Acid Sulfate Report

                             25 EDWARD STREET, NOOSAVILLE
                             PROPOSED DUPLEX DEVELOPMENT



Executive Summary
This report details the results of an acid sulfate soil (ASS) and geotechnical site investigation undertaken for
the proposed residential unit development at 25 Edward Street, Noosaville. The investigation was performed
by Tectonic for The Property Clinic Pty Ltd.
Proposed development is to comprise, a single two-storey residential duplex on the site. The site will be
partially filled by up to about 1.0 m as part of construction works, with ground disturbance expected to be
limited to stripping of topsoil, filling of the site, construction of a pool, construction of sewerage and
stormwater infrastructure and construction of footings. These disturbances are all expected to be limited to
within 2 m of the existing ground surface level.
Site investigation comprised the drilling of two boreholes (up to 6.0 m BGL) and dynamic cone penetrometer
(DCP) testing to assess ground conditions. Soil and groundwater samples were collected for ASS analysis.
Subsurface conditions were relatively consistent and generally supports the mapped geology, comprising
interlayered alluvial and estuarine (natural) soils. The observed soil profile encountered approximately 0.5 m
of fill material being very loose to loose, poorly graded silty sand, underlain by natural very loose to medium
dense sand (including a layer of very dense or indurated sand occurring between approximately 3.2 m to 4.5
m BGL), changing to firm sandy clay and medium dense clayey sand at depths below 4.5 m. A consistent
groundwater table was encountered at 1.2 m to 1.4 m within alluvial sand. Groundwater conditions are likely
to be affected by proximity to the Noosa River, and proposed filling and subsequent building loads are not
expected to have any impact on existing groundwater conditions at the site, or result in the mobilisation of
any acidic leachate which may be present.
Shallow excavations, comprising trenching for services and footings, are expected to be achievable using
conventional earthmoving plant (e.g. excavators with toothed buckets). Conventional earthworks practices
may be adopted for this site. Based on the results of the investigation, the site is classified as equivalent to
Class ‘H1’ in accordance with AS 2870-2011 Residential Slabs and Footings. The estimated characteristic
surface movement (‘ys’) due to volume change as a result of moisture content variations at this site is
expected to be less than 10 mm (assuming non-reactive fill is placed). However, settlement from fill and
building loads may be in the order of 30 mm to 40 mm (resulting from very loose to loose sand). It is our
recommendation that the proposed residence and any associated structures (e.g. pool and retaining walls)
should be supported on high level footings founding in future controlled (certified) fill. Conventional footings
(beams, strip, pads) may be adopted, and be designed for an allowable bearing capacity of 100 kPa. If
higher bearing capacity is required, deeper footings will need to be installed. Due to the loose nature of the
sands at this site, and in order to minimise ground vibrations, it is recommended that screw-in (helical) steel
piles be adopted for deeper footings. Piles founded on the dense sand layer at a depth of 3 m to 3.5 m BGL
may be designed using an allowable end bearing capacity of 300 kPa. Care must be taken so as not to
penetrate through the dense layer. Piling companies must provide their own assessment of suitable pile
types and capacity.
Sands observed to an approximate depth of 1.0 m BGL (typically above the groundwater table) were
characterised by quantitative laboratory analysis as containing no significant actual or potential ASS. Thus,
where disturbed, soils above 1.0 m BGL require no treatment or specific management (other than standard
construction based environmental controls). Sands sampled from below 1.0 m BGL (typically near or below
the groundwater table) were characterised as containing levels of oxidisable sulfur (PASS), averaging 0.05
%S (31 mol H+ per tonne). This material presents a moderate risk of oxidation and acid creation if disturbed.
These underlying soils are not likely to be disturbed by the proposed works and thus presents a low risk to
the overall development of the site.
Where construction of stormwater or sewer infrastructure may be likely to disturb small volumes (<100 m 3) of
soil from below 1.0 m BGL, the risk posed by disturbance of potential acidity within the underlying sand may
be mitigated by conventional lime neutralisation of the disturbed material, combined with management of any
related runoff.
Where sands below 1.0 m BGL are disturbed, fine grained agricultural lime shall be mixed with the disturbed
material prior to treated material being reused on site, or exported off site. The neutralising agent (fine
grained agricultural lime) shall be applied at a rate of 2 kg per cubic metre.


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