Acid Sulphate Soils Guideline

Draft Identification and investigation of acid sulfate soils and groundwater

Introduction

Investigations

Using Lab Results

Groundwater

Further Information

References

App. 1: Risk Map

App. 2: Indicators

App. 3: Soil pH

App. 4: Action Criteria

 

Draft Identification and investigation of acid sulfate soils and groundwater

Appendix 2: Soil and water indicators

The site investigation will involve the applicant undertaking a visual field investigation of soil and ground and surface water characteristics. Some helpful soil and water field indicators suggesting the presence of ASS are set out below. Some of the indicators will only be available when boreholes are augered.

Soil TypeIndicators
Actual acid
Sulfate soil
(AASS)

Soil characteristics

  • field pHF ≤4 (when field pHF >4 but <5 may indicate some existing acidity and other indicators should be used to confirm presence or absence);
  • presence of corroded shell;
  • any jarositic horizons or substantial iron oxide mottling in surface encrustations or in any material dredged or excavated and left exposed; and
    NB: Jarosite is a characteristic pale yellow mineral deposit that can precipitate as pore fillings and coatings on fissures. In the situation of a fluctuating watertable, jarosite may be found along cracks and root channels in the soil. However, jarosite is not always found in actual ASS.
  • sulfurous smell e.g. hydrogen sulfide or 'rotten egg' gas.

Water characteristics

  • water of pH <5.5 (and particularly below 4.5) in adjacent streams, drains, groundwater or ponding on the surface (this is not a definitive indicator as organic acids may contribute to low pH in some environments such as melaleuca swamps);
  • unusually clear or milky blue-green drain water flowing from or within the area (aluminium released by ASS acts as a flocculating agent); and
  • extensive iron stains on any drain or pond surfaces, or iron-stained water and ochre deposits.

Landscape and other characteristics

  • dead, dying, stunted vegetation*;
  • scalded or bare low-lying areas*; and
  • corrosion of concrete and/or steel structures*.
* May also be due to excessive salinity or to salinity in combination with AASS.
Potential acid sulfate soil (PASS)

Soil characteristics

  • waterlogged soils - unripe muds (soft, buttery, blue grey or dark greenish grey), silty sands or sands (mid to dark grey) or bottom sediments (dark grey to black e.g. monosulfides) possibly exposed at sides and bottoms of drains or cuttings, or in boreholes;
  • soil pHF <4 and commonly neutral (see also Appendix 3 for details on soil field pH tests);
  • soil pHFOX <3, with a large unit change from pHF to pHFOX, together with a strong reaction to peroxide;
  • reaction to peroxide using semi-microscopic screening techniques;
  • presence of shell; and
  • a sulfurous smell e.g. hydrogen sulfide or 'rotten egg' gas.

Water characteristics

  • water pH usually neutral but may be acid.
    NB: Caution should be taken when inspecting highly altered landscapes in the field (e.g. where inert fill has been placed over ASS material). Soil, water and landscape indicators may be masked by past landscape and drainage modifications and this should be taken into consideration when defining borehole locations.


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