, but excavated acid sulfate soil should not simply be treated as ordinary clean fill.

Where acid sulfate soil cannot be appropriately managed on site and needs to be transported and managed off site, the NSW EPA Waste Classification Guidelines, including Part 4: Acid Sulfate Soils, are relevant.

The waste generator is responsible for appropriately assessing and classifying the material.

Testing may therefore be required before the appropriate treatment, transport and disposal pathway can be established.

This is why identifying potential ASS early can be so important. Discovering it after excavation has commenced can leave a project with stockpiled material that cannot be transported to its originally intended destination.

Is Acid Sulfate Soil VENM?

Acid sulfate soil should not automatically be assumed to be Virgin Excavated Natural Material (VENM).

NSW EPA guidance specifically addresses sulfidic soils when determining whether excavated material satisfies the requirements for VENM.

Where Acid Sulfate Soil Risk Maps indicate a probability of actual or potential acid sulfate soil, appropriate assessment may be required.

There are specific provisions within the NSW Waste Classification Guidelines for certain potential acid sulfate soils, so the classification and management pathway should be determined based on the material and circumstances of the individual project rather than assuming excavated soil qualifies as VENM.

Treatment and Neutralisation of Acid Sulfate Soil

Neutralisation is an established method of managing acid sulfate soil.

Treatment commonly involves mixing an appropriate neutralising agent, such as agricultural lime, through the soil to neutralise its acidity or potential acidity.

The amount of neutralising material required should be based on appropriate soil assessment and testing rather than estimated in the field.

Effective treatment involves more than simply spreading lime across the surface of an excavated stockpile. The neutralising material needs to be appropriately incorporated throughout the soil in accordance with the treatment methodology applying to the project.

Further sampling and validation may also be required to demonstrate that the treatment requirements have been achieved.

The NSW Acid Sulfate Soil Order 2025

In December 2025, the NSW EPA introduced a new resource recovery pathway for eligible acid sulfate soil through the Acid Sulfate Soil Order 2025 and associated Acid Sulfate Soil Exemption 2025.

The Order establishes requirements for suppliers of eligible acid sulfate soil where that material is to be supplied for application to land for use as earthworks or engineering fill.

Importantly, this does not mean excavated acid sulfate soil can simply be treated and reused as fill.

The Order contains specific requirements relating to the soil, investigation, treatment, sampling, validation, record keeping and supply of the material.

The suitability of treated material for a particular engineering or load-bearing application also needs to be considered separately. Treatment of acid sulfate soil does not automatically establish its geotechnical suitability for use as engineering fill.

Projects considering this resource recovery pathway should ensure the requirements of the current NSW EPA Order and Exemption, as well as other applicable environmental, planning and project requirements, are satisfied.

Disposal of Acid Sulfate Soil

Where acid sulfate soil is being disposed of rather than managed under an appropriate resource recovery or other lawful pathway, the applicable NSW waste classification and disposal requirements need to be followed.

The requirements differ depending on whether the material is potential acid sulfate soil or actual acid sulfate soil and on the characteristics of the material.

Actual acid sulfate soil may require treatment before disposal, followed by appropriate assessment to establish its waste classification and determine a suitable facility.

This is an area where early testing and planning can save considerable time.

Knowing what material is being excavated, how it will be treated and where it can lawfully be taken before trucks begin leaving the site can prevent unnecessary double handling and project delays.

Why Early Planning Matters

Acid sulfate soil management is considerably easier when the likely soil conditions and management pathway are established before bulk excavation begins.

Early planning gives builders, civil contractors and project teams an opportunity to determine:

1. whether acid sulfate soil is likely to be present

2. what investigation and testing is required

3. how excavated material will be managed

4. whether treatment or neutralisation is required

5. whether material can remain on site

6. whether a resource recovery pathway may be available

7. the appropriate off-site destination where removal is required

8. what haulage and documentation will be needed.

For projects involving significant volumes of material, having these questions answered early can make the earthworks process considerably more efficient.

Acid Sulfate Soil Treatment, Haulage and Disposal in NSW

Acid Sulfate Soil Solutions works with builders, civil contractors, developers and project teams to provide practical solutions for managing acid sulfate soil generated during construction and earthworks.

Our services include:

• acid sulfate soil treatment and neutralisation

• excavation and material management

• compliant haulage

• off-site disposal

• coordination with environmental consultants and project teams

• treatment, transport and disposal documentation.

With in-house haulage capability, we can coordinate the movement of material as part of the overall solution, helping simplify the process for contractors managing complex excavation and earthworks projects.

Servicing Newcastle, the Hunter, Central Coast and Greater Sydney

Acid Sulfate Soil Solutions services construction and civil projects throughout Newcastle, the Hunter Region, Central Coast and Greater Sydney.

From smaller excavations through to projects generating hundreds of tonnes of acid sulfate soil, establishing the correct management pathway early can reduce delays and make the movement of material considerably easier to manage.

Need an Acid Sulfate Soil Solution for Your Project?

If acid sulfate soil or potential acid sulfate soil has been identified on your project, speak with Acid Sulfate Soil Solutions before excavation or removal begins.

Send through your project location, estimated quantities and any available soil testing, environmental reports or Acid Sulfate Soil Management Plan, and we can review the project requirements and discuss a practical treatment, haulage and disposal solution.

Acid Sulfate Soil Solutions NSW

Treatment | Neutralisation | Haulage | Disposal

Newcastle | Hunter | Central Coast | Greater Sydney