ADG1304.21 Dewatering Management Plan_Rev1.1_17.12.24

                                                                                          ADG Consulting Pty Ltd


3.2   Groundwater quality
      In the absence of any localised monitoring well data, and based on numerous groundwater investigations
      and dewatering monitoring projects that have been undertaken by ADG throughout the Noosa Coast
      Region 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) provided in 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 Noosa River.




 ADG1304.21 Dewatering Management Plan_Rev1.1_17.12.24                                                       Page 5