Acid Sulphate Soils

Background

 

The presence of acid sulphate soils can be a significant constraint on planning at regional and local levels, introducing restrictions on land use and development options. Hence, within areas of (suspected) acid sulphate soils, many construction or engineering activities warrant an assessment of the risk exposing acid sulphate soils.

 

What is Acid Sulfate Soils?

 

Acid sulphate soils are a mix of low-lying coastal clays and sands that contain sulphur bearing compounds at concentrations above 0.05% in clays and 0.01% in sands. Such soils are formed by the action of anaerobic bacteria on organic matter in the presence of seawater. Thus, the distribution of these soils commonly reflects the past and present distribution of coastal, estuarine wetlands. The sulphur bearing materials in the soil are the by-products of the bacterial breakdown of wetland vegetation using sulphate compounds from seawater in the absence of oxygen.

 

Potential acid sulphate soils are generally found less than 5 metres above sea level. When drained these produce sulphuric acid which can move through the soil affecting groundwater and surface waters, and consequently, urban areas, farm productivity and fish. This is a major issue along the coastal fringes of NSW and Australia.

 

Acid sulphate soils can have detrimental effects on:

 

  • Engineering and landscaping works – e.g. the type of concrete and other building materials required
  • Agricultural practices – e.g. the choice of crops and fertiliser requirements
  • Aquaculture management – e.g. pond design and management
  • Conservation of biodiversity and protection of wetlands and shallow freshwater aquifer systems – e.g. degradation of habitat and water quality

 

Assessment/Standards

 

All work is undertaken in accordance with Acid Sulphate Soils Assessment Guidelines issued by Acid Sulphate Soil Management Advisory Committee in 1998.

 

ADE Capabilities

 

ADE’s team of geo-chemists and environmental scientists provide highly skilled services relating to Actual Acid Sulphate Soils. Some of these services include:

 

1. Preliminary Desktop Assessment involving:

 

  • Establishment of characteristics of proposed works and whether they may impact upon Acid Sulphate Soils,
  • Desktop review of Acid Sulphate Planning maps, risk maps and any relevant planning instruments,
  • Consideration of soil and groundwater impacts if the proposed works are initiated,
  • If site characteristics suggest probability of Acid Sulphate Soils, an Acid Sulphate Soil Assessment is conducted.

 

2. Detailed Acid Sulphate Soil Assessment involving:

 

  • Background review of site information and detailed site inspection,
  • Drilling of boreholes by our own in-house drilling team,
  • Installation of groundwater monitoring wells,
  • Soil sampling at different depths and groundwater sampling,
  • Screening of collected soil samples for pH and laboratory analysis of samples exhibiting the lowest pH for acid sulphate,
  • Screening of collected groundwater samples for Dissolved Oxygen (DO), Electrical Conductivity (EC), pH, Redox potential and temperature and laboratory analysis for Chloride (Cl) and Sulphate (SO42-),
  • Cold storage of all samples collected,
  • Preparation of a report outlining: (i) whether an Acid Sulphate Soil Management Plan is warranted, (ii) baseline groundwater characterisation and (iii) site data and recommendations.

 

3. Acid Sulphate Soil Management Plan

 

  • A site-specific treatment strategy preventing the potential for on-site and off-site impacts,
  • Some management strategies include: avoidance of soil disturbance, preventing the oxidation of sulphides, oxidation of sulphide and neutralising acid as it produced, separating out and treating the sulphidic component and burial below water table.

 

ADE employs the most cost-effective and environmentally benign methods. All ADE investigations and reporting are conducted in accordance with the Acid Sulphate Soil Manual published by the Acid Sulphate Soils Management Advisory Committee.

 

ADE maintains the highest standards of security when conducting environmental assessments. All the details of the investigations are strictly confidential.