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

                                                                                       ADG Consulting Pty Ltd

      Groundwater drawdown may also oxidise potential acid sulfate soils within the cone of depression,
      subsequently producing acidic groundwater conditions and mobilising heavy metals. Monitoring of the
      extracted untreated groundwater will be undertaken to detect in‐situ oxidation of soils, as required and
      at the frequencies stated in Section 6.5.2. Groundwater monitoring bores for groundwater level gauging
      external to the excavation footprint are expected to be unable to be established and monitored prior to
      and during construction on the site, due to limited space (SCG Consulting Engineers).

      Civil Engineering plans of the proposed development and basement arrangement are provided at
      Appendix C.
5.6   Groundwater treatment
      All extracted groundwater will be treated on‐site using available technologies prior to discharge to the
      stormwater network. The following treatment measures (or similar depending on final dewatering
      contractor selection) will be adopted, and will be installed and operational prior to the commencement
      of dewatering:

      1.    A groundwater pH buffering treatment system (primary treatment)
      2.    A sedimentation tank to provide additional residence time and sedimentation (secondary
            treatment)
      3.    A fine media filtration system designed for effective removal of heavy metals (tertiary treatment),
                                                                                                   tert




            if required.

      Details of the treatment systems and methodologies are provided in Section 6 of this report.

      Note: Consideration should be taken regarding placement of treatment gear on site to enable easy
      cleaning and maintenance throughout the dewatering phase for the project. Consider the potential
      requirement for regular de‐sludging of sedimentation tank/s to suitable area onsite, if available (cost
      minimisation).
5.7   Nominated Hold Points
      In accordance with anticipated DA Conditions, nominated hold points to be enacted during construction
      have been proposed to facilitate for certification by the suitably qualified person experienced with Acid
      Sulfate Soils, as well as Council Development Engineer to ensure all possible avenues for continual
      dewatering below permanent groundwater level, including around pipework bedding that outlet to
      waterways, are appropriately sealed. The nominated hold points regarding dewatering for this project
      are:
      1. Prior to commencement of dewatering/initial pump out
      2. At finished excavation level, prior to blinding layer application
      3. External to basement service installation trench opening/s prior to backfilling.

      The above nominated hold points are subject to confirmation by the consulting engineer, and liaison with
      council representatives and the Site Manager.




 ADG1808.25 Dewatering Management Plan_Rev0_07.05.25                                                      Page 12