Acid Sulphate Soils

Industry leaders in treating acid sulphate soil with a cost-effective, timely approach. 

McMahon Services is a specialist treatment contractor providing innovative solutions in the treatment of Acid Sulphate Soils. Our proven methods and solid understanding of Acid Sulphate Soil treatment ensures a cost-effective and time efficient process.


Acid sulphate soil (ASS) is the common name given to soils and sediments containing iron sulfides, the most common being pyrite.

When exposed to air due to drainage or disturbance, these soils produce sulphuric acid from reacting with oxygen, often releasing toxic quantities of heavy metals to the wider environment.

Excavation of potential acid sulphate soils (PASS) can lead to the creation of actual acid sulphate soils (AASS).

To reduce the possibility of potential acid sulphate soils becoming actual acid sulphate soils, there are four main management techniques used to minimise this possibility and its effects.

These are:

  • Neutralisation
  • Minimising disturbance
  • Reclaiming land
  • Water cover


In many cases minimising disturbance is not possible especially in relation to construction projects. Reclaiming land and water cover are based on removing the possibility of oxygen coming into contact with the sulphate within the soil, but in many circumstances is not possible. Therefore neutralisation is the only management technique available in many situations where acid sulphate soil is present.

The way in which acid sulphate soil is neutralised is relatively simple in that a highly basic material, such as lime, is mixed with the acid sulphate soil.

The amount of lime required to be mixed with the acid sulphate soil is determined by analysing a sample of soil to calculate actual acidity and relating the amount of lime required to be added to effectively neutralise the soil. In many cases of acid sulphate soil treatment, agricultural lime is used to neutralise the soil.

However, there are other reagents available, which are effective such as hydrated lime, mixtures of hydrated lime and agricultural lime, and also lime slurries, which are added as a liquid.

Exposed acid sulphate soil.

Discharge of shallow acid groundwater from acid sulphate soil.

McMahon Services has a strong track record in treating acid sulphate soil using a range of innovative equipment and soil reagent products.

Our expert team has a solid understanding of the technical requirements of treating acid sulphate soil with a cost-effective and time efficient approach.

Revolutionary Reterra

Treatment of Acid Sulphate Soil centres on the Komatsu Reterra BZ210-1 G-Mode, a specialised soil recycler.

The Reterra is specifically designed to handle heavy marine sediments and accurately dose with a range of reagents. Reagents can range from dry hydrated lime, to wet agricultural lime as well as slurried reagents. Dosing hoppers and liquid manifolds are used to add the reagents with the Acid Sulphate Soil, all designed for maximum efficiency.

The G-Mode model offers a dramatically improved and increased workload capability and soil improvement efficiency, and most importantly has set a new benchmark for treating acid sulphate soils.

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Do you have a problem with Acid Sulphate Soils on your project? Contact the expert team at McMahon Services New Zealand to assist you with a cost-effective and innovative solution.
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Narrows Crossing – Acid Sulphate Soil Treatment
  • Environmental Remediation
  • Acid Sulphate Soils
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Reterra G-Mode

Model: BZ210-1
Type: Soil Blending Machine
Manufacturer: Komatsu

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