ADG1304.21 Dewatering Management Plan_Rev1.1_17.12.24

                                                                                              ADG Consulting Pty Ltd


3        Previous investigations
         This DMP is based on site specific information sourced from the following, provided to ADG by Metricon
         Homes QLD Pty Ltd:
              Preliminary Geotechnical Investigation, Proposed Residence, 38 Mossman Court, Noosa Heads.
               2021. Douglas Partners Pty Ltd. Ref: 206126.00.R.001.
              Design Plans, Pallazzesi Residence, Lot 145, 38 Mossman Crt, Noosa Heads. SCG Consulting
               Engineers. (December 2024).
         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 the site in July 2021 by Douglas Partners Pty
         Ltd (DP).
3.1.1 Soils
         A total of one (1) borehole (Bore 1) was drilled within the northern portion of the 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 the 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 reports, 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 indicate 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 – further information
         on the liming rate (if required) is available in Section 7.5.3 of the Preliminary Geotechnical Report
         prepared by DP. Given that ASS material has been identified within the 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 the Preliminary Geotechnical Investigation, 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).




    ADG1304.21 Dewatering Management Plan_Rev1.1_17.12.24                                                        Page 4