ADG1290.21 Dewatering Management Plan_Rev1_02.02.22 · OPW21/0315

                                                                                        ADG Consulting Pty Ltd


     indicates that these metals are present in insoluble form and should generally be readily settled with
     sufficient retention time and/or readily removed via specialised fine media filtration.
3.2 Groundwater quality
     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
     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.




ADG1290.21 Dewatering Management Plan_Rev1_02.02.22                                                        Page 6