Attachment H - Acid Sulfate Soils Assessment

                              PROPOSED COMERCIAL & RESIDENTIAL DEVELOPMENT
                              30 & 32 DOONELLA STREET, TEWANTIN


1.0      INTRODUCTION
Tectonic has undertaken an acid sulfate soil (ASS) assessment for a proposed commercial and residential
development at 30 & 32 Doonella Street, Tewantin. This report summarises the site conditions and
associated ASS hazard posed by the proposed works, to address Items 21 and 22(c) of Noosa Council
(NC) information request (Ref.: MCU21/0013 & OPW21/0031) and presents the results of our assessment
taking into consideration State guidelines and NC requirements pertaining to ASS.

In summary, the local geology, as identified by geotechnical investigation (Tectonic Report No. 18151-001,
dated 22 June 2018), primarily consists of residual soil associated with the Triassic to Jurassic age Myrtle
Creek Sandstone, which is not associated with the formation and occurrence of ASS. This understanding is
supported by published geological and ASS risk mapping.
Proposed site development will not generally involve disturbance of soil below an elevation of RL 5 m AHD,
however some minor disturbances to RL 4.4 m AHD may occur for construction of the lift overrun, water
detention tanks and a bio-retention basin. These works are expected to disturb only residual (non-ASS) soil,
totalling a relatively small total volume (~60 m3), and would therefore present negligible risk of ASS related
impact. Based on the limited extent of excavation below RL 5 m AHD, and presence of residual soils, the
proposed development is deemed to conform with performance outcome PO1 of NC’s ASS Overlay Code
(i.e. development does not disturb ASS). No further site assessment or specific management measures
regarding ASS are warranted for the proposed works.


2.0      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 m AHD. Such areas are often characterised by the presence of estuaries,
swamps, floodplains, salt marshes and mangroves, primarily occurring in estuarine based alluvial soil.

ASS affected soils contain iron sulfides, most frequently pyrite, which, when exposed to air can oxidise to
form sulfuric acid. Existing acidity attributed to the historic oxidation of iron sulfides may also be present
because of previous exposure of ASS material either by human interference or by natural processes.

When these soils are maintained in their natural setting (generally anaerobic conditions below the
groundwater table or sea level), the iron sulfides are unable to oxidise, therefore the ASS remains in a stable
state, and in equilibrium with the surrounding environment. 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.

The resulting creation of large volumes of acidity can occur rapidly, resulting in significant impacts to local
waterways, sensitive terrestrial environments, or in extreme cases, public health.


3.0      SITE DESCRIPTION
The subject site occupies two parcels of land described as Lot 32 on RP893427 (#30) and Lot 903 on T1631
(#32), situated on the northern side of Doonella Street, Tewantin. The site has an approximate 60 m
frontage to Doonella Street on its southern side and is otherwise bounded by commercial and residential
properties to the north and west and at-grade carparking to the east.
Ground surface elevations across the site range from RL 5 m to RL 9 m AHD and the property is mapped as
ASS Area 2, under NC’s ASS Overlay Code. Topographically, the site is situated on the flank of a gentle
hillslope with the ground surface sloping in a south/south-easterly direction toward Doonella Street.

The site location and general setting are illustrated in Text Figure 1 overpage.




26 May 2021
Report No. 18151-002-Rev0                               1