Acid Sulfate Report

                             25 EDWARD STREET, NOOSAVILLE
                             PROPOSED DUPLEX DEVELOPMENT

6.0       ACID SULFATE SOIL ASSESSMENT

6.1       Information on Acid Sulfate Soil
ASS is common in low-lying coastal areas of Queensland, typically in Holocene to Pleistocene age alluvial
sediments located below RL 5.0 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, oxidise 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 the potential effects of ASS disturbance, 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. This shall be achieved through the following overall development
outcomes:
    a) development ensures that the release of acid and associated metal contaminants into the
       environment is avoided by either:
          i.  not disturbing ASS when excavating or otherwise removing soil or sediment, extracting
              groundwater or filling land; or
         ii.  treating and, if required, undertaking ongoing management of any disturbed ASS and
              associated drainage waters.

6.2       Field Screen Analysis
A total of 16 samples were recovered and assessed by pH field screen analyses. Soil pH (pH F) ranged from
5.8 to 7.4, indicating slightly acidic to neutral soil conditions present at the site.
A combination of three factors is considered when arriving at a positive field sulfide identification using pH
field screen analysis.
      1. Strength of the reaction with peroxide.
      2. Level of difference between field pH (pHF) and oxidised pH (pHFOX)
      3. Actual value of oxidised pH (pHFOX)
On this basis, 15 samples (of 16) indicated a moderate or higher likelihood of PASS being present.
It is noted that pH screen testing is indicative only and cannot definitively confirm the presence of ASS, nor
can it quantify the nature or strength of any acidity present. Further quantitative laboratory testing was
therefore carried out on a range of samples in order to assess the strength of any acidity present, and to
quantify the level of oxidisable sulfur content, if any.
Results of field screen analysis are summarised in Table B1, attached in Appendix B.




25 August 2017
Report No. 17265-001-Rev0                               9