Reference Document - Dewatering Management Plan (For Stamping) MCU25/0053 & OPW25/0074

                                                                                                                    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




Document Set ID: 23735664
Version: 1, Version Date: 12/05/2025