Reference Document - OPW23 0189

                                                                                              ADG Consulting Pty Ltd


3        Previous investigations
         This DMP is based on site specific information sourced from the following, provided to ADG by SCG:
              Preliminary Geotechnical Investigation, Proposed Residence, 38 Mossman Court, Noosa Heads.
               2021. Douglas Partners Pty Ltd. Ref: 206126.00.R.001.
              Preliminary Concept Design, Noosa Villa, Set dated 11 July 2023. Chris Clout Design.
         A brief discussion of relevant soil and groundwater conditions is provided below.
3.1      Douglas Partners Pty Ltd 2021
         A preliminary Geotechnical Investigation was undertaken at a nearby site situated at 38 Mossman Court
         in July 2021 by Douglas Partners Pty Ltd (DP). This information has been used in preparing this report in
         the interim until site‐specific geotechnical and acid sulfate soils information becomes available, and is
         considered applicable given the short ~25 m horizontal distance between the two sites directly across
         the cul‐de‐sac bulge.
3.1.1 Soils
         A total of one (1) borehole (Bore 1) was drilled within the northern portion of the 38 Mossman Court site
         (due to limited rig access) to 6.0 m below ground level (bgl). Two additional dynamic cone penetrometer
         (DCP) tests were carried out within the southern portion of that site.

         The subsurface profile encountered generally comprised medium dense silty sand fill overlying medium
         dense to dense silty sand fill to approximately 0.9 m in depth. Natural medium dense silty sand was
         encountered to 3.7 m depth overlying dense silty sand to 4.7 m depth. Very dense silty sands were
         encountered to the termination depth of 6.0 m (Bore 1 only). DP reported that similar conditions were
         reported within the DCP holes, with relatively loose conditions encountered to 1.5 m depth.

         As part of the Preliminary Geotechnical Investigation (2021), Acid Sulfate Soil (ASS) samples were
         collected at 0.25 m intervals in Bore 1 to 4.0 m depth. A total of sixteen (16) samples were collected for
         ASS screening and four (4) samples were selected for further analysis by the Chromium Reducible Sulfur
         suite (CRS). Titratable actual acidity (TAA) concentrations were reported to be between 9 moles H+/tonne
         and 26 Moles H+/tonne, with one exceedance of the relevant QASSIT action criterion of 18 moles
         H+/tonne in Bore 1 at 1.0 m depth. Therefore, actual acid sulfate soils (AASS) should be expected to be
         present to at least 1.0 m depth bgl. Reported oxidisable sulfur concentrations reported as SCr ranged
         from 0.06 %S to 0.18 %S, all above the relevant action criterion of 0.03% S. The results indicated the
         presence of potential acid sulfate soils (PASS) to at least 3.25 m bgl.

         ADG notes that the testing was limited to one borehole with ASS testing to 4.0 m depth. DP summarised
         that within this depth profile both the existing sand fill and natural silty sands are considered to contain
         ASS and that neutralisation, using ag lime or similar will be required at a rate of 9.5 kg/m3 for the upper
         fill profile and at a rate of 12.5 kg/m3 for the natural silty sands on the site. In addition, to treatment of
         the excavated soil, a guard layer of ag lime (rate 4 kg/m3) should be applied to the basement excavation.

         It is expected that ASS impacted material will be excavated and removed from site for appropriate
         treatment and disposal at a licenced facility due to available area constraints on site. Given that ASS
         material has been identified within the locality sub‐soil profile, any leachate generated on the site must
         be suitably treated/neutralised before leaving the site and must not be directly discharged to stormwater.
3.1.2 Groundwater
         During drilling activities for a nearby Preliminary Geotechnical Investigation at 38 Mossman Court,
         groundwater seepage/inflow was encountered at 1.60 m depth below the ground surface, which
         corresponds to an elevation of approximately 0.5 m AHD (Douglas Partners, 2021).




    ADG1580.23 Dewatering Management Plan_Rev0_28.09.23                                                          Page 4