003 ECM_22828362_v1_Reference Document - OPW23 0189 · OPW26/0094

                                                                                                                    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




Document Set ID: 22828362
Version: 1, Version Date: 26/02/2024