RFI - ADG1451.22 Dewatering Management Plan_Rev0_28.02.23

                                                                                       ADG Consulting Pty Ltd


3    Previous investigations
     This DMP is based on site specific information sourced from the following, provided to ADG by
     SCG Consulting Engineers:
             Acid Sulfate Soil Investigation, Proposed Residential Development, 128 – 132 Gympie Terrace,
              Noosaville. November 2022. Pacific Geotech Pty Ltd. Ref: PG‐9236, 2022‐10‐31, ASR VER 1.
             Geotechnical Investigation, Proposed 128 – 132 Gympie Terrace, Noosaville. November 2022. Pacific
              Geotech Pty Ltd. Ref: PG‐9236, 2022‐11‐08, GR VER 1.
             Operational Works: Earthworks & Piling – 130 – 132 Gympie Terrace, Noosaville. Drawing No. 32225‐
              OW3.1. September 2022. SCG Consulting Engineers Pty Ltd.
     It is noted that dilapidation reports for surrounding structures and services are proposed to be
     undertaken prior to commencement of construction and dewatering, 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 Pacific Geotech Pty Ltd 2022
     A Geotechnical Investigation and concurrent Acid Sulfate Soils Investigation was undertaken at the site
     in October 2022 (reported November 2022) by Pacific Geotech Pty Ltd (PG).
3.1.1 Soils
     A total of four (4) boreholes (BH01 to BH04) were drilled on the proposed development footprint to
     between 4.0 and 9.0 mbgl.

     The subsurface profile encountered is generally described as clay and sand fill material at the ground
     surface, extending to depths ranging between 1.0 m and 1.1 m. Fill material is underlain by natural sand
     and silty sand which is initially medium dense, becoming loose with depth, extending to depths ranging
     between 2.5 m and 2.9 m. The upper‐level sand is underlain by very dense, indurated sand which extends
     to depths ranging between 2.8 m and 3.2 m. This indurated sand is underlain by stiff to hard, silty and
     sandy clay, which extends to the borehole termination depths.

     Alongside the Geotechnical Investigation (2021), Acid Sulfate Soil (ASS) samples were collected at 0.5 m
     intervals in BH01 & BH02 to 4.0 m depth. A total of sixteen (16) samples were collected for ASS screening
     and eight (8) samples were selected for further analysis by the Chromium Reducible Sulfur suite (CRS).

     ADG notes that the testing was limited to two boreholes with ASS testing to 4.0 m depth, and PG reports
     that within part of this depth profile the natural sands are considered to contain potential ASS requiring
     liming at rates of up to 8 kg/tonne. All excavated spoil from depths between 1.5 to 2.5 mbgl within the
     excavation footprint will be appropriately neutralised with lime and validated in accordance with
     recommendations by PG in the ASS Investigation Report (PG, 2022).
3.1.2 Groundwater
     During drilling activities for the Preliminary Geotechnical Investigation, groundwater seepage/inflow was
     encountered at 1.0 to 1.1 m depth below the ground surface (approx. 0.6 m AHD)(PG, 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 to the east and river to the north, albeit somewhat a dampened
     response to tidal variations.
3.2 Groundwater quality
     No groundwater quality data was obtained by PG as part of the preliminary geotechnical investigation.
     However, based on numerous groundwater investigations and dewatering monitoring projects that have


ADG1451.22 Dewatering Management Plan_Rev0_28.02.23                                                      Page 4