Appendix H - Dewatering Management Plan · MCU25/0053

                                                                                       ADG Consulting Pty Ltd

      sandy subsurface profile and proximity to the tidal canal network associated with Noosa Inlet these
      relative groundwater levels should be expected, with higher levels during or following periods of intense
      or extended rainfall.
3.2   Groundwater quality
      No site specific groundwater investigation was undertaken as part of the Geotechnical and ASS
      Investigations undertaken by PTG Consulting. However, ADG is of the opinion that localised monitoring
      well data can often be misleading and does not always accurately represent the properties of the
      groundwater that will be extracted and treated from the entire site and local surrounds during
      dewatering. Therefore, based on numerous groundwater investigations and dewatering monitoring
      projects that have been undertaken by ADG throughout the Noosa Coast and nearby sites in recent years.
      Our understanding of the groundwater quality in the region is provided below:
          Groundwater is generally mildly acidic to neutral, with pH levels ranging from approximately 5.5 to
           6.5 and electrical conductivity ranging from brackish to saline between 2,000 µS/cm to
           48,000 µS/cm. Groundwater pH has the potential to reduce (become more acidic) following
           oxidisation of PASS as dewatering progresses, particularly if re‐wetting of the soils occurs.

           Dissolved oxygen levels in static groundwater typically range from approximately 35 – 40 %
            saturation.

           The groundwater associated with indurated sand strata is moderately to highly turbid as a result of
            staining and organic content.

           Concentrations of dissolved metals are typically below the available marine water trigger values
            (MWTV’s) in ANZG (2018) which supersedes ANZECC/ARMCANZ (2000) for the receiving waters,
            however elevated levels of aluminium and particularly iron are expected in the untreated
            groundwater and have the potential to increase following oxidisation of PASS as dewatering
            progresses or as a result of existing acidic groundwater conditions.

           Given the location and previous use of the site, groundwater impacts resulting from site
            contamination are not anticipated.

      A groundwater investigation will be undertaken at the commencement of dewatering as described in
      Section 6.5.2 of this report. This assessment will be representative of the groundwater being extracted
      and treated from the entire site, as opposed to localised monitoring well data which is often misleading.
      Based on previous experience with dewatering in the area, ADG expects the groundwater to require
      treatment to increase pH and dissolved oxygen levels, as well as reduce turbidity, suspended sediments
      and dissolved metal concentrations prior to being discharged to the stormwater system.




 ADG1777.25 Dewatering Management Plan_Rev0_01.05.25                                                     Page 5