RESPONSE TO FURTHER ADVICE - ADG1808.25 Dewatering Management Plan_Rev0_07.05.25 · MCU25/0054

                                                                                             ADG Consulting Pty Ltd


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

              PTG Consulting. April 2025. Geotechnical Soils Investigation Report (Interim), Proposed Residential
               Development, 20 William Street, Noosaville. PTG/02023 – 001 – Rev 1.
              SCG Consulting. April 2025. Drawing Set. Operational Works for Residential Development Lot 3 on
               RP63813 No. 20 Wiliam St, Noosaville. Rev issued 15 April 2025. (see Appendix C).
              Skale Building Design. March 2025. Drawing Set. Duplex Residence 20 William Street, Noosaville.
               2502 – 07 – Rev DA01.

         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
         March 2025 (report dated April 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 attempted or drilled
         to depths of up to 3.0 m below ground level (bgl) using solid flight auger with a specialised 4WD truck‐
         mounted drill rig. BH1 was terminated at surface due to presence of astroturf underlain by concrete of
         unknown thickness. The sub‐surface soil profile encountered in the remaining boreholes generally
         comprised a thin silty sand topsoil layer underlain by silty sand/sand to the termination depth of up to
         3.0 mbgl. The sands were described as generally medium dense to dense, with some loose material
         encountered near the surface. PTG noted that additional investigation will be required to adequately
         characterise the subsurface profile.

         A total of fifteen (15) soil samples were recovered from boreholes (BH2 to BH3) at 0.25 m intervals from
         between 0.0 m and 3.0 m in depth. No samples were reported as being subject to laboratory analysis by
         the Chromium Reducible Sulfur suite (CRS), despite field screening indications of potential ASS, with PTG
         noting that additional CRS analysis has been arranged but not yet reported in the Interim Geotechnical
         Investigation Report.

         It is noted that the ASS investigation did not provide assessment of deeper soils (>3.0 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). However, ADG notes that
         groundwater levels can be perched and fluctuate seasonally and during heavy rainfall events. Due to the
         site’s close proximity to the tidal Noosa River and the permeable nature of the silty sand soils
         encountered, this 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 sandy subsurface profile and proximity to the tidal canal network associated with Noosa
         Inlet these relative groundwater levels should be expected, with higher levels during or following periods
         of intense or extended rainfall.
3.2      Groundwater quality
         No site specific groundwater investigation was undertaken as part of the preliminary Geotechnical and
         ASS Investigations undertaken by PTG Consulting. However, ADG is of the opinion that localised
         monitoring well data can often be misleading and does not always accurately represent the properties of
         the groundwater that will be extracted and treated from the entire site and local surrounds during

    ADG1808.25 Dewatering Management Plan_Rev0_07.05.25                                                      Page 4