Dewatering Management Plan · OPW24/0032

                                                                                          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.
             Preliminary Concept Design, Pallazzesi Residence, Part 1, 2D Set. 2021. Metricon Homes Pty Ltd.
     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_Rev0_08.10.21                                                          Page 4