Appendix H - Dewatering Management Plan · MCU25/0053

                                                                                              ADG Consulting Pty Ltd


3        Previous investigations
         This DMP is based on site specific information sourced from the following documentation provided to
         ADG by Seymour Group:

              PTG Consulting. February 2025. Geotechnical Investigation Report – Proposed Residential
               Development 7 Noosa Parade, Noosa Heads. PTG/01608 – 001 – Rev 0.
              PTG Consulting. April 2025. Acid Sulfate Soil Investigation Management Plan – Proposed Residential
               Development 7 Noosa Parade, Noosa Heads. PTG/01608 – 002 – Rev 0.
              SCG Consulting. May 2025. Operational Works for Residential Development Lot CP on BUP 10936
               No. 7 Noosa Pde, Noosa Heads. Rev issued 1 May 2025. (see Appendix C).
              Bureau Proberts. April 2025. Drawing. Proposed Residence 7 Noosa Parade. 24048 – AR 00.01 –
               Rev 4.

         A brief discussion of relevant soil and groundwater conditions is provided below.
3.1      PTG Consulting 2025
         A Geotechnical and Acid Sulfate Soil (ASS) Investigation was undertaken on the site by PTG Consulting in
         January 2025 (report dated February 2025). The following sections summarise the relevant information
         from the report provided.
3.1.1 Soils
         During the Geotechnical and ASS investigation four (4) boreholes (BH1 to BH4) were drilled to depths of
         4.5 m below ground level (bgl) using solid flight auger with a specialised 4WD truck‐mounted drill rig. The
         sub‐surface soil profile comprised a silty sand/ sand to the termination depth of 4.5 mbgl. The sands
         were described as generally medium dense to dense, with some loose material encountered near the
         surface.

         A total of seventy‐two (72) soil samples were recovered from boreholes (BH1 to BH4) at 0.25 m intervals
         from between 0.0 m and 4.5 m in depth. Based on field screening results, a total of eighteen (18) samples
         were selected for laboratory analysis by the Chromium Reducible Sulfur suite (CRS). The analysed samples
         reported the presence of low to high levels of potential acid sulfate soils (PASS) throughout the soil profile
         with titratable actual acidity (TAA) concentrations ranging from <10 to 128 moles H+/tonne (9 of 18
         samples reporting above the action criteria of 18 moles H+/tonne). Nine (9) samples reported oxidisable
         sulfur concentrations ranging from 0.066 to 0.194 %S which were at or above the relevant action criterion
         of 0.03 %S, indicating the presence of potential acid sulfate soils (PASS) within the soil profile to
         approximately 4.5 m (extent of investigation by PTG Consulting).

         PTG Consulting estimated, approximately 800 tonnes of soil will be disturbed below RL 5 m AHD. With
         the highest recorded net acidity value of 128 mol H+/t, a ‘Very High Level of Treatment’ is required. The
         results indicate soils contain high levels of existing and potential acidity and will therefore require
         management of actual acid sulfate soils. A maximum liming rate of 10 kg CaCO3/m3 was calculated for
         the site.

         It is noted that the ASS investigation did not provide assessment of deeper soils (>4.5 mbgl) or cone of
         depression that will be created during dewatering. Given ADG’s previous experience with ASS and
         dewatering operations in the local area, ASS conditions are likely to become more significant with
         increasing depth and rewetting of the soil structure in the cone of depression following commencement
         of dewatering.
3.1.2 Groundwater
         During the geotechnical and acid sulfate soil investigation, no groundwater was reported as being
         encountered during the drilling of the boreholes (PTG Consulting, 2025). PTG Consulting notes, that
         groundwater levels can be perched and fluctuate seasonally and during heavy rainfall events. Due to the
         site sites close proximity to the tidal Noosa River and the permeable natural of the soils encountered,
         increases the likelihood of groundwater fluctuations. In addition, ADGs recent previous experience in the
         locality has generally identified standing groundwater at or around RL 0.5 to 1.0 mAHD, and given the

    ADG1777.25 Dewatering Management Plan_Rev0_01.05.25                                                          Page 4