Reference Document - RAL25/0020 & OPW25/0194 (As Published)

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3.2    Acid Sulfate Soils

Acid sulfate soils (ASS) are naturally occurring sediments and soils containing iron sulfides or
sulfidic materials, often located over extensive low-lying coastal areas which are generally
geologically young, alluvial or estuarine sediments (ie. late Holocene age), predominately below
RL 5 AHD.

Reference to the Department of Natural Resources and Mines – Acid Sulfate Soils Map 2 Redcliffe
to Teewah, indicates that the site is considered as “land between the 5m AHD contour and the
outer limit of Holocene, estuarine ASS (ie land <5m AHD), with low probability of ASS occurrence.”

The presence or otherwise of ASS was determined through laboratory testing. The results of
laboratory testing are discussed in Sections 5.5 and 6.9 in this report.


4. Field Work

4.1    Field Work Methods

The field work was carried out on 8 September 2025 and comprised the drilling of six bores
(designated as Bores 1 to 6). The bore locations were set out with reference to site features, with
the bore locations and surface level recorded afterwards using a high precision differential global
positioning system (DGPS) receiver relative to GDA2020 and AHD. It is important to note that
Douglas is not a registered surveyor, hence the coordinates and elevations are considered to be
approximate. The approximate bore locations are indicated on Drawing 1 in Appendix B.

The bores were drilled to 3.0 m depth with a 4WD ute mounted Drillman GT10-KD drilling rig
using continuous flight augers fitted with a tungsten carbide (TC) bit. Dynamic cone
penetrometer (DCP) and pocket penetrometer (pp) testing was carried out to assess the relative
density and strength consistency of the subsurface soils. On completion of drilling following
observation for any groundwater seepage, the bores were backfilled with drill spoil which was
tamped into the holes.

The field work was undertaken by experienced geotechnical personnel who operated the drilling
rig, logged the bores, and collected samples for visual and tactile assessment and subsequent
laboratory testing. Strata identification was undertaken through observation of cutting returns
and recovered samples. Field descriptions and samples were checked by a geotechnical
engineer, with the borehole logs corrected where appropriate to reflect the available laboratory
test results.

4.2    Field Work Results

The subsurface conditions encountered in the bores are described in detail on the borehole logs
in Appendix C, together with notes which define the classification methods and descriptive terms
used. The depths were measured below existing surface levels at the time of investigation.

In summary, the subsurface conditions encountered in the bores typically comprised surficial
topsoil and/or sandy gravel fill, overlying localised sandy silt/silty sand and silty, sandy clays.
The subsurface conditions are further described below:




Proposed Subdivision                                                              237894.00.R.001.Rev0
12-14 Gympie Street, Tewantin                                                            October 2025