Compiled Reference Document - MCU25/0020 (As Published)

7.           Acid Sulfate soil assessment
7.1          Information on Acid Sulfate Soil
ASS is common in low-lying coastal areas of Queensland, typically in Holocene to Pleistocene age alluvial
and estuarine sediments located below RL 5 m AHD. Such areas are often characterised by the presence
of estuaries, swamps, floodplains, salt marshes and mangroves. The affected soils contain iron sulfides,
most frequently pyrite, which when exposed to air, oxidises to form sulfuric acid.
There are two basic types of ASS. These are actual acid sulfate soil (AASS), which is soil in which pyrite
has already oxidised and sulfuric acid is present in the soil, and potential acid sulfate soil (PASS), where
pyrite is present but has not been oxidised.
When these soils are maintained in their natural setting (generally anaerobic conditions below the
groundwater table or sea level), the iron sulfides (PASS) are unable to oxidise, therefore the ASS remains
in a stable state. However, where disturbances such as civil construction or development expose ASS to
aerobic conditions, the iron sulfides are able to oxidise and form sulfuric acid, resulting in the soil
becoming acidic. Existing acidity attributed to the oxidation of ASS (AASS) may also be present because
of previous exposure of ASS material either by human interference or by natural processes. This acidity
has the potential to mobilise metals which are naturally present in the soil, thereby producing a leachate
contaminated by both high levels of acidity and metals. The chemical reactions can also strip the
leachate of dissolved oxygen. Such leachate, if released into the environment, can have significant
adverse effects including degradation of the water quality in receiving areas, fish disease/kills, reduced
crop productivity, corrosion of built structures and health related issues.
In view of these potential effects, it is critical that any development that occurs within an area likely to
contain ASS is planned, managed and monitored appropriately so as to minimise or remove the risk of
adverse environmental outcomes. Development involving ASS must comply with the requirements of
state and local regulations pertaining to ASS, this includes Noosa Council’s Planning Policy and its
attendant guidelines.
This shall be achieved through the following overall development outcomes:
    Development ensures that the release of acid and associated metal contaminants into the
     environment is avoided by either:
    Not disturbing ASS when excavating or otherwise removing soil or sediment, extracting groundwater
     or filling land; or
    Treating and, if required, undertaking ongoing management of any disturbed ASS and associated
     drainage waters.
Other forms of acidity may be present in soil that is not sulfuric in nature, thus not produced or
associated with the occurrence of ASS. These can be commonly termed ‘acidic non-ASS.’ While these
soils are not regulated to the same extent as ASS, it is prudent to operate within the requirements of
Queensland environmental law and manage the acidity in line with best practice management criteria, as
set out within the Queensland ASS Technical Manual if these types of soil are going to be disturbed.




Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                                   19