ADG1290.21 Dewatering Management Plan_Rev1_02.02.22 · OPW21/0315

                                                                                          ADG Consulting Pty Ltd


3    Previous investigations
     This DMP is based on site specific information sourced from the following, provided to ADG by Chris Clout
     Designs:
              Preliminary Geotechnical Investigation, Proposed Residence 33 Wyuna Drive, Noosaville. 2020.
               Douglas Partners Pty Ltd. Ref: 95120.00.R.001.
              Additional Geotechnical Investigation, Proposed Residence 33 Wyuna Drive, Noosaville. 2022.
               Douglas Partners Pty Ltd. Ref: 95120.01.R.001.
     It is noted that dilapidation reports for surrounding structures and services have been undertaken which
     were not supplied to ADG for the purposes of preparing this DMP, however are to be provided to Council
     separately from this DMP.

     A brief discussion of relevant soil and groundwater conditions is provided below.
3.1 Douglas Partners Pty Ltd 2020 & 2022
     A preliminary Geotechnical Investigation was undertaken at the site in September 2020 by Douglas
     Partners Pty Ltd (DP), with an additional geotechnical and acid sulfate soil assessment undertaken in
     December 2021.
3.1.1 Soils
     Between the preliminary and additional investigations undertaken by DP, a total of four (4) boreholes
     (BH1 – BH4) were drilled on the proposed development footprint to 6.0 mbgl.

     The subsurface profile encountered is generally described as loose to medium dense brown, orange‐
     brown grey sand fill to between 2.2 and 2.3 mbgl, corresponding to approximate elevations of ‐0.3 to
     0.05 mAHD. Underlaying the fill layer were natural sands starting with a relative density of medium dense
     to dense at depth of silty sand to 3.3 m depth (approx. 0.9 mAHD), then a layer of medium dense, dense
     to very dense (indurated) sands from between 4.8 to 5.4 m depth (approx. ‐2.9 to ‐3.1) and continuing
     until the termination depth of 6.0 mbgl in all boreholes.

     As part of the Preliminary Geotechnical Investigation (2020) and Additional Geotechnical Investigation
     (2021), Acid Sulfate Soil (ASS) samples were collected at 0.25m intervals in BH1 to BH4 to 4.0 m depth. A
     total of 64 samples were collected for ASS screening and 11 samples were selected for further analysis
     by the Chromium Reducible Sulfur suite (CRS).

     ADG notes that the testing was generally in accordance with the National Acid Sulfate Soil guidance
     documents in terms of a minimum 4 test locations and to approximately 1.0 m below proposed extent of
     excavation and dewatering with ASS testing to 4.0 m depth. DP reports that within this depth profile both
     the existing sand fill and natural silty sand are considered to be mildly acidic, with both the fill layer and
     natural sands considered to contain low level PASS requiring liming at minimal rates of 2 kg/tonne.
3.1.2 Groundwater
     Groundwater seepage was recorded at between 1.65 to 2.35 mbgl (equating to approximate
     groundwater elevations of 0.25 to 0.05 mAHD), during preliminary and follow‐up geotechnical works
     (drilling) on the site by Douglas Partners in September 2020 and December 2021. Douglas Partners also
     undertook a follow‐up standing water level gauging of 1.7 mbgl (equating to groundwater elevation of
     0.2 mAHD). (Douglas Partners, 2020 & 2022).

     It should be noted however, that groundwater depths and ground moisture conditions are affected by
     weather and climatic conditions, tidal variations, surface and subsurface drainage/permeability
     conditions, and human influence and will therefore vary with time. Groundwater levels are expected to
     be similar to the water level in the canal at the rear of the site, albeit somewhat a dampened response
     to tidal variations.




ADG1290.21 Dewatering Management Plan_Rev1_02.02.22                                                          Page 4