Attachment 4 - Geotech Report · MCU23/0030

                              50 NOOSA PARADE, NOOSA HEADS
                              PROPOSED RESIDENCE

         An assessment of the depth of relatively impermeable indurated sand materials to provide a ‘cut off’
          into which the temporary retention system could be keyed into to resist against the upward migration
          of groundwater for the basement excavation.
         Increased information and data to refine the pile design for structures to the rear of the site.
         A review of global stability of the proposed works near the river revetment, which should consider
          detailed design of the landscaping proposed in that area.


7.0       ACID SULFATE SOIL ASSESSMENT

7.1       General
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, can 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 may also be present
because of previous exposure of ASS material either by human interference or by natural processes. This
acidity may become mobilised by ground disturbances.
The production, or mobilisation of acidity related to ASS, 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.

7.2       DERM ASS Mapping
An extract from the Queensland Government’s Redcliffe to Teewah Acid Sulfate Soils Map 2 (NR&M-SEA-I-
A0 3261) covering the region is shown in Text Figure 8 overleaf. The mapping classifies the site as ‘SDL’
(purple shading), which is described as “disturbed land…likely to contain ASS”, and that only a “limited field
investigation” has been undertaken as part of the mapping program.
It should be noted that ASS risk mapping does not definitively indicate the presence nor absence of ASS at a
particular site, but rather provides an indication of terrain where ASS is likely to occur. The presence or
absence of ASS at a site may only be confirmed by completion of a site investigation, involving an
appropriate degree of site assessment and quantitative analysis.




2 February 2023
Report No. 22500-001-Rev0                                13