Acid Sulfate Report

                              25 EDWARD STREET, NOOSAVILLE
                              PROPOSED DUPLEX DEVELOPMENT

4.0      INVESTIGATION FINDINGS

4.1       Subsurface Conditions
Subsurface conditions encountered in the boreholes were relatively consistent and generally supports the
mapped geology for the site, 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. PSD results confirm our visual classifications of the
soils in the field.
Any potential settlement of loose sand is not expected to cause any significant alteration to existing
groundwater conditions (being typically unconfined and within highly permeable sand), thus no significant
ASS related impacts are expected as a result of proposed filling at the site. Displacement of soil as a result
of filling works is also not expected to occur.

4.2       Groundwater Conditions
Groundwater was encountered in both boreholes between 1.2 m to 1.4 m BGL, occurring within highly
permeable alluvial sand. Groundwater quality was measured in the field, from a sample obtained from
borehole BH1, on 9 August 2017, with the results summarised in Table 1 below.
Table 1: Summary of Groundwater Monitoring

 Parameter                                            Units                                   BH1

 Depth                                               m BGL                                    1.4

 pH (field)                                          pH unit                                  6.98

 Electrical Conductivity (field)                     MS/cm                                    1.84

 REDOX Potential                                       mV                                      65

Testing indicates that the groundwater is neutral and slightly brackish, being common for shallow alluvial
groundwater along the Noosa coastal strip. Considering the close proximity of Noosa River to the north-
east, higher salinity may be encountered in groundwater at greater depths below the water table level
(‘fresher’ groundwater typically ‘perches’ above heavier saline waters).
Groundwater levels are expected to fluctuate with prevailing weather conditions, and may also be affected by
tidal variations given the low-lying nature of the site and proximity to Noosa River.
Given the high hydraulic permeability of the underlying alluvial sand, the placement of proposed fill across
the site and subsequent building load is not expected to have any significant impact on groundwater
conditions at the site, or result in the mobilisation of acidic leachate. It is noted that no dewatering of natural
groundwater conditions are expected to be necessary for construction.




25 August 2017
Report No. 17265-001-Rev0                                5