RESPONSE TO FURTHER ADVICE - ADG1808.25 Dewatering Management Plan_Rev0_07.05.25 · MCU25/0054

                                                                                      ADG Consulting Pty Ltd

     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.




ADG1808.25 Dewatering Management Plan_Rev0_07.05.25                                                     Page 5